Statistical Mechanics
Dissipative free fermions in disguise
Kohei Fukai, Hironobu Yoshida and Hosho Katsura
Recently, a class of
spin chains known as “free
fermions in disguise” (FFD) has been discovered, which possess hidden free-
fermion spectra even though they are not solvable via the standard Jordan-Wigner transformation. In this work, we extend this FFD framework to open
quantum systems governed by the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) equation. We establish a general class of exactly solvable open
quantum systems within the FFD framework: if the Liouvillian frustration graph is claw-free and has a simplicial clique, the Liouvillian possesses a hidden free-
fermion spectrum. In particular, the (even-hole, claw)-free condition automatically guarantees this, enabling exact computation of the Liouvillian gap and an infinite-temperature autocorrelation function. Our results provide the first realization of the FFD mechanism in open
quantum systems.
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Materials Science
Crystallographic Orientation-Dependent Magnetotransport in the Layered Antiferromagnet – CrSBr
Naresh Shyaga, Pankaj Bhardwaj, Rajib Sarkar et al. (+3 more)
Among two-dimensional
magnetic materials, CrSBr has attracted considerable
attention owing to its coexistence of
ferromagnetic and
antiferromagnetic ordering, which depends sensitively on crystallographic orientation. An additional distinguishing feature of CrSBr is its highly anisotropic
Fermi surface in momentum space. In this work, we present a comprehensive investigation of magnetoresistance by systematically orienting the bias current and the applied
magnetic field along all three crystallographic axes. We demonstrate that the magnetoresistance serves as a direct probe of electronic anisotropy, exhibiting pronounced variations when the current is applied along different crystallographic directions under a
magnetic field perpendicular to the sample plane. For in-plane
magnetic fields, we observe conventional anisotropic magnetoresistance accompanied by hysteresis, indicative of
ferromagnetic behavior. Overall, our study provides a complete picture of electronic transport in CrSBr as a function of bias current and
magnetic field orientation with respect to crystallographic directions, thereby opening pathways for future experiments requiring high sensitivity of electrical resistance to
magnetic field gradients.
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All authors Naresh Shyaga, Pankaj Bhardwaj, Rajib Sarkar, Jagadish Rajendran, Abhiram Soori, Dhavala Suri
Superconductivity
Transparency-controlled multiple charge transfer in superconducting junctions with local shot-noise scanning tunneling spectroscopy
Yudai Sato, Maialen Ortego Larrazabal, Jian-Feng Ge et al. (+6 more)
Charge transport in superconducting junctions at finite voltages is governed by Andreev reflections, including multiple Andreev reflections, which are processes that enable multiple charge transfer, a hallmark that shot noise can directly quantify. Since the effective charge extracted from shot noise measurements varies with the transparency of the junction, systematic control of transparency is essential but experimentally challenging. Here, we present shot noise scanning tunneling microscopy measurements enabled by a newly developed amplifier, allowing access to different transparency regimes. We perform shot noise measurements on Pb(111) with tunable transparency at 2.2 K and observe that the shot noise evolves from a single electron tunneling regime to multiple charge transfer regime as transparency increases. Our results are quantitatively consistent with theoretical simulations of Andreev reflections and multiple Andreev reflections for a single-channel system. These results establish junction transparency as the key parameter governing the
evolution of charge transport and demonstrate that noise-STM is a powerful platform for investigating microscopic charge transport mechanisms with controlled junction transparency at the atomic scale.
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All authors Yudai Sato, Maialen Ortego Larrazabal, Jian-Feng Ge, Ingmar Swart, Doohee Cho, Wolfgang Belzig, Juan Carlos Cuevas, Milan P. Allan, Jiasen Niu
Materials Science
Decoupling Precipitation and Surface Complexation during Mn(II) Removal by Biochar via Experiments and Atomistic Simulations
Audrey Ngambia, Anastasiia Gavrilova, Haitao Huang et al. (+4 more)
Manganese(II) mobilised by mining activity poses a persistent water-quality challenge, yet the mechanisms by which low-cost sorbents, such as biochar, sequester Mn(II) remain poorly resolved. This study identifies the specific chemical drivers of Mn(II) sequestration by combining fixed-bed column and batch experiments with atomistic molecular dynamics simulations. Oilseed rape straw biochars, produced at 350\textdegree C, 550\textdegree C, and 700\textdegree C, removed 20-50% of dissolved Mn from acidic influent (pH 4, 5 ppm). High-temperature biochar achieved the greatest removal ($\sim$50%) and rapidly increased effluent pH to 9, triggering alkaline precipitation. Conversely, lower-temperature biochars removed 20-30% of Mn while maintaining a near-neutral pH (7-7.5). Enhanced \ce{K+} release in these systems indicates significant cation exchange and non-precipitative pathways. Molecular simulations confirmed that while neutral surfaces show weak Mn(II) association, deprotonated sites drive strong adsorption through inner-sphere complexation ($\sim$50% removal) and outer-sphere association ($\sim$10%). These results establish a mechanistic framework to distinguish between precipitation-led and surface-complexation-led removal. By providing specific chemical criteria for Mn-targeted sequestration, this work enables the rational design of engineered biochars for sustainable water remediation.
