Showing 1–50 of 102 results for author: Pradhan, S

Mapping metallic d-wave altermagnetism across the TiNiSi structural family

Authors: Zhen Zhang, Subhadip Pradhan, Kirill D. Belashchenko, Vladimir Antropov

Abstract: The prospect of using altermagnets as switchable sources of perpendicularly polarized spin currents has intensified the search for candidate materials, yet metallic d-wave systems with sizable spin-splitter responses remain scarce. Here, we identify an empirical magnetic motif that supports metallic d-wave altermagnetism in the TiNiSi structural family: ferromagnetically ordered zigzag chains with… ▽ More The prospect of using altermagnets as switchable sources of perpendicularly polarized spin currents has intensified the search for candidate materials, yet metallic d-wave systems with sizable spin-splitter responses remain scarce. Here, we identify an empirical magnetic motif that supports metallic d-wave altermagnetism in the TiNiSi structural family: ferromagnetically ordered zigzag chains with antiferromagnetic interchain coupling in a relatively low-symmetry crystal environment. The TiNiSi structure type combines this motif with broad chemical flexibility and competing magnetic ground states. By combining first-principles screening of thermodynamic stability and magnetic ground states across 280 ternary systems, we identify 16 metallic d-wave altermagnets. This set recovers four experimentally known members---WFeB, NbMnP, TaMnP, and NbMnAs---and yields 12 new predictions, of which ScMnP, TaMnAs, ScMnAs, MoMnAs, MoMnSi, and WMnSi are the most promising. Noncollinear calculations indicate that the collinear altermagnetic configuration is the ground state across them. Each of the six leading new candidates has a nonzero spin-splitter angle and a finite anomalous Hall conductivity. Notably, ScMnP and TaMnAs exhibit strong spin-splitter responses despite modest altermagnetic band splitting. These results establish TiNiSi-type metallic d-wave altermagnets as a chemically versatile platform for efficient charge-to-spin conversion and provide an empirical magnetic-motif-guided route to identifying further candidates. △ Less

Submitted 24 August, 2026; originally announced August 2026.

Spin-phonon interaction in a symmetry-enforced spin-polarized state

Authors: Suman Kalyan Pradhan, Dayal Das, Shubham Patel, Subhajit Mahapatra, Sachin Majee, Dibyendu Majee, Arnab Bera, Achintya Singha, Snehasish Nandy, Samik DuttaGupta, Atindra Nath Pal

Abstract: Symmetry-governed magnetic materials have emerged as a promising platform for spintronic functionalities without net magnetization or stray magnetic fields, motivating the exploration of how lattice dynamics couple to symmetry-derived spin-polarized electronic states. Understanding spin-phonon coupling in these systems is therefore essential for uncovering the microscopic origin of spin-lattice in… ▽ More Symmetry-governed magnetic materials have emerged as a promising platform for spintronic functionalities without net magnetization or stray magnetic fields, motivating the exploration of how lattice dynamics couple to symmetry-derived spin-polarized electronic states. Understanding spin-phonon coupling in these systems is therefore essential for uncovering the microscopic origin of spin-lattice interactions and for enabling their control in quantum materials. However, this mechanism remains poorly understood because spin polarization originates from crystal symmetry rather than conventional magnetic order. Here, we address this issue in the g-type altermagnet CoNb4Se8 using temperature- and polarization-resolved Raman spectroscopy, complemented by measurements on a structurally analogous Co-deficient compound lacking well-defined long-range magnetic order. We observe pronounced symmetry-selective phonon renormalization across the magnetic transition in CoNb4Se8, while related phonon anomalies persist in the Co-deficient system, demonstrating that the lattice response cannot be explained solely by conventional exchange-striction associated with coherent magnetic ordering. First-principles calculations reveal that spin-orbit coupling establishes a symmetry-dependent interaction channel between lattice vibrations and symmetry-governed electronic states. Our results identify an alternative mechanism for spin-phonon coupling in symmetry-governed magnetic materials and demonstrate that phonons provide a sensitive probe of symmetry-driven spin polarization even without robust magnetic order. More broadly, this work provides a framework for understanding and engineering spin-lattice functionality in symmetry-driven quantum materials, offering design principles for coupling lattice dynamics to spin-polarized electronic states. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Phase-Topology Classification of Memristor Hysteresis Loops via Self-Crossings

Authors: Ovidiu-Zeno Lipan, Eric Neuhaus, Rafael Schio Wengenroth Silva, Soumen Pradhan, Fabian Hartmann, Leonardo K. Castelano, Ana Luiza Costa Silva, Sven Höfling, Victor Lopez-Richard

Abstract: Memristive devices have revolutionized non-volatile memory and neuromorphic computing, yet the geometry of their hysteresis loops -- in particular, the occurrence and robustness of multiple self-crossings -- remains poorly understood. Here we introduce a topological and algebraic framework that treats the number of transverse self-intersections of a memristor hysteresis loop as a robust integer-va… ▽ More Memristive devices have revolutionized non-volatile memory and neuromorphic computing, yet the geometry of their hysteresis loops -- in particular, the occurrence and robustness of multiple self-crossings -- remains poorly understood. Here we introduce a topological and algebraic framework that treats the number of transverse self-intersections of a memristor hysteresis loop as a robust integer-valued invariant. Drawing on differential topology, singularity theory, and cusp catastrophe, we employ discriminants and resultants to stratify the six-dimensional parameter space. This approach partitions the parameter space into structurally stable regions separated by explicitly computable catastrophe surfaces. We demonstrate that the crossing number remains strictly invariant under continuous deformations and changes only at self-tangencies or cusp singularities, thereby providing a complete classification of all multi-lobed hysteresis behaviors. These insights bridge device physics with modern singularity theory and suggest a clear roadmap for exploiting higher-order memory effects in next-generation electronics and brain-inspired hardware. △ Less

Submitted 26 May, 2026; originally announced May 2026.

Comments: 14 pages, 12 figures

Metallic d-wave altermagnetism in WFeB: a platform for electrically switchable perpendicular spin-splitter response

Authors: Eranga H. Gamage, Zhen Zhang, Subhadip Pradhan, Ajay Kumar, David R. Ramgern, V. Ovidiu Garlea, Yaroslav Mudryk, Saeed Kamali, Douglas Warnberg, Kirill D. Belashchenko, Vladimir Antropov, Kirill Kovnir

Abstract: We report the synthesis and magnetic characterization of WFeB and identify it as a metallic d-wave altermagnet representative of a broader TiNiSi-type family. Neutron diffraction, Mössbauer spectroscopy, and magnetometry establish a collinear altermagnetic ordering confirmed by first-principles calculations. The electronic structure shows a nonrelativistic spin splitting of approximately 100 meV,… ▽ More We report the synthesis and magnetic characterization of WFeB and identify it as a metallic d-wave altermagnet representative of a broader TiNiSi-type family. Neutron diffraction, Mössbauer spectroscopy, and magnetometry establish a collinear altermagnetic ordering confirmed by first-principles calculations. The electronic structure shows a nonrelativistic spin splitting of approximately 100 meV, but it also supports a strong spin-splitter transport response. This demonstrates that efficient spin-current generation can occur even with such modest band splitting. Symmetry analysis shows that selected film orientations permit deterministic switching of the Néel vector by current-induced staggered torques, enabling electrical control of a perpendicular spin-splitter response. These results establish WFeB and related TiNiSi-type antiferromagnets as a platform for electrically switchable charge-to-spin conversion driven by altermagnetic symmetry. △ Less

Submitted 31 March, 2026; originally announced April 2026.

Spin-reorientation as a switch for electronic topology in van der Waals ferromagnets

Authors: Satyabrata Bera, Sudipta Chatterjee, Suman Kalyan Pradhan, Subhadip Pradhan, Arnab Bera, Sk Kalimuddin, Ashis K. Nandy, Mintu Mondal

Abstract: The interplay between spin reorientation and topological electronic structure in two-dimensional (2D) van der Waals (vdW) ferromagnets is central to understanding how magnetic anisotropy shapes charge transport. Although spin-reorientation transitions (SRTs) are common in 2D metallic ferromagnets, their impact on electronic-topology-driven thermodynamic and transport properties remains largely une… ▽ More The interplay between spin reorientation and topological electronic structure in two-dimensional (2D) van der Waals (vdW) ferromagnets is central to understanding how magnetic anisotropy shapes charge transport. Although spin-reorientation transitions (SRTs) are common in 2D metallic ferromagnets, their impact on electronic-topology-driven thermodynamic and transport properties remains largely unexplored. Here we investigate this issue in Fe$_4$GeTe$_2$ (F4GT), a room-temperature quasi-2D vdW ferromagnet, using temperature-dependent magnetization, specific heat, magnetotransport, and thermoelectric measurements. Magnetization and specific heat establish a reorientation of the magnetic easy axis near $T_{\mathrm{SRT}} \sim 100$~K, in addition to ferromagnetic ordering at $T_C \sim 270$~K. Across the SRT, the Seebeck coefficient and anisotropic magnetoresistance show clear anomalies, indicating Fermi-surface reconstruction. The magnetoresistance exhibits a two-step field dependence: a low-field enhancement near the SRT associated with scattering from canted spins and evolving domains, followed by a higher-field negative response as spin fluctuations are suppressed. The simultaneous sign change of the ordinary Hall coefficient $R_0$ and the sharp anomaly in the anomalous Hall resistivity $ρ^{A}_{yx}$ further point to a temperature-driven modification of the underlying band topology. Analysis of the anomalous Hall conductivity $σ^{A}_{xy}$ and the scaling of $ρ^{A}_{yx}$ shows that the Berry-curvature-driven anomalous Hall response below $T_{\mathrm{SRT}}$ is strongly modified above the transition. Our results identify spin reorientation as an internal control parameter for switching between distinct topological transport regimes in a 2D vdW ferromagnet, providing a symmetry-controlled route to engineer spin-polarized electronic states and domain-texture-driven functionalities. △ Less

Submitted 20 March, 2026; originally announced March 2026.

Unusual magnetic and charge transport properties in In-Substituted Half-Metallic Kagome Ferromagnet Co3Sn2S2

Authors: Karan Singh, Subhadip Pradhan, K. Mukherjee, Ashis Kumar Nandy, Subhendra D. Mahanti, D. Topwal

Abstract: The kagome ferromagnet Co3Sn2S2 has been studied extensively for its unusual topology of electronic bands, origin of ferromagnetism and strong coupling between magnetism and charge transport. To understand the role of nonmagnetic element Sn, we have investigated magnetic, transport, and electronic structure of the isostructural compound Co3SnInS2, where all the Sn (divalent) atoms in the Co3Sn Kag… ▽ More The kagome ferromagnet Co3Sn2S2 has been studied extensively for its unusual topology of electronic bands, origin of ferromagnetism and strong coupling between magnetism and charge transport. To understand the role of nonmagnetic element Sn, we have investigated magnetic, transport, and electronic structure of the isostructural compound Co3SnInS2, where all the Sn (divalent) atoms in the Co3Sn Kagome layer are replaced by In (trivalent) atoms. We find long-range ferromagnetic order is nearly quenched in Co3SnInS2. The system exhibits predominantly antiferromagnetic correlations with only a very small net magnetic moment and turns ferromagnetic in the presence of an external magnetic field. Transport measurements show a semiconducting behaviour at low temperatures. Magnetoresistance shows a nonmonotonic field dependence, changing from negative to positive with increasing magnetic field. An anomalous Hall effect is observed, but its magnitude is significantly reduced compared to Co3Sn2S2 where the topological character of the Fermi surface plays a dominant role. These results indicate that substitution of Sn by In in the Co3Sn plane not only suppresses the topological electronic features of the transport electrons but drives the system away from the ferromagnetic Half-metallicity to an almost nonmagnetic semiconducting state with unusual paramagnetic response. Electronic structure calculations are consistent with some of these observations. △ Less

Submitted 3 March, 2026; originally announced March 2026.

