Statistical Mechanics
Hierarchical Reconstruction of Time-arrow from Multi-time Correlations
Yijia Cheng, Ruicheng Bao and Zhonghuai Hou
The
entropy production rate (EPR), a key measure of thermodynamic irreversibility in thermodynamics of small systems, is difficult to determine directly in experiments, motivating lower-bound-based estimation from observations. However, a systematic framework for organizing increasing amounts of the irreversibility information in experimental state observables into progressively tighter bounds remains lacking. Here, we show that multi-time correlations of a class of state observations naturally encode this information to provide a hierarchy. By defining a reconstruction operation as a combination of correlations, we obtain a sequence of lower bounds on the EPR. Correlations of higher order capture the thermodynamic information at greater temporal depth, thereby capturing more irreversibility and yielding tighter bounds. Under ideal conditions, this hierarchy converges to the full EPR in the limit of infinitely dense observations over a finite time window.
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Statistical Mechanics · Cross-listed from quant-ph
Toward fault-tolerant quantum computation exploiting quantum spatial distribution and gauge symmetry
Ryo Asaka
We explore how the integrated use of
quantum spatial distribution (QSD), or more specifically, a superposition of both
spin and position states of particles, and gauge
symmetry (GS) within Poulin's stabilizer formalism enhances
quantum error correction. The study employs $3+2$ particles on nested squares proposed in the companion paper (arXiv:2504.07941), where three of them encode Shor's nine-
qubit code and the remaining two detect errors in this code through their
spin state measurements. The first result is that the GS offers resilience against three types of noise acting on a particle: arbitrary decoherence of its
spin or position state, and dephasing of both states, which completely or partly destroys its QSD. To show that, we formulate a noise model unifying the above noise sources and prove the correctability of this unified model under our error-correcting scheme. The second result is that the QSD provides architectural flexibility, allowing us to stack the error-correcting systems both vertically and horizontally. Indeed, we present implementations of the error detection (stabilizer measurement), logical Hadamard and Toffoli gates, and a
quantum adder with the required interactions only between nearest-neighbor and next-nearest-neighbor particles. Here, our treatment of the dynamics of particles, each having
spin and position degrees of freedom, under nontrivial noise and gate operations indicates that the stabilizer formalism is a powerful tool for describing
quantum many-body dynamics.
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Statistical Mechanics
Universal transport of active colloids with sensory delay in motility landscapes
Adrià Garcés, Ueli Töpfer, Lucio Isa et al. (+2 more)
We experimentally, numerically and analytically explore the diffusive transport of active colloidal particles with sensory delay, navigating motility landscapes in which the self-propulsion speed depends on space. We show how the transport properties can be obtained by replacing the space dependence of the self-propulsion speed by a dynamical
stochastic switching process in the absence of delay, and extend the theory for systems with finite delayed responses. We obtain analytical results for the mean square displacement and the effective
diffusion coefficient which accurately predict experimental measurements and numerical simulations across multiple scales. We show how, within the regime of validity of the delay-extended theory, density patterns and effective
diffusion obey universal scaling forms. Our work provides minimal framework describing the transport properties of active swimmers with internal adaptation dynamics in motility landscapes.
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All authors Adrià Garcés, Ueli Töpfer, Lucio Isa, Demian Levis, Ignacio Pagonabarraga
Mesoscale and Nanoscale Physics
Magnetoplasma excitations in interacting GaAs disks
S.A. Andreeva, A.A. Gavrilov, K.R. Dzhikirba et al. (+5 more)
We investigate the effect of inter-disk coupling on the magnetoplasmon dispersion in a square
lattice of two-dimensional electron system (2DES) disks etched from a GaAs
quantum well. Using magneto-optical terahertz (THz) spectroscopy, we track the
evolution of the collective modes as disk
lattice period is systematically reduced, thereby increasing the coupling strength. At large distances, the system exhibits magnetoplasma modes corresponding to individual excitations in disks. As the inter-disk distance decreases, we observe a modification to magnetoplasma dispersion.
