Materials Science
A Comparative Study of Projected and Unprojected Schemes for Micromagnetic Simulations
Changjian Xie
In micromagnetic simulations, the constant magnitude of the magnetization can be derived from the continuity equation. Since the time
evolution of the magnetization in the continuity equation is perpendicular to the plane determined by the magnetization and the effective field, taking the inner product of both sides of the model with the magnetization shows that the
evolution rate of the magnitude of the magnetization is zero, thus keeping the magnitude constant. From this perspective, the equation itself can maintain the constraint of constant magnetization magnitude. We discretized the continuity equation and compared two first-order semi-implicit strategies in time: one is the implicit Gauss-Seidel method, and the other is the semi-implicit Backward Differentiation Formula (BDF) method. We considered the comparison between these two schemes with and without the projection step. The results of micromagnetic simulations show that when the dissipation coefficient is large, the implicit Gauss-Seidel method without the projection step has significant differences from the method with the projection step in both the achieved steady state and domain wall motion. When an appropriate dissipation coefficient is selected, the difference between the two narrows, and both the steady state and domain wall motion can be simulated. For the other method, BDF1, whether the dissipation coefficient is large or small, the results with and without the projection step are quite consistent, and it can effectively simulate the domain wall motion.
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Mesoscale and Nanoscale Physics
Emergent spin quantum Hall edge states at the boundary of two-dimensional electron gas proximitized by an $s$-wave superconductor
M. V. Parfenov, V. S. Khrapai and I. S. Burmistrov
Hybrid two-dimensional electron gas-
superconductor (2DEG-S) structures in a quantized
magnetic field offer a promising platform for realizing new topological phases. While recent experiments reveal
chiral Andreev edge states, their charge conductance is not integer quantized and is disorder sensitive, raising the question of whether topological protection survives. We argue that it does, but manifests in the
spin transport channel. The 2DEG-S system belongs to
symmetry class C of the Altland-Zirnbauer classification, which supports an even-integer quantized transverse
spin conductivity - the
spin quantum Hall effect, so far unobserved experimentally. We demonstrate that 2DEG-S hybrids host topologically protected edge states carrying a
spin current with an even-integer quantized
spin conductance robust against disorder. Finally, we propose an experimental setup to probe this protection via electrical measurements, establishing a concrete route to detect the class C origin of the
chiral Andreev edge states.
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Statistical Mechanics · Cross-listed from quant-ph
Pontus-Mpemba effect in cavity quantum electrodynamics
Stefano Longhi
The
quantum Pontus-Mpemba effect is a counterintuitive phenomenon in which a
quantum system relaxes faster through a two-step
evolution protocol than through a single, unquenched relaxation. This work proposes its realization in cavity
quantum electrodynamics using the Jaynes-Cummings model with
photon loss. The model captures the coherent interaction between a two-level atom and a single quantized mode of a lossy cavity, providing a minimal yet realistic setting to explore dissipative
quantum dynamics. Restricting the analysis to the single-excitation sector, the dynamics feature damped
vacuum Rabi oscillations for weak dissipation that transition to near-exponential atomic decay under strong dissipation. A sudden quench of the cavity decay rate generates distinct relaxation trajectories from the same initial atom-cavity state. The atomic excitation then displays a non-monotonic, accelerated decay, where a trajectory with a quenched dissipation relaxes faster than fixed-loss
evolution. The effect originates from the interplay between coherent atom-
photon exchange and cavity dissipation, establishing a clear and experimentally accessible realization of the
quantum Pontus-Mpemba effect in both optical and
circuit QED platforms.
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Superconductivity
Enhancement of $J$$_c$ by Proton Irradiation in HgBa$_2$Ca$_2$Cu$_3$O$_8$$_+$$_\delta$ Single Crystals
Wenjie Li, Ran Guo, Xin Zhou et al. (+10 more)
Critical current density is the key parameter for the practical application of superconductivity. In this study, 3 MeV
proton irradiation experiments were conducted on HgBa$_2$Ca$_2$Cu$_3$O$_8$$_+$$_\delta$ single
crystals to introduce pinning centers. The critical current density is found to be strongly enhanced after the irradiation with its maximum at a dose of 1$\times$10$^{16}$/cm$^2$, where the self-field critical current density at 2 K is enhanced from 5.5 MA/cm$^2$ to 26 MA/cm$^2$. At 77 K, the self-field critical current density for all irradiated
crystals is over 0.1 MA/cm$^2$. The power-law dependence of the critical current density on the
magnetic field is observed after irradiation, with a large power-law exponent $\alpha$ close to 1. A monotonic
magnetic field dependence of the normalized
magnetic relaxation rate is observed, which could be attributed to the low irreversibility field caused by the large anisotropy in Hg1223 single
crystals. Through the analysis of the pinning force density of the
crystal before and after irradiation, a clear mechanism change has been observed.
