Showing 1–50 of 1,329 results for author: Kim, K

Mobility-edge-embedded Hofstadter butterfly from a tilt-induced quasiperiodic potential

Authors: Sanghoon Lee, Kyoung-Min Kim

Abstract: The Hofstadter butterfly (HB) and mobility edges (MEs) are hallmark phenomena of quasiperiodic systems, yet their interplay remains elusive. Here, we demonstrate their convergence within a tilt-induced quasiperiodic potential on a square lattice, giving rise to a ``mobility-edge-embedded Hofstadter butterfly'' (MEE-HB). This potential is generated by aligning a periodic potential at an angle relat… ▽ More The Hofstadter butterfly (HB) and mobility edges (MEs) are hallmark phenomena of quasiperiodic systems, yet their interplay remains elusive. Here, we demonstrate their convergence within a tilt-induced quasiperiodic potential on a square lattice, giving rise to a ``mobility-edge-embedded Hofstadter butterfly'' (MEE-HB). This potential is generated by aligning a periodic potential at an angle relative to the lattice axes--a configuration readily accessible in optical lattice experiments. Using a tight-binding model, we show that the MEE-HB manifests as a fractal energy splitting pattern hosting MEs that separate extended and localized states. Our Harper-like equation shows that the fractal pattern originates from 1D quasiperiodic potentials, while MEs stem from effective long-range hopping. Notably, the MEE-HB exhibits a fractal dimension of 0.8--1.0, significantly exceeding the 0.4--0.6 range of the standard butterfly, indicating a denser spectral set. Our findings establish tilt-induced potentials as a versatile platform for exploring the interplay between fractal structures and localization. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: Supplementary information is not included in the present arXiv submission and will be provided in the published version

Orbital-driven emergent transport in altermagnets

Authors: Junyeong Choi, Kyoung-Whan Kim

Abstract: Altermagnets have recently emerged as a promising platform for spintronics due to their unique magnetic symmetry. However, most studies have focused on spin degrees of freedom, leaving the dynamic role of orbital degrees of freedom largely unexplored. In this work, we extend the altermagnet Hamiltonian to include the orbital degree of freedom as a dynamical variable and derive the resulting emerge… ▽ More Altermagnets have recently emerged as a promising platform for spintronics due to their unique magnetic symmetry. However, most studies have focused on spin degrees of freedom, leaving the dynamic role of orbital degrees of freedom largely unexplored. In this work, we extend the altermagnet Hamiltonian to include the orbital degree of freedom as a dynamical variable and derive the resulting emergent electromagnetic fields (EEMFs). This approach allows us to demonstrate emergent electric fields controllable via lattice anisotropy and the resulting orbital and magnetic multipole currents. Furthermore, we show that non-vanishing emergent electric fields can arise even in simplified spin and orbital textures, particularly in the presence of dynamic lattice distortion. This formalism is generalizable to high-order altermagnets beyond d-wave systems. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Potential energy landscape picture of zero-temperature avalanche criticality governing dynamics in supercooled liquids

Authors: Norihiro Oyama, Yusuke Hara, Takeshi Kawasaki, Kang Kim

Abstract: Supercooled liquids are metastable states realized by suppressing crystallization below the melting temperature. While it is well established that their dynamics slow down dramatically and become spatially heterogeneous upon cooling, the microscopic origin of these nontrivial glassy phenomena remains a matter of active debate. In the present study, by means of molecular dynamics simulations, we fi… ▽ More Supercooled liquids are metastable states realized by suppressing crystallization below the melting temperature. While it is well established that their dynamics slow down dramatically and become spatially heterogeneous upon cooling, the microscopic origin of these nontrivial glassy phenomena remains a matter of active debate. In the present study, by means of molecular dynamics simulations, we first demonstrate that nontrivial slow dynamics, such as structural relaxation and dynamical heterogeneity, can be consistently described within a zero-temperature avalanche criticality picture. Since this finding suggests that the potential energy landscape plays a crucial role in determining the dynamics, we further quantify the potential energy landscape from three distinct perspectives. Based on these analyses, we propose a potential-energy-landscape picture of avalanche criticality that is consistent with various previous studies. Our proposed picture explains in a unified manner previously unexplained observations near the mode-coupling transition, such as the saturation of the dynamical susceptibility and the localization of unstable modes in saddle configurations. △ Less

Submitted 4 April, 2026; originally announced April 2026.

Comments: 30 pages, 19 figures

Zero-temperature Avalanche Criticality Governing Dynamical Heterogeneity in Supercooled Liquids

Authors: Norihiro Oyama, Yusuke Hara, Takeshi Kawasaki, Kang Kim

Abstract: In supercooled liquids, mesoscale mobile and immobile domains are ubiquitously observed, a phenomenon known as dynamical heterogeneity. Extensive studies have established that the characteristic size of these domains grows upon cooling and exhibits system-size dependence. However, the physical origin of this domain growth remains a matter of active debate. In this work, using molecular simulations… ▽ More In supercooled liquids, mesoscale mobile and immobile domains are ubiquitously observed, a phenomenon known as dynamical heterogeneity. Extensive studies have established that the characteristic size of these domains grows upon cooling and exhibits system-size dependence. However, the physical origin of this domain growth remains a matter of active debate. In this work, using molecular simulations, we demonstrate that the temperature and system-size dependence of dynamical heterogeneity can be explained within a zero-temperature avalanche criticality picture. △ Less

Submitted 3 April, 2026; originally announced April 2026.

Comments: 9+3 pages, 5+3 figures

High performance imaging of $^{171}$Yb atom in shallow clock-magic tweezer by alternating dual-tone narrowline cooling

Authors: Yunheung Song, Kangheun Kim, Jeong Ho Han, Seungtaek Oh, Jongchul Mun

Abstract: We demonstrate imaging $^{171}$Yb single atoms in clock-magic tweezers of 759.4 nm wavelength, with above 99.9% fidelity and survival. We use alternating dual-tone narrowline imaging for more efficient three-dimensional cooling in tweezers, allowing several-millisecond imaging in 200 $μ$K trap depth, which is half of typical depth used for imaging in clock-magic tweezers. Accordingly, even without… ▽ More We demonstrate imaging $^{171}$Yb single atoms in clock-magic tweezers of 759.4 nm wavelength, with above 99.9% fidelity and survival. We use alternating dual-tone narrowline imaging for more efficient three-dimensional cooling in tweezers, allowing several-millisecond imaging in 200 $μ$K trap depth, which is half of typical depth used for imaging in clock-magic tweezers. Accordingly, even without repumping, imaging survival is still close to 99.9% with the high fidelity, which can enable high performance nondestructive qubit measurements based on metastable shelving. Moreover, our simulation predicts that more optimal configuration could further reduce the trap depth, as improving the imaging performance. This imaging capability in shallow traps opens high performance imaging for more general trap wavelength, and lays the foundation for large scale systems over 1,000 qubits, and highly repeatable tweezer clocks. △ Less

Submitted 28 March, 2026; originally announced March 2026.

Comments: 10 pages, 7 figures

Composition-dependent bulk properties of intercalated transition metal dichalcogenides $Co_{1/3(1\pmδ)}NbS_{2}$

Authors: Woonghee Cho, Kiwan Nam, Yeochan An, You Young Kim, Myung-Hwa Jung, Kee Hoon Kim, Je-Geun Park

Abstract: We report a systematic study of the composition-dependent bulk properties in $Co_{1/3(1\pmδ)}NbS_{2}$ single crystals across a series of precisely controlled cobalt compositions with -4%<$δ$<8%. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds… ▽ More We report a systematic study of the composition-dependent bulk properties in $Co_{1/3(1\pmδ)}NbS_{2}$ single crystals across a series of precisely controlled cobalt compositions with -4%<$δ$<8%. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds $δ$=+4%. We observe that the longitudinal conductivity is also strongly influenced by the cobalt composition, reaching its maximum value just before the disappearance of the topological Hall effect. Furthermore, heat capacity measurements reveal distinct Sommerfeld coefficients ($γ$) across different compositions, which exhibit a clear linear scaling with the inverse of the ordinary Hall coefficient ($R_H^{-1}$). These results demonstrate that composition tuning in $Co_{1/3(1\pmδ)}NbS_{2}$ systematically modifies the low-energy electronic degree of freedom, moving beyond a simple dilute impurity picture. Finally, we use the microscopic spin Hamiltonian to explain the stability of experimentally observed M-point modulation vector and the corresponding triple-Q magnetic order. Our findings highlight that the topological properties of this system are highly tunable through precise control of the intercalant concentration, offering a new perspective on the competition between electronic and magnetic orders in intercalated transition-metal dichalcogenides. △ Less

Submitted 31 March, 2026; v1 submitted 27 March, 2026; originally announced March 2026.

Comments: 16 pages, 8 figures

Deep learning of committor and explainable artificial intelligence analysis for identifying reaction coordinates

Authors: Toshifumi Mori, Kei-ichi Okazaki, Kang Kim, Nobuyuki Matubayasi

Abstract: In complex molecular systems, the reaction coordinate (RC) that characterizes transition pathways is essential to understand underlying molecular mechanisms. This review surveys a framework for identifying the RC by applying deep learning to the committor, which provides the most reliable measure of the progress along a transition path. The inputs to the neural network are collective variables (CV… ▽ More In complex molecular systems, the reaction coordinate (RC) that characterizes transition pathways is essential to understand underlying molecular mechanisms. This review surveys a framework for identifying the RC by applying deep learning to the committor, which provides the most reliable measure of the progress along a transition path. The inputs to the neural network are collective variables (CVs) expressed as functions of atomic coordinates of the system, and the corresponding RC is predicted as the output by training the network on the committor as the learning target. Because deep learning models typically operate in a black-box manner, it is difficult to determine which input variables govern the predictions. The incorporation of eXplainable Artificial Intelligence (XAI) techniques enables quantitative assessment of the contributions of individual input variables to the predictions. This approach allows the identification of CVs that play dominant roles and demonstrates that the committor distribution on the surface using important CVs is separated by well-defined boundaries. The framework provides an explainable deep learning strategy for assigning a molecular mechanism from the RC and is applicable to a wide range of complex molecular systems. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Comments: 17 pages, 12 figures

Classification of interfacial water governed by water-polymer interactions in hydrated polymers: A molecular dynamics simulation study of ethylene-based and acrylate polymers

