Showing 1–50 of 420 results for author: Singh, D

Transient Electrical Response Beyond Quasistatic Capacitance at Mechanically Excited Droplet--Dielectric Interfaces

Authors: Pramodt Srinivasula, Rameez Raja Khan, Diwakar Singh, Gaurav Bhutani

Abstract: Dynamic electrowetting of conducting droplets under mechanical deformation is conventionally modeled as a quasi-static variable-capacitance system, in which the electrical response is assumed to be governed solely by the evolution of the droplet--electrode contact area. Under the assumption of instantaneous charge equilibration, this framework successfully describes the cyclic steady-state electro… ▽ More Dynamic electrowetting of conducting droplets under mechanical deformation is conventionally modeled as a quasi-static variable-capacitance system, in which the electrical response is assumed to be governed solely by the evolution of the droplet--electrode contact area. Under the assumption of instantaneous charge equilibration, this framework successfully describes the cyclic steady-state electromechanical response of the system. However, its validity for transient interfacial electrical dynamics remains largely unexplored. Here, the transient electrowetting response of mercury droplets confined between a polymeric dielectric-coated electrode (PTFE or PVDF) and an opposing copper electrode is investigated under periodic mechanical excitation with multiple waveforms at 2 Hz. The measured contact area and corresponding capacitance evolve closely as predicted from instantaneous surface-energy minimization, confirming that the liquid-interface mechanics remain quasi-static. In contrast, the measured transient current and instantaneous electrical power exhibit pronounced asymmetric excitation and relaxation phases that are independent of the excitation waveform, demonstrating that transient charge evolution cannot be inferred from the instantaneous geometric capacitance alone. This transient behavior is phenomenologically interpreted using constituent first-order interfacial dielectric charge-relaxation kinetics, indicating that the measured current arises from slow dielectric charging followed by dielectric relaxation over the timescale of the imposed periodic mechanical oscillations during discharging. These findings establish that transient electrowetting is governed by the coupled interplay of droplet electrohydrodynamics and dielectric interfacial polarization, requiring a constitutive description beyond quasi-static variable-capacitance models based solely on contact-line dynamics. △ Less

Submitted 7 August, 2026; originally announced August 2026.

Comments: 17 pages, 8 figures

Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO$_3$

Authors: Shubham Farswan, Reshma Kumawat, Dipankar Sarkar, Deeksha Singh, Md. Atif Hasan, Devajyoti Mukherjee, Kaushik Sen

Abstract: We report a temperature-dependent investigation of orthoferrite TbFeO$_3$ using x-ray diffraction, DC magnetization, and Raman scattering, complemented by room-temperature x-ray photoelectron spectroscopy. X-ray diffraction reveals negative thermal expansion over 5-300 K, with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition. Raman… ▽ More We report a temperature-dependent investigation of orthoferrite TbFeO$_3$ using x-ray diffraction, DC magnetization, and Raman scattering, complemented by room-temperature x-ray photoelectron spectroscopy. X-ray diffraction reveals negative thermal expansion over 5-300 K, with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition. Raman scattering measurements identify the Raman-active phonon modes and show clear deviations from the conventional Klemens anharmonic decay model, particularly in phonon frequencies, indicating the presence of spin-phonon coupling. Two modes of $A_g$ and $B_{1g}$ symmetry exhibit a crossover from Gaussian-dominated line shapes at low temperatures to mixed Gaussian-Lorentzian profiles at higher temperatures, reflecting a transition from inhomogeneous broadening to lifetime-driven dynamics. High-energy Raman spectra reveal two-magnon excitations associated with the Fe sublattice, consistent with linear spin-wave theory, whose spectral weight shows only weak temperature dependence. In addition, a broad Raman mode emerging below $\sim 175$ K exhibits an order-parameter-like temperature evolution and coincides with the onset of phonon anomalies, while no corresponding strong anomaly is observed in the two-magnon response. Taken together, these results establish TbFeO$_3$ as a system with pronounced interplay among lattice dynamics, spin correlations, and emergent local magnetic-lattice anomalies. △ Less

Submitted 1 August, 2026; originally announced August 2026.

Comments: 22 pages, 19 figures

Spin-momentum locking of polariton edge states in honeycomb lattices

Authors: Andrea Herrero Otermin, Nicola Carlon Zambon, Dheerendra Singh, Neha Bhoria, Rimi Banerjee, Christian G. Mayer, Simon Betzold, Siddhartha Dam, Monika Emmerling, Sven Höfling, Luis Viña, Subhaskar Mandal, Carlos Antón-Solanas

Abstract: Transverse-electric/Transverse-magnetic splitting in dielectric-mirror microcavities introduces an effective spin-orbit coupling for photons. While the bulk states remain linearly polarized, for exponentially localized edge states in a photonic lattice, this coupling induces elliptical polarization whose handedness is locked to the propagation direction, analogous to the transverse spin of evanesc… ▽ More Transverse-electric/Transverse-magnetic splitting in dielectric-mirror microcavities introduces an effective spin-orbit coupling for photons. While the bulk states remain linearly polarized, for exponentially localized edge states in a photonic lattice, this coupling induces elliptical polarization whose handedness is locked to the propagation direction, analogous to the transverse spin of evanescent electromagnetic waves. We reveal spin-momentum locking through Stokes polarimetry of zigzag edge states in a honeycomb exciton-polariton lattice. The effect persists in a stretched honeycomb supporting a photonic bandgap, where spin-polarized carrier injection enables selective lasing of either chiral edge states. Our results provide a route toward ultrafast spin-controlled unidirectional propagation in polariton systems without external magnetic fields. △ Less

Submitted 24 July, 2026; v1 submitted 4 July, 2026; originally announced July 2026.

Comments: 4 figures, 7 pages

Response of a dipolar BEC to Laguerre-Gaussian beam driven STIRAP

Authors: Deepu Singh, Hari Sadhan Ghosh, Arpana Saboo, Soumyadeep Halder, Sonjoy Majumder

Abstract: Coherent light-matter coupling via STIRAP can offer a versatile route to nucleate quantized vortices in Bose-Einstein condensates through the orbital angular momentum transfer from a vortex beam, yet its efficacy in dipolar condensates remains an open question. Can the orbital angular momentum of a Laguerre-Gaussian beam be coherently transferred to a dipolar BEC via STIRAP? We investigate this fo… ▽ More Coherent light-matter coupling via STIRAP can offer a versatile route to nucleate quantized vortices in Bose-Einstein condensates through the orbital angular momentum transfer from a vortex beam, yet its efficacy in dipolar condensates remains an open question. Can the orbital angular momentum of a Laguerre-Gaussian beam be coherently transferred to a dipolar BEC via STIRAP? We investigate this for a quasi-two-dimensional trapped dipolar condensate using co-propagating Gaussian and Laguerre-Gaussian laser beams. The interplay between long-range dipole-dipole interactions and short-range contact interactions enables access to three interaction-driven phases: superfluid, droplet, and supersolid. We find that the amount of angular momentum transferred from the optical field to the dipolar condensate, along with the nucleation and persistence of vortices, depends strongly on the underlying phases of the dipolar BEC. In the superfluid, STIRAP achieves a near-complete population transfer and nucleates a long-lived quantized vortex, reflecting efficient transfer of angular momentum to the condensate. In the droplet phase, although the vortex remains pinned within the density profile, the angular momentum is partially retained and oscillatory, accompanied by droplet fragmentation and recombination. In the supersolid phase, when the external magnetic field is oriented perpendicular to the LG beam's propagation direction, the emergence of a modulated density distribution along with a slight reduction in inter-droplet coherence leads to vortex delocalization and eventually exits from the condensate along the field direction, yielding a vanishing average angular momentum. However, reorienting the magnetic polarization along the beam propagation direction restores efficient angular momentum transfer and stabilizes the vortex within the supersolid phase. △ Less

Submitted 9 June, 2026; v1 submitted 25 May, 2026; originally announced May 2026.

Comments: 14 pages, 7 figures

Electrochemical stability and lithium insertion at the Li|Li3OCl solid electrolyte interface

Authors: Deobrat Singh, Li-Yun Tian, Moyses Araujo, Raquel Lizarraga

Abstract: Solid-state lithium batteries have attracted considerable attention due to their potential to provide improved safety and higher energy density compared with conventional liquid electrolyte batteries. However, the stability of the interface between Li metal anodes and solid electrolytes remains a critical issue that strongly influences battery performance. In this work, first-principles density fu… ▽ More Solid-state lithium batteries have attracted considerable attention due to their potential to provide improved safety and higher energy density compared with conventional liquid electrolyte batteries. However, the stability of the interface between Li metal anodes and solid electrolytes remains a critical issue that strongly influences battery performance. In this work, first-principles density functional theory calculations are performed to investigate the interfacial properties of a solid-state battery system composed of Li metal anode and Li3OCl solid electrolyte. The structural stability, electronic structure, and electrochemical behavior of the Li|Li3OCl interface are systematically analyzed. Several interface orientations are constructed and compared in order to identify the most energetically favorable configuration. The electronic properties and interfacial charge redistribution are further examined to understand the nature of the interaction between Li metal and the Li3OCl electrolyte. Our results indicate that the Li|Li3OCl interface exhibits stable structural and electronic characteristics, with localized charge redistribution occurring near the interface region. The electrochemical stability against the insertion of an additional Li atom is also evaluated, showing that Li incorporation is energetically unfavorable in most layers of the electrolyte. These results suggest that the Li3OCl electrolyte maintains good electrochemical stability in contact with Li metal. The present study provides atomic-scale insight into the interfacial behavior of Li|Li3OCl and highlights the potential of Li3OCl as a promising solid electrolyte for solid-state lithium batteries. △ Less

Submitted 12 April, 2026; originally announced April 2026.