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All authors Audrey Ngambia, Anastasiia Gavrilova, Haitao Huang, Zhuodong Lyu, Ondřej Mašek, Margaret Graham, Valentina Erastova
Materials Science
Adsorption energies and decomposition barrier heights for ethylene carbonate on the surface of lithium from cluster-based quantum chemistry
Ethan A. Vo, Hung T. Vuong, Zachary K. Goldsmith et al. (+7 more)
For ethylene carbonate on the (100) surface of lithium, we calculate the adsorption energy in two binding motifs as well as the barrier height for a ring-opening decomposition reaction. We validate a scheme for producing results in the thermodynamic limit by correcting results obtained on finite lithium clusters containing only 40-100 atoms, which enables the use of hybrid density functionals, the random-phase approximation, and correlated wavefunction theories such as coupled-cluster theory and auxiliary-field
quantum Monte Carlo. We find that the high-level theories agree to within 2-5 kcal/mol and can therefore serve as
benchmarks for more affordable methods. Using our reference data, we demonstrate that generalized gradient approximation functionals, such as PBE, are not sufficiently accurate for reaction barrier heights, and we identify $\omega$B97X-V as an especially promising functional for the interfacial chemistry of electrolyte solvents at lithium metal anodes.
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All authors Ethan A. Vo, Hung T. Vuong, Zachary K. Goldsmith, Hong-Zhou Ye, Yujing Wei, Sohang Kundu, Ardavan Farahvash, Garvit Agarwal, Richard A. Friesner, Timothy C. Berkelbach
Strongly Correlated Electrons
Tangent equations of motion for nonlinear response functions
Atsushi Ono
Nonlinear response functions, formulated as multipoint correlation functions or Volterra kernels, encode the dynamical and spectroscopic properties of physical systems and underpin a wide range of nonlinear transport and optical phenomena. However, their evaluation rapidly becomes prohibitive at high orders because of combinatorial (often factorial) scaling or severe numerical errors. Here, we establish a systematic and efficient framework to compute nonlinear response functions directly from real-time dynamics, without explicitly constructing multipoint correlators or relying on numerically unstable finite-difference methods for order-resolved extraction. Our approach is based on the Gateaux derivative with respect to the external field in function space, which yields a closed hierarchy of tangent equations of motion (TEOM). Propagating the TEOM alongside the original dynamics isolates each perturbative order with high accuracy, providing a term-by-term decomposition of physical contributions. The computational cost scales exponentially with response order in the fully general setting and reduces to
polynomial complexity when all perturbation directions are identical; both regimes avoid the factorial scaling of explicit multipoint-correlator evaluations. We demonstrate the power of TEOM by computing frequency-resolved fifth-order response functions for a solid-state electron model and by obtaining nonlinear response functions up to the 49th order with controlled accuracy in a classical Duffing oscillator. We further show that our time-
evolution formulation allows optical conductivities to be evaluated directly while remaining numerically stable even near zero frequency. TEOM can be incorporated seamlessly into existing real-time
evolution methods, yielding a general framework for computing nonlinear response functions in
quantum and classical dynamical systems.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Non-Markovian renormalization of optomechanical exceptional points
Aritra Ghosh and M. Bhattacharya
We investigate how non-Markovian mechanical dissipation affects exceptional points in linearized optomechanical systems with red-sideband drive. For a chosen non-Ohmic mechanical bath, we derive analytical conditions for the
memory-renormalized exceptional point by employing a pseudomode mapping, thereby demonstrating that structured environments displace the mode coalescence away from the Markovian prediction. Crucially, we reveal that failing to account for this
memory-induced shift suppresses the divergent Petermann factor by orders of magnitude, showing that accurate bath modeling is essential for the successful operation of exceptional-point-based devices whenever reservoir-induced
memory is non-negligible. We finally show that non-Markovianity modifies the cavity reflection spectrum, manifesting as a shallower optomechanically-induced-transparency dip, providing therefore an experimentally-accessible signature of structured mechanical environments.