Authors: Atsuki Hashimoto, Kokoro Shikata, Kang Kim, Nobuyuki Matubayasi

Abstract: We perform molecular dynamics simulations to investigate hydration structures and dynamics in seven water-containing polymers: PVA, PHEA, PHEMA, PBA, PMEMA, PEG, and PMEA. The analysis integrates four perspectives: the water-content dependence of the glass transition temperature $T_g$, polymer chain fluctuations characterized by dihedral angle distributions, hydrogen-bond lifetimes… ▽ More We perform molecular dynamics simulations to investigate hydration structures and dynamics in seven water-containing polymers: PVA, PHEA, PHEMA, PBA, PMEMA, PEG, and PMEA. The analysis integrates four perspectives: the water-content dependence of the glass transition temperature $T_g$, polymer chain fluctuations characterized by dihedral angle distributions, hydrogen-bond lifetimes $τ_{\mathrm{HB}}$ between water and polymer functional groups, and the localization and exchange dynamics of confined water quantified by the distinct part of van Hove correlation function. Hydroxyl-containing polymers (PVA, PHEA, and PHEMA) exhibit relatively high dry-state $T_g$ values and its pronounced depression upon hydration. Chain fluctuations are limited, and $τ_{\mathrm{HB}}$ follows Arrhenius behavior, forming localized hydration shells. In contrast, PMEMA and PBA show low equilibrium water contents and hydrophobic character; although their dry-state $T_g$ values are moderately lower and less sensitive to water content, chain fluctuations remain small, and $τ_{\mathrm{HB}}$ also obeys Arrhenius behavior, with hydrophobic aggregation promoting water localization. PEG and PMEA display low dry-state $T_g$ values and weak water-content dependence. Greater rotational freedom around ether or methoxy oxygen atoms leads to larger chain fluctuations and loosely bound water. Below $T_g$, $τ_{\mathrm{HB}}$ between water and ether or methoxy oxygen atoms exhibits super-Arrhenius behavior. These results clarify three hydration types: highly hydrated (PVA, PHEA, and PHEMA), hydrophobic (PMEMA and PBA), and flexibly hydrated (PEG and PMEA), and provide a molecular-level framework for interpreting interfacial water governed by water-polymer interactions. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Comments: 11 pages, 7 figures for main text, 5 pages for supplementary material

Optimized control protocols for stable skyrmion creation using deep reinforcement learning

Authors: Ji Seok Song, Se Kwon Kim, Kyoung-Min Kim

Abstract: Generating stable magnetic skyrmions is essential for the practical application of skyrmion-based spintronic devices in thermally agitating environments. Recent advancements have enabled the creation of skyrmions by controlling stripe domain instability through dynamic magnetic-field control. However, deterministic skyrmion creation and effectively managing the thermal stability of skyrmions remai… ▽ More Generating stable magnetic skyrmions is essential for the practical application of skyrmion-based spintronic devices in thermally agitating environments. Recent advancements have enabled the creation of skyrmions by controlling stripe domain instability through dynamic magnetic-field control. However, deterministic skyrmion creation and effectively managing the thermal stability of skyrmions remain challenges. Here, we present a deep reinforcement learning (DRL) approach to identify advanced dynamic magnetic-field-temperature paths that create skyrmions while controlling stripe domain instability and enhancing their thermal stability. The trained DRL agent discovers an optimized field-temperature path that achieves a higher success rate for skyrmion formation in Fe3GeTe2 monolayers compared to previous fixed-temperature field sweeps. Additionally, the generated skyrmions exhibit longer lifetimes due to their isotropic shape, which tends to suppress internal excitation modes associated with skyrmion annihilation. We demonstrate that these advancements stem from the targeted minimization of the dissipated work, which ensures that the driven skyrmion states remain close to their equilibrium distributions by upper-bounding the Kullback-Leibler divergence. Our findings suggest that a DRL-powered search streamlines the identification of optimized protocols for skyrmion creation and control. △ Less

Submitted 25 March, 2026; originally announced March 2026.

Comments: Supplemental Material and Supplemental Vidoes will be provided with the published manuscript

Helicity-Selective Phonon Absorption and Phonon-Induced Spin Torque from Interfacial Spin-Lattice Coupling

Authors: Gyungchoon Go, Se Kwon Kim

Abstract: In magnetic heterostructures with broken inversion symmetry, the Rashba effect gives rise to a gradient-free interaction between magnons and phonons, which we term interfacial spin-lattice coupling. Here, we investigate the dynamic consequences of this interfacial coupling in ferromagnetic heterostructures. By expressing the interaction in terms of circular variables for magnetization and lattice… ▽ More In magnetic heterostructures with broken inversion symmetry, the Rashba effect gives rise to a gradient-free interaction between magnons and phonons, which we term interfacial spin-lattice coupling. Here, we investigate the dynamic consequences of this interfacial coupling in ferromagnetic heterostructures. By expressing the interaction in terms of circular variables for magnetization and lattice displacement, we reveal a direct interface-induced helicity-helicity coupling hat does not rely on lattice deformation gradients. Consequently, it leads to helicity-dependent phonon absorption, enabling in-plane acoustic waves to exert a spin torque on the magnetization, which becomes dominant in thin magnetic films. Our findings highlight the crucial, yet overlooked, role of inversion-asymmetric interfaces in angular-momentum conversion between spin and lattice, opening up possibilities for efficient phonon-driven magnetic devices that are enabled by interface engineering. △ Less

Submitted 20 March, 2026; originally announced March 2026.

Comments: 9 pages and 8 figures

Towards a Refinement of Krylov Complexity: Scrambling, Classical Operator Growth and Replicas

Authors: Hugo A. Camargo, Yichao Fu, Keun-Young Kim, Yeong Han Park

Abstract: We propose and test logarithmic Krylov (logK) complexity, an operator growth measure akin to Krylov complexity defined through a replica approach, as a viable probe of early-time operator scrambling without false positives. In finite-dimensional quantum systems, such as the Lipkin--Meshkov--Glick (LMG) model and the mixed-field Ising model at the chaotic point, we provide numerical evidence that l… ▽ More We propose and test logarithmic Krylov (logK) complexity, an operator growth measure akin to Krylov complexity defined through a replica approach, as a viable probe of early-time operator scrambling without false positives. In finite-dimensional quantum systems, such as the Lipkin--Meshkov--Glick (LMG) model and the mixed-field Ising model at the chaotic point, we provide numerical evidence that logK-complexity discriminates between genuine and saddle-dominated scrambling at early times, correctly avoiding the exponential contribution coming from the unstable saddle in the former case, and closely tracking the conventional Krylov complexity in the latter. In integrable quantum systems admitting infinite-dimensional Krylov subspaces, such as the SYK$_{2}$ model and the quantum inverted harmonic oscillator, we show that by modifying the Krylov spreading operator, obtained through generalizing the analytic continuation procedure in the replica trick, the logK complexity can be refined to capture the integrable properties of the theories. We supplement these analyses by extending the Krylov formalism in classical dynamical systems and defining classical versions of these operator growth measures, showing that the false positives arising from unstable saddles in classical phase space are non-existent. △ Less

Submitted 6 April, 2026; v1 submitted 19 March, 2026; originally announced March 2026.

Comments: 32 pages, 7 figures, 1 table;v2:minor changes, references updated

Stochastic Loop Corrections to Belief Propagation for Tensor Network Contraction

Authors: Gi Beom Sim, Tae Hyeon Park, Kwang S. Kim, Yanmei Zang, Xiaorong Zou, Hye Jung Kim, D. ChangMo Yang, Soohaeng Yoo Willow, Chang Woo Myung

Abstract: Tensor network contraction is a fundamental computational challenge underlying quantum many-body physics, statistical mechanics, and machine learning. Belief propagation (BP) provides an efficient approximate solution, but introduces systematic errors on graphs with loops. Here, we introduce a hybrid method that achieves accurate results by stochastically sampling loop corrections to BP and showca… ▽ More Tensor network contraction is a fundamental computational challenge underlying quantum many-body physics, statistical mechanics, and machine learning. Belief propagation (BP) provides an efficient approximate solution, but introduces systematic errors on graphs with loops. Here, we introduce a hybrid method that achieves accurate results by stochastically sampling loop corrections to BP and showcase our method by applying it to the two-dimensional ferromagnetic Ising model. For any pairwise Markov random field with symmetric edge potentials, our approach exploits an exact factorization of the partition function into the BP contribution and a loop correction factor summing over all valid loop configurations, weighted by edge weights derived directly from the potentials. We sample this sum using Markov chain Monte Carlo with moves that preserve the loop constraint, combined with umbrella sampling to ensure efficient exploration across all correlation strengths. Our stochastic approach provides unbiased estimates with controllable statistical error in any parameter regime. △ Less

Submitted 7 April, 2026; v1 submitted 9 March, 2026; originally announced March 2026.

Comments: 12+4 pages, 5+1 figures

Suppression of Spectral Gap and Flat Bands on a Cuprate Superconductor Side-Surface

Authors: Gabriele Domaine, Mihir Date, Sydney K. Y. Dufresne, Natalie Lehmann, Daiyu Geng, Tohru Kurosawa, Amit Kumar, Jiaju Wang, Tianlun Yu, Chien-Ching Chang, Swosti P. Sarangi, Ding Pei, Yiran Liu, Julia Küspert, Shigemi Terakawa, Markel Pardo Almanza, Jiabao Yang, Izabela Biało, Matthew D. Watson, Timur K. Kim, Stephen M. Hayden, Kritika Singh, Banabir Pal, Matteo Minola, Johan Chang , et al. (5 additional authors not shown)

Abstract: Side surfaces of cuprate superconductors are expected to display a suppressed $d$-wave order parameter and zero-energy topological flat bands with a large density of states, making them susceptible to symmetry broken orders. Yet such surfaces have never been investigated with momentum-resolved, surface-sensitive probes, because high-temperature superconductors rarely cleave along them. Using focus… ▽ More Side surfaces of cuprate superconductors are expected to display a suppressed $d$-wave order parameter and zero-energy topological flat bands with a large density of states, making them susceptible to symmetry broken orders. Yet such surfaces have never been investigated with momentum-resolved, surface-sensitive probes, because high-temperature superconductors rarely cleave along them. Using focused-ion-beam milling to define a controlled breaking point, we expose pristine (110) side surfaces of overdoped La$_{2-x}$Sr$_x$CuO$_4$ ($x=0.22$) suitable for angle-resolved photoemission. We observe the suppression of the superconducting spectral gap within our energy resolution ($\sim 4~\mathrm{meV}$), and surprisingly, the expected zero-energy flat band peak is also suppressed, despite the high topographic quality of the surface. Self-consistent Bogoliubov--de~Gennes calculations show that the measured geometric roughness of the cleaved surface is too weak to eliminate these modes. The calculations further demonstrate that bulk inhomogeneities characteristic of high-temperature superconductors, modelled as moderate Anderson-type disorder, can broaden the flat-band states beyond detectability. Our results provide the first momentum-resolved view of the electronic structure on a cuprate side surface and reveal disorder as the key factor currently preventing appearance of flat bands and their associated correlated orders. △ Less

Submitted 3 March, 2026; originally announced March 2026.