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All authors Wenjie Li, Ran Guo, Xin Zhou, Qiang Hou, Mengqin Liu, Longfei Sun, Yuhang Zu, Wenshan Hong, Yuan Li, Sheng Li, Yue Sun, Zhixiang Shi, Tsuyoshi Tamegai
Mesoscale and Nanoscale Physics
Thermodynamic incompleteness in non-Markovian Majorana transport
Yang Tian
We show that the complete knowledge of the non-Markovian island-state dynamics of a floating Majorana island does not, in general, determine the thermodynamic transport statistics measured in the leads. We demonstrate this statement in a Coulomb-blockaded island with $M$ Majorana zero modes coupled to structured reservoirs. In the cotunneling regime, a Schrieffer-Wolff transformation gives reservoir-assisted transitions generated by Majorana bilinears. After the reservoirs are traced out, the island state determines the
memory kernel associated with each bilinear, and this is enough to predict all island-state observables within the cotunneling approximation. It is not enough to determine which lead or detector channel supplied the electron, absorbed the electron, or carried the corresponding energy exchange. This is a genuine loss of thermodynamic information, not an error in the island equation. We formulate the result as a thermodynamic completeness criterion: an island
memory equation determines a transport observable only when that observable is constant over all assignments of reservoir channels that give the same island
memory kernel. The criterion gives a measurable prediction. Two structured-reservoir Majorana devices can have identical island-state
tomography and relaxation, but different charge noise measured separately in the leads, heat noise, and mixed charge-energy correlations. The geometry of the projection from reservoir records to island kernels and the
topology of the network of tunnel contacts identify which transport information is absent from island-state dynamics.
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Materials Science
Polarizable atomic multipoles for learning long-range electrostatics
Yoonjae Park, Dongjin Kim, Daniel S. King et al. (+5 more)
Long-range electrostatics and polarization remain central obstacles to extending machine learning interatomic potentials (MLIPs) to ionic, polar, and interfacial systems. Here we introduce a semi-local framework for learning electrostatics from energies and forces using polarizable atomic multipoles. Local equivariant descriptors predict environment-dependent latent monopoles, dipoles, and quadrupoles, while residual non-local charge transfer and polarization are captured by non-self-consistent linear response in induced charges and dipoles. Across four diverse
benchmarks and four short-range MLIP architectures, the multipole hierarchy and response terms systematically improve potential energy surface accuracy, with the largest gains in systems where long-range effects are essential. More importantly, physically meaningful electrical responses emerge without direct supervision. The learned latent multipoles yield accurate Born effective charge tensors and infrared spectra in close agreement with experiments. The induced-dipole extension introduces new capabilities: it predicts polarizabilities and thereby enables semi-quantitative Raman spectra for bulk water and hybrid MAPbI$_3$ perovskite, as well as the essential features of the surface-specific vibrational sum-frequency generation spectrum at the water-air interface. In ferroelectric HfO$_2$, the predicted electrical response also captures LO-TO splitting and polarization switching. This systematically improvable, physically transparent framework enables MLIPs trained on standard energy and force labels to predict polarization-sensitive observables.