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Mesoscale and Nanoscale Physics
Landau-Level-Resolved Mode Mixing and Shot Noise in Gate-Defined Graphene Quantum Point Contacts
Shakthidhar Vilvanathan, Jerin Saji, Kristiana Frei et al. (+2 more)
Graphene quantum point contacts (QPCs) in the
quantum Hall regime host competing transport mechanisms including
chiral edge propagation, valley degeneracy, and gate-induced mode mixing. Their interplay is not visible in conductance alone. Shot noise directly probes the statistics of transmission
eigenvalues, revealing microscopic mode partitioning that conductance cannot access. We develop a hybrid framework combining tight-binding simulations of gate-defined
graphene QPCs with random
matrix theory (RMT) to predict shot noise and Fano factor signatures across different
quantum Hall regimes, validated against experimental conductance maps of hBN-encapsulated
graphene Hall bars. Three distinct regimes are identified: adiabatic propagation, sharp mode filtering, and multi-mode mixing driven by localized states beneath the split gate. For higher Landau levels ($N_L > 0$), complete mode mixing produces the universal chaotic-cavity limit $F \simeq 1/4$. Strikingly, the zeroth Landau level ($N_L = 0$) converges to $F = 1/3$. This distinct value originates in the sublattice polarization of the $N_L = 0$ edge state: coupling to mixed-sublattice localized states beneath the gate is suppressed, confining transport to an effective single channel ($N = 1$). Complete mixing within this single channel yields a flat transmission
eigenvalue distribution and hence exactly $F = 1/3$ from single-channel RMT, numerically coincident with but mechanistically distinct from pseudo-diffusive zero-field
graphene transport. The $F = 1/3$ versus $F = 1/4$ crossover is a Landau-level-resolved noise signature absent in conductance, providing a direct discriminator between single-channel and multi-channel chaotic transport in
graphene QPCs.
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All authors Shakthidhar Vilvanathan, Jerin Saji, Kristiana Frei, Jakub Tworzydlo, Manohar Kumar
Materials Science
Interlayer coupling driven stabilization and superconductivity in bilayer CoTe$_2$
Wenping Chen, Ziyun Zhang and Feipeng Zheng
Interlayer coupling plays a critical role in van der Waals materials by governing
lattice stability and emergent
quantum phases, yet its impact on few-layer hexagonal CoTe$_2$ remains unclear. Here, using first-principles calculations, we systematically investigate monolayer and
bilayer CoTe$_2$ with an emphasis on their electronic structures,
lattice dynamics, and electron-
phonon coupling, and elucidate the underlying mechanisms driven by interlayer interactions. Our results show that monolayer CoTe$_2$ exhibits pronounced dynamical instability at low temperatures, whereas interlayer coupling stabilizes the
bilayer crystal structure and gives rise to
phonon-mediated superconductivity with a predicted critical temperature of about $4.7$~K when
spin-orbit coupling is included. The stabilization and superconductivity in
bilayer CoTe$_2$ are primarily attributed to interlayer-coupling-induced Te-$p_z$ charge redistribution and the associated modification of the
Fermi surface and electron-
phonon coupling. Finally, we discuss how
spin-orbit coupling in
bilayer CoTe$_2$ weakens the EPC and superconductivity. Our work clarifies how interlayer coupling can jointly tune structural stability and superconductivity in few-layer CoTe$_2$, providing insights for engineering
quantum phases in layered transition-metal dichalcogenides.
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Statistical Mechanics
Feedback percolation on complex networks
Hoseung Jang, Ginestra Bianconi and Byungjoon Min
Traditional percolation theory assumes static microscopic rules, limiting its ability to describe real-world complex systems where macroscopic order actively regulates local interactions. Here, we introduce feedback percolation, an unified framework that dynamically couples the microscopic activation probability to the macroscopic size of the
giant component. We show that this simple feedback mechanism produces a rich variety of behaviors both analytically and numerically. Depending on the feedback functions, the system exhibits explosive discontinuous jumps, hybrid transitions, limit-cycle oscillations, and routes to chaos, absent in classical percolation. Our findings establish that macroscopic feedback provides a unifying physical mechanism for phenomena ranging from self-regulating oscillations to systemic infrastructure collapse.