Quantum diffusion for a quantum particle with a correlated Gaussian noise

Authors: Yun Jeong Kang, Sung Kyu Seo, Kyungsik Kim

Abstract: We investigate the diffusive behavior of a quantum particle driven by a correlated Gaussian noise. We derive the analytical solution of the joint probability density function and obtain explicit expressions for the mean square momentum and the mean square displacement. We investigate the diffusive behavior of a quantum particle driven by a correlated Gaussian noise. We derive the analytical solution of the joint probability density function and obtain explicit expressions for the mean square momentum and the mean square displacement. △ Less

Submitted 8 March, 2026; v1 submitted 26 February, 2026; originally announced February 2026.

Comments: 7 Pages

Emergence of chiral $p$-wave and $d$-wave states in $g$-wave altermagnets

Authors: Tilen Cadez, Abraham Nathan Sunanta, Kyoung-Min Kim

Abstract: Altermagnets emerge as a novel platform for realizing unconventional superconductivity through their exotic momentum-dependent spin-splitting of electronic band structures. Recent experiments have uncovered a novel form of altermagnetism with distinctive $g$-wave symmetry in CrSb. However, the potential for unconventional superconductivity arising from $g$-wave altermagnetism in such systems remai… ▽ More Altermagnets emerge as a novel platform for realizing unconventional superconductivity through their exotic momentum-dependent spin-splitting of electronic band structures. Recent experiments have uncovered a novel form of altermagnetism with distinctive $g$-wave symmetry in CrSb. However, the potential for unconventional superconductivity arising from $g$-wave altermagnetism in such systems remains largely unexplored. In this study, we discover the emergence of chiral superconducting states in three-dimensional $g$-wave altermagnetic metals. Through systematic self-consistent mean-field analysis on the extended attractive Hubbard model combined with $g$-wave altermagnetic exchange fields in a three-dimensional hexagonal lattice, as observed in CrSb, we find that the altermagnetic spin splitting of Fermi surfaces favors chiral $p$-wave states as the dominant pairing channel under strong altermagnetic fields and high electron densities, while chiral $d$-wave states become predominant under weak altermagnetic fields and intermediate electron densities. Conversely, at weak altermagnetic fields and typical electron densities, non-chiral $s$-, extended $s$-, or $f$-wave states become stabilized. We also showcase the possible experimental detection using the quasiparticle energy dispersions and the density of states to distinguish different pairing symmetries. These findings underscore the potential of $g$-wave altermagnets to host sought-after chiral and gapless superconductivity. △ Less

Submitted 26 February, 2026; originally announced February 2026.

Comments: 14+14 pages, 7+3 figures

Analytical solutions for a charged particle with white, thermal, and active noises in the presence of a uniform magnetic field

Authors: Y. J. Kang, S. K. So, Kyungsik Kim

Abstract: We study the two-dimensional equations of motion for a charged particle subjected to white, thermal, and active noises in uniform a magnetic field. By deriving the corresponding Fokker Planck equation, analytical solutions for the joint probability density are obtained in different time domains. We study the two-dimensional equations of motion for a charged particle subjected to white, thermal, and active noises in uniform a magnetic field. By deriving the corresponding Fokker Planck equation, analytical solutions for the joint probability density are obtained in different time domains. △ Less

Submitted 20 February, 2026; originally announced February 2026.

Comments: 21 pages

Tuning magnetic, lattice, and transport properties in CoNb3S6 via Fe doping

Authors: Deepu Kumar, Joydev Khatua, Mukesh Suthar, Rajesh Kumar Ulaganathan, Jeonghun Kang, Hengbo Cui, Sihun Seong, Seo Hyoung Chang, Kee Hoon Kim, Raman Sankar, Maeng-Je Seong, Kwang-Yong Choi

Abstract: We present a comprehensive investigation of the effects of Fe doping on the lattice dynamics, magnetic ordering, and magneto-transport properties of the intercalated van der Waals antiferromagnets Co1-xFexNb3S6 (x = 0.1 and 0.3). Temperature- and polarization-dependent Raman scattering measurements reveal a pronounced blue shift of the 180 cm-1 phonon mode with increasing Fe concentration, indicat… ▽ More We present a comprehensive investigation of the effects of Fe doping on the lattice dynamics, magnetic ordering, and magneto-transport properties of the intercalated van der Waals antiferromagnets Co1-xFexNb3S6 (x = 0.1 and 0.3). Temperature- and polarization-dependent Raman scattering measurements reveal a pronounced blue shift of the 180 cm-1 phonon mode with increasing Fe concentration, indicating enhanced sensitivity of lattice vibrations to Fe-induced structural and mass effects. While the temperature evolution of the phonon modes is dominated by conventional anharmonic phonon softening, subtle anomalies observed near the Néel temperature for x = 0.1 point to weak spin-phonon coupling. Electrical transport and magnetic susceptibility data show clear signatures of the antiferromagnetic phase transitions at TN ~ 20.5-23.7 K for x = 0.1 and TN ~ 32.0 K for x = 0.3. Out-of-plane magnetization measurements reveal hysteretic behavior with two field-induced transitions for x =0.1, which evolve into a single hysteresis loop at x =0.3, signaling a subtle reconstruction of the magnetic ground state. Magneto-transport measurements for x = 0.1 further display a butterfly-shaped hysteretic magnetoresistance and a weak topological Hall effect; however, both features are strongly suppressed at x = 0.3. These results illustrate the critical role of Fe-induced magnetic structure reconstruction in fine-tuning topological and magnetic transport phenomena in intercalated van der Waals antiferromagnets. △ Less

Submitted 14 February, 2026; originally announced February 2026.

Cell strain-stiffening drives cell breakout from embedded spheroids

Authors: Shabeeb Ameen, Kyungeun Kim, Ligesh Theeyancheri, Minh Thanh, Mingming Wu, Alison E. Patteson, J. M. Schwarz, Tao Zhang

Abstract: Understanding how cells escape from embedded spheroids requires a mechanical framework linking stress generation within cells, across cells, and between cells and the surrounding extracellular matrix (ECM). We develop such a framework by coupling a 3D vertex model of a spheroid to a fibrous ECM network and deriving a 3D Cauchy stress tensor for deformable polyhedral cells, enabling direct cell-lev… ▽ More Understanding how cells escape from embedded spheroids requires a mechanical framework linking stress generation within cells, across cells, and between cells and the surrounding extracellular matrix (ECM). We develop such a framework by coupling a 3D vertex model of a spheroid to a fibrous ECM network and deriving a 3D Cauchy stress tensor for deformable polyhedral cells, enabling direct cell-level stress quantification in three dimensions. We analyze maximum shear stress in solid-like and fluid-like spheroids: solid-like spheroids exhibit broader stress distributions and radial stress gradients, while fluid-like spheroids show lower stresses with weak spatial organization. Cell shape anisotropy is not generically aligned with principal stress directions, indicating that morphology alone is an unreliable proxy for mechanical state. We further demonstrate strain stiffening at the single-cell level, where elongation produces nonlinear increases in maximum shear stress, allowing boundary cells in otherwise low-stress, fluid-like spheroids to transiently generate forces sufficient to remodel the matrix. To connect strain-induced stress amplification to invasion modes, we introduce an extended 3D vertex model with explicit, tunable cell-cell adhesion springs. In this minimal mechanical framework, single-cell breakout results from strain stiffening combined with reduced adhesion, whereas multi-cell streaming additionally requires anisotropic adhesion strengthened along the elongation axis and weakened orthogonally. Together, these results identify distinct mechanical pathways coupling cell strain, stress amplification, and adhesion organization to spheroid invasion. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Spectroscopic Evidence of Competing Diagonal Spin Interactions and Spin Disproportionation in the Bilayer Nickelate La$_3$Ni$_2$O$_7$

Authors: Dong-Hyeon Gim, Dirk Wulferding, Hengyuan Zhang, Meng Wang, Kee Hoon Kim

Abstract: A comprehensive spectroscopic map of the electronic, magnetic, and lattice excitations is presented for the bilayer nickelate La$_3$Ni$_2$O$_7$ using Raman scattering at ambient pressure. Upon entering the spin density wave state below 153 K, the $A_{1g}$ channel exhibits an abrupt electronic spectral gap with a clear isosbestic point. In contrast, the $B_{1g}$ and $B_{2g}$ channels are dominated… ▽ More A comprehensive spectroscopic map of the electronic, magnetic, and lattice excitations is presented for the bilayer nickelate La$_3$Ni$_2$O$_7$ using Raman scattering at ambient pressure. Upon entering the spin density wave state below 153 K, the $A_{1g}$ channel exhibits an abrupt electronic spectral gap with a clear isosbestic point. In contrast, the $B_{1g}$ and $B_{2g}$ channels are dominated by pronounced two-magnon (2M) excitations, representing an unambiguous signature of incipient Mottness. These 2M signals in both channels constitute direct evidence for two distinct in-plane spin exchange interactions along the Ni-O bonding and its diagonal directions. Calculations based on the spin wave theory further reveal that the 2M mode in the $B_{2g}$ channel arises from the competition between two bond-diagonal antiferromagnetic interactions mediated by nickel $d_{x^2-y^2}$ orbitals. Furthermore, emergent low-energy 2M excitations below 10 meV are found to originate from distinct, weaker spin moments, strongly supporting spin disproportionation. Simultaneously, an anomalous softening of $B_{1g}$ phonons from 280 down to 4.5 K is uncovered, suggesting the presence of an incipient lattice instability leading to checkerboard-type breathing modulations. Collectively, these findings identify a ground state of the bilayer nickelate characterized by competing bond-diagonal interactions, spin disproportionation, and an incipient lattice instability, establishing key ingredients for understanding the mechanism of nickelate superconductivity. △ Less

Submitted 5 February, 2026; originally announced February 2026.