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All authors Yoonjae Park, Dongjin Kim, Daniel S. King, Nam H. {\DJ}ào, Roya Savoj, Sebastien Hamel, Xiaoyu Wang, Bingqing Cheng
Statistical Mechanics · Cross-listed from physics.chem-ph
Density diversity in training data governs thermodynamic transferability of machine learning interatomic potentials
Minwoo Kim, Seungtae Kim, Je-Yeon Jung et al. (+2 more)
Machine learning interatomic potentials (MLIPs) offer first-principles accuracy with reduced computational cost, but their transferability across different thermodynamic states remains questionable, particularly for fluid systems where molecules experience local environments far from crystalline
equilibrium. Here, we demonstrate that diversifying the density of training configurations, rather than temperature, is the most effective strategy for building thermodynamically transferable MLIPs within a fixed computational budget. We first show that foundation MLIPs trained on solid-state databases accurately describe
liquid-like densities but fail at gas-like conditions, while molecular-database-trained models exhibit the opposite behavior. Controlled from-scratch training and
distillation experiments confirm that density-diverse
datasets resolve both failure modes, whereas temperature-diverse
datasets cannot compensate for missing density regimes. Coordination number analysis reveals the physical origin of this behavior: local coordination
topology is more susceptible to density than temperature, leading to further structural diversity. These results establish density diversity as a design principle for thermodynamically transferable MLIPs and provide a validation framework for assessing the thermodynamic coverage of both foundation and from-scratch models, enabling reliable atomistic simulation of fluid-phase processes across diverse operating conditions.
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All authors Minwoo Kim, Seungtae Kim, Je-Yeon Jung, Min Young Ha, Won Bo Lee
Mesoscale and Nanoscale Physics
Nonlinear Hall quantum oscillations to probe topological Brown-Zak fermions in graphene moiré systems
Jinrui Zhong, Huimin Peng, Yuqing Hu et al. (+7 more)
Due to the deep connection with the
quantum geometry of electronic Bloch wavefunctions, the second-order nonlinear
Hall effect (NLHE) has been an attractive topic since its proposal. However, studies on NLHE under a
magnetic field have been lacking. Given that
quantum oscillations in the linear response regime have been proven to be useful tools in investigating electronic systems, searching for
quantum oscillations in NLHE is of great interest and is expected to provide new avenues to unveil rich
quantum geometric properties of novel quasiparticles. Here, we propose a new type of NLHE
quantum oscillations and experimentally probe it in
graphene moiré systems. It stems from the alternation of the dominant NLHE mechanisms with recurring Bloch states under
magnetic field, which enables sensitive detection of Brown-Zak
fermions, giving an onset field as low as 0.5 T. Most importantly, when the commensurability condition is satisfied, the nonlinear transport of Brown-Zak
fermions is mainly governed by
quantum geometric contributions. Our findings not only establish a new type of
quantum oscillations, but also demonstrate the first experimental detection of the topological nature of Brown-Zak
fermions, shedding light on the exploration of novel topological quasiparticles.
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All authors Jinrui Zhong, Huimin Peng, Yuqing Hu, Qi Feng, Qiuli Li, Shihao Zhang, Qinsheng Wang, Jinhai Mao, Junxi Duan, Yugui Yao
Materials Science
A Scalable Translationally Invariant Variational Theory of Ab Initio Polarons
Moritz K. A. Baumgarten, Hamlin Wu, Tong Jiang et al. (+1 more)
We introduce a scalable, translationally invariant variational theory for ab initio polarons that remains applicable across coupling regimes without resorting to supercells. Our approach combines a momentum-projected Toyozawa-type wavefunction with a low-rank factorization of the electron-
phonon kernel, enabling near-linear scaling with the number of $\mathbf{k}$-points while capturing both delocalized and self-trapped carriers.
Benchmarks for the Fröhlich model, LiF, and anatase and rutile TiO$_2$ yield accurate polaron binding energies, thermodynamic-limit band structures, and transparent real-space measures of polaron extent. For LiF, comparison with first-principles diagrammatic Monte Carlo (DiagMC) reveals close agreement for the weak-coupling electron-polaron ground state and band structure. However, in the hole-polaron of LiF, which is in the strong-coupling regime, we found a significant bias in DiagMC results. These results establish momentum-projected variational wavefunctions as a systematically improvable route to thermodynamic limit studies of polarons in real materials.
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All authors Moritz K. A. Baumgarten, Hamlin Wu, Tong Jiang, Joonho Lee
Materials Science
Si/SiGe multi-channel superlattice structure epitaxial growth with segmented temperature control for Next-Generation Logic Devices
Wenlong Yao, Zhigang Li, Guobin Bai et al. (+5 more)
Stacking multiple SiSiGe channels in advanced logic devices faces severe thermal budget accumulation, which degrades interfaces via Ge-Si interdiffusion and strain relaxation.This strategy lowers the Ge
diffusion coefficient to 5.6-7% of its value at 650C (Arrhenius estimate), suppressing interdiffusion and preserving pseudomorphic strain. The 4 + 4 channel stack exhibits clear XRD satellite peaks, fully coherent strain state (reciprocal space mapping), sharp interfaces (1.5-2.6 nm transition width) and low RMS roughness (0.08 nm). Quantitative analysis from bottom to top reveals that prolonged high-temperature exposure broadens bottom interfaces and dilutes Ge concentration (from 20% to 18.5%), while the top stack maintains design targets. This work provides a process-physics understanding of thermal budget effects in multi-channel superlattices and establishes a high-quality material foundation for advanced logic devices beyond 2 nm node.
