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Screening-controlled dynamical criticality in the quantum Hall regime
Authors:
Tanima Chanda,
Simrandeep Kaur,
Anantbir Virk,
Kenji Watanabe,
Takashi Taniguchi,
G. J. Sreejith,
Yuval Gefen,
Aveek Bid
Abstract:
At continuous electronic phase transitions, Coulomb interactions can modify the relation between length, energy, and temperature, but experimentally disentangling their effects on spatial versus dynamical criticality has remained difficult, since finite-temperature scaling alone measures only the combined exponent $κ= 1/(zγ)$. Here, we introduce two advances that resolve this limitation. First, by…
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At continuous electronic phase transitions, Coulomb interactions can modify the relation between length, energy, and temperature, but experimentally disentangling their effects on spatial versus dynamical criticality has remained difficult, since finite-temperature scaling alone measures only the combined exponent $κ= 1/(zγ)$. Here, we introduce two advances that resolve this limitation. First, by combining temperature scaling with independent current scaling, we separately extract the dynamical exponent $z$ and the localization-length exponent $γ$ at the quantum Hall plateau transition -- rather than inferring one from an assumed value of the other. Second, using dual-graphite-gated graphene devices in which the effective Coulomb interaction range is tuned geometrically by the ratio of the magnetic length $l_B$ to the graphite-gate distance $d$, we track this separation across both screened and unscreened interaction regimes within the same device platform. Temperature scaling gives $κ\simeq 0.21$ in the screened regime and $κ\simeq 0.41$ in the unscreened regime; combining this with current scaling reveals that screening changes $z$ from $\simeq 1$ in the unscreened regime to $\simeq 2$ in the screened regime. In contrast, $γ$ remains close to $2.4$ throughout. Our results establish that gate-controlled screening selectively modifies the interaction-dependent dynamical sector of the quantum Hall transition, leaving the localization-length exponent $γ$ unchanged within experimental uncertainty. More broadly, this work establishes geometric screening as a versatile tool for controlling interactions and disentangling interaction and disorder effects in correlated two-dimensional systems, including fractional quantum Hall states, moiré materials, and other strongly localized electronic phases.
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Submitted 10 July, 2026;
originally announced July 2026.
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Multiscale modelling of diffusion and retention of hydrogen in multi-occupancy traps in irradiated bcc metals
Authors:
Daniel Mason,
Sanjeet Kaur,
Samanyu Tirumala,
Prashanth Srinivasan,
Ville Jantunen,
Max Boleininger
Abstract:
We use molecular dynamics simulations to directly compute the effective diffusivity of hydrogen gas atoms in homogeneous distributions of monovacancies in tungsten and vanadium, and voids in tungsten. Rather than fitting the results to an Arrhenius law, we compare to an analytic approximation for the effective diffusivity recently derived for multi-occupancy traps [Kaur et al (2025), Phys. Rev. Ma…
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We use molecular dynamics simulations to directly compute the effective diffusivity of hydrogen gas atoms in homogeneous distributions of monovacancies in tungsten and vanadium, and voids in tungsten. Rather than fitting the results to an Arrhenius law, we compare to an analytic approximation for the effective diffusivity recently derived for multi-occupancy traps [Kaur et al (2025), Phys. Rev. Mater. 9:125404]. We find good agreement between full atomistic simulation and our theory, validating the analytic model for diffusivity for materials containing nanoscale defects characteristic of radiation damage. There are no parameters fitted, only physically motivated quantities that can be computed with static density functional or atomistic potential calculations. In this study we prove rapid convergence of hydrogen trap occupation to the steady state using lattice kinetic Monte Carlo, the spontaneous emergence of voids in tungsten using atomistic simulation with empirical potentials, and molecular hydrogen formation in voids using molecular dynamics. We conclude with a prediction for diffusion and retention of hydrogen in voids in tungsten starting from first principles. This work shows that not only is the analytic form for diffusivity and retention in multi-occupancy traps a practical scheme for making predictive simulations of hydrogen isotope diffusion and retention in irradiated microstructures, derived and parameterized from first principles, it is superior to existing single-occupancy trap formalisms.
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Submitted 7 July, 2026;
originally announced July 2026.
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Layer-Polarization-Driven Metal-Insulator Transition in multi-band Graphene Moire' Superlattices
Authors:
Harsimran Kaur Mann,
Simrandeep Kaur,
Harsimran Singh,
Yashashwani Garg,
Amogh Waghmare,
Mohit Kumar Jat,
Kenji Watanabe,
Takashi Taniguchi,
Manish Jain,
Aveek Bid
Abstract:
Graphene/hBN moiré superlattices provide a highly tunable platform for exploring emergent quantum phases in low-dimensional systems. Here, we investigate the moiré superlattice formed between hBN and ABA-stacked trilayer graphene (TLG), an inherently multi-band system. We demonstrate that the moiré potential is not merely a perturbation but a tool to hybridize the distinct massless and massive ele…
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Graphene/hBN moiré superlattices provide a highly tunable platform for exploring emergent quantum phases in low-dimensional systems. Here, we investigate the moiré superlattice formed between hBN and ABA-stacked trilayer graphene (TLG), an inherently multi-band system. We demonstrate that the moiré potential is not merely a perturbation but a tool to hybridize the distinct massless and massive electronic sectors of TLG. By applying a perpendicular displacement field to tune layer polarization, we drive a fundamental reconstruction of the electronic band structure. Specifically, increasing the displacement field evolves the system from a multi-band regime to an effectively single-band regime at low energies, accompanied by a metal--insulator transition at the hole-doped secondary Dirac point. This transition originates from a redistribution of carriers across graphene layers that selectively enhances their coupling to the extrinsic moiré potential. Quantum capacitance measurements provide direct evidence for the suppression of the density of states at the hole-side secondary Dirac point, consistent with gap opening and the emergence of a displacement-field-tuned band gap. Theoretical calculations reproduce these observations and identify layer-selective coupling to the moiré potential as the underlying mechanism. These results demonstrate electrical control of an emergent insulating phase in a low-dimensional moiré system, and highlight that layer polarization and layer-selective coupling in multi-band moiré heterostructures provide a powerful route for engineering topological and correlated phases through band structure reconstruction and electron interactions.
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Submitted 5 June, 2026;
originally announced June 2026.