Comments: 30 pages, 14 figures, 2 tables

Structural constraints on mobility edges in one-dimensional quasiperiodic systems

Authors: Sanghoon Lee, Tilen Cadez, Kyoung-Min Kim

Abstract: Mobility edges commonly arise in one-dimensional quasiperiodic systems once exact self-duality is broken, yet their origin is typically understood only at the level of individual Hamiltonians. Here we show that mobility edge positions are not independent spectral features of individual Hamiltonians, but are structurally constrained across quasiperiodic Hamiltonians related by an isospectral dualit… ▽ More Mobility edges commonly arise in one-dimensional quasiperiodic systems once exact self-duality is broken, yet their origin is typically understood only at the level of individual Hamiltonians. Here we show that mobility edge positions are not independent spectral features of individual Hamiltonians, but are structurally constrained across quasiperiodic Hamiltonians related by an isospectral duality. Using a bichromatic Aubry--André model as a minimal setting, we demonstrate that this constraint is encoded in an exact identity for Lyapunov exponents derived from the Thouless formula. As a consequence, the mobility edge positions are restricted to a reduced set of energies. In the self-dual limit, these mobility edge positions coincide at a single localization--delocalization transition. This structural constraint enforces a linear critical scaling of the physical Lyapunov spectrum near the self-dual point. Numerical results confirm a critical exponent consistent with the standard Aubry--André value of $ν= 1$, while simultaneously revealing a novel, non-universal energy-dependent prefactor. △ Less

Submitted 22 January, 2026; originally announced January 2026.

Comments: 7 pages, 7 figures

Kineo-Elasticity and Nonreciprocal Phonons by Rashba-induced Interfacial Spin-Lattice Coupling

Authors: Gyungchoon Go, Se Kwon Kim

Abstract: We identify a previously unrecognized spin-lattice coupling that is allowed in the presence of broken inversion symmetry that can be considered as a lattice analogue to the electronic Rashba spin-orbit coupling. In the low-frequency regime with magnons integrated out, the interfacial spin-lattice coupling is shown to engender a kineo-elastic term in the phonon Lagrangian that couples the strain on… ▽ More We identify a previously unrecognized spin-lattice coupling that is allowed in the presence of broken inversion symmetry that can be considered as a lattice analogue to the electronic Rashba spin-orbit coupling. In the low-frequency regime with magnons integrated out, the interfacial spin-lattice coupling is shown to engender a kineo-elastic term in the phonon Lagrangian that couples the strain on the lattice to its velocity and thereby gives rise to a nonreciprocity in transverse phonon velocity. We further analyze the full magnon-phonon spectrum and uncover directional hybridization and absorption, leading to asymmetric phonon propagation lengths for opposite directions. Our results indicate that such interfacial spin-lattice coupling can serve as an efficient route to achieve nonreciprocal phonon propagation properties in magnetic heterostructures with strong Rashba spin-orbit coupling. △ Less

Submitted 18 January, 2026; originally announced January 2026.

Comments: 6 pages, 4 figures

Data-driven Prediction of Ionic Conductivity in Solid-State Electrolytes with Machine Learning and Large Language Models

Authors: Haewon Kim, Taekgi Lee, Seongeun Hong, Kyeong-Ho Kim, Yongchul G. Chung

Abstract: Solid-state electrolytes (SSEs) are attractive for next-generation lithium-ion batteries due to improved safety and stability but their low room-temperature ionic conductivity hinders practical application. Experimental synthesis and testing of new SSEs remain time-consuming and resource intensive. Machine learning (ML) offers an accelerated route for SSE discovery; however, composition-only model… ▽ More Solid-state electrolytes (SSEs) are attractive for next-generation lithium-ion batteries due to improved safety and stability but their low room-temperature ionic conductivity hinders practical application. Experimental synthesis and testing of new SSEs remain time-consuming and resource intensive. Machine learning (ML) offers an accelerated route for SSE discovery; however, composition-only models neglect structural factors important for ion transport while graph neural networks (GNNs) are challenged by the scarcity of structure-labeled conductivity data and the prevalence of crystallographic disorder in CIFs. Here, we train two complementary predictors on the same room-temperature, structure-labeled dataset (n = 499). A gradient-boosted tree regressor (GBR) combining stoichiometric and geometric descriptors achieves best performance (MAE = 0.543 in log(S cm-1)), and Shapley Additive exPlanations (SHAP) identifies probe-occupiable volume (POAV) and lattice parameters as key correlations for conductivity. In parallel, we fine-tune large language models (LLMs) using compact text prompts derived from CIF metadata (formula with optional symmetry and disorder tags), avoiding direct use of raw atomic coordinates. Notably, Llama-3.1-8B-Instruct achieves high accuracy (MAE = 0.657 in log(S cm-1)) using formula and symmetry information, eliminating the need for numerical feature extraction from CIF files. Together, these results show that global geometric descriptors improve tree-based predictions and enable interpretable structure-property analysis, while LLMs provide a competitive low-preprocessing alternative for rapid SSE screening. △ Less

Submitted 24 February, 2026; v1 submitted 16 January, 2026; originally announced January 2026.

Two-Dimensional Twisted Ferromagnetic Domain Wall as a Spin-Wave Diffraction Grating

Authors: Ehsan Faridi, Se Kwon Kim, Giovanni Vignale

Abstract: We present a theoretical study of spin-wave scattering by a twisted domain wall (DW) in a two-dimensional ferromagnet with easy-axis anisotropy. While the twisted DW generates an effective gauge field for spin waves, leading to a deflection of their trajectories, our main focus is on a distinct effect that arises when a hard-axis anisotropy is present in addition to the easy-axis anisotropy. In th… ▽ More We present a theoretical study of spin-wave scattering by a twisted domain wall (DW) in a two-dimensional ferromagnet with easy-axis anisotropy. While the twisted DW generates an effective gauge field for spin waves, leading to a deflection of their trajectories, our main focus is on a distinct effect that arises when a hard-axis anisotropy is present in addition to the easy-axis anisotropy. In this case, the translational symmetry of the spin-wave Hamiltonian along the DW is broken, resulting in a periodic modulation of the Hamiltonian. This periodicity leads to the formation of multiple diffracted spin wave modes on both sides of the DW, engendering a DW-induced magnonic diffraction pattern. The interplay between the emergent gauge field and the anisotropy-induced periodicity reveals rich spin-wave dynamics and suggests potential applications for manipulating magnon flow in two-dimensional magnetic textures. △ Less

Submitted 13 January, 2026; originally announced January 2026.

Aharonov-Casher Effect and the Coherent Flux Tunneling in the Hybrid Charge Quantum Interference Device

Authors: J. W. Dunstan, R. Shaikhaidarov, K. H. Kim, A. Shesterikov, I. Antonov, S. Linzen, E. V. Il'ichev, V. N. Antonov, O. V. Astafiev

Abstract: By exploiting the Aharonov-Casher effect we demonstrate a suppression of magnetic flux tunneling in a Hybrid Charge Quantum Interference Device. The main part of this device is two Josephson junctions with a small superconducting island between them. To minimize phase fluctuations across Josephson junctions, this structure is embedded in a compact super-inductive NbN loop. The Interference between… ▽ More By exploiting the Aharonov-Casher effect we demonstrate a suppression of magnetic flux tunneling in a Hybrid Charge Quantum Interference Device. The main part of this device is two Josephson junctions with a small superconducting island between them. To minimize phase fluctuations across Josephson junctions, this structure is embedded in a compact super-inductive NbN loop. The Interference between the flux tunneling paths is determined by the island-induced charge, which is controlled by an external voltage. The charge sensitive operation of the device is subjected to poisoning by the quasiparticles generated in the NbN film. △ Less

Submitted 10 January, 2026; originally announced January 2026.

Comments: 5 pages 4 figures

Observation of REBCO delamination in the resistive insulation nested coils

Authors: Jun Lu, Iain Dixon, Kwangmin Kim, Yan Xin, Hongyu Bai

Abstract: The REBCO coated conductor has the potential to be widely used in ultrahigh field magnets. It is well known, however, that it is not mechanically strong against delamination in the direction normal to its surface due to its intrinsic layered structure. Therefore, conductor delamination is one of the major design challenges for REBCO magnet coils. As a part of the development of the 40 T all-superc… ▽ More The REBCO coated conductor has the potential to be widely used in ultrahigh field magnets. It is well known, however, that it is not mechanically strong against delamination in the direction normal to its surface due to its intrinsic layered structure. Therefore, conductor delamination is one of the major design challenges for REBCO magnet coils. As a part of the development of the 40 T all-superconducting magnet at the National High Magnetic Field Laboratory, USA (NHMFL), a dry-wound resistive-insulation-nested-coils (RINC) was designed to reach 25.8 T. It used surface-treated stainless-steel tape as a co-wind to control the turn-to-turn contact resistance, and was fabricated and tested in a liquid helium bath. During the test, two of the double pancake modules exhibited resistive transitions at a current significantly lower than the designed value. The postmortem inspection of the REBCO conductor of these modules by reel-to-reel magnetization at 77 K found sections of very low critical current. Further investigations of one section by chemical etching, visual inspection, and electron microscopy revealed that conductor of this section was delaminated. We present the detailed findings of these postmortem characterizations. The implication of this type of delamination for future magnet designs will be discussed. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: International symposium on superconductivity (ISS2025), 9 pages, 8 figures

Unidirectional gliding of a cycloidal spin structure by an AC magnetic field

Authors: Dong Hui Han, Kyoung-Woong Moon, Kab-Jin Kim, Se Kwon Kim

Abstract: The dynamics of a cycloidal spin structure driven by an AC magnetic field is theoretically studied in the weak-field limit. A specific model Hamiltonian describing the cycloidal spin structure in a ferromagnetic thin film is constructed, and its dynamics is analyzed using the collective-coordinate approach within the Lagrangian formalism. We demonstrate that the cycloidal spin structure exhibits a… ▽ More The dynamics of a cycloidal spin structure driven by an AC magnetic field is theoretically studied in the weak-field limit. A specific model Hamiltonian describing the cycloidal spin structure in a ferromagnetic thin film is constructed, and its dynamics is analyzed using the collective-coordinate approach within the Lagrangian formalism. We demonstrate that the cycloidal spin structure exhibits a unidirectional gliding motion under an AC magnetic field, and an expression for the average velocity is derived as a function of the magnitude, the direction, and the frequency of the AC magnetic field. We compare our theoretical predictions with the results of micromagnetic simulations and identify two resonance frequencies determined by the eigenenergies of the excitation modes. Furthermore, evaluating spin motive forces induced by the dynamics reveals a substantial DC voltage, which may be exploited in energy-harvesting devices utilizing ambient electromagnetic radiation. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Deep learning of committor for ion dissociation and interpretable analysis of solvent effects using atom-centered symmetry functions

Authors: Kenji Okada, Kazushi Okada, Kei-ichi Okazaki, Toshifumi Mori, Kang Kim, Nobuyuki Matubayasi

Abstract: The association and dissociation of ion pairs in water are fundamental to physical chemistry, yet their reaction coordinates are complex, involving not only interionic distance but also solvent-mediated hydration structures. These processes are often represented by free-energy landscapes constructed from collective variables (CVs), such as interionic distance and water bridging structures; however… ▽ More The association and dissociation of ion pairs in water are fundamental to physical chemistry, yet their reaction coordinates are complex, involving not only interionic distance but also solvent-mediated hydration structures. These processes are often represented by free-energy landscapes constructed from collective variables (CVs), such as interionic distance and water bridging structures; however, it remains uncertain whether such representations reliably capture the transition pathways between the two associated and dissociated states. In this study, we employ deep learning to identify reaction coordinates for NaCl ion pair association and dissociation in water, using the committor as a quantitative measure of progress along the transition pathway through the transition state. The solvent environment surrounding the ions is encoded through descriptors based on atom-centered symmetry functions (ACSFs), which serve as input variables for the neural network. In addition, an explainable artificial intelligence technique is applied to identify ACSFs that contribute to the reaction coordinate. A comparative analysis of their correlation with CVs representing water bridging structures, such as interionic water density and the number of water molecules coordinating both ions, further provides a molecular-level interpretation of the ion association-dissociation mechanism in water. △ Less

Submitted 7 February, 2026; v1 submitted 10 December, 2025; originally announced December 2025.