Nodal-Surface and Flat-Band Driven Large Anomalous Nernst Effect in Epitaxial Ferromagnetic Weyl Metal Fe5Si3

Authors: Shubhashish Pati, Sonali Srotaswini Pradhan, Nanhe Kumar Gupta, Abhay Pandey, Nikita Sharma, Nakul Kumar, Saurav Singh, Yuya Sakuraba, V. Kanchana, Sujeet Chaudhary

Abstract: Magnetic topological materials such as Weyl and Dirac magnets exhibit unconventional electronic properties arising from the interplay between magnetic order and band topology, leading to remarkable thermomagnetic and thermoelectric effects. Here, we investigate the ANE in epitaxial thin films of the Weyl ferromagnet candidate Fe5Si3. A pronounced transverse Nernst response exceeding approximately… ▽ More Magnetic topological materials such as Weyl and Dirac magnets exhibit unconventional electronic properties arising from the interplay between magnetic order and band topology, leading to remarkable thermomagnetic and thermoelectric effects. Here, we investigate the ANE in epitaxial thin films of the Weyl ferromagnet candidate Fe5Si3. A pronounced transverse Nernst response exceeding approximately 1.50 microvolt per kelvin is observed at room temperature, together with a giant anomalous Nernst angle of about 0.56, indicating highly efficient conversion between thermal gradients and transverse electric fields. Beyond the anomalous contribution, a sizable topological Nernst signal of approximately 0.43 microvolt per kelvin persists above room temperature, suggesting the possible presence of real-space Berry curvature associated with nontrivial spin textures. First-principles density functional theory calculations combined with symmetry analysis reveal an unconventional electronic structure in which Weyl nodal lines, nodal surfaces, and nearly flat bands coexist near the Fermi level. This rare concurrence of multiple topological band features produces a strongly enhanced and sharply energy-dependent Berry curvature, which governs both the magnitude and temperature evolution of the observed Nernst response. The close quantitative agreement between calculated anomalous Nernst conductivity and experimental results establishes the topological electronic structure as the dominant origin of the observed thermomagnetic transport, highlighting Fe5Si3 as a chemically simple, low-cost binary topological magnet for exploring both real-space and momentum-space Berry-curvature-driven thermoelectric phenomena. △ Less

Submitted 10 February, 2026; originally announced February 2026.

Comments: 23 pages, 10 figures

Compact U(1) Lattice Gauge Theory in Superconducting Circuits with Infinite-Dimensional Local Hilbert Spaces

Authors: J. M. Alcaine-Cuervo, S. Pradhan, E. Rico, Z. Shi, C. M. Wilson

Abstract: We propose a superconducting-circuit architecture that realizes a compact U(1) lattice gauge theory using the intrinsic infinite-dimensional Hilbert space of phase and charge variables. The gauge and matter fields are encoded directly in the degrees of freedom of the rotor variables associated with the circuit nodes, and Gauss's law emerges exactly from the conservation of local charge, without au… ▽ More We propose a superconducting-circuit architecture that realizes a compact U(1) lattice gauge theory using the intrinsic infinite-dimensional Hilbert space of phase and charge variables. The gauge and matter fields are encoded directly in the degrees of freedom of the rotor variables associated with the circuit nodes, and Gauss's law emerges exactly from the conservation of local charge, without auxiliary stabilizers, penalty terms, or Hilbert-space truncation. A minimal gauge-matter coupling arises microscopically from Josephson nonlinearities, whereas the magnetic plaquette interaction is generated perturbatively via virtual matter excitations. Numerical diagonalization confirms the emergence of compact electrodynamics and coherent vortex excitations, underscoring the need for large local Hilbert spaces in the continuum regime. The required circuit parameters are within the current experimental capabilities. Our results establish superconducting circuits as a scalable, continuous-variable platform for analog quantum simulation of non-perturbative gauge dynamics. △ Less

Submitted 30 January, 2026; originally announced January 2026.

Comments: 21 pages, 12 figures

Report number: CERN-TH-2026-003

Magnetic field-induced non-trivial Lifshitz transition in TaCo2Te2

Authors: Suman Kalyan Pradhan, Xiaoming Ma, Jicheng Wang, Weiqi Liu, Yue Dai, Wenxing Chen, Xiaobai Ma, Wenyun Yang, Yu Wu, Zhaochu Luo, Raktim Datta, Arnab Bera, Samik DuttaGupta, Jinbo Yang, Yanglong Hou, Chang Liu, Rui Wu

Abstract: Magnetic-field-driven Lifshitz transitions are typically considered zero-temperature phenomena involving Fermi-surface reconstruction without symmetry breaking. Here, we report an unconventional Lifshitz transition in TaCo2Te2 that emerges exclusively within a narrow finite-temperature window under cooperative tuning by both temperature and magnetic field. Bulk-sensitive transport and thermoelectr… ▽ More Magnetic-field-driven Lifshitz transitions are typically considered zero-temperature phenomena involving Fermi-surface reconstruction without symmetry breaking. Here, we report an unconventional Lifshitz transition in TaCo2Te2 that emerges exclusively within a narrow finite-temperature window under cooperative tuning by both temperature and magnetic field. Bulk-sensitive transport and thermoelectric measurements demonstrate continuous Fermi-surface renormalization at low temperatures, where the transition is sharply triggered by a critical magnetic field. Crucially, neutron diffraction reveals the absence of structural or magnetic phase transitions, while angle-resolved photoemission spectroscopy shows no spectral anomalies in electronic structure without magnetic field. These observations constrain the mechanism to a Zeeman-driven process invisible to equilibrium probes, establishing a paradigm where Fermi-surface topology is jointly controlled by temperature and magnetic field. △ Less

Submitted 26 January, 2026; originally announced January 2026.

Comments: 4 figures

In-Substrate Imaging of Diamond hBN FET Current via Widefield Quantum Diamond Microscopy

Authors: Anuj Bathla, Subrat Kumar Pradhan, Ajit Kumar Dash, Prabhat Anand, M. Girish Chandra, Kenji Watanabe, Takashi Taniguchi, Akshay Singh, Veeresh Deshpande, Kasturi Saha

Abstract: We demonstrate widefield magnetic imaging of current flow in hydrogen terminated diamond field effect transistors (FETs) through in-substrate nitrogen vacancy (NV) centers. Hydrogen termination of the diamond surface induces a two dimensional hole gas (2DHG), while an ensemble of near surface NV centers located $ \sim 1~μm$ below the surface enables noninvasive magnetic imaging of current flow wit… ▽ More We demonstrate widefield magnetic imaging of current flow in hydrogen terminated diamond field effect transistors (FETs) through in-substrate nitrogen vacancy (NV) centers. Hydrogen termination of the diamond surface induces a two dimensional hole gas (2DHG), while an ensemble of near surface NV centers located $ \sim 1~μm$ below the surface enables noninvasive magnetic imaging of current flow with micrometer scale spatial resolution. The FETs were electrically characterized over a range of drain source biases $V_{ds}= 0$ to $-15V$ and gate voltages,$V_{gs}= +3$ to $-9V$ followed by in situ widefield NV magnetometry during device operation. Magnetic field maps and reconstructed current density distributions directly visualize current injection at the source drain contacts and transport beneath the hBN gated channel. Magnetic field maps reveal current density variations in the channel region owing to non-uniformities or defects in the gate dielectric. In addition, we observe a pronounced enhancement of the drain current ($\sim 600-900 μA$) and a shift in the apparent threshold voltage during laser illumination, reflecting photo induced changes in channel electrostatics. By correlating gate dependent magnetic images with simultaneous electrical measurements, we directly link spatial current distributions to FET transfer characteristics, providing new insight into buried interface transport and non-uniform gating effects in the transistor channel. As the methodology is compatible with top gated FETs, it can be used to map channel current distributions with micrometer resolution in emerging channel materials, such as 2D materials and wide bandgap channels, and establish widefield NV magnetometry as a powerful platform for probing charge transport in transistors and Van der Waals dielectric heterostructures. △ Less

Submitted 21 January, 2026; originally announced January 2026.

Room temperature intrinsic anomalous Hall effect in disordered half-metallic ferromagnetic quaternary Heusler alloy CoRuFeSi

Authors: Manikantha Panda, Sonali S. Pradhan, Prabuddha Kant Mishra, Alapan Bera, Rosni Roy, Rajib Mondal, Soumik Mukhopadhyay, V. Kanchana, Tapas Paramanik

Abstract: Quaternary Heusler alloys offer a versatile platform for engineering magnetic and topological transport phenomena through chemical flexibility and tunable disorder. Here, we report a comprehensive experimental and theoretical investigation of the magnetic, magnetotransport, and anomalous Hall properties of the quaternary Heusler alloy CoRuFeSi. The compound crystallizes in the LiMgPdSn-type struct… ▽ More Quaternary Heusler alloys offer a versatile platform for engineering magnetic and topological transport phenomena through chemical flexibility and tunable disorder. Here, we report a comprehensive experimental and theoretical investigation of the magnetic, magnetotransport, and anomalous Hall properties of the quaternary Heusler alloy CoRuFeSi. The compound crystallizes in the LiMgPdSn-type structure with significant Co--Ru antisite disorder and exhibits soft ferromagnetism with a saturation magnetization of $4.21~μ_{\mathrm{B}}/\mathrm{f.u.}$ at low temperature and a Curie temperature well above room temperature. Hall measurements reveal a robust anomalous Hall effect persisting up to 300~K, with an anomalous Hall conductivity of $\sim 74$~S/cm that is nearly temperature independent. Scaling analysis demonstrates that the anomalous Hall response is dominated by the intrinsic Berry-curvature mechanism. First-principles calculations identify CoRuFeSi as a topologically nontrivial nodal-line semimetal in its ordered phase. Incorporation of experimentally relevant Co--Ru antisite disorder redistributes the Berry curvature and quantitatively reproduces the experimentally observed anomalous Hall conductivity, while preserving half-metallicity. These results establish CoRuFeSi as a disorder-tolerant half-metallic ferromagnet with a sizable intrinsic anomalous Hall effect at room temperature, highlighting its potential for spintronic and Hall-based device applications. △ Less

Submitted 19 January, 2026; originally announced January 2026.