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Non-adiabatic phonon renormalization in metallic versus insulating rutile oxides
Authors:
Reshma Kumawat,
Shubham Farswan,
Simranjeet Kaur,
Kaushik Sen
Abstract:
We present a comparative Raman scattering study of metallic rutile oxides (RuO$_2$ and IrO$_2$) and insulating rutiles (TiO$_2$ and SnO$_2$). Temperature-dependent Raman spectra reveal that the metallic compounds exhibit pronounced phonon frequency hardening, $ω(11~\mathrm{K})-ω(300~\mathrm{K})=Δω\approx 6$-$10~\mathrm{cm}^{-1}$, whereas the insulating rutiles show only modest hardening,…
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We present a comparative Raman scattering study of metallic rutile oxides (RuO$_2$ and IrO$_2$) and insulating rutiles (TiO$_2$ and SnO$_2$). Temperature-dependent Raman spectra reveal that the metallic compounds exhibit pronounced phonon frequency hardening, $ω(11~\mathrm{K})-ω(300~\mathrm{K})=Δω\approx 6$-$10~\mathrm{cm}^{-1}$, whereas the insulating rutiles show only modest hardening, $Δω\approx 1$-$3~\mathrm{cm}^{-1}$. In contrast, the linewidth changes, $ΔΓ\approx 1$--$7~\mathrm{cm}^{-1}$, do not display a systematic metallic-insulating classification. Fits with the conventional Klemens anharmonic decay model reproduce the overall temperature trends but yield inconsistent anharmonic parameters for the metallic compounds when benchmarked against insulating rutile analogues. A modified Klemens framework, incorporating an additional $T^{2}$ correction to the phonon frequency arising from the electronic contribution to the phonon self-energy, quantitatively accounts for the enhanced renormalization observed in metallic systems. These results establish finite non-adiabatic electron-phonon coupling in metallic rutiles and demonstrate that phonon renormalization can be identified even in the absence of observable Fano asymmetry in the phonon line shapes.
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Submitted 24 June, 2026; v1 submitted 22 May, 2026;
originally announced May 2026.
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The effect of multi-occupancy traps on the diffusion and retention of multiple hydrogen isotopes in irradiated tungsten and vanadium
Authors:
Sanjeet Kaur,
Daniel R. Mason,
Prashanth Srinivasan,
Stephen Dixon,
Sid Mungale,
Teresa Orr,
Mikhail Yu. Lavrentiev,
Duc Nguyen-Manh
Abstract:
We propose a computational scheme for the diffusion and retention of multiple hydrogen isotopes (HI) with multi-occupancy traps parameterized by first principles calculations. We show that it is often acceptable to reduce the complexity of the coupled differential equations for gas evolution by taking the dynamic steady state, a generalisation of the Oriani equilibrium for multiple isotopes and mu…
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We propose a computational scheme for the diffusion and retention of multiple hydrogen isotopes (HI) with multi-occupancy traps parameterized by first principles calculations. We show that it is often acceptable to reduce the complexity of the coupled differential equations for gas evolution by taking the dynamic steady state, a generalisation of the Oriani equilibrium for multiple isotopes and multi-occupancy traps. The effective gas diffusivity varies most with mobile fraction when the total gas concentration approximates the trap density. We show HI binding to a monovacancy in vanadium produces a non-monotonic dependence between diffusivity and gas concentration, unlike the tungsten system. We demonstrate the difference between multiple single occupancy traps and multi-occupancy traps in long-term diffusion dynamics. The applicability of the multi-occupancy, multi-isotope model in steady state is assessed by comparison to an isotope exchange experiment between hydrogen and deuterium in self-ion irradiated tungsten. The vacancy distribution is estimated with molecular dynamics, and the retention across sample depth shows good agreement with experiment using no fitting parameters.
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Submitted 27 November, 2025; v1 submitted 21 August, 2025;
originally announced August 2025.
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Symmetry broken states at high displacement fields in ABA trilayer graphene
Authors:
Simrandeep Kaur,
Unmesh Ghorai,
Abhisek Samanta,
Kenji Watanabe,
Takashi Taniguchi,
Rajdeep Sensarma,
Aveek Bid
Abstract:
In this Letter, we present a comprehensive study of magnetotransport in high-mobility trilayer graphene (TLG) devices under a transverse displacement field, focusing on symmetry-broken Landau levels (LLs) from monolayer-like and bilayer-like bands. A striking displacement-field-induced enhancement of the Landé g-factor is observed in the zeroth Landau level of the monolayer-like band, highlighting…
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In this Letter, we present a comprehensive study of magnetotransport in high-mobility trilayer graphene (TLG) devices under a transverse displacement field, focusing on symmetry-broken Landau levels (LLs) from monolayer-like and bilayer-like bands. A striking displacement-field-induced enhancement of the Landé g-factor is observed in the zeroth Landau level of the monolayer-like band, highlighting the role of strong electron-electron interactions. Additionally, we find a rich landscape of LL crossings in the Dirac gully region, accompanied by phase transitions between spin-, gully-, and valley-polarized LLs. These experimental observations are successfully modeled using calculations based on optimized tight-binding parameters. Furthermore, our results reveal significant particle-hole asymmetry in the sequence of LLs in the Dirac gullies, attributed to differing g-factor values for electrons and holes. This asymmetry underscores the limitations of non-interacting models in capturing the complexities of strongly correlated multiband systems. This work provides new insights into the interplay of symmetry-breaking mechanisms and strong correlations in Bernal-stacked trilayer graphene, advancing our understanding of quantum transport phenomena in multiband systems.
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Submitted 27 March, 2025;
originally announced March 2025.