Comments: 10 pages, 6 figures, 2 tables for the main text, 1 page for supplementary material

Journal ref: J. Chem. Phys. 164, 094101 (2026)

Extreme Strain Controlled Correlated Metal-Insulator Transition in the Altermagnet CrSb

Authors: Cong Li, Mengli Hu, Jianfeng Zhang, Magnus H. Berntsen, Francesco Scali, Dibya Phuyal, Chun Lin, Wanyu Chen, Johan Chang, Oliver J. Clark, Timur K. Kim, Jacek Osiecki, Craig Polley, Balasubramanian Thiagarajan, Zhilin Li, Tao Xiang, Oscar Tjernberg

Abstract: Correlated flat bands and altermagnetism are two important directions in quantum materials, centred respectively on interaction-dominated phases and symmetry-enforced spin-textured states, yet both derive from lattice symmetry and orbital hybridization. This common origin implies that extreme crystal distortion, by narrowing bandwidths, enhancing correlations and reshaping the symmetries of alterm… ▽ More Correlated flat bands and altermagnetism are two important directions in quantum materials, centred respectively on interaction-dominated phases and symmetry-enforced spin-textured states, yet both derive from lattice symmetry and orbital hybridization. This common origin implies that extreme crystal distortion, by narrowing bandwidths, enhancing correlations and reshaping the symmetries of altermagnetic spin splittings, could unify flat-band and altermagnetic physics in a single material; in practice, however, achieving such large distortions in a crystalline altermagnet is a formidable challenge. Here we combine a dedicated strain device with a tailored single-crystal mounting scheme to impose a highly tensile strain gradient in bulk CrSb, a prototypical altermagnet, creating a near-surface layer in which the in-plane lattice is strongly distorted relative to the weakly strained bulk, while the average bulk distortion remains small. Angle-resolved photoemission reveals a reversible regime at moderate strain, where a deeper flat-band feature, attributed to a strain-gradient-driven suppression of Cr-Sb hybridization, coexists with a correlation-enhanced Cr 3d flat band, and an irreversible regime at larger strain where partial bond decoupling drives a predominantly insulating spectral response. Density-functional calculations show that an orbital-selective altermagnetic spin texture persists across this correlated regime despite strong bandwidth renormalisation. These results define a strain-symmetry-correlation map for CrSb and establish extreme tensile strain as a route to co-engineer flat-band tendencies and spin-textured, zero-net-moment correlated states in altermagnets, pointing toward strain-adaptive, spin-selective Mott filtering and related device concepts. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Comments: Main text: 21 pages, 4 figures; SI: 43 pages, 30 figures, which are too large to be included. Comments are welcome

Density of states of quantum systems from free probability theory: a brief overview

Authors: Keun-Young Kim, Kuntal Pal

Abstract: We provide a brief overview of approaches for calculating the density of states of quantum systems and random matrix Hamiltonians using the tools of free probability theory. For a given Hamiltonian of a quantum system or a generic random matrix Hamiltonian, which can be written as a sum of two non-commutating operators, one can obtain an expression for the density of states of the Hamiltonian from… ▽ More We provide a brief overview of approaches for calculating the density of states of quantum systems and random matrix Hamiltonians using the tools of free probability theory. For a given Hamiltonian of a quantum system or a generic random matrix Hamiltonian, which can be written as a sum of two non-commutating operators, one can obtain an expression for the density of states of the Hamiltonian from the known density of states of the two component operators by assuming that these operators are mutually free and by using the free additive convolution. In many examples of interacting quantum systems and random matrix models, this procedure is known to provide a reasonably accurate approximation to the exact numerical density of states. We review some of the examples that are known in the literature where this procedure works very well, and also discuss some of the limitations of this method in situations where the free probability approximation fails to provide a sufficiently accurate description of the exact density of states. Subsequently, we describe a perturbation scheme that can be developed from the subordination formulas for the Cauchy transform of the density of states and use it to obtain approximate analytical expressions for the density of states in various models, such as the Rosenzweig-Porter random matrix ensemble and the Anderson model with on-site disorder. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Universal Fabrication of Graphene/Perovskite Oxide Hybrid Heterostructures

Authors: Yeongju Choi, Seungjin Lee, Dongwon Shin, Sukhoon Sim, Min-Hyoung Jung, Dirk Wulferding, Minjae Kim, Jaesik Eom, Myeesha Mostafa, Wonhee Ko, SeungNam Cha, Jungseek Hwang, Hu Young Jeong, Ki Kang Kim, Woo Seok Choi

Abstract: Hybrid heterostructures composed of graphene and perovskite oxides provide a promising platform for exploiting synergetic interfacial functionalities. Conventional fabrication methods of the hybrid heterostructures rely on transferring graphene grown on metallic substrates-- a process that is time-consuming, labor-intensive, and prone to introducing numerous defects. In this study, we present a un… ▽ More Hybrid heterostructures composed of graphene and perovskite oxides provide a promising platform for exploiting synergetic interfacial functionalities. Conventional fabrication methods of the hybrid heterostructures rely on transferring graphene grown on metallic substrates-- a process that is time-consuming, labor-intensive, and prone to introducing numerous defects. In this study, we present a universal, catalyst-free method for the direct growth of graphene on insulating substrates by employing three different perovskite oxide substrates (SrTiO$_3$, LaAlO$_3$, and (La$_{0.18}$Sr$_{0.82}$)(Al$_{0.59}$Ta$_{0.41}$)O$_3$) using atmospheric chemical vapor deposition. Comprehensive characterization via Raman spectroscopy, X-ray spectroscopy, scanning probe microscopy, and electron microscopy confirmed the formation of a uniform, continuous monolayer graphene on all substrates. We identified that growth temperature critically governs graphene quality, as excessive active species may lead to secondary nucleation and the formation of multilayer graphene. Notably, all substrates shared the same optimal growth conditions. Low-temperature Raman spectroscopy and scanning tunneling microscopy of the graphene/SrTiO$_3$ hybrid heterostructure revealed cooperative phenomena, including substrate-induced lattice-phonon and electron-phonon coupling. Our work establishes a reproducible, transfer-free fabrication route for graphene/perovskite oxide hybrid heterostructures and provides empirical support for the universal growth of graphene on insulating substrates. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Comments: 44 pages, 25 figures, This work has been accepted for publication in Small Structures in November 2025. Yeongju Choi and Seungjin Lee contributed equally to this work. Woo Seok Choi and Ki Kang Kim are corresponding authors

Kinetic Inductance of Few-Layer NbSe$_2$ in the Two-Dimensional Limit

Authors: Sameia Zaman, Joel Î-j. Wang, Thomas Werkmeister, Miuko Tanaka, Thao Dinh, Max Hays, Daniel Rodan-Legrain, Aranya Goswami, Réouven Assouly, Ahmet Kemal Demir, David K. Kim, Bethany M. Niedzielski, Kyle Serniak, Mollie E. Schwartz, Kenji Watanabe, Takashi Taniguchi, Philip Kim, Riccardo Comin, Jeffrey A. Grover, Terry P. Orlando, Pablo Jarillo-Herrero, William D. Oliver

Abstract: Van der Waals (vdW) superconductors remain superconducting down to the monolayer limit, enabling the exploration of emergent physical phenomena and functionality driven by reduced dimensionality. Here, we report the characterization of the kinetic inductance of atomically thin NbSe$_2$, a two-dimensional van der Waals superconductor, using superconducting coplanar waveguides and microwave measurem… ▽ More Van der Waals (vdW) superconductors remain superconducting down to the monolayer limit, enabling the exploration of emergent physical phenomena and functionality driven by reduced dimensionality. Here, we report the characterization of the kinetic inductance of atomically thin NbSe$_2$, a two-dimensional van der Waals superconductor, using superconducting coplanar waveguides and microwave measurement techniques familiar to circuit quantum electrodynamics (cQED). The kinetic inductance scales inversely with the number of NbSe$_2$ layers, reaching 1.2 nH/$\Box$ in the monolayer limit. Furthermore, the measured kinetic inductance exhibits a thickness-dependent crossover from clean- to dirty-limit behavior, with enhanced dirty-limit contributions emerging in the ultra-thin regime. These effects are likely driven by increased surface scattering, multi-band superconductivity, and geometric confinement. Additionally, the self-Kerr nonlinearity of the NbSe$_2$ films ranges from $K/2π$ = -0.008 to -14.7 Hz/photon, indicating its strong potential in applications requiring compact, nearly linear, high-inductance superconducting quantum devices and detectors. The fabrication and characterization techniques demonstrated here are extensible to the investigation of other two-dimensional superconductors. △ Less

Submitted 5 January, 2026; v1 submitted 11 November, 2025; originally announced November 2025.