Gate-controlled analog memcapacitance in LaAlO3/SrTiO3 interface-based devices

Authors: Soumen Pradhan, Victor Lopez-Richard, Igor Ricardo Filgueira e Silva, Fabian Hartmann, Ana Luiza Costa Silva, Leonardo K. Castelano, Merit Spring, Silke Kuhn, Michael Sing, Ralph Claessen, Sven Höfling

Abstract: Current memcapacitor implementations typically demand complex fabrication processes or depend on organic materials exhibiting poor environmental stability and reproducibility. Here, we demonstrate memcapacitor structures utilizing a quasi 2-dimensional electron gas, formed at the crystalline LaAlO3/SrTiO3 heterointerface, as electrodes and SiO2/SrTiO3 as dielectric layer. The observed memcapacitan… ▽ More Current memcapacitor implementations typically demand complex fabrication processes or depend on organic materials exhibiting poor environmental stability and reproducibility. Here, we demonstrate memcapacitor structures utilizing a quasi 2-dimensional electron gas, formed at the crystalline LaAlO3/SrTiO3 heterointerface, as electrodes and SiO2/SrTiO3 as dielectric layer. The observed memcapacitance originates from the charge localization in a lateral floating gate, while an applied gate voltage enables reversible tuning of the device capacitance. Furthermore, preprogrammed or erased gate biases enable controllable shifts of the capacitance hysteresis window toward positive or negative bias, leading to an enlarged capacitance gap at zero bias. A memcapacitor model developed for this system reproduces the main features of the experimental capacitance hysteresis, capturing the effects of charge fluctuations and dielectric frequency modulation within the oxide layer. The demonstrated low-voltage operation and gate tunability of oxide interface-based memcapacitors highlight their potential for power-efficient, capacitor-based neuromorphic and synaptic electronic architectures. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 5 pages, 4 figures

Journal ref: Appl. Phys. Lett. 128, 123504 (2026)

Emergent Anomalous and Topological Hall Responses in an Epitaxial Ferromagnetic Weyl Nodal-Line metal Fe5Si3

Authors: Shubhashish Pati, Sonali Srotaswini Pradhan, Abhay Pandey, Nikita Sharma, Nanhe Kumar Gupta, Nakul Kumar, Nidhi Shukla, Saurav Singh, Vidhi Jain, Mitali, V. Kanchana, Sujeet Chaudhary

Abstract: The interplay between real and reciprocal space topology yields intrinsically linked transport phenomena in magnetic Weyl systems, wherein the broken time-reversal symmetry, strong Dzyaloshinskii-Moriya interaction, and pronounced uniaxial anisotropy stabilize the momentum-space Berry-curvature monopoles (Weyl nodes) and real-space chiral spin textures. We present a combined first-principles and e… ▽ More The interplay between real and reciprocal space topology yields intrinsically linked transport phenomena in magnetic Weyl systems, wherein the broken time-reversal symmetry, strong Dzyaloshinskii-Moriya interaction, and pronounced uniaxial anisotropy stabilize the momentum-space Berry-curvature monopoles (Weyl nodes) and real-space chiral spin textures. We present a combined first-principles and experimental study of epitaxial Fe5Si3 thin films, establishing them as a magnetic Weyl nodal-line material. First-principles Density Functional Theory (DFT) calculations unambiguously reveal that Fe5Si3 hosts a topologically nontrivial electronic structure containing six pairs of Weyl nodes at or near the Fermi level, accompanied by pronounced Berry curvature at high-symmetry points of the Brillouin Zone. High-quality epitaxial films exhibit robust ferromagnetism with a Curie temperature of ~370 K and strong magneto crystalline anisotropy. The magneto transport measurements on epitaxial films reveal the corresponding Berry curvature-driven responses, including a significantly large intrinsic anomalous Hall conductivity of 504 S/cm and a high anomalous Hall angle of 5.5%, which is in good agreement with DFT calculations. A negative and non-saturating longitudinal magnetoresistance is observed, consistent with a chiral-anomaly contribution from Weyl fermions near the Fermi level (EF). Furthermore, a substantial topological Hall resistivity of 1.6 μΩ cm robust across a wide temperature range, indicating the possibility of robust chiral spin textures in the thin-film geometry. These combined theoretical and experimental results establish Fe5Si3 as a unique, low-cost, centrosymmetric magnetic Weyl nodal-line material, providing a versatile platform for exploring coupled real and reciprocal space topologies in topological spintronic applications. △ Less

Submitted 29 November, 2025; originally announced December 2025.

Comments: 21 pages, 6 figures

Discovery and Synthesis of a Family of Boride Altermagnets

Authors: Zhen Zhang, Eranga H. Gamage, Genevieve Amobi, Subhadip Pradhan, Andrey Kutepov, Kirill D. Belashchenko, Yang Sun, Kirill Kovnir, Vladimir Antropov

Abstract: Borides are a rich material family. To push the boundaries of borides' properties and applications into broader fields, we have conducted systematic theoretical and experimental searches for synthesizable phases in ternary borides TM$_2$B$_2$ (T = 3d, M = 4d/5d transition metals). We find that TM$_2$B$_2$ in the FeMo$_2$B$_2$-type and CoW$_2$B$_2$-type structures form a large family of stable/meta… ▽ More Borides are a rich material family. To push the boundaries of borides' properties and applications into broader fields, we have conducted systematic theoretical and experimental searches for synthesizable phases in ternary borides TM$_2$B$_2$ (T = 3d, M = 4d/5d transition metals). We find that TM$_2$B$_2$ in the FeMo$_2$B$_2$-type and CoW$_2$B$_2$-type structures form a large family of stable/metastable materials of 120 members. Among them, we identify 40 materials with stable magnetic solutions. Further, we discover 11 altermagnets in the FeMo$_2$B$_2$-type structure. So far, boride altermagnets are rare. In these altermagnets, T = Fe or Mn atoms are arranged in parallel T-chains with strong ferromagnetic intrachain couplings and antiferromagnetic interchain couplings. They simultaneously exhibit electronic band spin splitting, typical of ferromagnetism, and zero net magnetization, typical of antiferromagnetism. They also exhibit magnonic band chiral splitting. Both effects originate from the unique altermagnetic symmetries crucially constrained by the nonmagnetic atoms in the structure. Transport properties of relevance to spintronic applications, including the strain-induced spin-splitter effect and anomalous Hall effect, are predicted. An iodine-assisted synthesis method for TM$_2$B$_2$ is developed, using which 7 of the predicted low-energy phases are experimentally synthesized and characterized, including 4 altermagnets. This work expands the realm of borides by offering new opportunities for studying altermagnetism and altermagnons in borides. It also provides valuable insights into the discovery and design of altermagnets. By demonstrating that altermagnets can exist as families sharing a common motif, this work paves a feasible route for discovering altermagnets by elemental substitutions and high-throughput computations. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Oxide Interface-Based Polymorphic Electronic Devices for Neuromorphic Computing

Authors: Soumen Pradhan, Kirill Miller, Fabian Hartmann, Merit Spring, Judith Gabel, Berengar Leikert, Silke Kuhn, Martin Kamp, Victor Lopez-Richard, Michael Sing, Ralph Claessen, Sven Höfling

Abstract: Aside from recent advances in artificial intelligence (AI) models, specialized AI hardware is crucial to address large volumes of unstructured and dynamic data. Hardware-based AI, built on conventional complementary metal-oxidesemiconductor (CMOS)-technology, faces several critical challenges including scaling limitation of devices [1, 2], separation of computation and memory units [3] and most im… ▽ More Aside from recent advances in artificial intelligence (AI) models, specialized AI hardware is crucial to address large volumes of unstructured and dynamic data. Hardware-based AI, built on conventional complementary metal-oxidesemiconductor (CMOS)-technology, faces several critical challenges including scaling limitation of devices [1, 2], separation of computation and memory units [3] and most importantly, overall system energy efficiency [4]. While numerous materials with emergent functionalities have been proposed to overcome these limitations, scalability, reproducibility, and compatibility remain critical obstacles [5, 6]. Here, we demonstrate oxide-interface based polymorphic electronic devices with programmable transistor, memristor, and memcapacitor functionalities by manipulating the quasi-two-dimensional electron gas in LaAlO3/SrTiO3 heterostructures [7, 8] using lateral gates. A circuit utilizing two polymorphic functionalities of transistor and memcapacitor exhibits nonlinearity and short-term memory, enabling implementation in physical reservoir computing. An integrated circuit incorporating transistor and memristor functionalities is utilized for the transition from short- to long-term synaptic plasticity and for logic operations, along with in-situ logic output storage. The same circuit with advanced reconfigurable synaptic logic operations presents high-level multi-input decision-making tasks, such as patient-monitoring in healthcare applications. Our findings pave the way for oxide-based monolithic integrated circuits in a scalable, silicon compatible, energy efficient single platform, advancing both the polymorphic and neuromorphic computings. △ Less

Submitted 6 August, 2025; v1 submitted 5 August, 2025; originally announced August 2025.

Comments: 20 pages, 5 figures

Report number: 11

Journal ref: Nat Commun 17, 3406 (2026)

Investigation of magnetic and magneto-transport properties in non-centrosymmetric antiferromagnetic semimetal GdGaSi

Authors: Manikantha Panda, Prabuddha Kant Mishra, Sonali S Pradhan, V. Kanchana, Tapas Paramanik

Abstract: In this work, we investigated the magneto-transport and magnetic properties of GdGaSi, having non-centrosymmetric tetragonal structure, with space group $I4_1md$. Our theoretical results are supported by experimental studies. First-principles calculations reveal that GdGaSi is an antiferromagnetic semimetallic system, characterized by dominant electron-type charge carriers. In addition, the possib… ▽ More In this work, we investigated the magneto-transport and magnetic properties of GdGaSi, having non-centrosymmetric tetragonal structure, with space group $I4_1md$. Our theoretical results are supported by experimental studies. First-principles calculations reveal that GdGaSi is an antiferromagnetic semimetallic system, characterized by dominant electron-type charge carriers. In addition, the possible nontriviality of the crossing at the Fermi energy is consistent with isostructural LaPtSi-structured materials. The compound shows robust antiferromagnetic (AFM) ordering with a Néel temperature of 19 K, and spin-reorientation signature below $T_N$. The semimetallic nature with positive magnetoresistance ($\simeq$ 2\% at 2 K and 8 T) is observed from the magnetotransport data, having electrons as majority charge carrier, established from the Hall measurements. The strong correlation in magnetism and transport is supported by various observations, like (1) concordant transitions in $M(T)$ and $ρ(T)$ data, (2) change in the concentration and mobility of electron below $T_N$, and (3) splitting of Kohler's plots in the two branches across the transition. Thus, our findings establish GdGaSi as a material with intertwined magnetic and transport degrees of freedom, within noncentrosymmetric lattice. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Roughening and dynamics of an electric flux string in a (2+1)D lattice gauge theory

Authors: Francesco Di Marcantonio, Sunny Pradhan, Sofia Vallecorsa, Mari Carmen Bañuls, Enrique Rico Ortega

Abstract: We investigate the roughening transition in the pure $\mathbb{Z}_2$ lattice gauge theory in (2+1) dimensions. Using numerical simulations with matrix product states, we explore the static and dynamical properties of an electric flux string between two static charges as the coupling is varied and approaches the deconfinement phase transition from the confined phase. Within the roughening region, we… ▽ More We investigate the roughening transition in the pure $\mathbb{Z}_2$ lattice gauge theory in (2+1) dimensions. Using numerical simulations with matrix product states, we explore the static and dynamical properties of an electric flux string between two static charges as the coupling is varied and approaches the deconfinement phase transition from the confined phase. Within the roughening region, we obtain the universal Lüscher correction to the confining potential and observe the expected restoration of rotational symmetry. Our simulations of the out-of-equilibrium evolution of a string reveal that the growth of the entanglement entropy of the state and the string width exhibit qualitatively different behavior in the roughening region compared to the deeply confined one. In particular, we find that the rate of entropy growth is consistent with an effective description of the string excitations by a bosonic model in the roughening phase. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 21 pages, 16 figures

Report number: CERN-TH-2025-105

Oddities in the Entanglement Scaling of the Quantum Six-Vertex Model

Authors: Sunny Pradhan, Jesús Cobos, Enrique Rico, Germán Sierra

Abstract: We investigate the entanglement properties of the Quantum Six-Vertex Model on a cylinder, focusing on the Shannon-Renyi entropy in the limit of Renyi order $n = \infty$. This entropy, calculated from the ground state amplitudes of the equivalent XXZ spin-1/2 chain, allows us to determine the Renyi entanglement entropy of the corresponding Rokhsar-Kivelson wavefunctions, which describe the ground s… ▽ More We investigate the entanglement properties of the Quantum Six-Vertex Model on a cylinder, focusing on the Shannon-Renyi entropy in the limit of Renyi order $n = \infty$. This entropy, calculated from the ground state amplitudes of the equivalent XXZ spin-1/2 chain, allows us to determine the Renyi entanglement entropy of the corresponding Rokhsar-Kivelson wavefunctions, which describe the ground states of certain conformal quantum critical points. Our analysis reveals a novel logarithmic correction to the expected entanglement scaling when the system size is odd. This anomaly arises from the geometric frustration of spin configurations imposed by periodic boundary conditions on odd-sized chains. We demonstrate that the scaling prefactor of this logarithmic term is directly related to the compactification radius of the low-energy bosonic field theory description, or equivalently, the Luttinger parameter. Thus, this correction provides a direct probe of the underlying Conformal Field Theory (CFT) describing the critical point. Our findings highlight the crucial role of system size parity in determining the entanglement properties of this model and offer insights into the interplay between geometry, frustration, and criticality. △ Less

Submitted 24 February, 2026; v1 submitted 26 February, 2025; originally announced February 2025.