Strain-tunable interface electrostatics in Janus MoSSe/silk vdW heterostructure for triboelectric nanogeneration

Authors: Deobrat Singh, Raquel Lizarraga

Abstract: Understanding and engineering interfacial electrostatics in hybrid two-dimensional (2D) and biomolecular material systems is essential for advancing high-performance triboelectric nanogenerators (TENGs). In this work, we systematically investigate the strain-dependent electronic structure and triboelectric response of Janus MoSSe, silk fibroin, and their van der Waals (vdW) heterostructure using f… ▽ More Understanding and engineering interfacial electrostatics in hybrid two-dimensional (2D) and biomolecular material systems is essential for advancing high-performance triboelectric nanogenerators (TENGs). In this work, we systematically investigate the strain-dependent electronic structure and triboelectric response of Janus MoSSe, silk fibroin, and their van der Waals (vdW) heterostructure using first-principles calculations. Tensile strain induces a pronounced band-gap reduction in the MoSSe/silk interface, exceeding that of the isolated constituents and indicating enhanced interlayer electronic coupling. The vdW heterostructure exhibits a significant work-function shift and a substantially larger dipole moment compared to MoSSe and silk alone, revealing strong interfacial charge redistribution driven by Fermi-level alignment and asymmetric polarization. This enhanced polarization directly amplifies the triboelectric surface charge density, producing values more than double those of pristine MoSSe and several orders of magnitude higher than silk. Consequently, the open-circuit voltage and overall triboelectric output are markedly improved across all strain levels. These results demonstrate that synergistic interfacial polarization and strain engineering can effectively elevate charge separation, storage, and transfer efficiencies, establishing the MoSSe/silk vdW heterostructure as a promising material for next-generation high-efficiency TENGs. △ Less

Submitted 12 April, 2026; originally announced April 2026.

Coherent Control of Nanoscale Nuclear Spin Ensembles in the Spin Noise Regime

Authors: Ana Martin, Roberto Rizzato, Carlos Munuera-Javaloy, Dileep Singh, Dominik B. Bucher, Jorge Casanova

Abstract: Spin defects in solids, such as the nitrogen-vacancy (NV) center in diamond, have emerged as a key tool for detecting nuclear spins at the nanoscale. While active nuclear spin control via radio-frequency (RF) irradiation is often unnecessary for standard spin-noise detection, it becomes essential for advanced protocols like multidimensional nanoscale NMR. In this work, we investigate nuclear spin… ▽ More Spin defects in solids, such as the nitrogen-vacancy (NV) center in diamond, have emerged as a key tool for detecting nuclear spins at the nanoscale. While active nuclear spin control via radio-frequency (RF) irradiation is often unnecessary for standard spin-noise detection, it becomes essential for advanced protocols like multidimensional nanoscale NMR. In this work, we investigate nuclear spin control using correlation spectroscopy techniques. We demonstrate, both theoretically and experimentally, that the resulting nuclear spin dynamics depend critically on the initial RF phase and its orientation relative to the NV crystalline axis. Depending on these parameters, identical nuclear rotations can yield full, partial, or even vanishing contrast in the NV readout. These findings highlight a previously underappreciated aspect of spin manipulation in the spin-noise regime: the link between the phase and direction of the applied RF field and its direct impact on correlation-based experiments. Consequently, imperfect calibration of these parameters can lead to ambiguous signal contrasts and misinterpretation of the underlying nuclear spin dynamics. Our results provide deeper insight into nanoscale spin control and pave the way toward reliable multidimensional spin resonance experiments. △ Less

Submitted 10 April, 2026; originally announced April 2026.

Comments: 5 pages, 2 figures and 3 appendices

Role of atomic vacancies and second-neighbor antiferromagnetic-exchange coupling in a ferromagnetic nanoparticle

Authors: Harun Al Rashid, Muskan Sharma, Shruti, Dheeraj Kumar Singh

Abstract: Several factors may be responsible for disorder and frustration in a magnetic nanoparticle, including atomic vacancies on the surface and inside, impurity atoms, long-range magnetic exchange coupling, etc. We use Monte-Carlo simulations within the Heisenberg model to examine the role of randomly distributed atomic vacancies and long-range magnetic-exchange coupling on the temperature-dependent mag… ▽ More Several factors may be responsible for disorder and frustration in a magnetic nanoparticle, including atomic vacancies on the surface and inside, impurity atoms, long-range magnetic exchange coupling, etc. We use Monte-Carlo simulations within the Heisenberg model to examine the role of randomly distributed atomic vacancies and long-range magnetic-exchange coupling on the temperature-dependent magnetic properties of ferromagnetic nanoparticles. In particular, we study the role of the second-neighbor antiferromagnetic exchange coupling and missing atoms inside the particle resulting in broken nearby bonds. We find that both factors may enhance the superparamagnetic behaviors of such particles. △ Less

Submitted 18 February, 2026; originally announced February 2026.

Comments: 11pages, 6 figures, typos corrected

DataScribe: An AI-Native, Policy-Aligned Web Platform for Multi-Objective Materials Design and Discovery

Authors: Divyanshu Singh, Doguhan Sarıtürk, Cameron Lea, Md Shafiqul Islam, Raymundo Arroyave, Vahid Attari

Abstract: The acceleration of materials discovery requires digital platforms that go beyond data repositories to embed learning, optimization, and decision-making directly into research workflows. We introduce DataScribe, an AI-native, cloud-based materials discovery platform that unifies heterogeneous experimental and computational data through ontology-backed ingestion and machine-actionable knowledge gra… ▽ More The acceleration of materials discovery requires digital platforms that go beyond data repositories to embed learning, optimization, and decision-making directly into research workflows. We introduce DataScribe, an AI-native, cloud-based materials discovery platform that unifies heterogeneous experimental and computational data through ontology-backed ingestion and machine-actionable knowledge graphs. The platform integrates FAIR-compliant metadata capture, schema and unit harmonization, uncertainty-aware surrogate modeling, and native multi-objective multi-fidelity Bayesian optimization, enabling closed-loop propose-measure-learn workflows across experimental and computational pipelines. DataScribe functions as an application-layer intelligence stack, coupling data governance, optimization, and explainability rather than treating them as downstream add-ons. We validate the platform through case studies in electrochemical materials and high-entropy alloys, demonstrating end-to-end data fusion, real-time optimization, and reproducible exploration of multi-objective trade spaces. By embedding optimization engines, machine learning, and unified access to public and private scientific data directly within the data infrastructure, and by supporting open, free use for academic and non-profit researchers, DataScribe functions as a general-purpose application-layer backbone for laboratories of any scale, including self-driving laboratories and geographically distributed materials acceleration platforms, with built-in support for performance, sustainability, and supply-chain-aware objectives. △ Less

Submitted 12 January, 2026; originally announced January 2026.

Probing the intermediate state of type-I superconductor SnAs using Muon Spin Spectroscopy

Authors: Shashank Srivastava, Omkar Kulkarni, Arushi, Deepak Singh, Poulami Manna, Priya Mishra, Suhani Sharma, Pabitra Kumar Biswas, Rhea Stewart, Adrian D. Hillier, Ravi Prakash Singh

Abstract: Superconductivity with non-trivial band topology provides a novel platform for exploring topological superconductivity and its quantum applications. A detailed microscopic understanding of the superconducting ground state in such materials is crucial. Here, we report the results of a muon spin rotation/relaxation study ($μ$SR) of the topologically non-trivial superconductor SnAs, which exhibits su… ▽ More Superconductivity with non-trivial band topology provides a novel platform for exploring topological superconductivity and its quantum applications. A detailed microscopic understanding of the superconducting ground state in such materials is crucial. Here, we report the results of a muon spin rotation/relaxation study ($μ$SR) of the topologically non-trivial superconductor SnAs, which exhibits superconductivity below 3.74(1) \si{K}. Zero-field (ZF) $μ$SR data reveal that this system is a time-reversal invariant superconductor, and systematic transverse-field (TF) $μ$SR measurements unveil the type-I nature of the SnAs superconductor. We have established the superconducting phase diagram to understand the intermediate state of type-I superconductors. Moreover, ab \textit{initio} band structure and phonon calculations are performed, which correlate with the experimental characterization. △ Less

Submitted 19 December, 2025; originally announced December 2025.

Comments: 8 pages, 6 figures

Formation of Light-Emitting Defects in Ag-based Memristors

Authors: Diana Singh, Maciej Ćwierzona, Régis Parvaud, Sebastian Maćkowski, Alexandre Bouhelier

Abstract: Optical memristors are innovative devices that enable the integration of electro-optical functionalities - such as light modulation, multilevel optical memory, and nonvolatile reprogramming - into neuromorphic networks. Recently, their capabilities have expanded with the development of light-emitting memristors, which operate through various emission mechanisms. One notable process involves the el… ▽ More Optical memristors are innovative devices that enable the integration of electro-optical functionalities - such as light modulation, multilevel optical memory, and nonvolatile reprogramming - into neuromorphic networks. Recently, their capabilities have expanded with the development of light-emitting memristors, which operate through various emission mechanisms. One notable process involves the electroluminescence of defects generated within the switching matrix during device activation. In this study, we explore the early-stage formation and evolution of the species responsible for light emission in Ag-based in-plane memristors. Our approach combines electrical stimulation with correlated optical electroluminescence and photoluminescence measurements. The findings provide valuable insights into controlling emission processes in memristors, paving the way for their integration as essential components in neuromorphic circuits. △ Less

Submitted 20 April, 2026; v1 submitted 26 November, 2025; originally announced November 2025.

Comments: 10 pages, 7 figures. Prepared for submission

Diode effect in a skyrmion-coupled high-temperature Josephson junction

Authors: Digvijay Singh, Pankaj Sharma, Narayan Mohanta

Abstract: We show that a planar Josephson junction having $d$-wave superconducting regions, with a skyrmion crystal placed underneath, produces a robust gate-tunable superconducting diode effect. The spatially-varying exchange field of the skyrmion crystal breaks both inversion and time-reversal symmetries, leading to an asymmetric current-phase relation with an anomalous phase shift. Our theoretical calcul… ▽ More We show that a planar Josephson junction having $d$-wave superconducting regions, with a skyrmion crystal placed underneath, produces a robust gate-tunable superconducting diode effect. The spatially-varying exchange field of the skyrmion crystal breaks both inversion and time-reversal symmetries, leading to an asymmetric current-phase relation with an anomalous phase shift. Our theoretical calculations, obtained using resistively and capacitively shunted junction model combined with Bogoliubov-de Gennes method, reveal that the diode efficiency is largely tunable by controlling external gate voltage and skyrmion radius. Incorporation of a $d$-wave superconductor such as high-$T_c$ Cuprate enables the diode to function at higher operating temperatures. Our results establish a unique and practically-realizable mechanism for devising tunable field-free superconducting diodes based on magnetic texture-superconductor hybrid platforms. △ Less

Submitted 1 November, 2025; originally announced November 2025.