Crossover from quantum correlation to hot-carrier transport in scattering-tolerant 2D transistors

Authors: Debottam Daw, Houcine Bouzid, Sung-Gyu Lee, Wujoon Cha, Ki Kang Kim, Min-kyu Joo, Yan Wang, Manish Chhowalla, Young Hee Lee

Abstract: Quantum correlation and hot-carrier transport represent two fundamentally distinct regimes of electronic conduction, rarely accessible within the same device. Here, we report a state-of-the-art monolayer transition metal dichalcogenides transistor architecture on a ferroelectric substrate that enables this crossover by leveraging the strong dielectric screening and in-plane gate control. At cryoge… ▽ More Quantum correlation and hot-carrier transport represent two fundamentally distinct regimes of electronic conduction, rarely accessible within the same device. Here, we report a state-of-the-art monolayer transition metal dichalcogenides transistor architecture on a ferroelectric substrate that enables this crossover by leveraging the strong dielectric screening and in-plane gate control. At cryogenic temperatures, the devices exhibit reproducible quasi-periodic current fluctuations, consistent with an emergent potential landscape driven by electron-electron interactions at low carrier densities. As the temperature increases, this correlated potential profile thermally dissolves and transport is dominated by the lateral gate-field that drives the carriers with high kinetic energy. These hot-carriers can efficiently surmount the scattering events, exhibiting a record-high room-temperature electron mobility of ~4,800 cm^2/Vs and a maximum on-current ~0.5 mA/μm, surpassing traditional FETs in key performance metrics. These findings establish a unified approach for probing intermediate mesoscopic orders, while advancing the transistor performance limits in scalable 2D transistors. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 66 pages, 4 main figures, 29 supporting figures

Dual holography as functional renormalization group

Authors: Ki-Seok Kim, Arpita Mitra, Debangshu Mukherjee, Seung-Jong Yoo

Abstract: We investigate the relationship between the functional renormalization group (RG) and the dual holography framework in the path integral formulation, highlighting how each can be understood as a manifestation of the other. Rather than employing the conventional functional RG formalism, we consider a functional RG equation for the probability distribution function, where the RG flow is governed by… ▽ More We investigate the relationship between the functional renormalization group (RG) and the dual holography framework in the path integral formulation, highlighting how each can be understood as a manifestation of the other. Rather than employing the conventional functional RG formalism, we consider a functional RG equation for the probability distribution function, where the RG flow is governed by a Fokker-Planck-type equation. The central idea is to reformulate the solution of Fokker-Planck type functional RG equation in a path integral representation. Within the semiclassical approximation, this leads to a Hamilton-Jacobi equation for an effective renormalized on-shell action. We then examine our framework for an Einstein-Hilbert action coupled to a scalar field. Applying standard techniques, we derive a corresponding functional RG equation for the distribution function, where the dual holographic path integral serves as its formal solution. By synthesizing these two perspectives, we propose a generalized dual holography framework in which the RG flow is explicitly incorporated into the bulk effective action. This generalization naturally introduces RG $β$-functions and reveals that the RG flow of the distribution function is essentially identical to that of the functional RG equation. △ Less

Submitted 14 March, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: Explicit derivation for FRG has been presented

Structural modulation, physical properties, and electronic band structure of the kagome metal UCr$_6$Ge$_6$

Authors: Z. W. Riedel, P. A. E. Murgatroyd, C. S. Kengle, P. M. T. Vianez, A. Schmidt, X. Du, K. Allen, T. K. Kim, C. Lane, Ying Wai Li, Jian-Xin Zhu, J. D. Thompson, F. Ronning, S. M. Thomas, P. F. S. Rosa, E. D. Bauer

Abstract: The chemical flexibility of the $RM_6X_6$ stoichiometry, where an $f$-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the $f$- and $d$-electron lattices. Yet, 5$f$ members of the ``166" compounds are underrepresented compared with 4$f$ members. Here… ▽ More The chemical flexibility of the $RM_6X_6$ stoichiometry, where an $f$-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the $f$- and $d$-electron lattices. Yet, 5$f$ members of the ``166" compounds are underrepresented compared with 4$f$ members. Here, we report single-crystal growth of UCr$_6$Ge$_6$, which crystallizes in a monoclinically distorted Y$_{0.5}$Co$_3$Ge$_3$-type structure. The real-space character of the modulation, which is unique within the $RM_6X_6$ family, is approximated by a 3$\times$1$\times$2 supercell of the average monoclinic cell. The compound has kagome-lattice flatbands near the Fermi level and a moderately enhanced electronic heat capacity, as evidenced by its low-temperature Sommerfeld coefficient ($γ=86.5$~mJ~mol$^{-1}$~K$^{-2}$) paired with band structure calculations. The small, isotropic magnetization and featureless resistivity of UCr$_6$Ge$_6$ suggest itinerant uranium 5$f$ electrons and Pauli paramagnetism. Angle-resolved photoemission spectroscopy results provide evidence for uranium 5$f$ weight at the Fermi level and for a flatband near the Fermi level associated with the chromium $3d$ kagome lattice. The isotropic magnetic behavior of the uranium 5$f$ electrons starkly contrasts with localized behavior in other uranium 166 compounds, highlighting the high tunability of the magnetic ground state across the material family. △ Less

Submitted 4 March, 2026; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: 20 pages, 18 figures; updates include the addition of ARPES and Hall resistivity data

Elucidation of the Correlation between Molecular Conformation and Shear Viscosity of Polymer Melts under Steady-State Shear Flow

Authors: Yuhi Sakamaki, Shota Goto, Kang Kim, Nobuyuki Matubayasi

Abstract: The rheological behavior of polymer melts is strongly influenced by parameters such as chain length, chain stiffness, and architecture. In particular, shear thinning, characterized by a power-law decrease in shear viscosity with increasing shear rate, has been widely investigated through molecular dynamics simulations. A central question is the connection between molecular conformation under stead… ▽ More The rheological behavior of polymer melts is strongly influenced by parameters such as chain length, chain stiffness, and architecture. In particular, shear thinning, characterized by a power-law decrease in shear viscosity with increasing shear rate, has been widely investigated through molecular dynamics simulations. A central question is the connection between molecular conformation under steady flow and the resulting shear-thinning response. In this study, we employ coarse-grained molecular dynamics simulations of linear and ring polymers with varying chain stiffness to examine this relationship, with chain conformations quantified by the gyration tensor. We identified a strong correlation between the velocity-gradient direction component of the gyration tensor and shear viscosity, which exhibits a clear scaling relationship. This indicates that chain extension along the velocity-gradient direction governs the effective frictional force. Notably, this behavior emerges as a general feature, independent of chain architecture and chain stiffness. In addition, shear viscosity was found to correlate with the component of the gyration tensor corresponding to the direction that is not directly influenced by advective effects of shear flow. Because advection is absent in the direction, polymer chains can be regarded as diffusing freely, and the extent of this diffusion appears to be controlled by the shear viscosity. △ Less

Submitted 19 December, 2025; v1 submitted 8 October, 2025; originally announced October 2025.

Comments: 6 pages, 5 figures, to appear in Nihon Reoroji Gakkaishi(J. Soc. Rheol., Jpn)

Journal ref: Nihon Reoroji Gakkaishi (J. Soc. Rheol. Jpn.) 54, 11-17 (2026)

Neural-Network-Assisted Boltzmann Approach for Dilute Microswimmer Suspensions

Authors: Haruki Hayano, Akira Furukawa, Kang Kim

Abstract: We introduce a neural-network-assisted Boltzmann framework that learns the binary-collision map of microswimmers directly from data and uses it to evaluate collision integrals efficiently. Using a representative model swimmer, the learned map quantitatively predicts translational and rotational diffusivities and enables a linear-stability analysis of isotropy against polar ordering in dilute suspe… ▽ More We introduce a neural-network-assisted Boltzmann framework that learns the binary-collision map of microswimmers directly from data and uses it to evaluate collision integrals efficiently. Using a representative model swimmer, the learned map quantitatively predicts translational and rotational diffusivities and enables a linear-stability analysis of isotropy against polar ordering in dilute suspensions. The resulting predictions closely match direct simulations. The present framework is agnostic to active matter models and broadly applicable: once two-body collision data are obtained -- either from simulations or experiments -- the same surrogate can be used to evaluate kinetic transport across dilute conditions where binary collisions dominate. Because the workflow relies only on pre- and post-collision statistics, the present approach provides a general data-driven route linking particle-scale interactions to macroscopic transport and collective behavior in active suspensions. △ Less

Submitted 28 October, 2025; v1 submitted 2 October, 2025; originally announced October 2025.

Comments: 5 pages, 4 figures

Ubiquitous Antiparallel Domains in 2D Hexagonal Boron Nitride Uncovered by Interferometric Nonlinear Optical Imaging

Authors: Yeri Lee, Juseung Oh, Kyung Yeol Ma, Seung Jin Lee, Eui Young Jung, Yani Wang, Kenji Watanabe, Takashi Taniguchi, Hailin Peng, Hiroki Ago, Ki Kang Kim, Hyeon Suk Shin, Sunmin Ryu

Abstract: Hexagonal boron nitride (hBN) supports a wide range of two-dimensional (2D) technologies, yet assessing its crystalline quality over large areas remains a fundamental challenge. Both antiparallel domains, an intrinsic outcome of epitaxy on high-symmetry substrates, and associated structural defects have long evaded optical detection. Here, we show that interferometric second-harmonic generation (S… ▽ More Hexagonal boron nitride (hBN) supports a wide range of two-dimensional (2D) technologies, yet assessing its crystalline quality over large areas remains a fundamental challenge. Both antiparallel domains, an intrinsic outcome of epitaxy on high-symmetry substrates, and associated structural defects have long evaded optical detection. Here, we show that interferometric second-harmonic generation (SHG) imaging provides a powerful, nondestructive probe of lattice orientation and structural integrity in chemical vapor deposition-grown hBN. This approach reveals the ubiquitous formation of antiparallel domains and quantifies their impact on crystalline order. SHG intensity also emerges as a direct optical metric of domain disorder, spanning three orders of magnitude across films produced by ten different growth routes. Correlation with Raman spectroscopy establishes a unified framework for evaluating crystalline quality. Beyond hBN, this method offers a high-throughput route to wide-area structural imaging in various non-centrosymmetric materials, advancing their deployment in electronics, photonics, and quantum technologies. △ Less

Submitted 2 April, 2026; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 22 pages, 5 figures

Magnetoelastic Coupling-Driven Chiral Spin Textures: A Skyrmion-Antiskyrmion-Like Array

Authors: Gyungchoon Go, Se Kwon Kim

Abstract: We theoretically demonstrate that sufficiently strong magnetoelastic coupling can change the ground state of otherwise uniform spin systems to chiral spin configurations. More specifically, we show that, a periodic array of chiral spin textures can spontaneously emerge in a two-dimensional ferromagnetic system on a substrate-even in the absence of Dzyaloshinskii-Moriya interaction. The resulting s… ▽ More We theoretically demonstrate that sufficiently strong magnetoelastic coupling can change the ground state of otherwise uniform spin systems to chiral spin configurations. More specifically, we show that, a periodic array of chiral spin textures can spontaneously emerge in a two-dimensional ferromagnetic system on a substrate-even in the absence of Dzyaloshinskii-Moriya interaction. The resulting spin texture resembles a skyrmion-antiskyrmion lattice, characterized by alternating scalar spin chirality and a nonuniform but sign-preserving out-of-plane spin profile. Our analysis reveals that such patterns form naturally when the magnetoelastic interaction is sufficiently strong, while the coupling between flexural phonons and the substrate is sufficiently weak. These findings uncover a previously unexplored mechanism for chiral spin texture formation driven purely by magnetoelastic coupling, signaling at potential utilities of materials with strong magnetoelastic responses. △ Less

Submitted 18 September, 2025; originally announced September 2025.