Comments: 10 pages, 7 figures

Journal ref: Phys. Rev. B 113, 094438 (2026)

Revisiting MnSe : a Magnetic Semiconductor with Spin-Phonon coupling

Authors: Suman Kalyan Pradhan, Arnab Bera, Soham Das, Yongli Yu, Jicheng Wang, Rui Wu

Abstract: Spin-phonon interactions in 2D magnetic materials are crucial in advancing next-generation spintronic devices. Therefore, identifying new materials with significant spin-phonon interactions is of great importance. In this context, MnSe, previously recognized as an exemplary non-layered p-type semiconductor emerges in this study as an intriguing material with notable spin-phonon characteristics. Th… ▽ More Spin-phonon interactions in 2D magnetic materials are crucial in advancing next-generation spintronic devices. Therefore, identifying new materials with significant spin-phonon interactions is of great importance. In this context, MnSe, previously recognized as an exemplary non-layered p-type semiconductor emerges in this study as an intriguing material with notable spin-phonon characteristics. The complex magnetism in pristine MnSe, primarily dominated by antiferromagnetism with a weak ferromagnetic component, gives rise to both spontaneous and conventional exchange bias effects at low temperatures. In an effort to understand this intriguing magnetism, we conducted a detailed Raman spectroscopy study, which reveals unconventional deviations from the usual phonon anharmonicity around Neel temperature (170 K), in the self-energies of the P1, P2, and P3 modes. Notably, the P1 mode is most sensitive to spin-phonon coupling, while the P2 mode is particularly responsive to the structural phase transition at 250 K. Therefore, these findings provide comprehensive insights into the phase transitions of pristine MnSe, particularly highlighting the previously unobserved interplay between its magnetic behavior and phonon dynamics. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Critical scaling behavior in skyrmion host ferromagnet CrTe1.38

Authors: Suman Kalyan Pradhan, Tuhin Debnath, Rui Wu

Abstract: Materials hosting diverse topological spin textures hold significant potential for spintronic applications. In this context, CrTe1.38, a quasi-two-dimensional material, stands out due to its stable N'eel-type skyrmion phase over a wide temperature range, both with and without an applied magnetic field [APL 125, 152402 (2024)]. Thus, it is a promising candidate for investigating complex magnetic ph… ▽ More Materials hosting diverse topological spin textures hold significant potential for spintronic applications. In this context, CrTe1.38, a quasi-two-dimensional material, stands out due to its stable N'eel-type skyrmion phase over a wide temperature range, both with and without an applied magnetic field [APL 125, 152402 (2024)]. Thus, it is a promising candidate for investigating complex magnetic phenomena, offering valuable insights into the underlying magnetic interactions. This study investigates the critical behavior of CrTe1.38 near TC by measuring DC magnetic isotherms. A systematic analysis of these isotherms with the magnetic field applied along the easy axis allows us to determine the asymptotic critical exponents: beta = 0.314, gamma = 1.069, and delta = 4.556, where the Widom scaling law and scaling equations are verified the self-consistency and reliability. In this system, the magnetic exchange coupling J(r) is the long-range type and decays spatially at a rate slower than approximately 4.651. Most notably, a series of vertical lines in the low-field region of the initial magnetization curves below TC supports the existence of a skyrmion phase in this compound △ Less

Submitted 25 February, 2025; originally announced February 2025.

Colossal magnetoresistance in a quasi-two-dimensional cluster glass semiconductor

Authors: Suman Kalyan Pradhan, Weiqi Liu, Jicheng Wang, Yongli Yu, Wenxing Chen, Jinbo Yang, Yanglong Hou, Rui Wu

Abstract: With a surge of interest in spintronics, the manipulation and detection of colossal magnetoresistance in quasi-two-dimensional layered magnetic materials have become a key focus, driven by their relatively scarce occurrence compared to giant magnetoresistance and tunneling magnetoresistance. This study presents an investigation into the desired colossal magnetoresistance, achieved by introducing m… ▽ More With a surge of interest in spintronics, the manipulation and detection of colossal magnetoresistance in quasi-two-dimensional layered magnetic materials have become a key focus, driven by their relatively scarce occurrence compared to giant magnetoresistance and tunneling magnetoresistance. This study presents an investigation into the desired colossal magnetoresistance, achieved by introducing magnetic frustration through Te doping in quasi-two-dimensional antiferromagnet Cr2Se3 matrix. The resulting Cr0.98SeTe0.27 exhibits cluster glass-like behavior with a freezing temperature of 28 K. Magnetotransport studies reveal a significant negative magnetoresistance of up to 32%. Additionally, angle-dependent transport measurements demonstrate a magnetic field-induced transition from positive to negative resistance anisotropy, suggesting a magnetic field-driven alteration in the electronic structure of this narrow band gap semiconductor, a characteristic feature of the colossal magnetoresistance effect. This behavior is further corroborated by density functional theory calculations. This systematic investigation provides a crucial understanding of the control of colossal magnetoresistance in quasi-two-dimensional materials via competing exchange interactions. △ Less

Submitted 25 February, 2025; originally announced February 2025.

Anomalous Hall and Nernst effect switching via staggered rotation in a kagome antiferromagnetic semimetal

Authors: Subhadip Pradhan, Kartik Samanta, Ashis K. Nandy

Abstract: The intricate interplay between magnetism and the topology of electronic structures provides a rich avenue for tailoring materials with unique and potent anomalous transport properties. In this paper, we present a strategy for inducing robust Berry curvature and anomalous transverse conductivity in noncollinear antiferromagnets through an unconventional approach termed ``small \textit{staggered ro… ▽ More The intricate interplay between magnetism and the topology of electronic structures provides a rich avenue for tailoring materials with unique and potent anomalous transport properties. In this paper, we present a strategy for inducing robust Berry curvature and anomalous transverse conductivity in noncollinear antiferromagnets through an unconventional approach termed ``small \textit{staggered rotation} of spin". Considering noncollinear Mn$_3$Sn, we demonstrate that the positive vector chirality antiferromagnetic configuration, typically associated with a vanishing anomalous Hall effect and Nernst effect, can be manipulated to exhibit finite anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) through \textit{staggered rotation}. Furthermore, we illustrate that the value and sign of both the AHC and ANC can be tuned through \textit{staggered rotation}. This tuning is intricately influenced by the spin-orbit coupling (SOC) induced gapped nodal line, revealing the critical role of electronic structure modifications in achieving precise control over transport properties. △ Less

Submitted 3 December, 2024; originally announced December 2024.

Comments: 9 pages, 7 figures

Accuracy Bottlenecks in Impedance Spectroscopy due to Transient Effects

Authors: Victor Lopez-Richard, Soumen Pradhan, Leonardo K. Castelano, Rafael Schio Wengenroth Silva, Ovidiu Lipan, Sven Höfling, Fabian Hartmann

Abstract: Impedance spectroscopy is vital for material characterization and assessing electrochemical device performance. It provides real-time analysis of dynamic processes such as electrode kinetics, electrons, holes or ion transport, and interfacial or defect driven phenomena. However, the technique is sensitive to experimental conditions, introducing potential variability in results. The intricate inter… ▽ More Impedance spectroscopy is vital for material characterization and assessing electrochemical device performance. It provides real-time analysis of dynamic processes such as electrode kinetics, electrons, holes or ion transport, and interfacial or defect driven phenomena. However, the technique is sensitive to experimental conditions, introducing potential variability in results. The intricate interplay of transient effects within the realm of spectral impedance analyses introduces a layer of complexity that may impede straightforward interpretations. This demands a nuanced approach for refining analytical methodologies and ensuring the fidelity of impedance characterization once the dynamic contributions of transient ingredients cannot be disentangled from the underlying steady-state characteristics. In our study, we experimentally identify that the transient effects in a memristor device are most pronounced near an optimal frequency related to intrinsic relaxation times, with these effects diminishing as the frequency varies beyond or below this range. While inherent systematic errors impose a practical limit (accuracy floor) on achievable measurement accuracy, this paper offers qualitative and quantitative insights into how specific procedures affect this limit and how to reduce it in orders of magnitude. Only by effectively addressing these errors we can push beyond this constraint. △ Less

Submitted 12 October, 2024; v1 submitted 11 June, 2024; originally announced June 2024.

Comments: 5 figures

Nonlinear mechanics of phase-change-induced accretion

Authors: Satya Prakash Pradhan, Arash Yavari

Abstract: In this paper, we formulate a continuum theory of solidification within the context of finite-strain coupled thermoelasticity. We aim to fill a gap in the existing literature, as the existing studies on solidification typically decouple the thermal problem (the classical Stefan's problem) from the elasticity problem, and often limit themselves to linear elasticity with small strains. Treating soli… ▽ More In this paper, we formulate a continuum theory of solidification within the context of finite-strain coupled thermoelasticity. We aim to fill a gap in the existing literature, as the existing studies on solidification typically decouple the thermal problem (the classical Stefan's problem) from the elasticity problem, and often limit themselves to linear elasticity with small strains. Treating solidification as an accretion problem, with the growth velocity correlated with the jump in the heat flux across the boundary, it presents an initial boundary-value problem (IBVP) over a domain whose boundary location is a priori unknown. This IBVP is solved numerically for the specific example of radially inward solidification in a spherical container. Several parametric studies are conducted to compare the numerical results with the rigid cases in the literature and gain insights into the role of elastic deformations in solidification. △ Less

Submitted 19 April, 2024; originally announced April 2024.