Comments: 8 pages, 4 figures

Structural transition and possible pressure-induced superconductivity in a suboxide La$_5$Pb$_3$O

Authors: Jiaqiang Yan, David Singh, Bayram Saparov, Huibo Cao, Yejun Feng, Jinguang Cheng, Yoshia Uwatoko, David Mandrus

Abstract: Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$_5$Pb$_3$O. Upon cooling through $T_t$ = 225 K, La$_5$Pb$_3$O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical… ▽ More Here we report a structural phase transition and its possible competition with superconductivity in the suboxide La$_5$Pb$_3$O. Upon cooling through $T_t$ = 225 K, La$_5$Pb$_3$O transforms from a high-temperature I4/mcm to a low-temperature P4/ncc structure in which La - Pb dimerization along the c-axis occurs. This transition is accompanied by anomalies in the temperature dependence of electrical resistivity and specific heat. High-pressure electrical transport measurements reveal that hydrostatic pressure suppresses the structural transition and possibly induces superconductivity with a maximum superconducting temperature of 10 K. Density functional theory calculations show minimal changes in the electronic density of states and no gap opening at $E_F$ across $T_t$, suggesting that the transition is driven by bonding effects rather than Fermi surface instability. These findings establish La$_5$Pb$_3$O as a promising platform for exploring the interplay between weak structural transitions and superconductivity. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 9 figures, 9 pages

Journal ref: Phys. Rev. Materials 9, 124801 (2025)

Non-reciprocal spin-wave excitations in Rashba-Hubbard ferromagnets

Authors: Aastha Jain, Dheeraj Kumar Singh

Abstract: We explore the nonreciprocity of spin-wave excitations in the Rashba-Hubbard ferromagnet on a square lattice. Our study reveals that the propagation of spin-wave excitations exhibit non-reciprocal behavior, i.e., spin waves traveling in opposite directions display asymmetry in energy dispersion $ω({\bf q}) \ne ω(-{\bf q)}$, which also results in an asymmetric behavior of group velocity, spin stiff… ▽ More We explore the nonreciprocity of spin-wave excitations in the Rashba-Hubbard ferromagnet on a square lattice. Our study reveals that the propagation of spin-wave excitations exhibit non-reciprocal behavior, i.e., spin waves traveling in opposite directions display asymmetry in energy dispersion $ω({\bf q}) \ne ω(-{\bf q)}$, which also results in an asymmetric behavior of group velocity, spin stiffness, etc. We find that this asymmetric behavior arises only when the magnetic moments are aligned inside the atomic plane, while the excitations remain symmetric for out-of-plane magnetization. The first dominating term in the low-energy dispersion is linear. However, if the magnetic moments are out-of-plane, then the first dominant term is quadratic instead. The low-energy non-quadratic behavior is examined in the intermediate-to-strong coupling regime for various strengths of Rashba spin-orbit coupling. △ Less

Submitted 8 November, 2025; v1 submitted 5 July, 2025; originally announced July 2025.

Comments: 10 pages, 8 figures

Carbon Nitride: Physical properties and Applications

Authors: Shilpi Kumari, Soubhagyam sharma, Manisha Kumari, Manish Kumar Singh, Rakesh K. Prasad, Kwang-geol Lee, Dilip K. Singh

Abstract: Graphitic carbon nitride has emerged as a versatile, metal-free semiconductor with applications spanning over broad range of domains encompassing energy storage, environmental remediation and sensing. Despite significant progress in recent years, there remains a lack of comprehensive discussion on the graphitic carbon nitride's evolving role in next-generation technologies and the engineering stra… ▽ More Graphitic carbon nitride has emerged as a versatile, metal-free semiconductor with applications spanning over broad range of domains encompassing energy storage, environmental remediation and sensing. Despite significant progress in recent years, there remains a lack of comprehensive discussion on the graphitic carbon nitride's evolving role in next-generation technologies and the engineering strategies needed to overcome existing challenges. In this review article, the critical assessment of the physicochemical properties of graphitic carbon nitride which holds potential to enable its function across diverse applications has been elucidated. Current advances in doping, heterojunction formation and composite engineering that enhances its catalytic and electronic performance has been summarized. The article also presents future research directions to unlock the full potential of graphitic carbon nitride as a useful material in sustainable and intelligent systems. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Spectrum Selective Interfaces and Materials towards Non-photothermal Saltwater Evaporation: Demonstration with a White Ceramic Wick

Authors: Navindra D. Singh, James Leung, Ji Feng, Alma K. González-Alcalde, Arial Tolentino, David Tuft, Juchen Guo, Luat T. Vuong

Abstract: Most solar desalination efforts are photothermal: they evaporate water with ``black'' materials that absorb as much sunlight as possible. Such ``brine-boiling'' methods are limited by the high thermal mass of water, i.e., its capacity to store and release heat. Here, we study the light-enhanced evaporation by a hard, white, aluminum nitride wick, and propose a route to selectively target salt-wate… ▽ More Most solar desalination efforts are photothermal: they evaporate water with ``black'' materials that absorb as much sunlight as possible. Such ``brine-boiling'' methods are limited by the high thermal mass of water, i.e., its capacity to store and release heat. Here, we study the light-enhanced evaporation by a hard, white, aluminum nitride wick, and propose a route to selectively target salt-water bonds instead of bulk heating via deep-UV interactions. Through experiments and analyses that isolate the effects of light absorption and heating in aluminum nitride, we provide experimental evidence of a light-driven, spectrum-selective path to non-photothermal saltwater evaporation. Leverage of these light-matter interactions in white ceramic wicks may achieve low-cost, low-energy desalination, reduce the heat island effects of traditional solar technologies, and contribute to future cooling technologies where drought is also a concern. △ Less

Submitted 8 October, 2025; v1 submitted 28 May, 2025; originally announced May 2025.

Comments: Accepted for publication in ACS: Applied Materials & Interfaces, October 2025

Metallic layered materials with magnetic frustration: An ARPES view of the SmAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$

Authors: P. Rezende-Gonçalves, A. Antezak, T. Kato, K. Feng, F. Fortuna, P. Le Fèvre, M. Rosmus, N. Olszowska, T. Sobol, D. J. Singh, R. E. Baumbach, A. F. Santander-Syro, E. Frantzeskakis

Abstract: Compounds of the new materials class LnTAl$_4$X$_2$ (Ln = lanthanide, X = tetrel, T = transition metal) host exotic magnetic phenomena due to geometric frustration induced by their triangular lattice. Complex spin arrangements, magnetic fluctuations and double magnetic transitions have been well observed by means of magneto-transport. Nevertheless, the experimental electronic structure of this fam… ▽ More Compounds of the new materials class LnTAl$_4$X$_2$ (Ln = lanthanide, X = tetrel, T = transition metal) host exotic magnetic phenomena due to geometric frustration induced by their triangular lattice. Complex spin arrangements, magnetic fluctuations and double magnetic transitions have been well observed by means of magneto-transport. Nevertheless, the experimental electronic structure of this family of materials has been poorly studied. We have investigated the experimental electronic structure of two members of this class of materials: SmAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$. By means of Angle-Resolved PhotoEmission Spectroscopy (ARPES) accompanied by Density Functional Theory calculations (DFT), we reveal common trends and features, the important effect of localized spin moments on the electronic structure, the presence of surface-localized electronic states and the nature of the surface termination layer. Low-dimensionality, exchange interaction, and spin-orbit coupling are all important ingredients of the electronic structure. △ Less

Submitted 26 May, 2025; originally announced May 2025.

Comments: 11 pages, 5 figures

Journal ref: Phys. Rev. B 111, 205114 (2025)

Fundamental Understanding of Exposure and Process Chemistry for Enhanced Lithography and Stability of Metal Oxide Resists

Authors: Kevin M. Dorney, Ivan Pollentier, Fabian Holzmeier, Roberto Fallica, Ying-Lin Chen, Lorenzo Piatti, Dhirendra Singh, Laura Galleni, Michiel J. van Setten, Hyo Seon Suh, Danilo De Simone, Geoffrey Pourtois, Paul van der Heide, John Petersen

Abstract: Metal oxide resists (MORs) have shown great promise for high resolution patterning in extreme ultraviolet (EUV) lithography, with potential for integration into high volume manufacturing. However, MORs have recently been shown to exhibit sensitivity to process conditions and environment, leading to critical dimension (CD) variation. While this variation can be reduced with proper process control,… ▽ More Metal oxide resists (MORs) have shown great promise for high resolution patterning in extreme ultraviolet (EUV) lithography, with potential for integration into high volume manufacturing. However, MORs have recently been shown to exhibit sensitivity to process conditions and environment, leading to critical dimension (CD) variation. While this variation can be reduced with proper process control, there is little knowledge on how these aspects affect the image formation mechanism. To bridge these knowledge gaps, we deploy a coordinated, fundamentals-focused approach to yield deep insights into MOR exposure and process chemistry. Our results on a model MOR, an n-butyl Sn-Oxo system, reveal how parameters such as exposure dose, post-exposure bake temperature, and atmospheric species influence the image formation mechanism. Our results, and the coordinated approach using correlative spectroscopies, provide a strong foundation for understanding the image formation mechanism in MOR materials with potential to link mechanistic aspects to CD variation. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Journal ref: Proc. SPIE 13428, Advances in Patterning Materials and Processes XLII, 134281C (22 April 2025)

Unraveling the Reaction Mechanisms in a Chemically Amplified EUV Photoresist from a Combined Theoretical and Experimental Approach

Authors: Laura Galleni, Dhirendra P. Singh, Thierry Conard, Geoffrey Pourtois, Paul van der Heide, John Petersen, Kevin M. Dorney, Michiel J. van Setten