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Disordered Systems and Neural Networks
Semiclassical picture of the Heisenberg spin glass in two dimensions: from weak localization to hydrodynamics
Giacomo Bracci-Testasecca, Jacopo Niedda, Aldo Coraggio et al. (+2 more)
The two-dimensional Heisenberg
spin-glass model is investigated by means of a semiclassical expansion around classical states. At leading order, we obtain an effective quadratic
spin-wave
Hamiltonian and study the localization properties of its spectrum and eigenfunctions. We find that the nature of the
spin-wave excitations, whether they are hydrodynamic or localized modes, depends crucially on the relevance/irrelevance – in the renormalization group sense – of the correlations induced by the underlying classical order in the
spin-wave
Hamiltonian matrix elements: low-energy excitations around magnetically ordered states are delocalized, whereas those around
spin-glass ordered states are localized, albeit weakly. We interpret this phenomenology by relating the spontaneous breaking of
spin-rotation
symmetry in the original Heisenberg model to the
symmetry and universality class of the resulting quadratic
spin-wave
Hamiltonian. We
conjecture that the hydrodynamic picture can be recovered through the inclusion of interactions among the
spin-wave excitations at higher order in the semiclassical expansion, favoring the onset of ergodic behavior.
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All authors Giacomo Bracci-Testasecca, Jacopo Niedda, Aldo Coraggio, Roderich Moessner, Antonello Scardicchio
Statistical Mechanics
Comment on: Discontinuous codimension-two bifurcation in a Vlasov equation (arXiv:2212.01250)
Tarcísio N. Teles, Renato Pakter and Yan Levin
We comment on the recent work by Yamaguchi and Barré [Phys. Rev. E 107, 054203 (2023)], which uses linear stability analysis of the Vlasov equation to characterize phase transitions in a generalized
Hamiltonian Mean Field (gHMF) model. By performing extensive molecular dynamics simulations with $N=10^8$ particles, we demonstrate that the bifurcation analysis of the initial stationary distribution is insufficient to predict either the location or the nature of the phase transition to a quasi-stationary state (qSS). Specifically, we show that for bimodal momentum distributions, the instability threshold identified by the authors does not correspond to a
ferromagnetic transition; instead, the system remains in a paramagnetic state characterized by magnetization oscillations with a zero time-average. We find that the true paramagnetic-
ferromagnetic transition is discontinuous (first-order) and occurs at significantly larger coupling strengths, characterized by a clear coexistence of states. These results indicate that linear bifurcation and
symmetry-breaking phase transitions are distinct phenomena in long-range interacting systems, and that the former lacks the predictive power to describe the long-time fate of the system.
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Mesoscale and Nanoscale Physics
Nonlinear suppression of dispersion broadening of ultrashort spin-wave pulses in thin YIG films
K.O. Nikolaev, D. Raskhodchikov, J. Bensmann et al. (+10 more)
We study experimentally the nonlinear propagation of short pulses of forward volume
spin waves in nanometer-thick YIG films. We show that nonlinearity of the
spin system can efficiently counteract dispersion broadening of the pulses, leading to the formation of envelope
solitons. We demonstrate that in microscopic YIG systems, microwave powers of the order of one milliwatt are sufficient to reach the
soliton formation threshold. At powers slightly above this threshold, we achieve transmission of 3-ns
spin-wave pulses over distances of up to 50 micrometers without increase in their temporal width. Our results demonstrate a promising way towards high-rate transmission of information in microscopic
spin-wave
circuits unaffected by detrimental dispersion effects.
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All authors K.O. Nikolaev, D. Raskhodchikov, J. Bensmann, I.V. Borisenko, E. Lomonte, L. Jin, R. Schmidt, J. Kern, S. Michaelis de Vasconcellos, R. Bratschitsch, S.O. Demokritov, W.H.P. Pernice, V.E. Demidov
Statistical Mechanics
The Nonintrinsic Sector of Landau Theory
Trey Li
Landau theory usually treats free-energy coefficients as intrinsic parameters fixed by thermodynamic variables. We show that externally written microscale fields can survive coarse graining and enter the free-energy functional as spatially prescribed coefficient fields. This defines a nonintrinsic sector of Landau theory. The key condition is a hierarchy of correlation, writing, and frustration lengths. We identify ion-patterned FeRh as a plausible realization.
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Strongly Correlated Electrons
Drinfeld Center as Quantum State Monodromy over Bloch Hamiltonians around Defects
Hisham Sati and Urs Schreiber
The Drinfeld center fusion category $\mathcal{Z}(\mathrm{Vec}_G)$ famously models anyons in certain
lattice models. Here we demonstrate how its fusion rules may also describe topological order in fractional topological
insulator materials, in the vicinity of point defects in the Brillouin zone. Concretely, we prove that $\mathcal{Z}(\mathrm{Vec}_G)$ reflects, locally over a punctured disk in the Brillouin zone, the monodromy (topological order) of gapped
quantum states over the parameter space of Bloch
Hamiltonians whose classifying space has fundamental group $G$.