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All authors S.A. Andreeva, A.A. Gavrilov, K.R. Dzhikirba, A.S. Astrakhantseva, A.V. Shchepetilnikov, O.V. Orlov, V.V. Solovyev, I.V. Kukushkin
Materials Science
Chemical transformation of MgH2/V2O5 composite to Mg-V-O rock salt and its influence on the electrochemical Li conversion and hydrogen storage characteristics of MgH2
D. Pukazhselvan, Ihsan Caha, Francisco J.A. Loureiro et al. (+5 more)
This study investigates the lithium conversion behavior of a hydrogen storage material based on vanadium
oxide added magnesium hydride. To understand the chemical interaction between vanadium
oxide and magnesium hydride, detailed X ray diffraction and X ray photoelectron spectroscopy analyses were performed on ball milled composites with varying compositions. The results confirm the formation of a combined magnesium vanadium
oxide with a rock salt structure, indicating strong chemical interaction between the components. It is further shown that the presence of a small amount of this
oxide additive significantly influences the lithium reaction with magnesium hydride, leading to a high initial discharge capacity and limited recharge capacity in lithium ion coin
cells. Post use analyses confirm the presence of magnesium hydride, suggesting that volume expansion is not responsible for the observed irreversibility. Electrochemical impedance spectroscopy using differential function of relaxation times indicates that electrolyte degradation is not a major issue. Instead, slow charge transfer processes are identified as the limiting factor, and these are sensitive to the composition of the additive. These findings highlight that improving electrode and electrolyte compatibility is essential for enhancing performance in this system.
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All authors D. Pukazhselvan, Ihsan Caha, Francisco J.A. Loureiro, Francis Leonard Deepak, Catarina de Lemos, Aliaksandr L. Shaula, Sergey M. Mikhalev, Duncan Paul Fagg
Strongly Correlated Electrons
Exact results for the Hubbard model on bipartite lattices in spatial dimensions $d>1$: Seven theorems from the full [SU(2)$\times$SU(2)$\times$U(1)]/$\mathbb{Z}_2^2$ symmetry
J. M. P. Carmelo
There are few exact results for the Hubbard model on bipartite
lattices of spatial dimension $d>1$. Nevertheless, the Hubbard model with transfer integral $t$ and onsite repulsion $U$ on bipartite
lattices with $N_a$ sites, such as the square, honeycomb, cubic, body-centered cubic, face-centered cubic, and diamond
lattices, provides the simplest toy model for describing electronic correlations in many condensed-matter systems and is therefore a
quantum problem of considerable physical interest. Seven exact
theorems that provide new physical insight into the model are established. Overall, the exact framework based on physical
spins and physical $\eta$-
spins for the Hubbard model on bipartite
lattices of spatial dimension $d>1$ introduced in this paper offers a robust foundation for future studies of the model, as well as of the condensed-matter materials, such as cuprate
superconductors,
graphene and
graphene-derived systems, and other
quantum systems, that it describes.
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Strongly Correlated Electrons
Validity of DFT+U band gaps in all its known functional forms
Andrew C. Burgess and David D. O'Regan
The Density Functional Theory plus Hubbard U (DFT+U) technique is one of the most widely used tools by condensed matter physicists and solid state chemists for the simulation of transition-metal and lanthanide bearing
crystals, and increasingly of much more diverse chemistries... Since the earliest days, the gap in the DFT+U single-particle eigenspectrum has been associated with the fundamental band gap, and the method has typically found more success for spectra than for total-energy derived properties. There has been some doubt, however, as to the conceptual validity of this association. Here, extending findings from recent years regarding local, semi-local, and hybrid functionals within the generalized Kohn-Sham framework, we prove and numerically demonstrate that the DFT+U eigenspectrum gap is conceptually valid, in the specific sense that it matches its own fundamental gap calculated using total-energy differences. We emphasize that this does not imply its agreement with experimental values, and indeed our argument is independent of the Hubbard U parameter. The result holds for pristine periodic systems with converged k-point sampling but not, however, for defective ones, isolated systems, or systems in which added charges exhibit spontaneous localization. We show that bandgap validity for pristine solids holds in the presence of pseudopotentials and PAW potentials, when using hybrid functionals, and in DFT+U(+J) irrespective of the level of subspace projection onto the band-edge states. We survey every collinear-
spin DFT+U-type functional known to have been published to date, within a unified notation... Returning to the related but different question of band-gap correction efficiency, we offer fresh analysis of DFT+U bandgap projection dependence, and each functional's effect on energies and gaps for the hydrogen
lattice in the Mott-Hubbard limit.