Abstract: Extreme ultraviolet (EUV) lithography has revolutionized high-volume manufacturing of nanoscale components, enabling the production of smaller, denser, and more energy efficient integrated circuit devices. Yet, the use of EUV light results in ionization driven chemistry within the imaging materials of lithography, the photoresists. The complex interplay of ionization, generation of primary and sec… ▽ More Extreme ultraviolet (EUV) lithography has revolutionized high-volume manufacturing of nanoscale components, enabling the production of smaller, denser, and more energy efficient integrated circuit devices. Yet, the use of EUV light results in ionization driven chemistry within the imaging materials of lithography, the photoresists. The complex interplay of ionization, generation of primary and secondary electrons, and the subsequent chemical mechanisms leading to image formation in photoresists has been notoriously difficult to study. In this work, we deploy photoemission spectroscopy with a 92 eV EUV light source combined with first-principles simulations to unravel the chemical changes occurring during exposure in a model chemically amplified photoresist. The results reveal a surprising chemical reaction pathway, namely the EUV-induced breakdown of the photoacid generator (PAG), which is a critical component in the EUV mechanism. This previously unobserved reaction mechanism manifests as changes in intensity of the valence band peaks of the EUV photoemission spectrum, which are linked to degradation of the PAG via an advanced atomistic simulation framework. Our combined experimental and theoretical approach shows that EUV photoemission can simultaneously resolve chemical dynamics and the production of primary and secondary electrons, giving unique insights into the chemical transformation of photoresist materials. Our results pave the way for utilizing accessible, table-top EUV spectroscopy systems for observing EUV photoresist chemical dynamics, with the potential for time-resolved measurements of photoemission processes in the future. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Journal ref: Proc. SPIE 13428, Advances in Patterning Materials and Processes XLII, 134281D (22 April 2025)

Peak Broadening in Photoelectron Spectroscopy of Amorphous Polymers: the Leading Role of the Electrostatic Landscape

Authors: Laura Galleni, Arne Meulemans, Faegheh S. Sajjadian, Dhirendra P. Singh, Shikhar Arvind, Kevin M. Dorney, Thierry Conard, Gabriele D'Avino, Geoffrey Pourtois, Daniel Escudero, Michiel J. van Setten

Abstract: The broadening in photoelectron spectra of polymers can be attributed to several factors, such as light source spread, spectrometer resolution, finite lifetime of the hole state, and solid-state effects. Here, for the first time, we set up a computational protocol to assess the peak broadening induced for both core and valence levels by solid-state effects in four amorphous polymers by using a com… ▽ More The broadening in photoelectron spectra of polymers can be attributed to several factors, such as light source spread, spectrometer resolution, finite lifetime of the hole state, and solid-state effects. Here, for the first time, we set up a computational protocol to assess the peak broadening induced for both core and valence levels by solid-state effects in four amorphous polymers by using a combination of density functional theory, many-body perturbation theory, and classical polarizable embedding. We show that intrinsic local inhomogeneities in the electrostatic environment induce a Gaussian broadening of $0.2$-$0.7$~eV in the binding energies of both core and semi-valence electrons, corresponding to a full width at half maximum (FWHM) of $0.5$-$1.7$~eV for the investigated systems. The induced broadening is larger in acrylate- than in styrene- based polymers, revealing the crucial role of polar groups in controlling the roughness of the electrostatic landscape in the solid matrix. △ Less

Submitted 8 May, 2025; originally announced May 2025.

Journal ref: J. Phys. Chem. Lett. 2024, 15, 3, 834-839

Phonon-polaritons in Zn(1-x)MgxTe (x<0.09): A Raman scattering study

Authors: D. Singh, A. Elmahjoubi, O. Pages, V. J. B. Torres, C. Gardiennet, G. Kervern, A. Polian, Y. Le Godec, J. -P. Itie, S. Diliberto, S. Michel, P. Franchetti, K. Strzalkowski

Abstract: Phonon-polaritons (PP) are phonon-photon coupled modes. Using near-forward Raman scattering, the PP of the cubic Zn(1-x)MgxTe (x<0.09) semiconductor alloy could be measured. While the PP-coupling hardly develops in pure ZnTe, minor Mg-alloying suffices to stabilize a long-lifetime PP strongly bound to the lattice, i.e., with a pronounced phonon character, and yet a fast one originating from the hi… ▽ More Phonon-polaritons (PP) are phonon-photon coupled modes. Using near-forward Raman scattering, the PP of the cubic Zn(1-x)MgxTe (x<0.09) semiconductor alloy could be measured. While the PP-coupling hardly develops in pure ZnTe, minor Mg-alloying suffices to stabilize a long-lifetime PP strongly bound to the lattice, i.e., with a pronounced phonon character, and yet a fast one originating from the highly dispersive photon-like bottleneck of the PP-dispersion. By combining the advantages of a phonon and of a photon, the long-lifetime PP generated by minor Mg-alloying of ZnTe marks an improvement over the PP of pristine ZnTe, that, from the Raman cross section calculation, can only achieve a balanced compromise between the two kinds of advantages, intensity and speed. The discussion of the PP-related lattice dynamics of Zn(1-x)MgxTe (x<0.09) is grounded in a preliminary study of the lattice macro- and microstructure using X-ray diffraction and solid-state nuclear magnetic resonance, respectively, and further relies on ab initio calculations of the native phonon modes behind the PP in the Mg-dilute limit of Zn(1-x)MgxTe (x~0), considering various Mg-isotopes. △ Less

Submitted 15 April, 2025; originally announced April 2025.

Comments: 19 pages, 7 figures

MSC Class: 70 ACM Class: J.2

Position-Momenta Uncertainties in Classical Systems

Authors: Dipesh K. Singh, P. K. Mohanty

Abstract: We design a thermal bath that preserves the conservation of a system's angular momentum or allows it to fluctuate around a specified nonzero mean while maintaining a Boltzmann distribution of energy in the steady state. We demonstrate that classical particles immersed in such baths exhibit position-momentum uncertainties with a strictly positive lower bound proportional to the absolute value of th… ▽ More We design a thermal bath that preserves the conservation of a system's angular momentum or allows it to fluctuate around a specified nonzero mean while maintaining a Boltzmann distribution of energy in the steady state. We demonstrate that classical particles immersed in such baths exhibit position-momentum uncertainties with a strictly positive lower bound proportional to the absolute value of the mean angular momentum. The proportionality constant, $c$, is dimensionless and does not depend explicitly on the system's parameters. Remarkably, while $c$ is universally bounded by unity, it attains the exact value $c=1/2$ for particles in central potentials. △ Less

Submitted 25 November, 2025; v1 submitted 31 March, 2025; originally announced March 2025.

Comments: 9 pages, 4 figures, Supplemental Material

Journal ref: Phys. Rev. E 112, 054129 (2025)

Ultrafast dynamics of carriers, coherent acoustic phonons and strain pulses in BiSbTe1.5Se1.5 topological insulator thin films

Authors: Anupama Chauhan, Sidhanta Sahu, Poulami Ghosh, Dheerendra Singh, Sambhu G Nath, Anjan Kumar N M, P. K. Panigrahi, Chiranjib Mitra, N. Kamaraju

Abstract: We Investigate the ultrafast carrier, coherent acoustic phonons (CAPs), and acoustic strain pulse dynamics in topological insulator BiSbTe1.5Se1.5 (BSTS) thin films of varying thickness using degenerate pump-probe reflection spectroscopy. Here, Sapphire has been chosen as the main substrate due to its maximum acoustic reflectivity at the BSTS-sapphire interface compared to BSTS-GaAs, BSTS-Si, and… ▽ More We Investigate the ultrafast carrier, coherent acoustic phonons (CAPs), and acoustic strain pulse dynamics in topological insulator BiSbTe1.5Se1.5 (BSTS) thin films of varying thickness using degenerate pump-probe reflection spectroscopy. Here, Sapphire has been chosen as the main substrate due to its maximum acoustic reflectivity at the BSTS-sapphire interface compared to BSTS-GaAs, BSTS-Si, and BSTS-MgO interfaces. For the films with thickness more than twice the penetration depth, the transient reflectivity data predominantly exhibits travelling acoustic strain pulses (TASP) on the top of single-exponential electronic decay (~ 2 ps). In contrast, films with thickness less than penetration depth are dominated by CAPs and a bi exponential electronic background with decay times of ~ 2 ps and ~ 260-380 ps. The observed TASP dynamics are well-described by a theoretical acoustic strain model. Further, to elucidate the underlying physical mechanisms governing the behavior of photo-excited carriers, CAPs, and strain pulses, we performed carrier density and temperature-dependent (7-294 K) studies on BSTS films with thicknesses of 22 nm and 192 nm. In the 22 nm film, the both fast and slow decay processes increase with carrier density at room temperature but decrease with temperature at a carrier density of 1.7*10^{19} cm^{-3}. A detailed analysis suggests that the faster decay arises from electron-phonon scattering and carrier diffusion, while the slower decay likely results from defect-assisted and phonon-assisted recombination. Furthermore, increasing the sample temperature leads to anharmonic decay induced softening of ~ 14 % in the phonon frequency and an anomalous ~ 48 % decrease in the phonon damping parameter due to reduced Dirac surface electron and acoustic phonon scattering. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Comments: 40 pages, 18 Figures

Insight into interplay between bandstructure and Coulomb interaction via quasiparticle interference

Authors: Garima Goyal, Dheeraj Kumar Singh

Abstract: Quasiparticle interference has been used frequently for the purpose of unraveling the electronic states in the vicinity of the Fermi level as well as the nature of superconducting gap in the unconventional superconductors. Using the metallic spin-density wave state of iron pnictides as an example, we demonstrate that the quasiparticle interference can also be used as a probe to provide crucial ins… ▽ More Quasiparticle interference has been used frequently for the purpose of unraveling the electronic states in the vicinity of the Fermi level as well as the nature of superconducting gap in the unconventional superconductors. Using the metallic spin-density wave state of iron pnictides as an example, we demonstrate that the quasiparticle interference can also be used as a probe to provide crucial insight into the interplay of the electronic bandstructure and correlation effects in addition to bringing forth the essential features of electronic states in the vicinity of the Fermi level. Our study reveals that the features of quasiparticle interference pattern can help us narrowing down the interaction parameter window and choose a more realistic tight-binding model. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Comments: 10 pages, 6 figures

Statistical Uncertainties of Limit Cycle Systems in Langevin Bath

Authors: Dipesh K. Singh, P. K. Mohanty

Abstract: We show that limit cycle systems in Langevin bath exhibit uncertainty in observables that define the limit-cycle plane, and maintain a positive lower bound. The uncertainty-bound depends on the parameters that determine the shape and periodicity of the limit cycle. In one dimension, we use the framework of canonical dissipative systems to construct the limit cycle, whereas in two dimensions, parti… ▽ More We show that limit cycle systems in Langevin bath exhibit uncertainty in observables that define the limit-cycle plane, and maintain a positive lower bound. The uncertainty-bound depends on the parameters that determine the shape and periodicity of the limit cycle. In one dimension, we use the framework of canonical dissipative systems to construct the limit cycle, whereas in two dimensions, particle in central potentials with radial dissipation provide us natural examples. We also investigate how uncertainties, which are absent in deterministic systems, increase with time when the systems are attached to a bath and eventually cross the lower bound before reaching the steady state. △ Less

Submitted 13 June, 2025; v1 submitted 18 February, 2025; originally announced February 2025.