MICROSIM: A high performance phase-field solver based on CPU and GPU implementations

Authors: Tanmay Dutta, Dasari Mohan, Saurav Shenoy, Nasir Attar, Abhikshek Kalokhe, Ajay Sagar, Swapnil Bhure, Swaroop . S. Pradhan, Jitendriya Praharaj, Subham Mridha, Anshika Kushwaha, Vaishali Shah, M. P. Gururajan, V. Venkatesh Shenoi, Gandham Phanikumar, Saswata Bhattacharyya, Abhik Choudhury

Abstract: The phase-field method has become a useful tool for the simulation of classical metallurgical phase transformations as well as other phenomena related to materials science. The thermodynamic consistency that forms the basis of these formulations lends to its strong predictive capabilities and utility. However, a strong impediment to the usage of the method for typical applied problems of industria… ▽ More The phase-field method has become a useful tool for the simulation of classical metallurgical phase transformations as well as other phenomena related to materials science. The thermodynamic consistency that forms the basis of these formulations lends to its strong predictive capabilities and utility. However, a strong impediment to the usage of the method for typical applied problems of industrial and academic relevance is the significant overhead with regard to the code development and know-how required for quantitative model formulations. In this paper, we report the development of an open-source phase-field software stack that contains generic formulations for the simulation of multi-phase and multi-component phase transformations. The solvers incorporate thermodynamic coupling that allows the realization of simulations with real alloys in scenarios directly relevant to the materials industry. Further, the solvers utilize parallelization strategies using either multiple CPUs or GPUs to provide cross-platform portability and usability on available supercomputing machines. Finally, the solver stack also contains a graphical user interface to gradually introduce the usage of the software. The user interface also provides a collection of post-processing tools that allow the estimation of useful metrics related to microstructural evolution. △ Less

Submitted 1 April, 2024; originally announced April 2024.

Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 single crystal

Authors: Sanand Kumar Pradhan, Sharadnarayan Pradhan, Priyanath Mal, P. Rambabu, Archana Lakhani, Bipul Das, Bheema Lingam Chittari, G. R. Turpu, Pradip Das

Abstract: Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni$_{3}$In$_{2}$Se$_{2}$ kagome topological semimetal. First-principle calculations indicate six endless Dirac nodal li… ▽ More Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni$_{3}$In$_{2}$Se$_{2}$ kagome topological semimetal. First-principle calculations indicate six endless Dirac nodal lines and two nodal rings with a $π$-Berry phase in the Ni$_{3}$In$_{2}$Se$_{2}$ compound. The temperature-dependent resistivity is dominated by two scattering mechanisms: $s$-$d$ interband scattering occurs below 50 K, while electron-phonon ($e$-$p$) scattering is observed above 50 K. The magnetoresistance (MR) curve aligns with the theory of extended Kohler's rule, suggesting multiple scattering origins and temperature-dependent carrier densities. A maximum MR of 120\% at 2 K and 9 T, with a maximum estimated mobility of approximately 3000 cm$^{2}$V$^{-1}$s$^{-1}$ are observed. The Ni atom's hole-like d$_{x^{2}-y^{2} }$ and electron-like d$_{z^{2}}$ orbitals exhibit peaks and valleys, forming a local indirect-type band gap near the Fermi level (E$_{F}$). This configuration enhances the motion of electrons and holes, resulting in high mobility and relatively high magnetoresistance. △ Less

Submitted 6 January, 2024; originally announced January 2024.

Pressure-Driven Transitions in La2CoTiO6: Antiferromagnetic Insulator to Nonmagnetic Metal via Antiferromagnetic Metal in a Double Perovskite Oxide

Authors: Sromona Nandi, Subhadip Pradhan, Ashis K. Nandy, Rudra Sekhar Manna

Abstract: In double perovskite oxides (A$_2$BB$^\prime$O$_6$), magnetism often arises from diluted magnetic lattices, created by combining a perovskite structure with localized 3$d$ magnetic elements (B) alongside another perovskite lattice containing nearly nonmagnetic delocalized 4$d$/$5d$ elements (B$^\prime$). Alternatively, the magnetic lattice can consist entirely of 3$d$ elements, with one being comp… ▽ More In double perovskite oxides (A$_2$BB$^\prime$O$_6$), magnetism often arises from diluted magnetic lattices, created by combining a perovskite structure with localized 3$d$ magnetic elements (B) alongside another perovskite lattice containing nearly nonmagnetic delocalized 4$d$/$5d$ elements (B$^\prime$). Alternatively, the magnetic lattice can consist entirely of 3$d$ elements, with one being completely nonmagnetic with $d^0$ state. La$_2$CoTiO$_6$ (LCTO), a representative double perovskite oxide, contains Ti in a nonmagnetic state with a $d^0$ electron configuration due to its $4^+$ oxidation state. Experimental evidence shows that LCTO possesses a monoclinic structure (space group $P2_1/n$) and behaves as an antiferromagnet with a Néel temperature of 14.6 K. Through first-principle electronic structure calculations, we uncover that adjusting external hydrostatic pressure induces a sequence of phase transitions: from antiferromagnetic insulator (AFM-I) to antiferromagnetic metal (AFM-M), and ultimately to itinerant nonmagnetic metal (NM-M). The transition from AFM-I to AFM-M at $\sim$ 42 GPa pressure coincides with a shift in spin states, moving from a high-spin (HS) state to a low-spin (LS) state, while Co retains a $d^7$ configuration. Distortion within the monoclinic structure under pressure plays a pivotal role in the spin-state transition. At the AFM-I to AFM-M transition, we observe a sharp decrease in the ratio of the octahedral volumes occupied by Co and Ti. Such change in ratio is linked to variations in octahedral volumes, akin to a breathing mode distortion. We explore the impact of the breathing mode distortion by examining a highly symmetric theoretical structure (space-group $I4/mmm$), achieved by optimizing the structure with all $\angle${Co-O-Ti} angles set to 180$^{\circ}$. △ Less

Submitted 26 July, 2024; v1 submitted 9 October, 2023; originally announced October 2023.

Journal ref: Phys. Rev. B 110, 085101 (2024)

Anomalous Hall effect induced by Berry curvature in topological nodal-line van der Waals ferromagnet Fe$_4$GeTe$_2$

Authors: Satyabrata Bera, Sudipta Chatterjee, Subhadip Pradhan, Suman Kalyan Pradhan, Sk Kalimuddin, Arnab Bera, Ashis K. Nandy, Mintu Mondal

Abstract: The exploration of nontrivial transport phenomena associated with the interplay between magnetic order and spin-orbit coupling (SOC), particularly in van der Waals (vdW) systems has gained a resurgence of interest due to their easy exfoliation, ideal for two-dimensional (2D) spintronics. We report the near room temperature quasi-2D ferromagnet, Fe$_4$GeTe$_2$ from the iron-based vdW family (Fe… ▽ More The exploration of nontrivial transport phenomena associated with the interplay between magnetic order and spin-orbit coupling (SOC), particularly in van der Waals (vdW) systems has gained a resurgence of interest due to their easy exfoliation, ideal for two-dimensional (2D) spintronics. We report the near room temperature quasi-2D ferromagnet, Fe$_4$GeTe$_2$ from the iron-based vdW family (Fe$_n$GeTe$_2$, $n$=3,4,5), exhibiting a large anomalous Hall conductivity (AHC), $σ^A_{xy}$ $\sim$ 490 $Ω^{-1}\textrm{cm}^{-1}$ at 2 K. The near quadratic behavior of anomalous Hall resistivity ($ρ^{A}_{xy}$) with the longitudinal resistivity ($ρ_{xx}$) suggests that a dominant AHC contribution is coming from an intrinsic Berry curvature (BC) mechanism. Concomitantly, the electronic structure calculations reveal a large BC arising from SOC induced gaped nodal lines around the Fermi level, governing such large AHC property. Moreover, we also report an exceptionally large anomalous Hall angle ($\simeq$ 10.6\%) and Hall factor ($\simeq$ 0.22 V$^{-1}$) values which so far, are the largest in compared to those for other members in this vdW family. △ Less

Submitted 18 August, 2023; originally announced August 2023.

Comments: 7 pages, 4 figures, supplementary

Raman signatures of lattice dynamics across inversion symmetry breaking phase transition in quasi-1D compound, (TaSe$_4$)$_3$I

Authors: Arnab Bera, Partha Sarathi Rana, Suman Kalyan Pradhan, Mainak Palit, Sk Kalimuddin, Satyabrata Bera, Tuhin Debnath, Soham Das, Deep Singha Roy, Hasan Afzal, Subhadeep Datta, Mintu Mondal

Abstract: Structural phase transition can occur due to complex mechanisms other than simple dynamical instability, especially when the parent and daughter structure is of low dimension. This article reports such an inversion symmetry-breaking structural phase transition in a quasi-1D compound (TaSe$_4$)$_3$I at T$_S\sim$ 141~K studied by Raman spectroscopy. Our investigation of collective lattice dynamics r… ▽ More Structural phase transition can occur due to complex mechanisms other than simple dynamical instability, especially when the parent and daughter structure is of low dimension. This article reports such an inversion symmetry-breaking structural phase transition in a quasi-1D compound (TaSe$_4$)$_3$I at T$_S\sim$ 141~K studied by Raman spectroscopy. Our investigation of collective lattice dynamics reveals three additional Raman active modes in the low-temperature non-centrosymmetric structure. Two vibrational modes become Raman active due to the absence of an inversion center, while the third mode is a soft phonon mode resulting from the vibration of Ta atoms along the \{-Ta-Ta-\} chains. Furthermore, the most intense Raman mode display Fano-shaped asymmetry, inferred as the signature of strong electron-phonon coupling. The group theory and symmetry analysis of Raman spectra confirm the displacive-first-order nature of the structural transition. Therefore, our results establish (TaSe$_4)_3$I as a model system with broken inversion symmetry and strong electron-phonon coupling in the quasi-1D regime. △ Less

Submitted 21 July, 2023; originally announced July 2023.

Comments: Main text - 6 figures, 11 pages, supplementary - 10 figures, 13 pages

Quantum Fisher Information and multipartite entanglement in spin-1 chains

Authors: Federico Dell'Anna, Sunny Pradhan, Cristian Degli Esposti Boschi, Elisa Ercolessi

Abstract: In this paper, we study the ground state Quantum Fisher Information (QFI) in one-dimensional spin-1 models, as witness to Multipartite Entanglement. The models addressed are the Bilinear-Biquadratic model, the most general isotropic SU(2)-invariant spin-1 chain, and the XXZ spin-1 chain, both with nearest-neighbor interactions and open boundary conditions. We show that the scaling of the QFI of st… ▽ More In this paper, we study the ground state Quantum Fisher Information (QFI) in one-dimensional spin-1 models, as witness to Multipartite Entanglement. The models addressed are the Bilinear-Biquadratic model, the most general isotropic SU(2)-invariant spin-1 chain, and the XXZ spin-1 chain, both with nearest-neighbor interactions and open boundary conditions. We show that the scaling of the QFI of strictly non-local observables can be used for characterizing the phase diagrams and, in particular, for studying topological phases, where it scales maximally. Analysing its behavior at the critical phases we are also able to recover the scaling dimensions of the order parameters both for local and string observables. The numerical results have been obtained by exploiting the Density Matrix Renormalization Group algorithm and Tensor Network techniques. △ Less

Submitted 19 November, 2023; v1 submitted 5 July, 2023; originally announced July 2023.