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All authors Wenlong Yao, Zhigang Li, Guobin Bai, Jianfeng Gao, Jiahan Yu, Junfeng Li, Xiaolei Wang, Jun Luo
Mesoscale and Nanoscale Physics
Inter-harmonic ratio structure and saturation of Bernstein modes in graphene
Miguel Tierz
Bernstein modes (BM) in
graphene are finite-wavevector magnetoplasmons excited by contact near fields, whereas ordinary cyclotron resonance (CR) probes $q\approx0$. We derive the BM peak absorption in the quasiclassical ballistic regime and show that it factorizes into a launch spectrum, Bernstein-mode splitting, turning-point enhancement, and residual dielectric-response factor. At fixed excitation frequency, BM overtones ($n\ge2$) are sampled, to leading order, at the same momentum $q\simeq\omega/v_F$. Smooth launch and screening factors therefore cancel in inter-harmonic peak ratios, yielding $I_n/I_m\simeq m/n$, modified by linewidth corrections and one residual response ratio for each harmonic pair. In smooth-launcher synthetic tests, noisy full-$q$ spectra recover the residual ratio within errors: moderate launcher/dielectric misspecification within this
benchmark family shifts it by only $\sim\!1$–$2\%$, whereas linewidth assumptions shift it by $\sim\!10$–$30\%$. The same factorization connects low-power amplitudes to nonlinear saturation. If BM harmonics share the same cooling region and bolometric readout, the low-power slope times onset intensity is harmonic independent, while BM and CR power sweeps obey distinct normalized saturation curves with linewidth scalings $\Gamma^{-1/2}$ and $\Gamma^{-1}$.
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Materials Science
Physics-Grounded Understanding of Thermal Boundary Conductance between Ga$_2$O$_3$ and SiC from a Feedforward Neural Network Potential
Nuohao Liu, Chen Shen, Yue Cao et al. (+7 more)
Ga$_2$O$_3$/SiC heterointegration is attractive for ultra-wide-bandgap power electronics, but interfacial thermal boundary conductance (TBC) remains a major heat-removal bottleneck. Direct experimental access to intrinsic atomistic interfacial transport remains limited, particularly for ideally synthesized materials with defect-free interfacial contact. First-principles simulations are too expensive at relevant length and time scales, while empirical Molecular Dynamics (MD) potentials often lack transferability across
oxide and carbide bonding environments. We develop a unified feedforward neural network potential and validate it against density-functional data, bulk
phonon dispersions, and anisotropic thermal-conductivity trends in both $\beta$-Ga$_2$O$_3$ and SiC. Nonequilibrium simulations show that TBC decreases with transport length, increases with temperature, and is consistently higher for Ga$_2$O$_3$$(\bar{2}01)$/SiC(0001) than for Ga$_2$O$_3$(100)/SiC(0001). These trends are explained by attenuation of long-mean-free-path carriers, enhanced incoherent and anharmonic interfacial exchange within broadly unchanged spectral channels, and stronger bonding and vibrational coupling at the $(\bar{2}01)$ interface. The results show how a single transferable feedforward neural network potential can enable large-scale transport prediction and physics-grounded mechanistic understanding of thermal boundary conductance. Code for NEP training and simulation workflows is available at the project repository https://github.com/knowhow07/TBC_Ga2O3_SiC.git
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All authors Nuohao Liu, Chen Shen, Yue Cao, Song Xue, Pingfan Wu, Zongfang Lin, Masood Mortazavi, Liang Peng, Izabela Szlufarska, Jiechen Wang
Materials Science
Tuning charge-transport properties and magnetic order in metallic EuTiO$_{3-\delta}$
Xing He, Chiou Yang Tan, Issam Khayr et al. (+9 more)
The stoichiometric
antiferromagnetic insulator EuTiO$_3$ is proximate to a ferroelectric phase. Whereas cation substitution has been used as a tuning parameter to introduce charge carriers and manipulate the magnetism, the effects of oxygen-vacancy doping have been less explored. Here we report a detailed study of the charge transport and
magnetic properties of metallic, oxygen-vacancy-doped EuTiO$_{3-\delta}$. Using CaH$_2$ as an oxygen getter to achieve a higher carrier concentration than previously reported, we find that the phase diagram of the oxygen-vacancy-doped system is distinct from that obtained via cation doping. In particular, we uncover a change from
antiferromagnetic to
ferromagnetic order in the metallic state, with a maximum Curie temperature of TC $\approx$ 11 K at the highest carrier concentration of n $\approx$ 10$^{21}$ cm$^{-3}$. These findings are supported by density functional theory calculations, which indicate a significant change in the nearest-neighbor
magnetic exchange constant with increasing electron doping. We also present x-ray diffuse scattering and complementary first-principles results that reveal that, similar to the prominent incipient ferroelectric perovskite SrTiO$_3$, the data for EuTiO$_3$ are consistent with thermal diffuse scattering and with the absence of quasi-elastic contributions. Finally, we report specific heat measurements that confirm the
magnetic transition temperatures deduced from magnetization measurements and corroborate the
lattice dynamics picture inferred from the diffuse scattering data.