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Materials Science · Cross-listed from physics.optics
Ultra-high THz-field-confinement at LaAlO3 twin walls
Jakob Wetzel, Javier Taboada-Gutiérrez, Matthias Roeper et al. (+13 more)
The control and steering of light at nanometre length scales is crucial for the development of both fundamental science and nanophotonic technologies. Recent advancements have been achieved by exploiting various crystalline anisotropies, allowing for subdiffractional and diffraction-less canalisation of energy. These studies in particular benefit from stacking and twisting of 2D materials, whereas corresponding capabilities of anisotropic bulk
crystals are rather unexplored. In this work, we show that ferroelastic twin walls - crystallographically perfect 2D-sheets that separate regions of differently oriented domains - in the distorted perovskite LaAlO3 provide a natural platform for broadband lateral confinement and superb canalisation of light at the nanoscale. Without fabrication processes, the electromagnetic fields localised at such walls exhibit lateral optical sizes up to 260 times smaller than the free-space wavelength. Depending on the adjacent domain orientation and frequency, the twin wall pattern preferentially concentrates or repels the electromagnetic energy, constituting a natural building block towards broadband MIR and THz nanophotonics for polaritonic circuitry.
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All authors Jakob Wetzel, Javier Taboada-Gutiérrez, Matthias Roeper, Felix G. Kaps, Giuliano Esposito, Drini Marchese, Robin Buschbeck, Pauline Lenz, J. Michael Klopf, Hans A. Bechtel, Stephanie N. Gilbert Corder, Jeremie Teyssier, Susanne C. Kehr, Lukas M. Eng, Alexey B. Kuzmenko, Samuel D. Seddon
Materials Science
In-plane and out-of-plane electric dipoles and phase transitions in 2D-layered TlGaS2
A. D. Molchanova, L. H. Yin, L. P. Gao et al. (+4 more)
Out-of-plane and in-plane electric polarization, which rarely coexist in a two-dimensional (2D) ferroelectric material, offer different advantages in ferroelectricity-based devices. Here, we report the coexistence of in-plane and out-of-plane electric dipoles, along with various phase transitions, in 2D van der Waals layered TlGaS2 single
crystal.
Quantum paraelectricity was observed along both in-plane and out-of-plane directions of the TlGaS2
crystal. Detailed investigation of the
quantum paraelectric soft-mode behavior reveals a close correlation between the electric dipoles and the off-center displacement of Tl1+ ions with 6s2 lone pairs in TlGaS2. Anomalies near temperatures of about 120 K and 60-75 K in dielectric and/or infrared spectra indicate the existence of local or weak long-range structural transitions in TlGaS2. Our results provide important experimental evidence for elucidating the phase transitions and coexistence of in-plane and out-of-plane electric dipoles in 2D layered TlGaS2.
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All authors A. D. Molchanova, L. H. Yin, L. P. Gao, W. H. Song, Y. P. Sun, K. R. Allahverdiyev, M. N. Popova
Strongly Correlated Electrons · Cross-listed from hep-th
Correction exponents in the chiral Heisenberg model at $1/N^2$: singular contributions and operator mixing
Alexander N. Manashov and Leonid A. Shumilov
We calculate the correction exponents in the
chiral Heisenberg model in the $1/N$ expansion. These exponents are related to the slopes of $\beta$ functions at the phase transition point. We present the results at order $1/N^2$ and check that they agree with the results of the $\epsilon$ expansion near $d = 4$. We find that one of the correction exponents diverges as $d \to 3$. We argue that the appearance of the pole is a rather general phenomenon and is associated with operator mixing involving the system of four-
fermion operators. After analyzing the operator mixing structure, we propose a resummation procedure which modifies the exponents already at leading order. We also perform calculations directly in the three-dimensional model and find complete agreement with the resummed exponents.
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Mesoscale and Nanoscale Physics
Spin Elasticity
Zhong-Chen Gao, Tianyi Zhang, Feifei Wang et al. (+3 more)
Elasticity has long been regarded as a property exclusive to material media. Here we uncover its hidden existence in the
spin degree of freedom. We introduce
spin elasticity-an intrinsic mechanism that governs recoverable deformation of
spin morphology. This discovery reveals a previously unrecognized universality: elasticity operates in both matter and
spin spaces, underpinning structural integrity across physical realms. By establishing the missing
spin counterpart, this work completes the elastic picture and points toward a broader paradigm where elasticity transcends its conventional boundaries.