Comments: 9 pages + 6 figures + supplemental material

Orbital correlations in bilayer nickelates: roles of doping and interlayer coupling

Authors: Garima Goyal, Aastha Jain, Dheeraj Kumar Singh

Abstract: We study the nature of orbital correlations present in the bilayer nickelate within a minimal two-orbital tight-binding model to gain insights into their possible role in stabilizing the less-known weakly-insulating state. The latter has been observed experimentally at ambient pressure. In order to achieve this objective, we examine the static orbital susceptibilities within the random-phase appro… ▽ More We study the nature of orbital correlations present in the bilayer nickelate within a minimal two-orbital tight-binding model to gain insights into their possible role in stabilizing the less-known weakly-insulating state. The latter has been observed experimentally at ambient pressure. In order to achieve this objective, we examine the static orbital susceptibilities within the random-phase approximation. Our study highlights the sensitivity of orbital correlations to various factors including the interlayer coupling, carrier concentration, band-structure details such as the orbital contents, the number of bands contributing at the Fermi level etc. We relate this sensitiveness to the modification of the Fermi surfaces as well as their orbital contents dependent on aforementioned factors. △ Less

Submitted 8 March, 2025; v1 submitted 2 February, 2025; originally announced February 2025.

Comments: 5 pages, 7 figures

Role of Dirac cones in the anisotropic properties associated with the spin-density wave state of iron pnictides

Authors: Garima Goyal, Dheeraj Kumar Singh

Abstract: The origin of unusual anisotropic electronic properties in the spin-density wave state of iron pnictides has conventionally been attributed to the breaking of four-fold rotational symmetry associated with the collinear magnetic order. By using a minimal two-orbital model, we show that a significant portion of the contribution to the anisotropy may come from the Dirac cones, which are not far away… ▽ More The origin of unusual anisotropic electronic properties in the spin-density wave state of iron pnictides has conventionally been attributed to the breaking of four-fold rotational symmetry associated with the collinear magnetic order. By using a minimal two-orbital model, we show that a significant portion of the contribution to the anisotropy may come from the Dirac cones, which are not far away from the Fermi level. We demonstrate this phenomenon by examining optical conductivity and quasiparticle interference in the Dirac-semimetallic state with spin-density wave order, and the latter can be obtained by choosing appropriate interaction parameters and orbital splitting between the $d_{xz}$ and $d_{yz}$ orbitals. We further extend this study to investigate the low-energy spin-wave excitations in the Dirac-semimetallic state with spin-density wave order. △ Less

Submitted 2 February, 2025; originally announced February 2025.

Comments: 9 pages, 7 figures

Transition Metal-Driven Variations in Structure, Magnetism, and Photocatalysis of Monoclinic M3Se4 (M = Fe, Co, Ni) Nanoparticles

Authors: Monika Ghalawat, Inderjeet Chauhan, Dinesh Singh, Chinnakonda S. Gopinath, Pankaj Poddar

Abstract: The transition metal selenides (MxSey) have gained attention for their unique physical and chemical properties, especially those associated with the transition metal (M). Despite advancements in synthesis, fabricating these selenides is challenging due to their complex stoichiometry and high asymmetry. One such system is monoclinic iron selenide (Fe3Se4), which can be used in permanent-magnet tech… ▽ More The transition metal selenides (MxSey) have gained attention for their unique physical and chemical properties, especially those associated with the transition metal (M). Despite advancements in synthesis, fabricating these selenides is challenging due to their complex stoichiometry and high asymmetry. One such system is monoclinic iron selenide (Fe3Se4), which can be used in permanent-magnet technologies and serve as a model system for understanding magnetism. This study focuses on fabricating monoclinic M3Se4 (M = Fe, Co, or Ni) compounds via thermal decomposition, examining how solution chemistry influences their morphology and properties. With a Curie temperature of about 322 K, Fe3Se4 is ferrimagnetic, whereas Co3Se4 and Ni3Se4 are paramagnetic between 5 and 300 K. The latter two compounds also show higher catalytic activity for hydrogen evolution in water splitting, with maximum H2-evolution rates of 1.01, 5.16, and 6.83 mmol h-1g-1 for Fe3Se4, Co3Se4, and Ni3Se4, respectively. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Comments: 52 Pages, 20 Figures, 4 Tables including supporting information

Time-Reversal Symmetry Breaking in Re-Based Kagome Lattice Superconductor

Authors: Manasi Mandal, A. Kataria, P. K. Meena, R. K. Kushwaha, D. Singh, P. K. Biswas, R. Stewart, A. D. Hillier, R. P. Singh

Abstract: We investigated the Re-based kagome superconductor Re$_2$Zr through various measurements, including resistivity, magnetization, specific heat, and muon spin rotation and relaxation spectroscopy. These results suggest that Re$_2$Zr is a moderately coupled potential two-gap superconductor. Zero-field muon relaxation data indicate the possible presence of a time-reversal symmetry-breaking state in th… ▽ More We investigated the Re-based kagome superconductor Re$_2$Zr through various measurements, including resistivity, magnetization, specific heat, and muon spin rotation and relaxation spectroscopy. These results suggest that Re$_2$Zr is a moderately coupled potential two-gap superconductor. Zero-field muon relaxation data indicate the possible presence of a time-reversal symmetry-breaking state in the superconducting ground state. Our investigation identifies Re$_{2}$Zr as a new unconventional superconductor with a potential complex order parameter that warrants considerable experimental and theoretical interest. △ Less

Submitted 17 September, 2024; originally announced September 2024.

Comments: 9 pages, 6 figures

Possible pairing states in the superconducting bilayer nickelate

Authors: Dheeraj Kumar Singh, Garima Goyal, Yunkyu Bang

Abstract: We examine various possibilities for the pairing mechanisms in the recently discovered bilayer-nickelate superconductor within the Bardeen-Cooper-Schrieffer framework. Unlike earlier studies, where only a pure $d$-wave or sign-changing $s$-wave superconductivity instability was investigated, our study explores the possibilities of mixed-state superconducting instability such as the one involving b… ▽ More We examine various possibilities for the pairing mechanisms in the recently discovered bilayer-nickelate superconductor within the Bardeen-Cooper-Schrieffer framework. Unlike earlier studies, where only a pure $d$-wave or sign-changing $s$-wave superconductivity instability was investigated, our study explores the possibilities of mixed-state superconducting instability such as the one involving both $d$- and sign-changing $s$-waves. While assuming that the superconductivity arises because of the magnetic correlations, we examine the nature of the superconducting gap function associated density of states with various possible magnetic correlation wavevectors arising out as a result of multiple pockets owing to the multiple orbitals and bilayer splitting. We also explore the effect of differences in the nature of Fermi surfaces suggested by various studies. △ Less

Submitted 4 October, 2024; v1 submitted 14 September, 2024; originally announced September 2024.

Comments: 6 pages, 11 figures

Nanocomposites of ferrocenyl-modified gold clusters and semiconducting polymers that integrate field-effect transistor and flash memory in a single neuromorphic device

Authors: Deepa Singh, Praveen N. Gunawardene, Mark S. Workentin, Giovanni Fanchini

Abstract: We demonstrate that electroactive thin films incorporating semiconducting polymers and deterministic functionalized gold nanoclusters (ncAu25) lead to integration of the functions of resistive memory device and field-effect transistor (FETs) within a single component (mem-transistor) in a neuromorphic system. Memristor functions originate from ferrocenyl-modified gold nanoclusters (ncAu25-Fc) embe… ▽ More We demonstrate that electroactive thin films incorporating semiconducting polymers and deterministic functionalized gold nanoclusters (ncAu25) lead to integration of the functions of resistive memory device and field-effect transistor (FETs) within a single component (mem-transistor) in a neuromorphic system. Memristor functions originate from ferrocenyl-modified gold nanoclusters (ncAu25-Fc) embedded in polymethyl-methacrylate (PMMA) and devices optimized for maximum 1/0 'flash' memory effect are found to contain 15 wt% ncAu25-Fc. Integrated memristor and neuromorphic functions are obtained by replacing PMMA with poly(3-hexylthiophene) (P3HT) in the active layer, from which transistor effects are derived. Based on the energy band diagrams of ncAu25, PMMA and P3HT, percolation theory is used to explain the memristor 1/0 on/off ratio as a function of ncAu25-Fc concentration. The use of ncAu25-Fc with charge-tunable, ferrocene-modified, ligands is critical toward better cluster-polymer interfaces. Our work shows that nanostructures of polymers and metalorganic frameworks bear strong potential towards neuromorphic devices and the circuital simplification of data storage technology. △ Less

Submitted 7 August, 2024; originally announced August 2024.