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Disordered Systems and Neural Networks · Cross-listed from math-ph
Griffiths inequalities and Gibbs-Bogoliubov inequality for general gauge glasses with Gaussian disorder on Nishimori line
Manaka Okuyama and Masayuki Ohzeki
We consider a class of gauge glass models with Gaussian disorder on the Nishimori line, including the Ising
spin glass, the $XY$ gauge glass, the $Z_q$ gauge glass, and the gauge-invariant Potts model. We prove that the first and second Griffiths inequalities hold for these models on arbitrary
lattice structures. As a consequence, both the pressure and the correlation functions are monotonically increasing with respect to the inverse temperature along the Nishimori line. Furthermore, we establish an analogue of the Gibbs–Bogoliubov inequality for this class of models. This result implies that, on the Nishimori line, the approximate quenched free energy obtained via the replica method with a replica-symmetric mean-field approximation is always greater than the true quenched free energy. Our results provide a broad generalization of previous results established for the Ising
spin glass with Gaussian disorder on the Nishimori line.
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Quantum Gases
Nitin Kaloya and Kuldeep Suthar
We examine the two-dimensional
spin-orbit-coupled
bosons in the presence of an anisotropic dipolar interaction in square
lattices. The
spin-orbit coupling leads to finite-momentum superfluid and supersolid states, while the nearest-neighbour interaction induces crystalline characteristics in the
quantum phases of soft-core
bosons. We employ site-decoupled Gutzwiller ansatz and mean-field decoupling theory to obtain the phase diagrams and investigate the effects of the tilt of
magnetic dipoles with respect to the polarization axis. Our study reveals the intriguing
quantum phase transition of checkerboard finite-momentum phase-twisted and phase-stripe states into their stripe counterparts at a magic tilt angle, at which the off-site interaction along one of the directions becomes zero. At smaller tilt angles, the checkerboard charge-density-wave phase intervened by two compressible finite-momentum phases, and at strong
spin-orbit coupling strengths, the phase-twisted supersolid and superfluid phases emerge. At larger tilt angles, a transition between the striped order of phase-twisted states and phase-stripe states occurs. The inclusion of off-site inter-component correlation leads to density-correlated phases,
lattice-induced supersolid, and
ferromagnetic quantum phases. Our study highlights novel finite-momentum
crystal phases of
spin-orbit-coupled dipolar
bosons and provides a parameter space to observe them in
quantum gas experiments.
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Quantum Gases · Cross-listed from math-ph
Co-rotating Vortices on Surfaces of Variable Negative Curvature: Hamiltonian Structure and Curvature-Induced Drift
Gaurang Mangesh Joshi and Rickmoy Samanta
Vortices in fluids and superfluids are fundamental to phenomena ranging from Bose-Einstein condensates and superfluid films to
neutron stars and hydrodynamic micro-rotors, where background geometry often plays an important role.
Curvature can induce
vortex motion distinct from planar domains. We study
Hamiltonian vortex motion on a catenoid, a minimal surface of variable negative
curvature, and derive explicit equations of motion and conserved quantities for co-rotating
vortex pairs. For two identical
vortices we find an exact analytic solution in which the pair rotates rigidly at fixed latitude, with angular velocity $\Omega=(\Gamma/16\pi)\,K'(V)/\sqrt{-K(V)}$, where $K(V)$ is the Gaussian
curvature. Thus the motion is governed by the
curvature gradient rather than the
curvature itself. This state is linearly unstable, with growth rate $\lambda=\sqrt{3}|\Omega|$, in agreement with numerical simulations. For generic co-rotating pairs, conservation of the
Hamiltonian and rotational momentum reduces the nonlinear dynamics to a single quadrature, yielding bounded relative oscillations together with a secular azimuthal drift. Simulations of the full equations confirm this and reveal the same
curvature-induced azimuthal drift in a localized many-
vortex cluster, motivating a broader theory of collective
vortex drift on curved surfaces.
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Materials Science
Spin-Axis-Layer Locking for Intrinsic Bipolar Altermagnetic Semiconductors: Proof-of-Concept in Bilayer CuBr2
Wei Ma, Dengpan Ma, Zhiheng Lv et al. (+1 more)
Electrical control of
spin and
magnetic sublattice degrees of freedom is essential for multifunctional and low-power spintronic devices. Bipolar altermagnetic
semiconductors (BAMSs)-characterized by opposite
spin polarizations at the valence and conduction band edges-offer such control, yet known systems require external strain and sizable valley polarization for gate-tunable switching. Here, we propose a universal
spin-axis-layer locking (SALL) paradigm to overcome these limitations. By stacking two quasi-1D
ferromagnetic monolayers with a 90 degrees twist, the
bilayer reconstructs altermagnetic
symmetry, yielding an intrinsic BAMS state where carrier
spin is locked to specific layers and transport directions. Using synthesized CuBr2 monolayers as proof-of-concept, we demonstrate via first-principles calculations a robust BAMS state. Electrostatic gating enables simultaneous, reversible switching of carrier type,
spin, and active layer, generating fully
spin-polarized axial charge currents and directionally controllable pure
spin currents with near-unity charge-to-
spin conversion efficiency. This SALL model establishes a versatile, strain-independent strategy for advanced all-electrical altermagnetic devices.