Comments: 12 pages, 6 figures, 5 tables

Journal ref: Phys. Rev. B 108, 144414, 2023

Accretion-Ablation Mechanics

Authors: Satya Prakash Pradhan, Arash Yavari

Abstract: In this paper we formulate a geometric nonlinear theory of the mechanics of accreting-ablating bodies. This is a generalization of the theory of accretion mechanics of Sozio and Yavari (2019). More specifically, we are interested in large deformation analysis of bodies that undergo a continuous and simultaneous accretion and ablation on their boundaries while under external loads. In this formulat… ▽ More In this paper we formulate a geometric nonlinear theory of the mechanics of accreting-ablating bodies. This is a generalization of the theory of accretion mechanics of Sozio and Yavari (2019). More specifically, we are interested in large deformation analysis of bodies that undergo a continuous and simultaneous accretion and ablation on their boundaries while under external loads. In this formulation the natural configuration of an accreting-ablating body is a time-dependent Riemannian 3-manifold with a metric that is an unknown a priori and is determined after solving the accretion-ablation initial-boundary-value problem. In addition to the time of attachment map, we introduce a time of detachment map that along with the time of attachment map, and the accretion and ablation velocities describes the time-dependent reference configuration of the body. The kinematics, material manifold, material metric, constitutive equations, and the balance laws are discussed in detail. As a concrete example and application of the geometric theory, we analyze a thick hollow circular cylinder made of an arbitrary incompressible isotropic material that is under a finite time-dependent extension while undergoing continuous ablation on its inner cylinder boundary and accretion on its outer cylinder boundary. The state of deformation and stress during the accretion-ablation process, and the residual stretch and stress after the completion of the accretion-ablation process are computed. △ Less

Submitted 13 August, 2023; v1 submitted 30 June, 2023; originally announced July 2023.

High transport spin polarization in the van der Waals ferromagnet Fe$_4$GeTe$_2$

Authors: Deepti Rana, Monika Bhakar, Basavaraja G., Satyabrata Bera, Neeraj Saini, Suman Kalyan Pradhan, Mintu Mondal, Mukul Kabir, Goutam Sheet

Abstract: The challenging task of scaling-down the size of the power saving electronic devices can be accomplished by exploiting the spin degree of freedom of the conduction electrons in van der Waals (vdW) spintronic architectures built with 2D materials. One of the key components of such a device is a near-room temperature 2D ferromagnet with good metallicity that can generate a highly spin-polarized elec… ▽ More The challenging task of scaling-down the size of the power saving electronic devices can be accomplished by exploiting the spin degree of freedom of the conduction electrons in van der Waals (vdW) spintronic architectures built with 2D materials. One of the key components of such a device is a near-room temperature 2D ferromagnet with good metallicity that can generate a highly spin-polarized electronic transport current. However, most of the known 2D ferromagnets have either a very low temperature ordering, poor conductivity, or low spin polarization. In this context, the Fe$_n$GeTe$_2$ (with $n\geq3$) family of ferromagnets stand out due to their near-room temperature ferromagnetism and good metallicity. We have performed spin-resolved Andreev reflection spectroscopy on Fe$_4$GeTe$_2$ ($T_{Curie} \sim$ 273 K) and demonstrated that the ferromagnet is capable of generating a very high transport spin polarization, exceeding 50$\%$. This makes Fe$_4$GeTe$_2$ a strong candidate for application in all-vdW power-saving spintronic devices. △ Less

Submitted 1 June, 2023; originally announced June 2023.

Comments: Accepted for publication in Physical Review B

Centrosymmetric-noncentrosymmetric Structural Phase Transition in Quasi one-dimensional compound, (TaSe$_4$)$_3$I

Authors: Arnab Bera, Samir Rom, Suman Kalyan Pradhan, Satyabrata Bera, Sk Kalimuddin, Tanusri Saha-Dasgupta, Mintu Mondal

Abstract: (TaSe$_4$)$_3$I, a compound belonging to the family of quasi-one-dimensional transition-metal tetrachalcogenides, has drawn significant attention due to a recent report on possible coexistence of two antagonistic phenomena, superconductivity and magnetism below 2.5~K (Bera et. al, arXiv:2111.14525). Here, we report a structural phase transition of the trimerized phase at temperature, $T~\simeq$~14… ▽ More (TaSe$_4$)$_3$I, a compound belonging to the family of quasi-one-dimensional transition-metal tetrachalcogenides, has drawn significant attention due to a recent report on possible coexistence of two antagonistic phenomena, superconductivity and magnetism below 2.5~K (Bera et. al, arXiv:2111.14525). Here, we report a structural phase transition of the trimerized phase at temperature, $T~\simeq$~145~K using Raman scattering, specific heat, and electrical transport measurements. The temperature-dependent single-crystal X-ray diffraction experiments establish the phase transition from a high-temperature centrosymmetric to a low-temperature non-centrosymmetric structure, belonging to the same tetragonal crystal family. The first-principle calculation finds the aforementioned inversion symmetry-breaking structural transition to be driven by the hybridization energy gain due to the off-centric movement of the Ta atoms, which wins over the elastic energy loss. △ Less

Submitted 11 April, 2023; originally announced April 2023.

Comments: 11 pages, 5 figures, Under review as a regular article

Topological Superconductivity by Engineering Noncollinear Magnetism in Magnet/ Superconductor Heterostructures: A Realistic Prescription for 2D Kitaev Model

Authors: Pritam Chatterjee, Sayan Banik, Sandip Bera, Arnob Kumar Ghosh, Saurabh Pradhan, Arijit Saha, Ashis K. Nandy

Abstract: We report on a realistic and rather general scheme where noncollinear magnetic textures proximitized with the most common $s$-wave superconductor can appear as the alternative to $p$-wave superconductor{--}the prime proposal to realize two-dimensional (2D) Kitaev model for topological superconductors (TSCs) hosting Majorana flat edge mode (MFEM). A general minimal Hamiltonian suitable for magnet/s… ▽ More We report on a realistic and rather general scheme where noncollinear magnetic textures proximitized with the most common $s$-wave superconductor can appear as the alternative to $p$-wave superconductor{--}the prime proposal to realize two-dimensional (2D) Kitaev model for topological superconductors (TSCs) hosting Majorana flat edge mode (MFEM). A general minimal Hamiltonian suitable for magnet/superconductor heterostructures reveals robust MFEM within the gap of Shiba bands due to the emergence of an effective ``$p_x+p_y$"-type $p$-wave pairing, spatially localized at the edges of a 2D magnetic domain of spin-spiral. We finally verify this concept by considering Mn (Cr) monolayer grown on a $s$-wave superconducting substrate, Nb(110) under strain (Nb(001)). In both 2D cases, the antiferromagnetic spin-spiral solutions exhibit robust MFEM at certain domain edges that is beyond the scope of the trivial extension of 1D spin-chain model in 2D. This approach, particularly when the MFEM appears in the TSC phase for such heterostructure materials, offers a perspective to extend the realm of the TSC in 2D. △ Less

Submitted 12 March, 2024; v1 submitted 7 March, 2023; originally announced March 2023.

Comments: This is the published version

Journal ref: Phys. Rev. B (Letter) 109, L121301 (2024)

Enhanced coercivity and emergence of spin cluster glass state in 2D ferromagnetic material Fe3GeTe2

Authors: Satyabrata Bera, Suman Kalyan Pradhan, Riju Pal, Buddhadeb Pal, Arnab Bera, Sk Kalimuddin, Manjil Das, Deep Singha Roy, Hasan Afzal, Atindra Nath Pal, Mintu Mondal

Abstract: Two-dimensional (2D) van der Waals (vdW) magnetic materials with high coercivity and high $T_\text{C}$ are desired for spintronics and memory storage applications. Fe$_3$GeTe$_2$ (F3GT) is one such 2D vdW ferromagnet with a reasonably high $T_\text{C}$, but with a very low coercive field, $H_\text{c}$ ($\lesssim$100~Oe). Some of the common techniques of enhancing $H_\text{c}$ are by introducing pi… ▽ More Two-dimensional (2D) van der Waals (vdW) magnetic materials with high coercivity and high $T_\text{C}$ are desired for spintronics and memory storage applications. Fe$_3$GeTe$_2$ (F3GT) is one such 2D vdW ferromagnet with a reasonably high $T_\text{C}$, but with a very low coercive field, $H_\text{c}$ ($\lesssim$100~Oe). Some of the common techniques of enhancing $H_\text{c}$ are by introducing pinning centers, defects, stress, doping, etc. They involve the risk of undesirable alteration of other important magnetic properties. Here we propose a very easy, robust, and highly effective method of phase engineering by altering the sample growth conditions to greatly enhance the intrinsic coercivity (7-10 times) of the sample, without compromising its fundamental magnetic properties ($T_\text{C}\simeq$210K). The phase-engineered sample (F3GT-2) comprises of parent F3GT phase with a small percentage of randomly embedded clusters of a coplanar FeTe (FT) phase. The FT phase serves as both mosaic pinning centers between grains of F3GT above its antiferromagnetic transition temperature ($T_\text{C1}\sim$70~K) and also as anti-phase domains below $T_\text{C1}$. As a result, the grain boundary disorder and metastable nature are greatly augmented, leading to highly enhanced coercivity, cluster spin glass, and meta-magnetic behavior. The enhanced coercivity ($\simeq$1~kOe) makes F3GT-2 much more useful for memory storage applications and is likely to elucidate a new route to tune useful magnetic properties. Moreover, this method is much more convenient than hetero-structure and other cumbersome techniques. △ Less

Submitted 29 December, 2022; originally announced December 2022.

Comments: 12 pages, 11 figures

Solar energy harvesting in magnetoelectric coupled manganese ferrite nanoparticles incorporated nanocomposite polymer films

Authors: Sonali Pradhan, Pratik P. Deshmukh, S. N. Jha, S. Satapathy, S. K. Majumder

Abstract: Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based pyroelectric as well as magnetoelectric materials offer great promises for energy harvesting for flexible and wearable applications. Hence, this work focus on solar energy harvesting as well as magnetoelectric phenomenon in two phase nanocomposite film where the constituting phases are manganese ferrite (MnFe2O4) nanoparticles and P… ▽ More Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based pyroelectric as well as magnetoelectric materials offer great promises for energy harvesting for flexible and wearable applications. Hence, this work focus on solar energy harvesting as well as magnetoelectric phenomenon in two phase nanocomposite film where the constituting phases are manganese ferrite (MnFe2O4) nanoparticles and P(VDF-TrFE) polymer. Composite films have been prepared using solution casting technique. X-ray diffraction result shows higher crystallinity of these films. The ferroelectric, magnetic and magnetoelectric properties in variation with applied field and volume percentage of ferrite nanoparticles have been investigated. The preparation condition was optimized in such a way that it results improved ferroelectric polarization of nanocomposite film after incorporation of small amount of ferrite nanoparticles. The maximum magnetoelectric-coupling coefficient of about 156 mV/Oe-Cm was obtained for optimum nanocomposite film when DC bias field was applied perpendicular to electric polarization direction. From a pyroelectric device perspective, solar energy harvesting is also reported. An open circuit voltage of 5V and short circuit current of order of ~1 nA is demonstrated without any pre amplification. Hence, the combination of magnetoelectric and pyroelectric properties of nanocomposite film presented here indicate as a perfect candidate for smart materials, spintronics devices and specified magnetoelectric-based applications. △ Less

Submitted 22 December, 2022; v1 submitted 2 November, 2022; originally announced November 2022.