Comments: 5 pages, 5 figures

Benchmarking thermostat algorithms in molecular dynamics simulations of a binary Lennard-Jones glass-former model

Authors: Kumpei Shiraishi, Emi Minamitani, Kang Kim

Abstract: A systematic comparison was carried out to assess the influence of representative thermostat methods in constant-temperature molecular dynamics simulations. The thermostat schemes considered include the Nosé--Hoover thermostat and its chain generalisation, the Bussi velocity rescaling method, and several implementations of the Langevin dynamics. Using a binary Lennard-Jones liquid as a model glass… ▽ More A systematic comparison was carried out to assess the influence of representative thermostat methods in constant-temperature molecular dynamics simulations. The thermostat schemes considered include the Nosé--Hoover thermostat and its chain generalisation, the Bussi velocity rescaling method, and several implementations of the Langevin dynamics. Using a binary Lennard-Jones liquid as a model glass former, we investigated how the sampling of physical observables, such as particle velocities and potential energy, responds to changes in time step across these thermostats. While the Nosé--Hoover chain and Bussi thermostats provide reliable temperature control, a pronounced time-step dependence was observed in the potential energy. Amongst the Langevin methods, the Grønbech-Jensen--Farago scheme provided the most consistent sampling of both temperature and potential energy. Nonetheless, Langevin dynamics typically incurs approximately twice the computational cost due to the overhead of random number generation, and exhibits a systematic decrease in diffusion coefficients with increasing friction. This study presents a broad comparison of thermostat methods using a binary Lennard-Jones glass-former model, offering practical guidance for the choice of thermostats in classical molecular dynamics simulations. These findings provide useful insights for diverse applications, including glass transition, phase separation, and nucleation. △ Less

Submitted 16 September, 2025; originally announced September 2025.

Comments: 25 pages, 14 figures

Reconfigurable, non-volatile control of optical anisotropy in ReS2 via ferroelectric gating

Authors: Mahfujur Rahaman, Seunguk Song, Aaliyah C. Khan, Bongjun Choi, Aaron M. Schankler, Kwan-Ho Kim, Wonchan Lee, Jason Lynch, Hyeon Suk Shin, Andrew M. Rappe, Deep Jariwala

Abstract: Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect t… ▽ More Electrically tunable linear dichroism (LD) with non-volatile properties represents a critical yet elusive feature for next-generation integrated photonic elements in practical device architectures. Here, we demonstrate record-breaking, non-volatile control of optical anisotropy in two-dimensional ReS2 via ferroelectric gating with aluminum scandium nitride (AlScN). Our ferroelectric field-effect transistors achieve near-unity (~95%) LD tunability of differential reflectance at room temperature--the highest reported for any electrically controlled 2D optical system. Crucially, the programmed optical states exhibit exceptional retention exceeding 12,000 seconds without applied bias, enabling true non-volatile optical memory. Through combined experimental characterization and ab initio calculations, we reveal that ferroelectric polarization switching induces substantial asymmetric charge transfer to ReS2, selectively populating conduction band states and triggering structural distortions that dramatically enhance optical anisotropy in the "up" polarization state while leaving the "down" state unperturbed. This ferroelectric-semiconductor coupling provides a universal platform for voltage-programmable, energy-efficient photonic devices with dynamic polarization control, addressing critical needs in integrated photonics as well as programmable far-field optics and telecommunications infrastructure. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 5 main figures

Hidden Moiré Topology of Low-Symmetry Weyl Surfaces

Authors: Cong Li, Zhilong Yang, Hongxiong Liu, Magnus H. Berntsen, Francesco Scali, Dibya Phuyal, Jianfeng Zhang, Timur K. Kim, Jacek Osiecki, Balasubramanian Thiagarajan, Youguo Shi, Tao Xiang, Quansheng Wu, Oscar Tjernberg

Abstract: Topological materials are defined by the correspondence between bulk topology and boundary states, yet this correspondence becomes enigmatic on low-symmetry surfaces where bulk and surface periodicities are inherently mismatched. Here we reveal a hidden moiré topology emerging on the (103) surface of the Weyl semimetal NdAlSi. Angle-resolved photoemission spectroscopy uncovers closed Fermi-arc loo… ▽ More Topological materials are defined by the correspondence between bulk topology and boundary states, yet this correspondence becomes enigmatic on low-symmetry surfaces where bulk and surface periodicities are inherently mismatched. Here we reveal a hidden moiré topology emerging on the (103) surface of the Weyl semimetal NdAlSi. Angle-resolved photoemission spectroscopy uncovers closed Fermi-arc loops and momentum-space moiré modulations, phenomena unanticipated in conventional topological theory. We show that these emerge from incomplete bulk projection and multi-cell interference governed by a least-common-multiple framework. Least-common-multiple guided DFT and Green's-function calculations quantitatively reproduce the observed spectra, establishing the universality of this commensuration rule. These findings transform a long-standing paradox of bulk-boundary correspondence into a new paradigm of momentum-space moiré reconstruction, bridging crystalline and quasicrystalline topologies and opening routes to flat-band engineering on complex surfaces. △ Less

Submitted 7 December, 2025; v1 submitted 12 September, 2025; originally announced September 2025.

Comments: Main text: 19 pages, 4 figures; SI: 35 pages, 18 figures. Comments are welcome

Neural Scaling Laws for Deep Regression

Authors: Tilen Cadez, Kyoung-Min Kim

Abstract: Neural scaling laws--power-law relationships between generalization errors and characteristics of deep learning models--are vital tools for developing reliable models while managing limited resources. Although the success of large language models highlights the importance of these laws, their application to deep regression models remains largely unexplored. Here, we empirically investigate neural… ▽ More Neural scaling laws--power-law relationships between generalization errors and characteristics of deep learning models--are vital tools for developing reliable models while managing limited resources. Although the success of large language models highlights the importance of these laws, their application to deep regression models remains largely unexplored. Here, we empirically investigate neural scaling laws in deep regression using a parameter estimation model for twisted van der Waals magnets. We observe power-law relationships between the loss and both training dataset size and model capacity across a wide range of values, employing various architectures--including fully connected networks, residual networks, and vision transformers. Furthermore, the scaling exponents governing these relationships range from 1 to 2, with specific values depending on the regressed parameters and model details. The consistent scaling behaviors and their large scaling exponents suggest that the performance of deep regression models can improve substantially with increasing data size. △ Less

Submitted 24 November, 2025; v1 submitted 12 September, 2025; originally announced September 2025.

Comments: Supplementary Information will be provided with the published manuscript

Journal ref: Machine Learning: Science and Technology, 7 025011 (2026)

Unusual ferromagnetic band evolution and high Curie temperature in monolayer 1T-CrTe2 on bilayer graphene

Authors: Kyoungree Park, Ji-Eun Lee, Dongwook Kim, Yong Zhong, Camron Farhang, Hyobeom Lee, Hayoon Im, Woojin Choi, Seha Lee, Seungrok Mun, Kyoo Kim, Jun Woo Choi, Hyejin Ryu, Jing Xia, Heung-Sik Kim, Choongyu Hwang, Ji Hoon Shim, Zhi-Xun Shen, Sung-Kwan Mo, Jinwoong Hwang

Abstract: 2D van der Waals ferromagnets hold immense promise for spintronic applications due to their controllability and versatility. Despite their significance, the realization and in-depth characterization of ferromagnetic materials in atomically thin single layers, close to the true 2D limit, has been scarce. Here, a successful synthesis of monolayer (ML) 1T-CrTe2 is reported on a bilayer graphene (BLG)… ▽ More 2D van der Waals ferromagnets hold immense promise for spintronic applications due to their controllability and versatility. Despite their significance, the realization and in-depth characterization of ferromagnetic materials in atomically thin single layers, close to the true 2D limit, has been scarce. Here, a successful synthesis of monolayer (ML) 1T-CrTe2 is reported on a bilayer graphene (BLG) substrate via molecular beam epitaxy. Using angle-resolved photoemission spectroscopy and magneto-optical Kerr effect measurements, that the ferromagnetic transition is observed at the Curie temperature (TC) of 150 K in ML 1T-CrTe2 on BLG, accompanied by unconventional temperature-dependent band evolutions. The spectroscopic analysis and first-principle calculations reveal that the ferromagnetism may arise from Goodenough-Kanamori super-exchange and double-exchange interactions, enhanced by the lattice distortion and the electron doping from the BLG substrate. These findings provide pivotal insight into the fundamental understanding of mechanisms governing 2D ferromagnetism and offer a pathway for engineering higher TC in 2D materials for future spintronic devices. △ Less

Submitted 11 September, 2025; originally announced September 2025.

Comments: 26 pages, 4 figures

Journal ref: Small 2025

Path integral approach to quantum thermalization

Authors: Alexander Altland, Kun Woo Kim, Tobias Micklitz

Abstract: We introduce a quasiclassical Green function approach describing the unitary yet irreversible dynamics of quantum systems effectively acting as their own environment. Combining a variety of concepts of quantum many-body theory, notably the nonlinear $σ$-model of disordered systems, the $G Σ$-formalism for strong correlations, and real time path integration, the theory is capable of describing a wi… ▽ More We introduce a quasiclassical Green function approach describing the unitary yet irreversible dynamics of quantum systems effectively acting as their own environment. Combining a variety of concepts of quantum many-body theory, notably the nonlinear $σ$-model of disordered systems, the $G Σ$-formalism for strong correlations, and real time path integration, the theory is capable of describing a wide range of system classes and disorder models. It extends previous work beyond perturbation theory (in inverse Hilbert space dimensions), enabling a description of thermalization dynamics from short scattering times, through the onset of ergodicity at an effective `Thouless time', up to the many-body Heisenberg time. We illustrate the approach with two case studies, (i) a brickwork model of unitarily coupled quantum circuits with and without conserved symmetries, and (ii) an array of capacitively coupled quantum dots. Using the spectral form factor as a test observable, we find good agreement with numerical simulations. We present our formalism in a self-contained and pedagogical manner, aiming to provide a transferable toolbox for the first-principles description of many-body chaotic quantum systems in regimes of strong entanglement. △ Less

Submitted 7 September, 2025; originally announced September 2025.