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All authors Wei Ma, Dengpan Ma, Zhiheng Lv, Zhifeng Liu
Materials Science · Cross-listed from physics.optics
Thermo-optic dynamics of effective epsilon-near-zero media
Jiaye Wu, Xuanyi Liu, Marco Clementi et al. (+4 more)
Epsilon-near-zero (ENZ) photonic media exhibit extreme optical dispersion that enables unconventional light-matter interactions and enhanced optical nonlinearities. Recent studies suggested that thermo-optic effects, traditionally regarded as slow and secondary, can be strongly modified under the ENZ condition. Here we establish thermo-optic reconfiguration of effective media as a unified physical framework to describe both static and transient thermo-optic phenomena in ENZ systems. Using a CMOS-compatible effective medium operating in the visible spectral range, we experimentally demonstrate that temperature variation, whether under thermal
equilibrium or transient excitation, reconfigures the constitutive parameters defining the ENZ condition, giving rise to pronounced linear and nonlinear optical responses. At thermal
equilibrium, this reconfiguration manifests itself as static ENZ wavelength shift with an unprecedentedly large thermal-spectral modulation rate and an effective thermo-optic coefficient on the order of $10^{-1}$ K$^{-1}$. Under ultrafast excitation, we observe a picosecond-scale thermo-optic nonlinear response induced by transient heating. This response can be consistently interpreted as a time-dependent reconfiguration of the effective ENZ medium, corresponding to a transient
evolution of its optical parameters. By reframing thermo-optic effects as a process of static and dynamic reconfiguration of effective media, this work provides a unified perspective that bridges thermo-optic physics, effective-medium theory, and time-varying photonics.
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All authors Jiaye Wu, Xuanyi Liu, Marco Clementi, Shuang Qiu, Limin Lin, Zhang-Kai Zhou, Camille-Sophie Brès
Statistical Mechanics · Cross-listed from quant-ph
Continuous Reset-Induced Phase Transition in Measurement-Free Random Quantum Circuits
Hinata Yokoyama, Kengo Anzai, Dina Syverud-Lindland et al. (+2 more)
We study a random
unitary quantum circuit with only reset channels, which has high feasibility for real
quantum devices. In particular, we investigate the many-body statistical physics properties, “reset-induced”
entanglement phase transitions comparing the classical statistical picture in the large “$d$” limit of qudits. In the property of the reset-induced phase transition the parameter of qudit $d$ is essential. That is, the transition properties induced by the reset channel significantly depend on $d$. We numerically elucidate this statement employing efficient stabilizer
circuit simulations for $d=2$. Specifically, critical fluctuations that grow with system size are observed near the transition point, and the finite-size scaling analyses yield data collapse consistent with a continuous mixed-state phase transition.} This behavior differs from expectations based on the classical statistical mapping in the large-$d$ limit.
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All authors Hinata Yokoyama, Kengo Anzai, Dina Syverud-Lindland, Yoshihito Kuno, Hiroaki Matsueda
Strongly Correlated Electrons
Collective and separate metal-insulator transitions in correlated vanadium dioxide
Xuanchi Zhou, Xiaohui Yao, Wentian Lu et al. (+2 more)
Deciphering the complicated interplay between collective and separate behaviors lies at the heart of first-order metal-
insulator transition (MIT) in correlated electron systems, enabling the rational design of exotic electronic states and functionalities. The critical balance between collective and separate behaviors defines a fundamental collective length scale, typically shorter than 5 nm, that governs emergent
quantum orders, yet active control over this dichotomy remains elusive. Here, we realize on-demand manipulation of the collective and separate MIT within the correlated VO2 system in a reversible fashion. Artificially designing the oxygen deficiency in VO2/VO2-x homojunction fosters a collective MIT with an extended collective length scale, whereas the introduction of a TiO2 interlayer drives a crossover from this collective to a two-step separate MIT via decoupling of the electronic order parameter. Incorporating mobile hydrogens into the VO2/TiO2/VO2-x trilayer enables reversible control over electronic phase modulations, transitioning a two-step MIT towards either a one-step MIT or collective electron localization. This ionic control over the electronic band structure of VO2 flexibly triggers multi-state MIT, a process governed by hydrogen-related band filling. Our findings transform the collective length scale from a passive threshold into a dynamic design parameter, establishing a viable handle for engineering collective and separate MIT for adaptive correlated electronics.