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Anomalous lattice anharmonicity and spin-lattice coupling in spin orbit coupled halide K2IrBr6
Authors:
S. Bhatia,
A. Ahmad,
M. Zeeshan,
S. Kaur,
J. K. Anand,
A. Goswami,
B. K. Mani,
K. Sen
Abstract:
The interplay between lattice distortions, magnetism, and spin-orbit coupling in 5d transition-metal halides offers a fertile platform for exploring correlated spin-lattice dynamics. Here, we investigate the impact of structural symmetry breaking on lattice vibrations and local spin environments in the antifluorite compound K2IrBr6 using temperature dependent Raman spectroscopy, electron paramagne…
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The interplay between lattice distortions, magnetism, and spin-orbit coupling in 5d transition-metal halides offers a fertile platform for exploring correlated spin-lattice dynamics. Here, we investigate the impact of structural symmetry breaking on lattice vibrations and local spin environments in the antifluorite compound K2IrBr6 using temperature dependent Raman spectroscopy, electron paramagnetic resonance (EPR), and first-principles lattice dynamics calculations. K2IrBr6 undergoes successive cubic-to-tetragonal and tetragonal-to-monoclinic phase transitions at 170 K and 122 K, respectively, driven by cooperative distortions of the IrBr6 octahedra. Raman spectroscopy reveals anomalous phonon linewidth broadening and unconventional temperature dependence of phonon energies near these transitions, indicating that dynamic spin-phonon coupling is significant well above the Neel temperature (16 K). First-principles phonon calculations support the mode assignments and demonstrate that symmetry-lowering distortions significantly renormalize vibrational modes, consistent with the experimental observations. Complementary EPR measurements detect anisotropic g-factors, resonance field shifts, and linewidth narrowing across the structural transitions, reflecting the emergence of static spin-lattice correlations mediated by spin-orbit entanglement. These findings establish K2IrBr6 as a model system where halide ligand fields, octahedral distortions, and SOC collaboratively govern spin-lattice coupling, providing chemical pathways to engineer quantum materials with tunable magnetic and lattice responses.
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Submitted 29 January, 2026; v1 submitted 11 March, 2025;
originally announced March 2025.
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Tunable Band Inversion in Trilayer Graphene
Authors:
Harsimran Kaur Mann,
Simrandeep Kaur,
Safil Mullick,
Priya Tiwari,
Kenji Watanabe,
Takashi Taniguchi,
Aveek Bid
Abstract:
Displacement field control of elecronic bands in low-dimensional systems is a promising route toward engineering emergent quantum phases. Here, we report displacement-field-induced band inversion and modulation of the Berry phase of low-energy quasi particles in high-mobility Bernal-stacked trilayer graphene (TLG). Using quantum oscillations, we track the evolution of the Fermi surface and topolog…
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Displacement field control of elecronic bands in low-dimensional systems is a promising route toward engineering emergent quantum phases. Here, we report displacement-field-induced band inversion and modulation of the Berry phase of low-energy quasi particles in high-mobility Bernal-stacked trilayer graphene (TLG). Using quantum oscillations, we track the evolution of the Fermi surface and topological properties of Dirac-like gully bands that emerge under a finite interlayer potential. We observe a striking sequence of transitions: at low displacement field $D$, the gullies are characterized by a Berry phase of $2π$ and large effective mass, indicating massive fermions. As $D$ increases, the Berry phase abruptly shifts to $π$ and the effective mass reaches a minimum, signaling the onset of massless Dirac behavior. At higher $D$, the Berry phase returns to $2π$, and the effective mass increases again, consistent with a band inversion. These findings demonstrate a rare, reversible topological phase transition - massive to massless to massive - driven entirely by an external displacement field. Despite robust theoretical predictions [\textit{Phys. Rev. B} \textbf{87}, 085424 (2013), \textit{Phys. Rev. B} \textbf{87}, 115422 (2013), and \textit{Phys. Rev. B} \textbf{101}, 245411 (2020)], this evolution of the band topology had escaped experimental detection. Our results establish TLG as a tunable platform for nanoscale control of band topology. They establish a means to tune between massive and Dirac-like dispersions dynamically providing a foundation for exploring field-switchable topological phenomena in layered 2D systems.
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Submitted 10 June, 2025; v1 submitted 21 February, 2025;
originally announced February 2025.
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Even-denominator fractional quantum Hall states in the zeroth Landau level of ABA trilayer graphene
Authors:
Tanima Chanda,
Simrandeep Kaur,
Harsimran Singh,
Kenji Watanabe,
Takashi Taniguchi,
Manish Jain,
Udit Khanna,
Ajit C. Balram,
Aveek Bid
Abstract:
Even-denominator fractional quantum Hall states (FQHSs) at half filling are of particular interest because they can host non-Abelian quasiparticles. Here we report the emergence of such states in the zeroth Landau level ($N=0$) of ABA trilayer graphene (TLG), challenging the conventional expectation that they are confined to the first excited Landau level. We observe robust incompressible states a…
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Even-denominator fractional quantum Hall states (FQHSs) at half filling are of particular interest because they can host non-Abelian quasiparticles. Here we report the emergence of such states in the zeroth Landau level ($N=0$) of ABA trilayer graphene (TLG), challenging the conventional expectation that they are confined to the first excited Landau level. We observe robust incompressible states at $ν=7/2$, $9/2$, and $5/2$ with their associated Levin--Halperin daughter states: $ν=59/17$ and $46/13$ near $7/2$; $ν=58/13$ and $77/17$ near $9/2$; and $ν=43/17$ near $5/2$. These states appear exclusively within a finite displacement-field window coincident with crossings between symmetry-broken $N=0$ Landau levels carrying distinct isospin indices. The quantitative correspondence between the calculated crossing loci and the experimentally determined stability regions identifies Landau-level mixing as the microscopic origin. We attribute the stabilization of these even-denominator states to inversion-symmetry breaking in TLG, which enhances valley-resolved Landau-level hybridization and renormalizes short-range Coulomb interactions. Our results expand the landscape of even-denominator FQHSs to multilayer graphene and establish TLG as a tunable platform for realizing non-Abelian anyons.
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Submitted 16 July, 2026; v1 submitted 10 February, 2025;
originally announced February 2025.