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All authors Zhong-Chen Gao, Tianyi Zhang, Feifei Wang, Jingguo Hu, Peng Yan, Xiufeng Han
Mesoscale and Nanoscale Physics
Electrically controllable valence-conduction band reversals in helical trilayer graphene
Matan Bocarsly, Indranil Roy, Weifeng Zhi et al. (+11 more)
In moiré
graphene systems, electronic interactions lift
spin and valley degeneracies, leading to
symmetry-broken ground states. In helical trilayer
graphene (HTG), we uncover a distinct interaction-driven mechanism in which the roles of sublattice-polarized valence and conduction bands are cyclically reversed. Using scanning nano-SQUID magnetometry, we detect a series of sharp
magnetic signatures consistent with seesaw-like transitions, where occupied and unoccupied valence and conduction bands interchange repeatedly with doping, accompanied by a novel form of
magnetic hysteresis. These transitions occur entirely within metallic regimes and leave only weak fingerprints in transport measurements. Self-consistent Hartree-Fock calculations reveal that interactions reorganize all eight low-energy flat bands, driving abrupt changes in orbital magnetization. Our results establish HTG as the first system where electronic interactions provide doping-controlled access to all three internal degrees of freedom -
spin, valley, and sublattice - introducing a new class of correlated phase transitions.
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All authors Matan Bocarsly, Indranil Roy, Weifeng Zhi, Li-Qiao Xia, Aviram Uri, Yves H. Kwan, Aaron Sharpe, Matan Uzan, Yuri Myasoedov, Kenji Watanabe, Takashi Taniguchi, Trithep Devakul, Pablo Jarillo-Herrero, Eli Zeldov
Materials Science
Visualizing spin-polarization of an altermagnet KV$_2$Se$_2$O via spin-selective tunneling
Guofei Yang, Chuang Li, Chengwei Wang et al. (+16 more)
Altermagnetism, a recently identified
magnetic phase that combines vanishing net magnetization with momentum-dependent
spin splitting, challenges the conventional dichotomy between ferromagnets and antiferromagnets. While several candidate materials have been proposed, direct experimental evidence linking
crystal symmetry, electronic structure and d-wave
spin polarization remains scarce. Here we report the visualization of a metallic d-wave altermagnet in KV2Se2O. Through
spin-selective scanning tunneling microscopy powered by a topological
insulator tip, we uncover
symmetry-protected momentum-dependent
spin splitting that follows a characteristic d-wave form factor. Our results establish KV2Se2O as a tunable platform to study the interplay between
spin-valley locking,
Fermi-surface instability and unconventional magnetism, and open a pathway toward
symmetry-engineered spintronics without net magnetization.
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All authors Guofei Yang, Chuang Li, Chengwei Wang, Xudong Zhao, Yifan Wan, Hengrui Gui, Guoqing Zeng, Saizheng Cao, Chuqiao Hu, Qihe Yu, Yujia Zhang, Dong Chen, Yu Liu, Yu Song, Yongjun Zhang, Fei Liu, Lun-Hui Hu, Lin Jiao, Huiqiu Yuan
Strongly Correlated Electrons · Cross-listed from quant-ph
Non-Hermiticity induced thermal entanglement phase transition
Bikashkali Midya
Theoretical analysis of a prototypical two-
qubit effective non-Hermitian system characterized by asymmetric Heisenberg $XY$ interactions in the absence of external
magnetic fields demonstrates that maximal bipartite
entanglement and
quantum phase transitions can be induced exclusively through non-Hermiticity. At thermal
equilibrium as $T\rightarrow 0$, the system attains maximal
entanglement ${C}=1$ for values of the non-Hermiticity parameter greater than a critical value $\gamma>\gamma_c=J\sqrt{(1-\delta^2)}$, where $J$ denotes the exchange interaction and $\delta$ represents the anisotropy of the system; conversely, for $\gamma < \gamma_c$,
entanglement is nonmaximal and given by ${C} = \sqrt{(1 - (\gamma/J)^2)}$. The
entanglement undergoes a discontinuous transition to zero precisely at $\gamma = \gamma_c$. This phase transition originates from the closing of the energy gap at a non-Hermiticity-driven ground state degeneracy, which is fundamentally different from an exceptional point. This work suggests the use of singular-value-decomposition generalized density
matrix for the computation of
entanglement in bi-orthogonal systems.
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Mesoscale and Nanoscale Physics
Engineering chiral-induced spin selectivity in an artificial topological quantum well
Lizhou Liu, Peng-Yi Liu, Tian-Yi Zhang et al. (+1 more)
Chiral-induced
spin selectivity (CISS) is a striking phenomenon in which
spin-unpolarized electrons become
spin-polarized after traversing a
chiral medium. Theoretical studies have shown that
spin-orbit coupling,
geometric chirality, and dephasing act cooperatively for this effect to emerge. Inspired by this, we demonstrate a solid-state realization of CISS in an engineered InAs/GaSb
quantum well where
geometric chirality and dephasing can be introduced controllably. Introducing a
chiral structure produces a clear
spin polarization whose sign reverses when the chirality is flipped, and whose magnitude grows systematically with the number of dephasing electrodes, while achiral configurations exhibit no
spin selectivity. The polarization remains robust even under strong Anderson disorder, showing that the engineered
chiral structures provides an intrinsically stable route to
spin-selective transport. These results establish a solid-state platform in the topological
quantum well system for controllably generating the CISS effect.