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All authors Xing He, Chiou Yang Tan, Issam Khayr, Zach Van Fossan, Richard J. Spieker, Dayu Zhai, Sarah Anderson, Dinesh Shukla, Suchismita Sarker, Javier Garcia-Barriocanal, Turan Birol, Martin Greven
Quantum Gases · Cross-listed from quant-ph
Dynamical Signatures of Floquet Topology in Wave Packet Dynamics
Xin Shen, Bing Lu and Yan-Qing Zhu
Periodically driven
quantum systems, known as Floquet systems, provide a versatile platform for engineering novel topological phases absent in static settings. However, dynamically characterizing these non-
equilibrium topological invariants remains a challenge. Here, we develop a Floquet perturbation theory in the extended
Hilbert space to analytically describe the center-of-mass (CoM) dynamics of a wave packet. When applied to the driven Su-Schrieffer-Heeger model, our theory reveals that the CoM exhibits multi-frequency Zitterbewegung oscillations, whose spectral composition and phase are directly tied to the system's Floquet band structure. Crucially, we find that band inversions at topological phase transitions imprint distinct signatures in the CoM dynamics, including the emergence of low-frequency modes and phase shifts of the oscillatory trajectory. These dynamical signatures offer a practical protocol for detecting Floquet topological invariants, which we demonstrate for both high-frequency and strongly driven regimes. Our work establishes CoM dynamics as a simple and experimentally accessible probe for exploring topological phase transitions in Floquet systems.
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Statistical Mechanics · Cross-listed from quant-ph
Temporal Coarse-Graining as the Origin of Macroscopic Friction in Quantum Spin Chains via Data-Driven Liouvillian Extraction
Seiki Saito
Understanding how macroscopic irreversible hydrodynamics emerges from the reversible
unitary dynamics of isolated
quantum many-body systems remains a central challenge. Conventional approaches force
spin density dynamics into purely diffusive models, obscuring the interplay of pressure,
spin current, and local friction, and leave open the role of the observer's temporal resolution. We introduce a fully data-driven framework based on generalized Extended Dynamic Mode Decomposition (gEDMD) integrated with the Mori-Zwanzig projection. By expanding the observable dictionary to include
spin currents, we extract the Navier-Stokes hydrodynamic coefficients from a chaotic XXZ
spin chain across temporal coarse-graining scales. Our unconstrained extraction reveals a dichotomy: the mechanical elasticity ($c^2$) derives from the exact
unitary dynamics, preserving microscopic reversibility, whereas the macroscopic friction ($\gamma$) and kinematic viscosity ($\nu$) show zero net dissipation, oscillating rapidly around zero in the exact-derivative limit. Genuine macroscopic transport therefore requires finite temporal coarse-graining: at a finite observation timescale ($\Delta t_{cg} > 0$) the system passes through a crossover where these fluctuations average out, establishing an intermediate functional regime with strictly positive friction and viscosity. We further show that the coarse-grained generator is a predictive reduced model requiring only $O(N)$ macroscopic observables, and that the sign of the emergent friction is inherited from the causal, forward-in-time direction of the inference: time-symmetric
estimators yield zero net dissipation at any coarse-graining scale. Macroscopic friction in isolated
quantum systems is thus not an absolute property but an emergent phenomenon dictated by the temporal resolution and causal direction of the observer's description.