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Bulk-like structural, magnetic and optical properties of (111)- and (001)-NiO thin films
Authors:
S. Kaur,
Smriti Bhatia,
Pooja,
Kshitij Sharma,
V. K. Malik,
J. P. Singh,
K. Sen
Abstract:
We have grown (111)- and (001)-oriented NiO thin films on (0001)-Sapphire and (001)-MgO substrates using pulsed laser deposition (PLD), respectively. DC magnetic susceptibility measurements underline that the Néel temperatures of the samples are beyond room-temperature. This is further confirmed by the presence of two-magnon Raman scattering modes in these films in ambient conditions. Moreover, re…
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We have grown (111)- and (001)-oriented NiO thin films on (0001)-Sapphire and (001)-MgO substrates using pulsed laser deposition (PLD), respectively. DC magnetic susceptibility measurements underline that the Néel temperatures of the samples are beyond room-temperature. This is further confirmed by the presence of two-magnon Raman scattering modes in these films in ambient conditions. Moreover, relative intensity of the two magnon-mode with respect to a neighboring phonon mode in the films, at least down to 30 nm thickness, is comparable to the same for bulk NiO. UV-vis spectroscopy and spectroscopic ellipsometry determined that the bandgap of the films is 3.6 eV which is well within the range for bulk NiO. Thus, these indicate that the thin films are bulk-like. Further, photoluminescence measurements on (111)-NiO films obtained two-radiative transitions at 385 and 405 nm. The linewidth of the latter broadens towards low temperatures, indicating a plausible exciton-magnon coupling. Overall, these PLD-grown oxide films hold significant technological importance due to their optical transparency and their capacity to host robust magnons at room temperature.
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Submitted 4 December, 2024;
originally announced December 2024.
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Controlling particle-hole symmetry of fractional quantum hall states in trilayer graphene
Authors:
Simrandeep Kaur,
Harsimran Singh,
Kenji Watanabe,
Takashi Taniguchi,
Unmesh Ghorai,
Manish Jain,
Rajdeep Sensarma,
Aveek Bid
Abstract:
We present a detailed experimental study of the particle-hole symmetry (PHS) of the fractional quantum Hall (FQH) states about half filling in a multiband system. Specifically, we focus on the lowest Landau level of the monolayer-like band of Bernal stacked trilayer graphene (TLG). In pristine TLG, the excitation energy gaps, Landé g-factor, effective mass, and disorder broadening of the odd-denom…
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We present a detailed experimental study of the particle-hole symmetry (PHS) of the fractional quantum Hall (FQH) states about half filling in a multiband system. Specifically, we focus on the lowest Landau level of the monolayer-like band of Bernal stacked trilayer graphene (TLG). In pristine TLG, the excitation energy gaps, Landé g-factor, effective mass, and disorder broadening of the odd-denominator FQH states are identical to their hole-conjugate counterpart. This precise PH symmetry stems from the lattice mirror symmetry that precludes Landau-level mixing. Introducing a non-zero displacement field \(D\) disrupts this mirror symmetry, facilitating the hybridization between the monolayer-like and bilayer-like Landau levels. This inter-band coupling enhances the Landau level mixing factor $η$ and activates three-body interactions -- both of which explicitly break the PHS of FQHs. As a result, conventional FQHs are completely destabilized, offering a route to engineer symmetry breaking of FQHs in a controlled way. We establish that the PHS breaking in TLG is of extrinsic origin and is fundamentally distinct from the intrinsic, interaction-driven symmetry breaking observed in the lowest Landau levels of single-layer and bilayer graphene.
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Submitted 13 May, 2025; v1 submitted 27 November, 2024;
originally announced November 2024.
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Potential of Raman scattering in probing magnetic excitations and their coupling to lattice dynamics
Authors:
Reshma Kumawat,
Shubham Farswan,
Simranjeet Kaur,
Smriti Bhatia,
Kaushik Sen
Abstract:
Raman scattering is an excellent method for simultaneously determining the dynamics of lattice, spin, and charge degrees of freedom. Furthermore, polarization selection rules in Raman scattering enable momentum-resolved quasiparticle dynamics. In this review, we highlight the potential of Raman scattering in probing magnetic quasiparticles or excitations in various magnetic materials. We demonstra…
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Raman scattering is an excellent method for simultaneously determining the dynamics of lattice, spin, and charge degrees of freedom. Furthermore, polarization selection rules in Raman scattering enable momentum-resolved quasiparticle dynamics. In this review, we highlight the potential of Raman scattering in probing magnetic quasiparticles or excitations in various magnetic materials. We demonstrate how temperature-dependent Raman scattering data can confirm the existence of magnons in long-range ordered magnets and fractionalized excitations in Kitaev spin liquid candidates. To make this review easily understandable to novices, we provide background information on magnons and fractionalized excitations, and explain how they become visible in the Raman scattering process. We also show how to estimate magnetic exchange interactions from the data. For both types of magnetic materials, we discuss the impact of spin-phonon coupling on the lineshape of the phonon modes. In terms of materials, we present magnetic Raman scattering data of antiferromagnetic Sr2IrO4 and La2CuO4, ferromagnetic CrI3 monolayers, and Kitaev spin liquid candidates α-RuCl3 and \b{eta}-Li2IrO3. Overall, our review demonstrates the versatility of the Raman scattering technique in probing quasiparticles in magnetic quantum materials. The review aims to inform young experimental researchers about the potential of Raman scattering, thereby motivating them to use this technique in their research.
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Submitted 30 August, 2024;
originally announced September 2024.
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Universality of Quantum Phase Transitions in the Integer and Fractional Quantum Hall Regimes
Authors:
Simrandeep Kaur,
Tanima Chanda,
Kazi Rafsanjani Amin,
Divya Sahani,
Kenji Watanabe,
Takashi Taniguchi,
Unmesh Ghorai,
Yuval Gefen,
G. J. Sreejith,
Aveek Bid
Abstract:
Fractional quantum Hall (FQH) phases emerge due to strong electronic interactions and are characterized by anyonic quasiparticles, each distinguished by unique topological parameters, fractional charge, and statistics. In contrast, the integer quantum Hall (IQH) effects can be understood from the band topology of non-interacting electrons. We report a surprising super-universality of the critical…
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Fractional quantum Hall (FQH) phases emerge due to strong electronic interactions and are characterized by anyonic quasiparticles, each distinguished by unique topological parameters, fractional charge, and statistics. In contrast, the integer quantum Hall (IQH) effects can be understood from the band topology of non-interacting electrons. We report a surprising super-universality of the critical behavior across all FQH and IQH transitions. Contrary to the anticipated state-dependent critical exponents, our findings reveal the same critical scaling exponent $κ= 0.41 \pm 0.02$ and localization length exponent $γ= 2.4 \pm 0.2$ for fractional and integer quantum Hall transitions. From these, we extract the value of the dynamical exponent $z\approx 1$. We have achieved this in ultra-high mobility trilayer graphene devices with a metallic screening layer close to the conduction channels. The observation of these global critical exponents across various quantum Hall phase transitions was masked in previous studies by significant sample-to-sample variation in the measured values of $κ$ in conventional semiconductor heterostructures, where long-range correlated disorder dominates. We show that the robust scaling exponents are valid in the limit of short-range disorder correlations.