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All authors Lizhou Liu, Peng-Yi Liu, Tian-Yi Zhang, Qing-Feng Sun
Superconductivity
A possible superconducting gap signature with filling temperature around 40 K in hexagonal iron telluride islands
Guanyang He, Yuxuan Lei, Tianheng Wei et al. (+2 more)
Superconductivity in the iron-chalcogenide series FeSe-Fe(Te, Se)-FeTe has been restricted to the near neighbor of iron selenide (FeSe), with a general consensus that iron telluride (FeTe) is not superconducting. In this study, we report the method to grow FeTe islands with atomically flat surface and hexagonal
lattice on SrTiO3 (001) substrates, in which a gap structure with a gap-filling temperature close to 40 K is detected by scanning tunneling spectroscopy. Such signature is examined under various conditions and reminiscent of a superconducting gap structure. This work might offer a potential platform to explore new
superconductors at ambient pressure.
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All authors Guanyang He, Yuxuan Lei, Tianheng Wei, Yanzhao Liu, Jian Wang
Mesoscale and Nanoscale Physics
Floquet generation of hybrid-order topology and $\mathbb{Z}_2$-like bipolar localization
Koustav Roy, Latu Kalita, Bilal Tanatar et al. (+1 more)
Periodic driving offers a powerful tool to engineer topological phases and even induce phase transitions that are inaccessible in static settings. In this work, we demonstrate that a suitable driving protocol applied to the Benalcazar-Bernevig-Hughes (BBH) model, a canonical quadrupolar
insulator with a pi-flux-induced projective PT, gives rise to a hybrid-order topological phase in which the dispersive first-order edge states and localized higher-order corner modes are shown to coexist at distinct quasienergies. Further, extending the scenario to non-reciprocal hopping induced non-Hermiticity, we uncover a Z2-like skin effect characterized by a sharp transition from a unipolar to a bipolar eigenstate-localized phase. Remarkably, this phenomenon, which is established as a prerogative for spinful systems, emerges here purely from the interplay between the embedded gauge structure and Floquet-renormalized
symmetry constraints, without invoking physical
spin degrees of freedom. Further, the broken bulk-boundary correspondence in this driven non-Hermitian setting, can be restored via computing the two-dimensional generalized Brillouin zone (GBZ), which we construct through a
symmetry-reduced mapping onto an effective one-dimensional problem. The resulting non-Bloch invariants faithfully capture both the higher-order
topology and the unipolar to bipolar transition. These findings reveal periodic driving as a versatile and controllable handle for sculpting the interplay of higher-order
topology,
symmetry transmutation, and non-Hermitian skin physics in a single unified platform.
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All authors Koustav Roy, Latu Kalita, Bilal Tanatar, Saurabh Basu
Quantum Gases
Emergent thermal fluctuations and non-Hermitian phase transitions in open photon condensates
Moritz Janning, Roman Kramer, Aya Abouelela et al. (+3 more)
Driven-dissipative Bose-Einstein condensates of
photons in optical resonators have been shown theoretically to exist as a long-lived, yet metastable state stabilized by a ghost attractor, despite continuous driving [Phys. Rev. Lett. 135, 053402 (2025)]. Here we analyze the properties of this metastable condensate as well as the relaxation dynamics into and out of this state by means of the Lindblad master-equation approach, treating the condensate and the equal-time, noncondensed fluctuations on the same footing. Despite its nonequilibrium origin, the quasistationary condensate exhibits thermal behavior in that the order-parameter fluctuations scale with system size as in thermodynamic
equilibrium, and the
photon-number distribution in multimode resonators is in excellent agreement with a Bose-Einstein distribution. A linear stability analysis further reveals the presence of several exceptional points, resulting in multiple non-Hermitian phase transitions associated with the relaxation dynamics into and out of the metastable condensate. These behaviors reconcile apparently contradictory experimental results.