Effect of nano-size on magnetostriction of BiFeO3 and exceptional magnetoelectric coupling properties of BiFeO3_P(VDF-TrFE) polymer composite films for magnetic field sensor application

Authors: Sonali Pradhan, Pratik P. Deshmukh, Rahul C. Kambale, Tulshidas C. Darvade, Shovan Kumar Majumder, S. Satapathy

Abstract: The existence of magnetostriction in bulk BiFeO3 is still a matter of investigation and it is also an issue to investigate the magnetostriction effect in nano BiFeO3. Present work demonstrates the existence of magnetostrictive strain in superparamagnetic BiFeO3 nanoparticles at room temperature and the magnetoelectric coupling properties in composite form with P(VDFTrFE). Despite few reports on th… ▽ More The existence of magnetostriction in bulk BiFeO3 is still a matter of investigation and it is also an issue to investigate the magnetostriction effect in nano BiFeO3. Present work demonstrates the existence of magnetostrictive strain in superparamagnetic BiFeO3 nanoparticles at room temperature and the magnetoelectric coupling properties in composite form with P(VDFTrFE). Despite few reports on the magnetostriction effect in bulk BiFeO3 evidenced by the indirect method, the direct method (strain gauge) was employed in this work to examine the magnetostriction of superparamagnetic BiFeO3. In addition, a high magnetoelectric coupling coefficient was observed by the lock-in technique for optimized BiFeO3_P(VDF-TrFE) nanocomposite film. These nanocomposite films also exhibit room-temperature multiferroic properties. These results provide aspects of material with immense potential for practical applications in spintronics and magneto-electronics applications. We report a magnetoelectric sensor using superparamagnetic BiFeO3_P(VDF-TrFE) nanocomposite film for detection of ac magnetic field. △ Less

Submitted 22 December, 2022; v1 submitted 2 November, 2022; originally announced November 2022.

Observation of anisotropic Dirac cones in the topological material Ti2Te2P

Authors: Gyanendra Dhakal, Firoza Kabir, Ashis K. Nandy, Alex Aperis, Anup Pradhan Sakhya, Subhadip Pradhan, Klauss Dimitri, Christopher Sims, Sabin Regmi, M. Mofazzel Hosen, Yangyang Liu, Luis Persaud, Dariusz Kaczorowski, Peter M. Oppeneer, Madhab Neupane

Abstract: Anisotropic bulk Dirac (or Weyl) cones in three dimensional systems have recently gained intense research interest as they are examples of materials with tilted Dirac (or Weyl) cones indicatig the violation of Lorentz invariance. In contrast, the studies on anisotropic surface Dirac cones in topological materials which contribute to anisotropic carrier mobility have been limited. By employing angl… ▽ More Anisotropic bulk Dirac (or Weyl) cones in three dimensional systems have recently gained intense research interest as they are examples of materials with tilted Dirac (or Weyl) cones indicatig the violation of Lorentz invariance. In contrast, the studies on anisotropic surface Dirac cones in topological materials which contribute to anisotropic carrier mobility have been limited. By employing angle-resolved photoemission spectroscopy and first-principles calculations, we reveal the anisotropic surface Dirac dispersion in a tetradymite material Ti2Te2P on the (001) plane of the Brillioun zone. We observe the quasi-elliptical Fermi pockets at the M -point of the Brillouin zone forming the anisotropic surface Dirac cones. Our calculations of the Z2 indices confirm that the system is topologically non-trivial with multiple topological phases in the same material. In addition, the observed nodal-line like feature formed by bulk bands makes this system topologically rich. △ Less

Submitted 15 September, 2022; originally announced September 2022.

Comments: 21 pages, 17 figures, Supplementary Information included

Journal ref: Phys. Rev. B 106, 125124 (2022)

Discrete Abelian lattice gauge theories on a ladder and their dualities with quantum clock models

Authors: Sunny Pradhan, Andrea Maroncelli, Elisa Ercolessi

Abstract: We study a duality transformation from the gauge-invariant subspace of a $\mathbb{Z}_N$ lattice gauge theory on a two-leg ladder geometry to an $N$-clock model on a single chain. The main feature of this mapping is the emergence of a longitudinal field in the clock model, whose value depends on the superselection sector of the gauge model, implying that the different sectors of the gauge theory ca… ▽ More We study a duality transformation from the gauge-invariant subspace of a $\mathbb{Z}_N$ lattice gauge theory on a two-leg ladder geometry to an $N$-clock model on a single chain. The main feature of this mapping is the emergence of a longitudinal field in the clock model, whose value depends on the superselection sector of the gauge model, implying that the different sectors of the gauge theory can show quite different phase diagrams. In order to investigate this and see if confined phases might emerge, we perform a numerical analysis for $N = 2, 3, 4$, using exact diagonalization and DMRG. △ Less

Submitted 11 February, 2024; v1 submitted 5 August, 2022; originally announced August 2022.

Comments: 12 pages, 10 figures

Journal ref: Phys. Rev. B 109, 064410 (2024)

Tailoring phase transition from topological superconductor to trivial superconductor induced by magnetic textures of a spin-chain on a $p$-wave superconductor

Authors: Pritam Chatterjee, Saurabh Pradhan, Ashis K. Nandy, Arijit Saha

Abstract: We theoretically investigate the phase transition from a non-trivial topological $p$-wave superconductor to a trivial $s$-wave like superconducting phase through a gapless phase, driven by different magnetic textures as an one-dimensional spin-chain impurity, e.g. Bloch-type, in-plane and out-of-plane Néel-type spin-chains etc. In our proposal, the chain of magnetic impurities is placed on a spin-… ▽ More We theoretically investigate the phase transition from a non-trivial topological $p$-wave superconductor to a trivial $s$-wave like superconducting phase through a gapless phase, driven by different magnetic textures as an one-dimensional spin-chain impurity, e.g. Bloch-type, in-plane and out-of-plane Néel-type spin-chains etc. In our proposal, the chain of magnetic impurities is placed on a spin-triplet $p$-wave superconductor where we obtain numerically as well as analytically an effective $s$-wave like pairing due to spin rotation, resulting in gradual destruction of the Majorana zero modes present in the topological superconducting phase. In particular, when the impurity spins are antiferromagnetically aligned i.e. spiral wave vector $G_{s}=π$, the system becomes an effective $s$-wave superconductor without Majorana zero modes in the local density of states. The Shiba bands, on the other hand, formed due to the overlapping of Yu-Shiba-Rusinov states play a crucial role in this topological to trivial superconductor phase transition, confirmed by the sign change in the minigap within the Shiba bands. We also characterize this topological phase transition via gap closing and winding number analysis. Moreover, interference of the Shiba bands exhibiting oscillatory behavior within the superconducting gap, $-Δ_{p}$ to $Δ_{p}$, as a function of $G_{s}$, also reflects an important evidence for the formation of an effective $s$-wave pairing. Such oscillation is absent in the $p$-wave regime. △ Less

Submitted 5 March, 2023; v1 submitted 30 June, 2022; originally announced June 2022.

Comments: This is the published version

Journal ref: Phys. Rev. B 107, 085423 (2023)

Vector Chirality $κ$ Driven Topological Phase Transition and the Associated Anomalous Hall Conductivity Tuning in a Non-Collinear Antiferromagnet

Authors: Subhadip Pradhan, Kartik Samanta, Kush Saha, Ashis K. Nandy

Abstract: Based on the first-principles electronic structure calculations and subsequent symmetry adapted effective low-energy $\textbf{k.p}$ theory, we show the switching of the vector chirality, $κ$, in a noncollinear antiferromagnet (AFM), Mn$_3$Sn, as an unconventional route to topological phase transition from a nodal-ring to a Weyl point semimetal. Specifically, we find that the switching of $κ$ leads… ▽ More Based on the first-principles electronic structure calculations and subsequent symmetry adapted effective low-energy $\textbf{k.p}$ theory, we show the switching of the vector chirality, $κ$, in a noncollinear antiferromagnet (AFM), Mn$_3$Sn, as an unconventional route to topological phase transition from a nodal-ring to a Weyl point semimetal. Specifically, we find that the switching of $κ$ leads to gaping out an elliptic nodal-ring everywhere at the Fermi-level except for a pair of points on the ring. As a consequence, the topological phase transition switches the anomalous Hall conductivity (AHC) from zero to a giant value. Furthermore, we theoretically demonstrate how the controlled manipulation of the chiral AFM order keeping $κ$ unaltered favors unusual rotation of Weyl-points on the ring. This in turn enables us to tune in-plane components of the AHC by a collective uniform rotations of spins in the AFM unit cell. △ Less

Submitted 27 September, 2023; v1 submitted 30 June, 2022; originally announced June 2022.

Comments: 6 pages, 3 figures

Journal ref: Commun Phys 6, 272 (2023)

Nonlinear coherent light-matter interaction in 2D MoSe$_2$ nanoflakes for all-optical switching and logic applications

Authors: Sk Kalimuddin, Biswajit Das, Nabamita Chakraborty, Madhupriya Samanta, Satyabrata Bera, Arnab Bera, Deep Singha Roy, Suman Kalyan Pradhan, Kalyan K. Chattopadhyay, Mintu Mondal

Abstract: We report a strong nonlinear optical response of 2D MoSe$_2$ nanoflakes (NFs) through spatial self-phase modulation (SSPM) and cross-phase modulation (XPM) induced by nonlocal coherent light-matter interactions. The coherent interaction of light and MoSe$_2$ NFs creates the SSPM of laser beams, forming concentric diffraction rings. The nonlinear refractive index ($n_2$) and the third-order broadba… ▽ More We report a strong nonlinear optical response of 2D MoSe$_2$ nanoflakes (NFs) through spatial self-phase modulation (SSPM) and cross-phase modulation (XPM) induced by nonlocal coherent light-matter interactions. The coherent interaction of light and MoSe$_2$ NFs creates the SSPM of laser beams, forming concentric diffraction rings. The nonlinear refractive index ($n_2$) and the third-order broadband nonlinear optical susceptibility ($χ^{(3)}$) of MoSe$_2$ NFs are determined from the self diffraction pattern at different exciting wavelengths of 405, 532, and 671 nm with varying the laser intensity. The evolution and deformation of diffraction ring patterns are observed and analyzed by the `wind-chime' model and thermal effect. By taking advantage of the reverse saturated absorption of 2D SnS$_2$ NFs compared to MoSe$_2$, an all-optical diode has been designed with MoSe$_2$/SnS$_2$ hybrid structure to demonstrate the nonreciprocal light propagation. Also a few other optical devices based on MoSe$_2$ and other semiconducting materials such as Bi$_2$Se$_3$, CuPc, and graphene have been investigated. The all-optical logic gates and all-optical information conversion have been demonstrated through the XPM technique using two laser beams. The proposed optical scheme based on MoSe$_2$ NFs has been demonstrated as a potential candidate for all-optical nonlinear photonic devices such as all-optical diodes and all-optical switches. △ Less

Submitted 25 June, 2022; originally announced June 2022.

Comments: 20 pages, 6 figures, accepted in advanced optical materials

Revisiting the magnetic ordering through anisotropic magnetic entropy change in quasi-two-dimensional metallic ferromagnet, Fe$_4$GeTe$_2$

Authors: Satyabrata Bera, Suman Kalyan Pradhan, Md Salman Khan, Riju Pal, Buddhadeb Pal, Sk Kalimuddin, Arnab Bera, Biswajit Das, Atindra Nath Pal, Mintu Mondal

Abstract: We have investigated the nature of ferromagnetic order and phase transitions in two dimensional (2D) van der Waals (vdW) layered material, Fe$_4$GeTe$_2$ through measurements of magnetization, magneto-caloric Effect (MCE), and heat capacity. Fe$_4$GeTe$_2$ hosts a complex magnetic phase with two distinct transitions: paramagnetic to ferromagnetic at around $T_\text{C}$ $\sim$ 266 K and another spi… ▽ More We have investigated the nature of ferromagnetic order and phase transitions in two dimensional (2D) van der Waals (vdW) layered material, Fe$_4$GeTe$_2$ through measurements of magnetization, magneto-caloric Effect (MCE), and heat capacity. Fe$_4$GeTe$_2$ hosts a complex magnetic phase with two distinct transitions: paramagnetic to ferromagnetic at around $T_\text{C}$ $\sim$ 266 K and another spin reorientation transition (SRT) at around $T_\text{SRT}$ $\sim $ 100 K. The magnetization measurements shows a prominent thermal hysteresis in proximity to $T_\text{SRT}$ at $H\parallel c$, which implies the first-order nature of SRT. Reasonable MCE has been observed around both transition temperatures ( at around $T_\text{C}$, -$Δ$S$_M^\text{max}$ = 1.95 and 1.99 J.Kg$^{-1}$K$^{-1}$ and at around $T_\text{SRT}$, -$Δ$S$_M^\text{max}$= 3.9 and 2.4 J.Kg$^{-1}$K$^{-1}$ along $H\parallel ab$ and $H\parallel c$ respectively) at 50 kOe magnetic field change. The above results reveal higher MCE value at $T_\text{SRT}$ compared to the values of MCE at $T_\text{C}$. The scaling analysis of MCE at $T_\text{C}$, shows that the rescaled $Δ$S$_M (T, H)$ follow a universal curve confirming the second-order character of the ferromagnetic transition. The same scaling analysis of MCE breaks down at $T_\text{SRT}$ suggesting that SRT is not a second order phase transition. The exponent $n$ from field dependence of magnetic entropy change presents a maximum of $|n|>2$ confirming the first-order nature of SRT. △ Less

Submitted 25 June, 2022; originally announced June 2022.