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Submitted 8 October, 2024; v1 submitted 11 December, 2023;
originally announced December 2023.
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Dispersion of Multiferroic Nanoparticles in a Bent-Core Nematic Liquid Crystal: Experimental and Theoretical Study
Authors:
Dhananjoy Mandal,
Yiwei Wang,
Supreet Kaur,
Golam Mohiuddin,
Apala Majumdar,
Aloka Sinha
Abstract:
A novel nanocomposite system has been prepared by dispersing multiferroic bismuth ferrite nanoparticles (BiFeO$_3$) in a bent-core nematic liquid crystal (8-F-OH) that exhibits cybotactic clusters. Transition temperature, optical textures, order parameter $S_m$, and dielectric spectroscopy experiments are performed in the doped system, and the results are compared with the pure one. The main exper…
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A novel nanocomposite system has been prepared by dispersing multiferroic bismuth ferrite nanoparticles (BiFeO$_3$) in a bent-core nematic liquid crystal (8-F-OH) that exhibits cybotactic clusters. Transition temperature, optical textures, order parameter $S_m$, and dielectric spectroscopy experiments are performed in the doped system, and the results are compared with the pure one. The main experimental outcome is that the doped system has increased orientational order parameters, even though the cybotactic cluster size is reduced due to the incorporation of multiferroic BiFeO$_3$ nanoparticles. The transition temperature, as observed under polarising optical microscopy, clearly indicates a reduction of $1 - 2~ ^\circ{\rm C}$ in the doped system compared to the pure one, and we conjecture this is due to the disordering of the cybotactic cluster in the doped system. Based on the experimental findings, a Landau-de Gennes-type free energy model is developed. The model qualitatively explains the increased mean order parameter and the disordering of cybotactic clusters with increasing polarization value of nanoparticles. This is corroborated by experimental findings.
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Submitted 9 July, 2024; v1 submitted 26 June, 2023;
originally announced June 2023.
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Novel Emergent Phases in a Two-Dimensional Superconductor
Authors:
Simrandeep Kaur,
Hemanta Kumar Kundu,
Sumit Kumar,
Anjana Dogra,
Rajesh Narayanan,
Thomas Vojta,
Aveek Bid
Abstract:
In this letter, we report our observation of an extraordinarily rich phase diagram of a LaScO$_3$/SrTiO$_3$ heterostructure. Close to the superconducting transition temperature, the system hosts a superconducting critical point of the Infinite-randomness type characterized by an effective dynamical exponent $νz$ that diverges logarithmically. At lower temperatures, we find the emergence of a magne…
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In this letter, we report our observation of an extraordinarily rich phase diagram of a LaScO$_3$/SrTiO$_3$ heterostructure. Close to the superconducting transition temperature, the system hosts a superconducting critical point of the Infinite-randomness type characterized by an effective dynamical exponent $νz$ that diverges logarithmically. At lower temperatures, we find the emergence of a magnetic field-tuned metallic phase that co-exists with a quantum Griffiths phase (QGP). Our study reveals a previously unobserved phenomenon in 2D superconductors -- an unanticipated suppression of the QGP below a crossover temperature in this system. This concealment is accompanied by the destruction of the superconducting quantum critical point signaled by a power-law divergence (in temperature) of the effective dynamical exponent. These observations are entirely at odds with the predictions of the infinite-randomness scenario and challenge the very concept of a vanishing energy scale associated with a quantum critical point. We develop and discuss possible scenarios like smearing of the phase transition that could plausibly explain our observations. Our findings challenge the notion that QGP is the ultimate ground state in two-dimensional superconductors.
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Submitted 8 October, 2024; v1 submitted 21 June, 2022;
originally announced June 2022.
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Absorption kinetics of vacancies by cavities in Aluminum: numerical characterization of sink strengths and first-passage statistics through Krylov subspace projection and eigenvalue deflation
Authors:
Savneet Kaur,
Manuel Athènes,
Jérôme Creuze
Abstract:
Modeling the microstructural evolution of metal and alloys, specifically under irradiation, is essential to predict the aging properties of materials. Many models are based on a transition rate matrix describing the jump frequencies of defects and involve a master equation governing the time evolution of a state probability vector. Here, we present non-stochastic numerical techniques to characteri…
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Modeling the microstructural evolution of metal and alloys, specifically under irradiation, is essential to predict the aging properties of materials. Many models are based on a transition rate matrix describing the jump frequencies of defects and involve a master equation governing the time evolution of a state probability vector. Here, we present non-stochastic numerical techniques to characterize the motion of individual defects migrating over long distances prior to recombining or being absorbed by another defect, resorting to the theory of absorbing Markov chains. These important events are fully determined by their first-passage time distribution to distant locations, no-passage distribution ,and walker fluxes to the sinks. We show that these functions can be efficiently computed using a method combining Krylov subspace projection and eigenvalue deflation. For a model system describing the absorption of a vacancy by a cavity in aluminum, the use of a small Krylov subspace deflated by the unique eigenmode corresponding to the quasi-stationary distribution is sufficient to capture the kinetics of the defect absorption faithfully. This method can be used in kinetic Monte Carlo simulations to perform stochastic non-local moves or in cluster dynamics simulations to compute sink strengths.
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Submitted 3 December, 2021;
originally announced December 2021.