Comments: The following article has been accepted in Applied Physics Letters. After it is published, it will be found at https://pubs.aip.org/aip/apl with DOI 10.1063/5.0219013 Copyright (2024) D. Singh, P.N. Gunawardene, M.S. Workentin & G. Fanchini. This article is distributed under a CC BY-NC-ND License. https://creativecommons.org/licenses/by-nc-nd/4.0. 15 pages, 5 figures

Unconventional Pressure Dependent Interorbital and Interlayer Doping in Superconducting Nickelates

Authors: Y. N. Huang, D. J. Singh

Abstract: The discovery of nickelate superconductivity provided the first example of a non-copper-based material with superconductivity strongly analogous to the cuprates, but recent findings raise questions and inconsistencies around the electron counts and doping phase diagrams. We show using superconducting La$_4$Ni$_3$O$_{10}$ that there are unconventional interlayer and interorbital intrinsic doping ef… ▽ More The discovery of nickelate superconductivity provided the first example of a non-copper-based material with superconductivity strongly analogous to the cuprates, but recent findings raise questions and inconsistencies around the electron counts and doping phase diagrams. We show using superconducting La$_4$Ni$_3$O$_{10}$ that there are unconventional interlayer and interorbital intrinsic doping effects that render the $d_{x^2-y^2}$ orbital occupation similar to the cuprates. The results enable a consistent framework for nickelate superconductivity, while maintaining the connection between cuprate and nickelate superconductors. △ Less

Submitted 23 July, 2024; originally announced July 2024.

Journal ref: Physical Review B 110, 174501 (2024)

Photoemission Spectroscopy on photoresist materials: A protocol for analysis of radiation sensitive materials

Authors: Faegheh S. Sajjadian, Laura Galleni, Kevin M. Dorney, Dhirendra P. Singh, Fabian Holzmeier, Michiel J. van Setten, Stefan De Gendt, Thierry Conard

Abstract: Device architectures and dimensions are now at an unimaginable level not thought possible even 10 years ago. The continued downscaling, following the so-called Moore's law, has motivated the development and use of extreme ultraviolet (EUV) lithography scanners with specialized photoresists. Since the quality and precision of the transferred circuit pattern is determined by the EUV induced chemical… ▽ More Device architectures and dimensions are now at an unimaginable level not thought possible even 10 years ago. The continued downscaling, following the so-called Moore's law, has motivated the development and use of extreme ultraviolet (EUV) lithography scanners with specialized photoresists. Since the quality and precision of the transferred circuit pattern is determined by the EUV induced chemical changes in the photoresist, having a deep understanding of these chemical changes is of pivotal importance. For this purpose, several spectroscopic and material characterization techniques have already been employed so far. Among them, photoemission can be essential as it not only allows direct probing of chemical bonds in a quantitative way but also provides useful information regarding the generation and distribution of primary and secondary electrons. However, since high energy photons are being employed for characterization of a photosensitive material, modification of the sample during the measurement is possible and this must be considered when investigating the chemical changes in the photoresist before and after exposure to EUV light. △ Less

Submitted 30 May, 2024; originally announced June 2024.

Journal ref: J. Vac. Sci. Technol. A 41, 053206 (2023)

Enhancing Ionic Conductivity of ceramic Na3Zr2Si2PO12 via NaI Substitution

Authors: Aditya Sekhar, Nikesh Lilani, M. Dinachandra Singh

Abstract: The high ionic conducting sodium superionic conductor Na3Zr2Si2PO12 -NaI composites have been prepared successfully via solid state reaction route. As the NaI content increases, the ionic conductivity significantly changes. The composites with 4% NaI show a maximum ionic conductivity of ~ 3 x 10-4 Ω-1cm-1 at 200oC which is one order of magnitude rise as compared to pristine sample. Further crystal… ▽ More The high ionic conducting sodium superionic conductor Na3Zr2Si2PO12 -NaI composites have been prepared successfully via solid state reaction route. As the NaI content increases, the ionic conductivity significantly changes. The composites with 4% NaI show a maximum ionic conductivity of ~ 3 x 10-4 Ω-1cm-1 at 200oC which is one order of magnitude rise as compared to pristine sample. Further crystal structure and surface morphology also reveal the formation of a glassy phase due to the presence of Na-Si-P-O-I interaction. △ Less

Submitted 3 May, 2024; originally announced May 2024.

Comments: 8 pages, 4 figures, Presented at 9th IAPT National Student Symposium on Physics (NSSP-2022)

Evidence for conventional superconductivity in Bi$_2$PdPt and prediction of topological superconductivity in disorder-free $γ$-BiPd

Authors: S. Sharma, A. D. S. Richards, Sajilesh K. P., A. Kataria, B. S. Agboola, M. Pula, J. Gautreau, A. Ghara, D. Singh, S. Marik, S. R. Dunsiger, M. J. Lagos, A. Kanigel, E. S. Sørensen, R. P. Singh, G. M. Luke

Abstract: We present comprehensive investigations into the structural, superconducting, and topological properties of Bi$_2$PdPt. Magnetization and heat capacity measurements performed on polycrystalline Bi$_2$PdPt demonstrate a superconducting transition at $\approx$ 0.8 K. Moreover, muon spin relaxation/rotation ($μ$SR) measurements present evidence for a time reversal symmetry preserving, isotropically g… ▽ More We present comprehensive investigations into the structural, superconducting, and topological properties of Bi$_2$PdPt. Magnetization and heat capacity measurements performed on polycrystalline Bi$_2$PdPt demonstrate a superconducting transition at $\approx$ 0.8 K. Moreover, muon spin relaxation/rotation ($μ$SR) measurements present evidence for a time reversal symmetry preserving, isotropically gapped superconducting state in Bi$_2$PdPt. We have also performed density-functional theory (DFT) calculations on Bi$_2$PdPt alongside the more general isostructural systems, BiPd$_{x}$Pt$_{1-x}$, of which Bi$_2$PdPt and $γ$-BiPd are special cases for $x=0.5$ and $x=1$ respectively. We have calculated the $Z_2$ topological index from our DFT calculations for a range of substitution fractions, $x$, between $x=0$ and $x=1$ characterizing the topology of the band structure. We find a non-trivial topological state when $x>0.75$ and a trivial topological state when $x<0.75$. Therefore our results indicate that BiPd$_{x}$Pt$_{1-x}$ could be a topological superconductor for $x>0.75$. △ Less

Submitted 27 March, 2024; originally announced March 2024.

Comments: 10 pages, 7 figures

Altermagnetism in NiSi and antiferromagnetic candidate materials with non-collinear spins

Authors: Deepak K. Singh, Sang-Wook Cheong, Jiasen Guo

Abstract: Recently, a new class of magnetic phenomenon, called altermagnetism, was proposed where the underlying spin configuration resembles antiferromagnetic structure, but the system violates \textbf{PT} (PT: Parity times Time reversal) symmetry due to the alternation of crystalline symmetry across magnetic ions. Although the original idea was proposed for the collinear spin structure, a recent report by… ▽ More Recently, a new class of magnetic phenomenon, called altermagnetism, was proposed where the underlying spin configuration resembles antiferromagnetic structure, but the system violates \textbf{PT} (PT: Parity times Time reversal) symmetry due to the alternation of crystalline symmetry across magnetic ions. Although the original idea was proposed for the collinear spin structure, a recent report by Cheong et al. has suggested that antiferromagnetic materials with non-collinear spin structure and local alternation of crystalline arrangement can also manifest altermagnetism. Besides breaking the \textbf{PT} symmetry, altermagnetic compounds are also expected to exhibit anomalous Hall effects of odd orders. Here, we discuss possible candidates in this regard. One example is nickel monosilicide, which was recently shown to exhibit high temperature antiferromagnetism with non-collinear spin structure. It fulfills both criteria of breaking the \textbf{PT} symmetry and manifesting nonlinear anomalous Hall effect. In addition to NiSi, we also discuss other potential antiferromagnetic materials with non-collinear spin configuration for the exploration of altermagnetic states. △ Less

Submitted 23 June, 2024; v1 submitted 27 February, 2024; originally announced February 2024.

Comments: 13 pages, 13 figures, perspective

Emergent topological quasiparticle kinetics in constricted nanomagnets

Authors: J. Guo, D. Hill, V. Lauter, L. Stingaciu, P. Zolnierczuk, C. A. Ullrich, D. K. Singh

Abstract: The ubiquitous domain wall kinetics under magnetic field or current application describes the dynamic properties in nanostructured magnets. However, when the geometrical size of a nanomagnetic system is constricted to the limiting domain wall length scale, the competing energetics between anisotropy, exchange and dipolar interactions can cause emergent kinetics due to quasiparticle relaxation, sim… ▽ More The ubiquitous domain wall kinetics under magnetic field or current application describes the dynamic properties in nanostructured magnets. However, when the geometrical size of a nanomagnetic system is constricted to the limiting domain wall length scale, the competing energetics between anisotropy, exchange and dipolar interactions can cause emergent kinetics due to quasiparticle relaxation, similar to bulk magnets of atomic origin. Here, we present a joint experimental and theoretical study to support this argument -- constricted nanomagnets, made of antiferromagnetic and paramagnetic neodymium thin film with honeycomb motif, reveal fast kinetic events at ps time scales due to the relaxation of chiral vortex loop-shaped topological quasiparticles that persist to low temperature in the absence of any external stimuli. Such phenomena are typically found in macroscopic magnetic materials. Our discovery is especially important considering the fact that paramagnets or antiferromagnets have no net magnetization. Yet, the kinetics in neodymium nanostructures is quantitatively similar to that found in ferromagnetic counterparts and only varies with the thickness of the specimen. This suggests that a universal, topological quasiparticle mediated dynamical behavior can be prevalent in nanoscopic magnets, irrespective of the nature of underlying magnetic material. △ Less

Submitted 17 February, 2024; v1 submitted 15 February, 2024; originally announced February 2024.