Comments: 12 pages, 10 figures + appendix

Schrodinger dynamics and Berry phase of undulatory locomotion

Authors: Alexander E. Cohen, Alasdair D. Hastewell, Sreeparna Pradhan, Steven W. Flavell, Jorn Dunkel

Abstract: Spectral mode representations play an essential role in various areas of physics, from quantum mechanics to fluid turbulence, but they are not yet extensively used to characterize and describe the behavioral dynamics of living systems. Here, we show that mode-based linear models inferred from experimental live-imaging data can provide an accurate low-dimensional description of undulatory locomotio… ▽ More Spectral mode representations play an essential role in various areas of physics, from quantum mechanics to fluid turbulence, but they are not yet extensively used to characterize and describe the behavioral dynamics of living systems. Here, we show that mode-based linear models inferred from experimental live-imaging data can provide an accurate low-dimensional description of undulatory locomotion in worms, centipedes, robots, and snakes. By incorporating physical symmetries and known biological constraints into the dynamical model, we find that the shape dynamics are generically governed by Schrodinger equations in mode space. The eigenstates of the effective biophysical Hamiltonians and their adiabatic variations enable the efficient classification and differentiation of locomotion behaviors in natural, simulated, and robotic organisms using Grassmann distances and Berry phases. While our analysis focuses on a widely studied class of biophysical locomotion phenomena, the underlying approach generalizes to other physical or living systems that permit a mode representation subject to geometric shape constraints. △ Less

Submitted 14 April, 2023; v1 submitted 21 May, 2022; originally announced May 2022.

Comments: title change; additional section and figure on time-dependent effective Hamiltonians and Berry phases; additional biological examples; new numerical analysis added to the SI

Defect Modulated Band Modification in Ion Implanted MgO Crystal: Experimental and Ab Initio Calculations

Authors: Sourav Bhakta, Subhadip Pradhan, Ashis K. Nandy, Pratap K. Sahoo

Abstract: Defects creation and annihilation is a fundamental concept in device fabrication. This report studies the optical bandgap modification in MgO by MeV Ni ion irradiation-induced defect states between valance and conduction band. Ion implantation on MgO single crystal produces substitutional defect states along with F (anionic vacancy center), $F_2$, other oxygen vacancy center and V (cationic vacanc… ▽ More Defects creation and annihilation is a fundamental concept in device fabrication. This report studies the optical bandgap modification in MgO by MeV Ni ion irradiation-induced defect states between valance and conduction band. Ion implantation on MgO single crystal produces substitutional defect states along with F (anionic vacancy center), $F_2$, other oxygen vacancy center and V (cationic vacancy center) centers confirmed from absorption and photoluminescence spectra that can be applied as filament in valance charge memory based resistive random access memories. The variation of optical bandgap with Ni ion fluences is ascertained by modifying the electronic band structure. Density Functional Theory (DFT) calculation assists in understanding the evolution of electronic band structure for vacancies and substitutional defects consisting of MgO structures. △ Less

Submitted 14 February, 2022; originally announced February 2022.

Cooperative dynamics in the Fiber Bundle Model

Authors: Bikas K. Chakrabarti, Soumyajyoti Biswas, Srutarshi Pradhan

Abstract: We discuss the cooperative failure dynamics in the Fiber Bundle Model where the individual elements or fibers are Hookean springs, having identical spring constant but different breaking strengths. When the bundle is stressed or strained, especially in the equal-load-sharing scheme, the load supported by the failed fiber gets shared equally by the rest of the surviving fibers. This mean-field type… ▽ More We discuss the cooperative failure dynamics in the Fiber Bundle Model where the individual elements or fibers are Hookean springs, having identical spring constant but different breaking strengths. When the bundle is stressed or strained, especially in the equal-load-sharing scheme, the load supported by the failed fiber gets shared equally by the rest of the surviving fibers. This mean-field type statistical feature (absence of fluctuations) in the load-sharing mechanism helped major analytical developments in the study of breaking dynamics in the model and precise comparisons with simulation results. We intend to present a brief review on these developments. △ Less

Submitted 23 December, 2020; originally announced December 2020.

Comments: Invited review paper for the Spl. Issue on "The Fiber Bundle" in Frontiers in Physics (in Press)

Buckling of chiral rods due to coupled axial and rotational growth

Authors: Satya Prakash Pradhan, Prashant Saxena

Abstract: We present a growth model for special Cosserat rods that allows for induced rotation of cross-sections. The growth law considers two controls, one for lengthwise growth and other for rotations. This is explored in greater detail for straight rods with helical and hemitropic material symmetries by introduction of a symmetry preserving growth to account for the microstructure. The example of a guide… ▽ More We present a growth model for special Cosserat rods that allows for induced rotation of cross-sections. The growth law considers two controls, one for lengthwise growth and other for rotations. This is explored in greater detail for straight rods with helical and hemitropic material symmetries by introduction of a symmetry preserving growth to account for the microstructure. The example of a guided-guided rod possessing a chiral microstructure is considered to study its deformation due to growth. We show the occurrence of growth induced out-of-plane buckling in such rods. △ Less

Submitted 8 January, 2021; v1 submitted 4 September, 2020; originally announced September 2020.

MSC Class: 74B20; 74G60; 74K10

Yu-Shiba-Rusinov states of single magnetic molecule in an $s-wave$ superconductor

Authors: Saurabh Pradhan, Jonas Fransson

Abstract: We use the numerical renormalization group theory to investigate the Yu-Shiba-Rusinov (YSR) bound state properties of single magnetic molecules placed in an s-wave superconducting substrate. The molecule consist of a large core spin and a single orbital, coupled via an exchange interaction. The critical Coulomb interaction for the singlet/doublet transition decreases in the presence of this exchan… ▽ More We use the numerical renormalization group theory to investigate the Yu-Shiba-Rusinov (YSR) bound state properties of single magnetic molecules placed in an s-wave superconducting substrate. The molecule consist of a large core spin and a single orbital, coupled via an exchange interaction. The critical Coulomb interaction for the singlet/doublet transition decreases in the presence of this exchange interaction for both ferro and anti-ferromagnetic couplings. The number of YSR states also increase to two pairs, however, in the singlet phase, one of the pairs have zero spectral weight. We explore the evolution of the in-gap states using the Anderson model. Away from the particle-hole symmetry point, the results suggest a doublet-singlet-doublet transition as the on-site energy is lowered while keeping the Coulomb interaction fixed. To understand these results, we write down an effective model for the molecule in the limit of large superconducting order parameter. Qualitatively, it explains the various phase transitions and spectral nature of the in-gap states. Finally, we analyze the effects of magnetic anisotropic fields of the core spin on in-gap states. Due to internal degrees of freedom of the spin excited states, a multitude of new states emerges within the gap. Depending on the sign and strength of the uniaxial anisotropic field, the results indicate up to three pairs of YSR states. △ Less

Submitted 31 January, 2020; originally announced January 2020.

Journal ref: Phys. Rev. B 102, 085136 (2020)

Strongly anharmonic collective modes in a coupled electron-phonon-spin problem

Authors: Sauri Bhattacharyya, Sankha Subhra Bakshi, Saurabh Pradhan, Pinaki Majumdar

Abstract: We solve for the finite temperature collective mode dynamics in the Holstein-double exchange problem, using coupled Langevin equations for the phonon and spin variables. We present results in a strongly anharmonic regime, close to a polaronic instability. For our parameter choice the system transits from an `undistorted' ferromagnetic metal at low temperature to a structurally distorted paramagnet… ▽ More We solve for the finite temperature collective mode dynamics in the Holstein-double exchange problem, using coupled Langevin equations for the phonon and spin variables. We present results in a strongly anharmonic regime, close to a polaronic instability. For our parameter choice the system transits from an `undistorted' ferromagnetic metal at low temperature to a structurally distorted paramagnetic insulator at high temperature, through a short range charge ordered (CO) phase near the ferromagnetic crossover at $T_{FM}$. The small amplitude harmonic phonons at low temperature cross over to large amplitude dynamics around $0.5 T_{FM}$ due to thermally generated short range correlated polarons. The rare thermal ``tunneling'' of CO domains generates a hitherto unknown momentum selective spectral weight at very low energy. We compare our results to inelastic neutron data in the manganites and suggest how the singular low energy features can be probed. △ Less

Submitted 16 December, 2019; originally announced December 2019.

Comments: 10 pages, 8 figures, supersedes 1806.06577

Journal ref: Phys. Rev. B 101, 125130 (2020)

Investigation of the Yu-Shiba-Rusinov states of a multi-impurity Kondo system

Authors: A. Kamlapure, L. Cornils, R. Žitko, M. Valentyuk, R. Mozara, S. Pradhan, J. Fransson, A. I. Lichtenstein, J. Wiebe, R. Wiesendanger

Abstract: Recent studies of mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to the potential realization of topological superconductivity. The Kondo exchange coupling J_K of such atoms with the electrons in the superconductor has a pair-breaking effect which produces so-called Yu-Shiba-Rusinov (YSR) states within the superconducting energy gap, whose energet… ▽ More Recent studies of mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to the potential realization of topological superconductivity. The Kondo exchange coupling J_K of such atoms with the electrons in the superconductor has a pair-breaking effect which produces so-called Yu-Shiba-Rusinov (YSR) states within the superconducting energy gap, whose energetic positions are intimately connected with the requirements for topological superconductivity. Here, using the tip of a scanning tunneling microscope, we artificially craft a multi-impurity Kondo system coupled to a superconducting host consisting of an Fe adatom interacting with an assembly of interstitial Fe atoms on an oxygen-reconstructed Ta(100) surface and we experimentally investigate the signatures of Kondo screening and the YSR states. With the help of numerical renormalization group (NRG) calculations, we show that the observed behavior can be qualitatively reproduced by a two-impurity Kondo system whose inter-impurity antiferromagnetic interaction J is adjusted by the number of interstitial Fe atoms in the assembly. When driving the system from the regime of two decoupled Kondo singlets (small J) to that of an antiferromagnetic dimer (large J), the YSR state shows a characteristic cross-over in its energetic position and particle-hole asymmetry. △ Less

Submitted 9 November, 2019; originally announced November 2019.

Comments: 34 pages, 4 figures, 6 supplementary figures