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Transition from three- to two-dimensional Ising superconductivity in few-layer NbSe2 by proximity effect from van der Waals heterostacking
Authors:
Prakiran Baidya,
Divya Sahani,
Hemanta Kumar Kundu,
Simrandeep Kaur,
Priya Tiwari,
Vivas Bagwe,
John Jesudasan,
Awadhesh Narayan,
Pratap Raychaudhuri,
Aveek Bid
Abstract:
We report the experimental observation of Ising superconductivity in 3-dimensional NbSe2 stacked with single-layer MoS2. The angular dependence of the upper critical magnetic field and the temperature dependence of the upper parallel critical field confirm the appearance of two-dimensional Ising superconductivity in the 3-dimensional NbSe2 with single-layer MoS2 overlay. We show that the supercond…
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We report the experimental observation of Ising superconductivity in 3-dimensional NbSe2 stacked with single-layer MoS2. The angular dependence of the upper critical magnetic field and the temperature dependence of the upper parallel critical field confirm the appearance of two-dimensional Ising superconductivity in the 3-dimensional NbSe2 with single-layer MoS2 overlay. We show that the superconducting phase has strong Ising spin-orbit correlations which make the holes spin non-degenerate. Our observation of Ising superconductivity in heterostructures of few-layer NbSe2 of thickness ~ 15 nm with single-layer MoS2 raises the interesting prospect of observing topological chiral superconductors with nontrivial Chern numbers in a momentum-space spin-split fermionic system.
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Submitted 12 November, 2021;
originally announced November 2021.
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Impact of Size and Thermal Gradient on Supercooling of Phase Change Materials for Thermal Energy Storage
Authors:
Drew Lilley,
Jonathan Lau,
Chris Dames,
Sumanjeet Kaur,
Ravi Prasher
Abstract:
Phase change material based thermal energy storage has many current and potential applications in the heating and cooling of buildings, battery and electronics thermal management, thermal textiles, and dry cooling of power plants. However, connecting lab scale thermal data obtained on DSC to the performance of large-scale practical systems has been a major challenge primarily due to the dependence…
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Phase change material based thermal energy storage has many current and potential applications in the heating and cooling of buildings, battery and electronics thermal management, thermal textiles, and dry cooling of power plants. However, connecting lab scale thermal data obtained on DSC to the performance of large-scale practical systems has been a major challenge primarily due to the dependence of supercooling on the size and temperature gradient of the system. In this work we show how a phase change material's supercooling behavior can be characterized experimentally using common lab scale thermal analysis techniques. We then develop a statistics based theoretical model that uses the lab scale data on small samples to quantitatively predict the supercooling performance for a general thermal energy storage application of any size with temperature gradients. Finally, we validate the modeling methodology by comparing to experimental results for solid-solid phase change in neopentyl glycol, which shows how the model successfully predicts the changes in supercooling temperature across a large range of cooling rates (2 orders of magnitude) and volumes (3 orders of magnitude). By accounting for thermal gradients, the model avoids ~2x error incurred by lumped approximations.
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Submitted 21 October, 2020;
originally announced October 2020.
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Effect of Twist Angle on Structural, Electronic and Magnetic Properties of Carbon Nano Hybrids: A DFT Study
Authors:
Amrish Sharma,
Sandeep Kaur,
Hitesh Sharma,
Neha Kapila,
V. K. Jindal,
Vladimir Bubanja,
Isha Mudahar
Abstract:
Density functional calculations of hybrids consisting of a single wall carbon nanotube and a graphene nanoribbon have been performed. We consider the dependence of the structural, electronic and magnetic properties of the hybrids on the twist angle between their subunits. We calculated the binding energies, pyramidalization angles, Mulliken charge, and HOMO-LUMO gaps as functions of the twist angl…
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Density functional calculations of hybrids consisting of a single wall carbon nanotube and a graphene nanoribbon have been performed. We consider the dependence of the structural, electronic and magnetic properties of the hybrids on the twist angle between their subunits. We calculated the binding energies, pyramidalization angles, Mulliken charge, and HOMO-LUMO gaps as functions of the twist angle. We find that, owing to the asymmetrical spin density distributions of their subunits, the hybrids have finite magnetic moments.
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Submitted 13 June, 2020;
originally announced June 2020.
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Substitutional Doping of Symmetrical Small Fullerene Dimers
Authors:
Sandeep Kaur,
Amrish Sharma,
Hitesh Sharma,
Shobhna Dhiman,
Isha Mudahar
Abstract:
Magnetic carbon nano-structures have potential applications in the field of spintronics as they exhibit valuable magnetic properties. Symmetrically sized small fullerene dimers are substitutional doped with nitrogen (electron rich) and boron (electron deficient) atoms to visualize the effect on their magnetic properties. Interaction energies suggests that the resultant dimer structures are energet…
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Magnetic carbon nano-structures have potential applications in the field of spintronics as they exhibit valuable magnetic properties. Symmetrically sized small fullerene dimers are substitutional doped with nitrogen (electron rich) and boron (electron deficient) atoms to visualize the effect on their magnetic properties. Interaction energies suggests that the resultant dimer structures are energetically favourable and hence can be formed experimentally. There is significant change in the total magnetic moment of dimers of the order of 0.5 uB after the substitution of C atoms with N and B, which can also be seen in the change of density of states. The HOMO-LUMO gaps of spin up and spin down electronic states have finite energy difference which confirm their magnetic behaviour, whereas for non-magnetic doped dimers, the HOMO-LUMO gaps for spin up and down states are degenerate. The optical properties show that the dimers behave as optical semiconductors and are useful in optoelectronic devices. The induced magnetism in these dimers makes them fascinating nanocarbon magnetic materials.
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Submitted 4 June, 2020;
originally announced June 2020.
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Graphene Nanoribbons Under Axial Compressive and Point Tensile Stresses
Authors:
Sandeep Kaur,
Hitesh Sharma,
V. K. Jindal,
Vladimir Bubanja,
Isha Mudahar
Abstract:
The geometric, electronic and magnetic properties of strained graphene nanoribbons were investigated using spin polarized calculations within the framework of density functional theory. Cases of compressive stress along the longer axis of a nanoribbon and tensile stress at the midpoint and perpendicular to the plane of the nanoribbon were considered. Significant structural changes were observed in…
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The geometric, electronic and magnetic properties of strained graphene nanoribbons were investigated using spin polarized calculations within the framework of density functional theory. Cases of compressive stress along the longer axis of a nanoribbon and tensile stress at the midpoint and perpendicular to the plane of the nanoribbon were considered. Significant structural changes were observed including the formation of nanoripples. The calculated electronic and magnetic properties strongly depend on the size and shape of nanoribbons. The tunable magnetic properties of strained nanoribbons can be employed for designing magnetic nano-switches.
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Submitted 1 June, 2020;
originally announced June 2020.