Comments: 26 pages, 11 figures (main text 9 pages, 4 figures; supplementary material 17 pages, 7 figures). arXiv admin note: text overlap with arXiv:2305.00093

Weyl semimetallic state with antiferromagnetic order in Rashba-Hubbard model

Authors: Aastha Jain, Garima Goyal, Dheeraj Kumar Singh

Abstract: We study the phase diagram of Rashba-Hubbard model by employing the Hartree-Fock meanfield theory, and thereby establish the existence of an antiferromagnetically ordered Weyl semimetallic state with in-plane magnetic moments. This phase is found to be sandwiched in between the antiferromagnetic insulator and Rashba metal in the interaction vs spin-orbit coupling phase diagram. The antiferromagnet… ▽ More We study the phase diagram of Rashba-Hubbard model by employing the Hartree-Fock meanfield theory, and thereby establish the existence of an antiferromagnetically ordered Weyl semimetallic state with in-plane magnetic moments. This phase is found to be sandwiched in between the antiferromagnetic insulator and Rashba metal in the interaction vs spin-orbit coupling phase diagram. The antiferromagnetically-ordered topological semimetallic state exists in the presence of combined time-reversal and inversion symmetry though individually both are broken. The study of the static magnetic susceptibility indicates the robustness of the antiferromagnetic order within a realistic range of interaction and spin-orbit coupling parameters. In addition to the edge states associated with the Weyl points, we also investigate the spin-resolved quasiparticle interference, which provides important insight into the possible spin texture of the bands especially in the vicinity of Weyl points. △ Less

Submitted 18 February, 2026; v1 submitted 3 February, 2024; originally announced February 2024.

Comments: 11 pages, 11 figures, typos corrected

Optical anisotropy and nonlinearity in deep ultraviolet fluorooxoborates

Authors: Bing-Hua Lei, Chao Cao, David J. Singh

Abstract: Optical anisotropy and nonlinearity are two tantalizingly important and enticing properties of an optical crystal. Combining these two features will have a miraculous effect. The up conversion can extend solid state laser sources to the ultraviolet and deep ultraviolet (DUV) ranges through harmonic generation and for down conversion needed for quantum information technology, but only a few suitabl… ▽ More Optical anisotropy and nonlinearity are two tantalizingly important and enticing properties of an optical crystal. Combining these two features will have a miraculous effect. The up conversion can extend solid state laser sources to the ultraviolet and deep ultraviolet (DUV) ranges through harmonic generation and for down conversion needed for quantum information technology, but only a few suitable materials are known as the medium because of the combination of properties that are required. These include suitable band gaps, moderate optical anisotropy for phase matching and strong nonlinear optical (NLO) response. Fluorooxoborates are a new ideal platform for this effect in DUV. Here we demonstrate that fluorooxoborate is the optimal framework for DUV NLO material and show that the significance of the incorporation of fluorine in borates. The NLO performance of fluorooxoborates is strongly improved in terms of local crystal structure and distribution of electronic states. Importantly, the role of fluorine is to control the structure, while maintaining high band gaps but does not directly provide large contributions to birefringence and the second harmonic generation as the conventional assumptions. This is a consequence of the microscopic electron distribution and the energy position of the fluorine states well below the valence band maxima. Based on our understandings, we constructed two artificial structure and they all behave as anticipated. △ Less

Submitted 20 December, 2023; v1 submitted 4 December, 2023; originally announced December 2023.

Comments: This manuscript contain many errors

Unidirectional charge correlations in hole-doped cuprates

Authors: Dheeraj Kumar Singh, Yunkyu Bang

Abstract: We examine charge correlations and instabilities in the pseudogap phase of high-$T_c$ cuprates modeled by $d$-density wave ordering. The latter has a gap symmetry similar to the one observed in the $d$-wave superconductor. We use $t$-$J$ model to describe the charge correlations in the presence of electron-phonon interaction. Our finding suggest that the charge instability in the normal state is d… ▽ More We examine charge correlations and instabilities in the pseudogap phase of high-$T_c$ cuprates modeled by $d$-density wave ordering. The latter has a gap symmetry similar to the one observed in the $d$-wave superconductor. We use $t$-$J$ model to describe the charge correlations in the presence of electron-phonon interaction. Our finding suggest that the charge instability in the normal state is dominating at an incommensurate wavevector along (1, 1) instead of (1, 0) for a realistic interaction parameter. The dominance at the diagonal wavevector is further enhanced if the coupling between electron and bond-buckling $B_{1g}$ phonon is incorporated. On the other hand, a dominating charge-density correlation develops along (1, 0) at an incommensurate wavevector in the $d$-density wave ordered state, which shows a qualitative agreement with the experiments. The correlation becomes robust only in the presence of $B_{1g}$ phonon. △ Less

Submitted 15 October, 2023; originally announced October 2023.

Comments: 7 pages, 8 figures

Effect of next-nearest neighbor hopping on the single-particle excitations

Authors: Harun Al Rashid, Dheeraj Kumar Singh

Abstract: In the half-filled one-orbital Hubbard model on a square lattice, we study the effect of next-nearest neighbor hopping on the single-particle spectral function at finite temperature using an exact-diagonalization + Monte-Carlo based approach to the simulation process. We find that the pseudogap-like dip, existing in the density of states in between the Néel temperature $T_N$ and a relatively highe… ▽ More In the half-filled one-orbital Hubbard model on a square lattice, we study the effect of next-nearest neighbor hopping on the single-particle spectral function at finite temperature using an exact-diagonalization + Monte-Carlo based approach to the simulation process. We find that the pseudogap-like dip, existing in the density of states in between the Néel temperature $T_N$ and a relatively higher temperature $T^*$, is accompanied with a significant asymmetry in the hole- and particle-excitation energy along the high-symmetry directions as well as along the normal-state Fermi surface. On moving from ($π/2, π/2$) toward $(π, 0)$ along the normal state Fermi surface, the hole-excitation energy increases, a behavior remarkably similar to what is observed in the $d$-wave state and pseudogap phase of high-$T_c$ cuprates, whereas the particle-excitation energy decreases. The quasiparticle peak height is the largest near ($π/2, π/2$) whereas it is the smallest near $(π, 0)$. These spectral features survive beyond $T_N$. The temperature window $T_N \lesssim T \lesssim T^*$ shrinks with an increase in the next-nearest neighbor hopping, which indicates that the next-nearest neighbor hopping may not be supportive to the pseudogap-like features. △ Less

Submitted 15 October, 2023; originally announced October 2023.

Comments: 7 pages, 7 figures

Dislocation breakaway from nanoparticle array linear complexions: Plasticity mechanisms and strength scaling laws

Authors: Divya Singh, Daniel S. Gianola, Timothy J. Rupert

Abstract: Linear complexions are stable defect states, where the stress field associated with a dislocation induces a local phase transformation that remains restricted to nanoscale dimensions. As these complexions are born at the defects which control plasticity in metals, it is crucial to understand their impact on subsequent mechanical properties. In this work, atomistic modeling is used to understand ho… ▽ More Linear complexions are stable defect states, where the stress field associated with a dislocation induces a local phase transformation that remains restricted to nanoscale dimensions. As these complexions are born at the defects which control plasticity in metals, it is crucial to understand their impact on subsequent mechanical properties. In this work, atomistic modeling is used to understand how dislocation mechanics are altered by the presence of nanoparticle array linear complexions in a Ni-Al alloy. Molecular dynamics simulations are used to identify the critical shear stress needed to drive dislocation breakaway, first for nanoparticle arrays formed by Monte Carlo/molecular dynamics methods to represent realistic configurations and subsequently for simplified models that allow the effects of particle spacing and size to be varied in a controlled manner. A combined bowing and progressive unpinning mechanism is uncovered, leading to the demonstration of a new strength scaling law that differs in keys ways from classical Orowan bowing. △ Less

Submitted 10 October, 2023; v1 submitted 29 August, 2023; originally announced August 2023.

High-Index Topological Insulator Resonant Nanostructures from Bismuth Selenide

Authors: Sukanta Nandi, Shany Z. Cohen, Danveer Singh, Michal Poplinger, Pilkhaz Nanikashvili, Doron Naveh, Tomer Lewi

Abstract: Topological insulators (TIs) are a class of materials characterized by an insulting bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic and transport properties have been extensively studied, their optical properties and prospective photonic capabilities have not been fully uncovere… ▽ More Topological insulators (TIs) are a class of materials characterized by an insulting bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic and transport properties have been extensively studied, their optical properties and prospective photonic capabilities have not been fully uncovered. Here, we use a combination of far-field and near-field nanoscale imaging and spectroscopy, to study CVD grown Bi2Se3 nanobeams (NBs). We first extract the mid-infrared (MIR) optical constants of Bi2Se3, revealing refractive index values as high as n ~6.4, and demonstrate that the NBs support Mie-resonances across the MIR. Local near-field reflection phase mapping reveals domains of various phase shifts, providing information on the local optical properties of the NBs. We experimentally measure up to 2π phase-shift across the resonance, in excellent agreement with FDTD simulations. This work highlights the potential of TI Bi2Se3 for quantum circuitry, non-linear generation, high-Q metaphotonics, and IR photodetection. △ Less

Submitted 18 August, 2023; originally announced August 2023.

Piezo-resistive pressure sensor based on CVD-grown ZnO nanowires on Polyethylene Tetrathalate substrate

Authors: Manisha Kumari, Rakesh K. Prasad, Manish K. Singh, Parameswar K. Iyer, Dilip K. Singh

Abstract: Recent developments in the domain of electronic materials and devices have attracted the interest of researchers toward flexible and printable electronic components like organic transistors, printable electrodes and sensors. Zinc Oxide (ZnO) nanowires (NWs) possess a number of excellent properties like high mobility, large exciton binding energy and the direct-band gap in addition to large piezoel… ▽ More Recent developments in the domain of electronic materials and devices have attracted the interest of researchers toward flexible and printable electronic components like organic transistors, printable electrodes and sensors. Zinc Oxide (ZnO) nanowires (NWs) possess a number of excellent properties like high mobility, large exciton binding energy and the direct-band gap in addition to large piezoelectric coefficients. Here, we report on flexible piezo-resistive sensor based on Indium tin oxide (ITO)-coated Polyethylene tetrathalate (PET) substrate. The device shows sensitivity in terms of change in resistance from 100 Ω to 2.4 KΩ at an applied potential of 5V upon bending from flat to 95 degrees. The 1-D nanowire flexible device in its flat state shows saturated output current. We observed ten folds enhanced variation as compared to previous reports. Improved sensitivity was observed in our experiments due to fewer defects in CVD-grown NWs as compared to others where hydrothermally grown nanowires were used. The methodology of device fabrication reported here requires less time and enables efficient devices for the realization of flexible and wearable technology. △ Less

Submitted 16 June, 2023; originally announced July 2023.