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Materials Science
Strain-Dependent Ionic Transport in Li3YCl6 Solid Electrolytes
Wei-Fan Huang, Jin Dai, Jiahui Pan et al. (+1 more)
Solid-state batteries require electrolytes that sustain high ionic conductivity under the mechanical environment of a functioning
cell.
Lattice strain, arising from stack pressure, thermal cycling, or
lattice mismatch at interfaces, can either enhance or suppress Li+ transport in solid electrolytes, yet how it couples to the underlying
diffusion mechanism remains poorly understood. Using Li3YCl6 halide superionic conductor, we address this with large-scale molecular dynamics simulations driven by an Atomic Cluster Expansion (ACE) machine learning interatomic potential trained on first-principles data. The ACE model faithfully reproduces experimental and ab initio structural, mechanical, and transport properties of Li3YCl6. We find that Li+
diffusion in Li3YCl6 follows a two-regime Arrhenius behavior, crossing over at a critical temperature $T_c$ from one-dimensional hopping at low temperature to three-dimensional cooperative
diffusion at high temperature. Strain substantially modulates diffusivity: tensile strain enhances it while compressive strain suppresses it, yet leaves $T_c$ invariant, indicating that strain tunes
diffusion efficiency without reshaping the underlying transport framework. In each regime, the mechanistic origin differs: altered activation barriers dominate at low temperature, while modified pre-exponential factors become critical at high temperature. These results establish
lattice strain as a design lever for ionic conductivity in Li3YCl6 solid-state electrolytes.
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All authors Wei-Fan Huang, Jin Dai, Jiahui Pan, Mingjian Wen
Strongly Correlated Electrons
Algebraic Structure of Finite-Size Bethe Solutions in the Heisenberg Chain
Oliver R. Bellwood and William J. Munro
The
spin-$1/2$ Heisenberg
antiferromagnetic chain is the canonical example of an integrable
quantum many-body model. Despite its exact solvability, explicit finite-size solutions are typically only accessible via numerical evaluation of the Bethe ansatz equations. Here, we analyse the algebraic structure of the exact, symbolic ground states for chains up to twelve sites using the Bethe ansatz. We find that the algebraic degree of the ground state
magnon phases and Bethe roots scale with respect to system size at a different rate to the ground-state energy and wavefunction coefficients. The ground-state Bethe roots and energy are found to become Galois unsolvable for ten or more sites, thus demonstrating the lack of a symbolic analytical solution in a
quantum integrable model due to algebraic complexity.
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Mesoscale and Nanoscale Physics
Collective quantum state at the atomic limit
Fan Zhang, Yanxing Li, Chengye Dong et al. (+9 more)
Collective
quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger
liquids provide a paradigmatic example of one-dimensional collective
quantum matter characterized by
spin-charge separation. Using low-temperature scanning tunneling microscopy and spectroscopy, we directly visualize quantized collective modes in atomically confined mirror twin boundary segments of monolayer WSe2. Distinct standing-wave branches associated with fractionalized
spin and charge excitations persist in segments as short as one nanometer, establishing the atomic-scale confinement limit of Luttinger-
liquid behavior. These ultrashort segments form a new class of many-body
quantum dots whose discrete spectra arise from confined collective bosonic modes rather than single-particle electron states. When assembled into ordered chains, inter-dot coupling reshapes electron-like fundamental states while collective
spin/charge excitations remain largely intact, revealing distinct coupling responses of emergent many-body modes. Our results demonstrate that collective
quantum matter can persist and exhibit fundamentally distinct coupling behavior at atomic length scales, establishing a novel platform for engineering strongly correlated
quantum phases from atomically confined building blocks.