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Structural and magnetic properties of small symmetrical and asymmetrical sized fullerene dimers
Authors:
Sandeep Kaur,
Amrish Sharma,
Hitesh Sharma,
Isha Mudahar
Abstract:
Magnetism in carbon nanostructures is of high scientific interest, which could lead to novel magnetic materials. The magnetic properties of symmetrical and asymmetrical sized small fullerene dimers have been investigated using spin polarized density functional theory. The interaction energies depict that small fullerene cages form stable dimer structures and symmetrical sized fullerene dimers are…
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Magnetism in carbon nanostructures is of high scientific interest, which could lead to novel magnetic materials. The magnetic properties of symmetrical and asymmetrical sized small fullerene dimers have been investigated using spin polarized density functional theory. The interaction energies depict that small fullerene cages form stable dimer structures and symmetrical sized fullerene dimers are found more stable than asymmetrical sized dimers. The dimerization of fullerene cages in different modes leads to change in their magnetic properties. The non-magnetic fullerene cages become magnetic after formation of dimer (C20-C20, C24-C24, C32-C32, C40-C40, C20-C24, C40-C44 and C44-C50),whereas the magnetism of magnetic fullerenes is enhanced or lowered after dimerization (C28-C28 C36-C36, C24-C28, C28-C32, C32-C36 and C36-C40). The individual cages of dimer structures show ferromagnetic interactions amongst them and resultant magnetic moment strongly depends on the type of inter-connecting bonds. The magnetism may also be explained based on distortion of carbon cages and change in the density of states (DOS) in dimer configuration. The calculations presented show strong possibility of experimental synthesis of small fullerene based magnetic dimers.
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Submitted 3 June, 2020;
originally announced June 2020.
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Electronic and Magnetic Properties of Small Fullerene Carbon Nanobuds: A DFT Study
Authors:
Amrish Sharma,
Sandeep Kaur,
Hitesh Sharma,
Isha Mudahar
Abstract:
The electronic and magnetic properties of carbon nanobuds have been investigated using density functional theory. The carbon nanobuds are formed by attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with (5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having binding energies within the range -0.93eV to -4.06eV. The C-C bond lengths near the attachment re…
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The electronic and magnetic properties of carbon nanobuds have been investigated using density functional theory. The carbon nanobuds are formed by attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with (5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having binding energies within the range -0.93eV to -4.06eV. The C-C bond lengths near the attachment region increase from the original C-C bond lengths. The relative stabilities of the nanobuds are closely related to C-C bond lengths and bond angles in cycloaddition reaction. Nanobuds formed by bond cycloaddition are energetically most favorable amongst all cycloadditions. The electronic and magnetic properties of nanobuds depend strongly on electronic properties of its building blocks. The attachment of C20 and C40 on CNTs open up the HOMO-LUMO gaps of nanobuds whereas C28 and C36 results in addition of impurity states near the Fermi level. The total magnetic moment of nanobuds vary from 0.28μB to 4.00μB which depend on the nature of bonding between fullerene and CNTs. The results outline the potential of nanobuds as hybrid carbon nanostructures and how their properties can be tuned with the size and type of fullerene attached.
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Submitted 3 June, 2020;
originally announced June 2020.
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Microrheology to Probe Smectic Clusters in Bent-core Nematic Liquid Crystals
Authors:
Sathyanarayana Paladugu,
Supreet Kaur,
Golam Mohiuddin,
Ravi Kumar Pujala,
Santanu Kumar Pal,
Surajit Dhara
Abstract:
Many bent-core nematic liquid crystals exhibit unusual physical properties due to the presence of smectic clusters, known as "cybotactic" clusters in the nematic phase. Effect of these clusters on complex shear modulus ($G^*(ω)$) of such liquid crystals hitherto unexplored. Here, we study flow viscosities and complex shear modulus of two asymmetric bent-core liquid crystals using microrheology tec…
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Many bent-core nematic liquid crystals exhibit unusual physical properties due to the presence of smectic clusters, known as "cybotactic" clusters in the nematic phase. Effect of these clusters on complex shear modulus ($G^*(ω)$) of such liquid crystals hitherto unexplored. Here, we study flow viscosities and complex shear modulus of two asymmetric bent-core liquid crystals using microrheology technique. The results are corroborated with the measurements of curvature elastic constants. Compound with shorter hydrocarbon chain (8OCH$_\text{3}$) exhibit only nematic (N) phase whereas the compound with longer chain (16OCH$_\text{3}$) exhibits both nematic (N) and smectic-A (SmA) phases. Our results show that the directional shear modulus of 16OCH$_\text{3}$, just above the SmA to N transition temperature is strikingly different than 8OCH$_\text{3}$, owing to these smectic clusters. Thus, microrheology enables us to probe smectic clusters in bent-core nematic liquid crystals.
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Submitted 3 May, 2020;
originally announced May 2020.
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Analysis and Improvement of the Hot Disk Transient Plane Source Method for Low Thermal Conductivity Materials
Authors:
Qiye Zheng,
Sumanjeet Kaur,
Chris Dames,
Ravi S. Prasher
Abstract:
The hot disk transient plane source (TPS) method is a widely used standard technique (ISO 22007-2) for the characterization of thermal properties of materials, especially the thermal conductivity, k. Despite its well-established reliability for a wide variety of common materials, the hot disk TPS method is also known to suffer from a substantial systematic errors when applied to low-k thermal insu…
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The hot disk transient plane source (TPS) method is a widely used standard technique (ISO 22007-2) for the characterization of thermal properties of materials, especially the thermal conductivity, k. Despite its well-established reliability for a wide variety of common materials, the hot disk TPS method is also known to suffer from a substantial systematic errors when applied to low-k thermal insulation materials. Here, we present a combined numerical and experimental study on the influence of the geometry of hot disk sensor on measured value of low-k materials. We demonstrate that the error is strongly affected by the finite thickness and thermal mass of the sensor's insulation layer was well as the corresponding increase of the effective heater size beyond the radius of the embedded metal heater itself. We also numerically investigate the dependence of the error on the sample thermal properties, confirming that the errors are worse in low-k samples. A simple correction function is also provided, which converts the apparent (erroneous) result from a standard hot disk TPS measurement to a more accurate value. A standard polyimide sensor was also optimized using both wet and dry etching to provide more accurate measurement directly. Experimentally corrected value of k for Airloy x56 aerogel and a commercial silica aerogel using the numerical correction factor derived based on the standard TPS sensor is in excellent agreement with the directly measured value from the TPS sensor using the optimized polyimide sensor. Both of these methods can reduce the errors to less than 4% as compared to around 40% error of overestimation from raw values measured with the pristine sensor. Such results show that both the numerical correction to a pristine senor or an optimized sensor are capable of providing highly accurate value of thermal conductivity for such materials.