Comments: 24 pages, 5 figures

Strain and spin orbit coupling effects on electronic and optical properties of 2D CX/graphene (X = S, Se, Te) vdW heterostructure for solar energy harvesting

Authors: Amit K Bhojani, Hardik L Kagdada, Dheeraj K Singh

Abstract: Vertically stacked two-dimensional (2D) graphene-based van der Waals (vdW) heterostructures have emerged as the technological materials for electronic and optoelectronic device applications. In this regard, for the first time, we systematically predicted the electronic and optical properties of CX/G (X = S, Se and Te; G = graphene) heterostructures under biaxial strain and spin orbit coupling (SOC… ▽ More Vertically stacked two-dimensional (2D) graphene-based van der Waals (vdW) heterostructures have emerged as the technological materials for electronic and optoelectronic device applications. In this regard, for the first time, we systematically predicted the electronic and optical properties of CX/G (X = S, Se and Te; G = graphene) heterostructures under biaxial strain and spin orbit coupling (SOC) by first-principles calculations. Strain is induced by applying mechanical stress to the heterostructures, while SOC arises due to the interaction between the electron spin and its orbital motion. The electronic property calculations reveal that all three heterostructures exhibit indirect semiconducting nature with a narrow bandgap of 0.47-0.62 eV and remain indirect under compressive and tensile strains. Strong band splitting of 78.4 meV has been observed in the conduction band edge of CTe/G heterostructure in the presence of SOC due to the lack of an inversion center attributed to the large hole effective mass. Under compressive strain, the p-type of Schottky contact of CX/G heterostructures is converted into p-type Ohmic contact because of nearly negligible Schottky barrier height. Further, the optical property assessment reveals red and blue shifts in the absorption peak of CX/G heterostructures with regard to tensile and compressive strains, respectively. Despite this, the CTe/G heterostructure achieves a remarkable high η of 24.53% in the strain-free case whereas, it reaches to 28.31% with 4% compressive strain, demonstrating the potential for solar energy conversion device applications. Our findings suggest that CX/G heterostructures could be promising candidates for high-performance optoelectronic devices. △ Less

Submitted 11 June, 2023; originally announced June 2023.

Ultrahigh electrostrain > 1% in lead-free piezoceramics: A critical review

Authors: Gobinda Das Adhikary, Digivijay Narayan Singh, Getaw Abebe Tina, Gudeta Jafo Muleta, Rajeev Ranjan

Abstract: Recently, a series of reports showing ultra-high electrostrain (> 1 %) have appeared in several Pb-free piezoceramics. The ultrahigh electrostrain has been attributed exclusively to the defect dipoles created in these systems. We examine these claims based on another report arXiv:2208.07134 which demonstrated that the measured electric field driven strain increased dramatically simply by reducing… ▽ More Recently, a series of reports showing ultra-high electrostrain (> 1 %) have appeared in several Pb-free piezoceramics. The ultrahigh electrostrain has been attributed exclusively to the defect dipoles created in these systems. We examine these claims based on another report arXiv:2208.07134 which demonstrated that the measured electric field driven strain increased dramatically simply by reducing the thickness of the ceramic discs. We prepared some representative Pb-free compositions reported to exhibit ultrahigh strain and performed electrostrain measurements. We found that these compositions do not show ultrahigh electrostrain if the thickness of the discs is above 0.3 mm (the disc diameters were in the range 10- 12 mm diameter). The ultrahigh strain values were obtained when the thickness was below 0.3 mm. We compare the electrostrain obtained from specimens designed to exhibit defect dipoles with specimens that were not designed to have defect dipoles in Na0.5Bi0.5TiO3 (NBT) and K0.5Na0.5NbO3 (KNN) -based lead-free systems and could obtain much higher strain levels (4- 5 %) in the defect dipole free piezoceramics in the small thickness regime. Our results do not favor the defect dipole theory as the exclusive factor for causing ultrahigh strain in piezoceramics. A new approach is called for to understand the phenomenon of ultrahigh electrostrain caused by the thickness reduction of piezoceramic discs. △ Less

Submitted 5 June, 2023; originally announced June 2023.

Comments: 9 pages, 5 figures, lab report

Persistent dynamic magnetic state in artificial honeycomb spin ice

Authors: Jiasen Guo, Pousali Ghosh, Daniel Hill, Yiyao Chen, Laura Stingaciu, Piotr. Zolnierczuk, Carsten A. Ullrich, Deepak K. Singh

Abstract: Topological magnetic charges, arising due to the non-vanishing magnetic flux on spin ice vertices, serve as the origin of magnetic monopoles that traverse the underlying lattice effortlessly. Unlike spin ice materials of atomic origin, the dynamic state in artificial honeycomb spin ice is conventionally described in terms of finite size domain wall kinetics that require magnetic field or current a… ▽ More Topological magnetic charges, arising due to the non-vanishing magnetic flux on spin ice vertices, serve as the origin of magnetic monopoles that traverse the underlying lattice effortlessly. Unlike spin ice materials of atomic origin, the dynamic state in artificial honeycomb spin ice is conventionally described in terms of finite size domain wall kinetics that require magnetic field or current application. Contrary to this common understanding, here we show that thermally tunable artificial permalloy honeycomb lattice manifests a perpetual dynamic state due to self-propelled magnetic charge defect relaxation in the absence of any external tuning agent. Quantitative investigation of magnetic charge defect dynamics using neutron spin echo spectroscopy reveals sub-ns relaxation times that are comparable to monopole's relaxation in bulk spin ices. Most importantly, the kinetic process remains unabated at low temperature where thermal fluctuation is negligible. This suggests that dynamic phenomena in honeycomb spin ice are mediated by quasi-particle type entities, also confirmed by quantum Monte-Carlo simulations that replicate the kinetic behavior. Our research unveils a new `macroscopic' magnetic particle that shares many known traits of quantum particles, namely magnetic monopole and magnon. △ Less

Submitted 28 April, 2023; originally announced May 2023.

Comments: 12 figures, 15 pages

Journal ref: Nature Communications, 14, 5212 (2023)

Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO$_4$

Authors: P. Mohanty, N. Sharma, D. Singh, Y. Breard, D. Pelloquin, S. Marik, R. P. Singh

Abstract: Geometrically frustrated structures combined with competing exchange interactions that have different magnitudes are known ingredients for achieving exotic properties. Herein, we studied detailed structural, magnetic, thermal (specific heat), magneto-dielectric, and magnetic exchange bias properties of a mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed magnetization, heat capacity… ▽ More Geometrically frustrated structures combined with competing exchange interactions that have different magnitudes are known ingredients for achieving exotic properties. Herein, we studied detailed structural, magnetic, thermal (specific heat), magneto-dielectric, and magnetic exchange bias properties of a mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed magnetization, heat capacity, and neutron powder diffraction studies (NPD) highlight long-range ferrimagnetic ordering with an onset at 355 K. The magnetic structure is established using a ferrimagnetic model (collinear-type) that has a propagation vector k = 0, 0, 0. The magneto-dielectric effect appears below the magnetic ordering temperature, and the exchange bias (EB) effect is observed in field cooled (FC) conditions below 355 K. The magneto-dielectric coupling in CoFeRhO$_4$ originates due to the frustration in the structure, collinear ferrimagnetic ordering, and uncompensated magnetic moments. The unidirectional anisotropy resulting from the uncompensated magnetic moments causes the room-temperature exchange bias effect. Remarkably, the appearance of technologically important properties (ferromagnetism, magnetodielectric effect, and EB) at room temperature in CoFeRhO$_4$ indicates its potential use in sensors or spintronics. △ Less

Submitted 27 April, 2023; originally announced April 2023.

Comments: 8 pages, 11 Figures

Journal ref: Phys. Rev. Materials 7, 084408 (2023)

Antiferromagnetically ordered Dirac semimetal in Hubbard model with spin-orbit coupling

Authors: Garima Goyal, Dheeraj Kumar Singh

Abstract: We examine the possible existence of Dirac semimetal with magnetic order in a two-dimensional system with a nonsymmorphic symmetry by using the Hartree-Fock mean-field theory within the Hubbard model. We locate the region in the second-neighbor spin-orbit coupling vs Hubbard interaction phase diagram, where such a state is stabilized. The edge states for the ribbons along two orthogonal directions… ▽ More We examine the possible existence of Dirac semimetal with magnetic order in a two-dimensional system with a nonsymmorphic symmetry by using the Hartree-Fock mean-field theory within the Hubbard model. We locate the region in the second-neighbor spin-orbit coupling vs Hubbard interaction phase diagram, where such a state is stabilized. The edge states for the ribbons along two orthogonal directions concerning the orientation of in-plane magnetic moments are obtained. Finally, the effect of the in-plane magnetic field, which results in the stabilization of the Weyl semimetallic state, and the nature of the edge states corresponding to the Weyl semimetallic state for ribbon geometries are also explored. △ Less

Submitted 7 January, 2024; v1 submitted 29 March, 2023; originally announced March 2023.

Comments: 9 pages, 10 figures

Sparse Distributed Memory is a Continual Learner

Authors: Trenton Bricken, Xander Davies, Deepak Singh, Dmitry Krotov, Gabriel Kreiman

Abstract: Continual learning is a problem for artificial neural networks that their biological counterparts are adept at solving. Building on work using Sparse Distributed Memory (SDM) to connect a core neural circuit with the powerful Transformer model, we create a modified Multi-Layered Perceptron (MLP) that is a strong continual learner. We find that every component of our MLP variant translated from bio… ▽ More Continual learning is a problem for artificial neural networks that their biological counterparts are adept at solving. Building on work using Sparse Distributed Memory (SDM) to connect a core neural circuit with the powerful Transformer model, we create a modified Multi-Layered Perceptron (MLP) that is a strong continual learner. We find that every component of our MLP variant translated from biology is necessary for continual learning. Our solution is also free from any memory replay or task information, and introduces novel methods to train sparse networks that may be broadly applicable. △ Less

Submitted 20 March, 2023; originally announced March 2023.

Comments: 9 Pages. ICLR Acceptance

Journal ref: ICLR 2023