Comments: 28 pages, 15 figures

Effect of Magnetic Anisotropy on Magnetoelastic Waves in Ni/LiNbO3 Hybrid Device

Authors: Minwoo Yu, Moojune Song, Minseok Kang, Mujin You, Yunyoung Hwang, Albert Min Gyu Park, Byong-Guk Park, Kab-Jin Kim, Junho Suh

Abstract: We study the effects of magnetic anisotropy and crystalline axes in surface acoustic waves (SAWs) driven magnetic resonances of Ni/LiNbO3 hybrid devices. SAW absorption from the interaction with magnons in Ni displays a strong anisotropic dependence on the direction of the applied in-plane magnetic field. Magnetic anisotropy is further investigated by magneto-optical Kerr effect measurements to sh… ▽ More We study the effects of magnetic anisotropy and crystalline axes in surface acoustic waves (SAWs) driven magnetic resonances of Ni/LiNbO3 hybrid devices. SAW absorption from the interaction with magnons in Ni displays a strong anisotropic dependence on the direction of the applied in-plane magnetic field. Magnetic anisotropy is further investigated by magneto-optical Kerr effect measurements to show both uniaxial and biaxial anisotropy components in Ni films on LiNbO3. By introducing a dipolar interaction term in addition to the anisotropies, we successfully explain the anisotropic SAW absorption in our devices. These findings show the importance of substrate-induced anisotropy and long-range dipolar effects in SAW-magnons hybrid devices and indicate future directions for optimizing these spin-acoustic devices through comprehensive anisotropy engineering. △ Less

Submitted 3 September, 2025; originally announced September 2025.

Comments: 20 pages, 6 figures, 1 table

Materials and Design Strategies of Fully 3D Printed Biodegradable Wireless Devices for Biomedical Applications

Authors: Ju-Yong Lee, Jooik Jeon, Joo-Hyeon Park, Se-Hun Kang, Yea-seol Park, Min-Sung Chae, Jieun Han, Kyung-Sub Kim, Jae-Hwan Lee, Sung-Geun Choi, Sun-Young Park, Young-Seo Kim, Yoon-Nam Kim, Seung-Min Lee, Myung-Kyun Choi, Jun Min Moon, Joon-Woo Kim, Seung-Kwon Seol, Jeonghyun Kim, Jahyun Koo, Ju-Young Kim, Woo-Byoung Kim, Kang-Sik Lee, Jung Keun Hyun, Seung-Kyun Kang

Abstract: Three-dimensional (3D) printing of bioelectronics offers a versatile platform for fabricating personalized and structurally integrated electronic systems within biological scaffolds. Biodegradable electronics, which naturally dissolve after their functional lifetime, minimize the long-term burden on both patients and healthcare providers by eliminating the need for surgical retrieval. In this stud… ▽ More Three-dimensional (3D) printing of bioelectronics offers a versatile platform for fabricating personalized and structurally integrated electronic systems within biological scaffolds. Biodegradable electronics, which naturally dissolve after their functional lifetime, minimize the long-term burden on both patients and healthcare providers by eliminating the need for surgical retrieval. In this study, we developed a library of 3D-printable, biodegradable electronic inks encompassing conductors, semiconductors, dielectrics, thereby enabling the direct printing of fully functional, multi-material, customizable electronic systems in a single integrated process. Especially, conjugated molecules were introduced to improve charge mobility, energy level alignment in semiconducting inks. This ink platform supports the fabrication of passive/active components and physical/chemical sensors making it suitable for complex biomedical applications. Versatility of this system was demonstrated through two representative applications: (i) wireless pressure sensor embedded within biodegradable scaffolds, (ii) wireless electrical stimulators that retain programmable electrical functionality in vivo and degrade post-implantation. This work establishes a foundation of modules for autonomous, biodegradable bioelectronic systems fabricated entirely via 3D printing, with implications for personalized diagnostics, therapeutic interfaces, and transient medical devices. △ Less

Submitted 21 August, 2025; originally announced September 2025.

Comments: 50 pages, 7 figures

Experimental realization of dice-lattice flat band at the Fermi level in layered electride YCl

Authors: Songyuan Geng, Xin Wang, Risi Guo, Chen Qiu, Fangjie Chen, Qun Wang, Kangjie Li, Peipei Hao, Hanpu Liang, Yang Huang, Yunbo Wu, Shengtao Cui, Zhe Sun, Timur K. Kim, Cephise Cacho, Daniel S. Dessau, Benjamin T. Zhou, Haoxiang Li

Abstract: Flat electronic bands, where interactions among electrons overwhelm their kinetic energies, hold the promise for exotic correlation physics. The dice lattice has long been theorized as a host of flat bands with intriguing band topology. However, to date, no material has ever been found to host the characteristic flat bands of a dice lattice. Here, using angle-resolved photoemission spectroscopy (A… ▽ More Flat electronic bands, where interactions among electrons overwhelm their kinetic energies, hold the promise for exotic correlation physics. The dice lattice has long been theorized as a host of flat bands with intriguing band topology. However, to date, no material has ever been found to host the characteristic flat bands of a dice lattice. Here, using angle-resolved photoemission spectroscopy (ARPES), we discover a dice-lattice flat band at $E_F$ in the van der Waals (vdW) electride [YCl]$^{2+}$: 2e-. In this system, excess valence electrons from Y deconfine from the cation framework to form an interstitial anionic electron lattice that constitutes the dice lattice. Our ARPES measurements unambiguously identify two sets of dice-lattice bands in YCl, including a nearly dispersionless band at the Fermi level. The flat bands and other dispersive bands observed in ARPES find excellent agreement with first-principles calculations, and theoretical analysis reveals that the near-$E_F$ electronic structure is well captured by a simple dice-lattice model. Our findings thus end the long quest of a real dice flat band material and establish vdW electride YCl as a prototype of dice metals. Our results further demonstrate the anionic electron lattice as a novel scheme for realizing lattice geometries and electronic structures rare to find in conventional crystalline systems. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Journal ref: Nat Commun 17, 2213 (2026)

Crystalline-to-Crystalline Phase Transition between Germanium Selenide Polymorphs with High Resistance Contrast

Authors: Joonho Kim, Kihyun Lee, Joong-Eon Jung, Han Joo Lee, Seongil Im, Kwanpyo Kim

Abstract: Understanding phase transitions between crystalline phases of a material is crucial for both fundamental research and potential applications such as phase-change memory. In this study, we investigate the phase transition between GeSe crystalline polymorphs induced by either global annealing at moderate temperatures or localized laser-induced heating. The highly conductive gamma-GeSe transforms int… ▽ More Understanding phase transitions between crystalline phases of a material is crucial for both fundamental research and potential applications such as phase-change memory. In this study, we investigate the phase transition between GeSe crystalline polymorphs induced by either global annealing at moderate temperatures or localized laser-induced heating. The highly conductive gamma-GeSe transforms into semiconducting, single-crystalline alpha-GeSe while preserving a well-aligned crystal orientation. The distinct structural and electronic properties at the gamma-GeSe/alpha-GeSe interface were investigated by transmission electron microscopy analysis. We propose that the clustering of Ge vacancies in the gamma-GeSe phase at elevated temperatures is a key mechanism driving the transition, leading to the formation of alpha-GeSe through the segregation of a minor GeSe2 phase. Furthermore, we observe a high electrical resistance contrast of approximately 10^7 between gamma-GeSe and alpha-GeSe, underscoring the potential of GeSe as a model polymorphic system for electronic applications, including phase-change memory. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 25 pages, 4 figures

Deterministic Control of Photon-Number Probabilities via Phase-Controlled Quantum Interference

Authors: Sang Kyu Kim, Eduardo Zubizarreta Casalengua, Yeji Sim, Friedrich Sbresny, Carolin Calcagno, Hubert Riedl, Jonathan J. Finley, Elena del Valle, Carlos Antón-Solanas, Kai Müller, Lukas Hanschke

Abstract: Deterministically tailoring optical Fock states beyond the single-photon level is crucial for boson sampling, loss-tolerant photonic qubits, and quantum-enhanced sensing, however has yet remained elusive. Here, we report an all-linear-optical protocol that converts a resonantly driven single-photon emitter into a deterministic generator of vacuum--single-photon--two-photon states. A phase-stabiliz… ▽ More Deterministically tailoring optical Fock states beyond the single-photon level is crucial for boson sampling, loss-tolerant photonic qubits, and quantum-enhanced sensing, however has yet remained elusive. Here, we report an all-linear-optical protocol that converts a resonantly driven single-photon emitter into a deterministic generator of vacuum--single-photon--two-photon states. A phase-stabilized, path-unbalanced Mach-Zehnder interferometer combines vacuum--single-photon interference and Hong-Ou-Mandel effect, providing two knobs to shape photon-number probabilities. By tuning these knobs, we observe a dynamic transition from antibunching to strong bunching in correlation measurements. A fully quantum-mechanical, discrete time-bin model maps these results onto the tailored photon statistics. The same framework predicts that two indistinguishable emitters would extend the accessible space to deterministic NOON states and single-photon filtering. This protocol relying on linear optics and available single-photon sources provides a scalable, chip-compatible, and platform-independent route to on-demand and deterministic few-photon resources for quantum metrology, photonic computing, as well as long-distance quantum networks. △ Less

Submitted 21 August, 2025; originally announced August 2025.

Comments: 14 pages, 11 figures

Deterministic time rewinding of waves in time-varying media

Authors: Seulong Kim, Kihong Kim

Abstract: Temporal modulation of material parameters offers unprecedented control over wave dynamics, enabling phenomena beyond the capabilities of static systems. Here we introduce and analyze a robust mechanism for time rewinding, whereby a temporally evolved wave is fully restored to its original state through a carefully engineered sequence of temporal modulations. In electromagnetic systems, time rewin… ▽ More Temporal modulation of material parameters offers unprecedented control over wave dynamics, enabling phenomena beyond the capabilities of static systems. Here we introduce and analyze a robust mechanism for time rewinding, whereby a temporally evolved wave is fully restored to its original state through a carefully engineered sequence of temporal modulations. In electromagnetic systems, time rewinding emerges from impedance-matched or anti-matched hierarchical bilayer structures with matched modulation durations, exploiting total transmission or reflection and reversed phase accumulation. In Dirac systems, it arises via complete interband transition driven by time-dependent vector potentials. Unlike time-reversal holography or quantum time mirrors, which produce wave echoes but only partial waveform recovery, our approach achieves deterministic and complete reconstruction of the entire wave state, including both amplitude and phase. Analytical conditions for robust amplitude and phase restoration are derived and validated through simulations of discrete and continuous modulations, demonstrating resilience to modulation complexity and temporal asymmetry. These findings establish a versatile platform for secure information retrieval, temporal cloaking, programmable metamaterials, and wave-based logic devices. △ Less

Submitted 19 August, 2025; originally announced August 2025.

Comments: 11 pages, 8 figures

Journal ref: Nanophotonics 14(20), 3287-3298 (2025)