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Submitted 30 October, 2019; v1 submitted 4 October, 2019;
originally announced October 2019.
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Monolayer, Bilayer and Heterostructures of Green Phosphorene for Water Splitting and Photovoltaics
Authors:
Sumandeep Kaur,
Ashok Kumar,
Sunita Srivastava,
K. Tankeshwar,
Ravindra Pandey
Abstract:
We report the results of density functional theory (DFT) based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe2. Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10^{4} cm^{2}V^{-1}s^{-1}. In bilayers, pressure of about 9 GPa induces the semiconductor-metal transition. Mo…
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We report the results of density functional theory (DFT) based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe2. Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10^{4} cm^{2}V^{-1}s^{-1}. In bilayers, pressure of about 9 GPa induces the semiconductor-metal transition. Moreover, the band gap depends strongly on the thickness of the films and the external electric field. By employing strain-engineering under suitable solution conditions, monolayer and AC-stacked bilayer green phosphorene offer the band edge alignments which can be used for water splitting. The upper limit of the power conversion efficiencies for monolayer, AB- and AC-stacked bilayer green phosphorene heterostructures with MoSe_{2} is calculated to be 18-21 %. Our results show the possibility of green phosphorene to be used as photocatalytic and photovoltaic material in the energy-related applications.
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Submitted 23 November, 2018;
originally announced November 2018.
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Stability and Carrier Transport Properties of Phosphorene Based Polymorphic Nanoribbons
Authors:
Sumandeep Kaur,
Ashok Kumar,
Sunita Srivastava,
Ravindra Pandey,
K. Tankeshwar
Abstract:
A few-layer black phosphorene has recently gained significant interest in the scientific community. In this paper, we consider several polymorphs of phosphorene nanoribbons (PNRs) and employ deformation potential theory within the effective mass approximation together with density functional theory to investigate their structural, mechanical and electronic properties. The results show that stabili…
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A few-layer black phosphorene has recently gained significant interest in the scientific community. In this paper, we consider several polymorphs of phosphorene nanoribbons (PNRs) and employ deformation potential theory within the effective mass approximation together with density functional theory to investigate their structural, mechanical and electronic properties. The results show that stability of PNRs strongly depends on the direction along which they can be cut from 2D counterpart. PNRs also exhibit a wide range of line stiffness ranging from 6x10^10 eV/m to 18x10^11 eV/m which has little dependence on the edge passivation. Likewise, the calculated electronic properties of PNRs display them to be either narrow-gap semiconductor (Eg < 1 eV) or wide-gap semiconductor (Eg > 1 eV). The carrier mobility of PNRs is found to be comparable to that of the black phosphorene. Some of the PNRs show n-type (p-type) semiconducting character owing to their higher electron (hole) mobility. Passivation of the edges leads to n-type <-> p-type transition in many of the PNRs considered. The predicted novel characteristics of PNRs with a wide range of mechanical and electronic properties make PNRs to be potentially suitable for the use in nanoscale devices.
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Submitted 7 February, 2018;
originally announced February 2018.
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Van der Waals Heterostructures Based on Allotropes of Phosphorene and MoSe2
Authors:
Sumandeep Kaur,
Ashok Kumar,
Sunita Srivastava,
K. Tankeshwar
Abstract:
The van der Waals heterostructures of allotropes of phosphorene ($α$- and $β-P$) with MoSe2 (H-, T-, ZT- and SO-MoSe2) are investigated in the framework of state-of-the-art density functional theory. The semiconducting heterostructures, $β$-P /H-MoSe2 and $α$-P / H-MoSe2, forms anti-type structures with type I and type II band alignments, respectively, whose bands are tunable with external electri…
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The van der Waals heterostructures of allotropes of phosphorene ($α$- and $β-P$) with MoSe2 (H-, T-, ZT- and SO-MoSe2) are investigated in the framework of state-of-the-art density functional theory. The semiconducting heterostructures, $β$-P /H-MoSe2 and $α$-P / H-MoSe2, forms anti-type structures with type I and type II band alignments, respectively, whose bands are tunable with external electric field. $α$-P / ZT-MoSe2 and $α$-P / SO-MoSe2 form ohmic semiconductor-metal contacts while Schottky barrier in $β$-P / T-MoSe2 can be reduced to zero by external electric field to form ohmic contact which is useful to realize high-performance devices. Simulated STM images of given heterostructures reveal that $α$-P can be used as a capping layer to differentiate between various allotropes of underlying MoSe2. The dielectric response of considered heterostructures is highly anisotropic in terms of lateral and vertical polarization. The tunable electronic and dielectric response of van der Waals phosphorene/MoSe2 heterostructure may find potentials applications in the fabrication of optoelectronic devices.
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Submitted 1 August, 2017;
originally announced August 2017.
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On-chip artificial magnon-polariton device for voltage control of electromagnetically induced transparency
Authors:
S. Kaur,
B. M. Yao,
Y. S. Gui,
C. -M. Hu
Abstract:
We demonstrate an on-chip device utilizing the concept of artificial cavity magnon-polariton (CMP) coupling between the microwave cavity mode and the dynamics of the artificial magnetism in a split ring resonator. This on-chip device allows the easy tuning of the artificial CMP gap by using a DC voltage signal, which enables tuneable electrodynamically induced transparency. The high tunability of…
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We demonstrate an on-chip device utilizing the concept of artificial cavity magnon-polariton (CMP) coupling between the microwave cavity mode and the dynamics of the artificial magnetism in a split ring resonator. This on-chip device allows the easy tuning of the artificial CMP gap by using a DC voltage signal, which enables tuneable electrodynamically induced transparency. The high tunability of the artificial magnon-polariton system not only enables the study of the characteristic phenomena associated with distinct coupling regimes, but also may open up avenues for designing novel microwave devices and ultra-sensitive sensors.
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Submitted 24 July, 2015;
originally announced July 2015.