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All authors Moritz Janning, Roman Kramer, Aya Abouelela, Michael Turaev, Sayak Ray, Johann Kroha
Mesoscale and Nanoscale Physics
Efficient photo-Nernst terahertz emission in single heavy-metal films
Lei Wang, Linxuan Song, Elbert E. M. Chia et al. (+5 more)
State-of-the-art metallic terahertz (THz) emitters rely predominantly on spintronic
heterostructures, where heavy metals serve as passive
spin-to-charge converters. Here, we demonstrate efficient THz radiation from standalone Pt nanofilms at cryogenic temperatures and under external
magnetic fields. The governing mechanism is identified as the ultrafast photo-Nernst effect, wherein a transient thermal gradient drives a transverse charge current. The THz emission polarity is directly dictated by the sign of the Nernst coefficient, as verified by the phase reversal observed between Pt and W or Ta. Remarkably, both thickness scaling and alloying-induced suppression of thermal conductivity independently amplify the single-layer emission to levels comparable with
benchmark spintronic
bilayers. These findings redefine the established role of heavy metals from passive
spin-sinks to active THz emitters, uncovering a universal emission paradigm applicable across diverse spintronic and
quantum materials.
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All authors Lei Wang, Linxuan Song, Elbert E. M. Chia, Peijie Sun, Jianlin Luo, Rongyan Chen, Yong-Chang Lau, Xinbo Wang
Materials Science
Magnetocaloric Effect of Pure and Diluted Quantum Magnet Yb$_3$Ga$_5$O$_{12}$
E. Riordan, E. Lhotel, N.-R. Camara et al. (+2 more)
The magnetocaloric effect in the
quantum dipolar magnet Yb$_3$Ga$_5$O$_{12}$ is studied both for pure material and with non-
magnetic substitution: (Yb$_{1-x}$Y$_x$)$_3$Ga$_5$O$_{12}$. Magnetization measurements have been performed on a single
crystal, $x=0$, and on powder samples with $x = 0.2$ and 0.4 in the temperature range between 70 mK to 300 K and in
magnetic fields up to 8 T. The
magnetic entropy change $\Delta S_m$, a key figure of merit for adiabatic demagnetization refrigeration, has been derived from the magnetization data. The $x=0.2$ sample exhibits the volumetric
entropy variation comparable to, and at low fields even enhanced relative to, the pure compound. In contrast, the 40%\ diluted sample shows a reduced effect, consistent with the conventional dilution picture. The Curie-Weiss law fits reveal positive Curie temperatures in both diluted samples, indicating the persistence of
ferromagnetic correlations. The robustness of the magnetocaloric response upon moderate dilution highlights the potential of YbGG-based materials for low-temperature
magnetic cooling applications, particularly in addressing thermal conductivity challenges through the chemical substitution without compromising cooling power.
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All authors E. Riordan, E. Lhotel, N.-R. Camara, C. Marin, M. E. Zhitomirsky
Soft Condensed Matter
Mechanical stress induced by the polymerisation of an active gel near a surface
Kristiana Mihali, Dennis Wörthmüller and Pierre Sens
Actin flow in the cortical cytoskeleton underneath the
cell membrane generates mechanical stresses that shape the
cell surface. We study this mechanism using a hydrodynamic model of a compressible active gel polymerizing at the membrane and undergoing turnover. We determine how actin flow, density relaxation and friction of actin with the membrane generate stress on a corrugated membrane at the linear order in deformation. Analytical solutions in limiting regimes, combined with finite element methods in the general case, provide a map of normal and tangential stresses as functions of compressibility, interfacial friction and actin turnover, and determine the conditions under which actin polymerization can render the membrane linearly unstable. The non-linear regime is also briefly discussed.
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Materials Science · Cross-listed from physics.chem-ph
Molecular dynamics simulation of high slip flow of water confined between graphene nanochannels at experimentally accessible strain rates
Carmelo Civello, Luca Maffioli, Edward Smith et al. (+4 more)
The transient time correlation function method (TTCF) has emerged as a powerful methodology for accurately probing systems at low shear rates. In the present study, TTCF was used to evaluate the shear rate dependence of the slip length in a high-slip system consisting of water confined between
graphene walls at experimentally accessible shear rates, for which classical nonequilibrium molecular dynamics (NEMD) is unfeasible. The corresponding Navier friction coefficient was computed for all shear rates spanning six orders of magnitude and compared with the
equilibrium limit. We report for the first time NEMD results obtained at experimentally accessible shear rates using the TTCF approach for a system that has attracted significant interest over the past decades. The slip length calculated with TTCF is in good agreement with previous
equilibrium molecular dynamics simulations and experiments. Our aim here is to highlight the extraordinary power of TTCF, particularly for high-slip (low strain-rate) systems, and to verify that
equilibrium methods directly match NEMD measurements at experimentally accessible strain rates.
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All authors Carmelo Civello, Luca Maffioli, Edward Smith, James Ewen, Peter Daivis, Daniele Dini, Billy Todd