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All authors Fan Zhang, Yanxing Li, Chengye Dong, Ninad Kailas Dongre, Viet-Anh Ha, Yu-Chuan Lin, Yiyuan Luo, Hyunsue Kim, Joshua A. Robinson, Feliciano Giustino, Fan Zhang, Chih-Kang Shih
Mesoscale and Nanoscale Physics
Multifrequency Floquet Engineering of Magnon Polaritons
L. Hackner, A. R. Myatt, W. Wustmann et al. (+1 more)
Floquet engineering of cavity
magnon-polaritons by periodically modulating the
magnon frequency has recently attracted much interest as a way to manipulate the energy spectrum of
magnon-
photon hybrid systems. However, modulating the frequency of
magnons by a time-varying bias
magnetic field can be challenging. We demonstrate cavity
magnon-polariton Floquet engineering by modulating the microwave cavity frequency, allowing large modulation depth and bandwidth. We apply commensurate two-frequency Floquet modulations with the higher frequency at twice and three times the lower frequency, and demonstrate that the resulting spectrum depends on the relative amplitude and phase of the two drive tones. In comparison with single-frequency Floquet modulations, the spectrum has qualitatively different features; in particular, new anticrossings appear between previously uncoupled sidebands. Our platform offers an alternative way to manipulate Floquet quasi-energy levels in hybrid systems.
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All authors L. Hackner, A. R. Myatt, W. Wustmann, N. J. Lambert
Mesoscale and Nanoscale Physics
Tunable Interlayer Charge-transfer States in MoSe$_2$/WS$_2$ Moiré Superlattices
Zheyu Lu, Jiahui Nie, Tianle Wang et al. (+15 more)
Moiré superlattices formed by transition metal dichalcogenide (TMD) heterobilayers provide a versatile platform for studying strongly correlated electronic, excitonic, and topological phenomena in solids. In particular, angle-aligned MoSe$_2$/WS$_2$ heterobilayers, which have a Type-I band
alignment at zero vertical electric field, host rich correlated
spin and charge physics. Here, combining large-scale first-principles calculations and optical reflection spectroscopy, we report a thorough study of the emergent moiré excitonic states and interlayer charge-transfer states in angle-aligned electron-doped MoSe$_2$/WS$_2$ moiré superlattices. The moiré excitonic states serve as sensitive optical probes to the localization profile of doped electrons. We observe a series of interlayer charge-transfer transitions from n/n$_0$ = 1 to 4 (where n$_0$ denotes the moiré density) when the vertical electric field switches the
heterostructure band
alignment from Type-I to Type-II. By tuning the vertical electric field, we can precisely control the interlayer electron localization, realizing a
Fermi-Hubbard model with a tunable charge-transfer band on an effective honeycomb
lattice. Furthermore, Monte Carlo simulation of the doping dependence of the electric-field susceptibility predicts that multiple correlated charge-ordered states appear at both integer and fractional fillings. Our results provide a holistic understanding of the emergent optical excitations and the correlated charge-transfer states in electron-doped MoSe$_2$/WS$_2$ moiré superlattices.
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All authors Zheyu Lu, Jiahui Nie, Tianle Wang, Rwik Dutta, Ruishi Qi, Jingxu Xie, Can Uzundal, Jianghan Xiao, Ziyu Wang, Yibo Feng, Kenji Watanabe, Takashi Taniguchi, James R. Chelikowsky, Archana Raja, Steven G. Louie, Mit H. Naik, Michael P. Zaletel, Feng Wang
Statistical Mechanics
Thermodynamics and emergent thermomechanical response of a quantum ring with nonminimal spin–orbit coupling
João A. A. S. Reis, L. Lisboa-Santos and Edilberto O. Silva
We investigate the thermodynamic and emergent thermomechanical properties of
fermions confined to a one-dimensional
quantum ring with effective
spin–orbit interactions induced by nonminimal couplings to antisymmetric tensor fields. Using the exact spectrum obtained in the companion work, we develop canonical and grand-canonical descriptions and show that the coupling parameter~$\xi$ deforms the angular-momentum branches, reorganizing the low-energy spectrum and leaving clear signatures in the internal energy,
entropy, heat capacity, and
spin–orbit response functions. We also formulate an effective thermomechanical description by treating the ring circumference as a quasi-static thermodynamic variable. This leads to a pressure-like quantity and associated response coefficients, directly linked to the microscopic spectrum. In the grand-canonical ensemble,
Fermi statistics strongly enhance the response, producing coupling-dependent instabilities and sign changes reminiscent of mesoscopic de~Haas–van Alphen oscillations. Finally, we introduce a phenomenological interacting extension based on an exponential resummation of the free energy, showing that collective effects can sharpen the thermomechanical response and induce anomalous thermal contraction. Our results connect spectral deformation, finite-size thermodynamics, and emergent mechanical behavior in
spin–orbit-active
quantum rings.
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