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All authors Xuanchi Zhou, Xiaohui Yao, Wentian Lu, Chunwei Yao, Xiaomei Qiao
Mesoscale and Nanoscale Physics
Binary topological logic gates in Kane-Mele nanostructures via local control of edge-state transport
K. Zberecki
Topological edge states offer a promising basis for post-CMOS device concepts. However, their use in elementary logic requires simple and physically transparent architectures. Here we study binary logic in Kane-Mele nanostructures with spatially localized control regions. Logical inputs are encoded by local electrostatic, exchange-like, and Rashba-type perturbations. The output is read from terminal transmission within the Landauer-Buttiker framework. We demonstrate working NOT and AND gates in multiterminal honeycomb geometries. Real-space current maps show that their operation is governed by controlled rerouting of edge currents rather than by finely tuned interference. Both gates reproduce the complete truth table in all 50 Anderson-disorder realizations at each tested disorder strength up to W/t=0.1. The NOT gate also remains correctly classified at all 441 points of a two-parameter control scan.
Geometric tests confirm stable operation for several patch lengths and branch widths. These results establish Kane-Mele nanostructures as a transparent and numerically robust platform for primitive topological binary logic.
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Materials Science
Physical properties of transition metal hydride superconductors Mg2TmH6 (Tm = Rh, Pd, Ir, Pt) by first-principles calculations
Md Ashraful Alam, Md Abdul Hadi Shah, F. Parvin et al. (+1 more)
In this work, a comprehensive first-principles investigation of the structural, hydrogen storage potential, electronic, elastic, mechanical, thermophysical, superconducting, and optical properties of Mg2TmH6 (Tm = Rh, Pd, Ir, Pt) hydrides is presented. Obtained results demonstrate that Mg2TmH6 hydrides combine favorable hydrogen storage, mechanical robustness, superconductivity, and multifunctional optical properties, making them promising candidates for energy storage, superconducting and advanced optoelectronic applications.
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All authors Md Ashraful Alam, Md Abdul Hadi Shah, F. Parvin, S. H. Naqib
Materials Science
Substitutional platinum as an efficient nonradiative recombination center in silicon
Zhenxing Dai, Menglin Huang, Xin-Gao Gong et al. (+1 more)
Platinum (Pt) is widely used for carrier-lifetime control in silicon power devices, yet the microscopic nonradiative recombination mechanism of the substitutional platinum ($\text{Pt}_\text{Si}$) dopant remains debated. Using first-principles calculations combined with nonradiative multiphonon theory, we systematically investigate the electronic structures and carrier capture dynamics of $\text{Pt}_\text{Si}$. Our results show that both the donor ($+/0$) and acceptor ($0/-$) levels of $\text{Pt}_\text{Si}$ exhibit large capture cross sections for electron and hole carriers, thereby making $\text{Pt}_\text{Si}$ an effective recombination center. Notably, the calculated capture cross sections are sensitive to the
symmetry-equivalent defect configurations with different Jahn-Teller distortions. By accounting for two different $D_{2d}$ configurations of neutral $\text{Pt}_\text{Si}$ during transitions properly, our calculated carrier capture cross sections align well with experimental values. This work provides a microscopic picture of the carrier capture processes induced by $\text{Pt}_\text{Si}$ and emphasizes the importance of
symmetry-equivalent configurations in defect-assisted nonradiative recombination.
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All authors Zhenxing Dai, Menglin Huang, Xin-Gao Gong, Shiyou Chen
Strongly Correlated Electrons
Observation and Control of Moiré-Tailored Topological Dirac States
R. Ganser, M. P. T. Masilamani, B. Geldiyev et al. (+6 more)
Moiré
heterostructures provide a powerful framework for tailoring electronic band structures via controlled long-range periodic superlattice potentials. Beyond widely studied moiré-tailored flat bands, folded band structures can host emergent Dirac states, which have recently attracted considerable interest. Direct momentum-resolved observation of gapless moiré-Dirac quasiparticles, however, is challenging and has so far remained elusive. By performing angle-resolved photoemission spectroscopy measurements on an epitaxial surface-moiré structure, we here provide direct spectroscopic evidence of moiré-dressed Dirac states with topological character. Driven by the one-dimensional superlattice potential, electrons propagate anisotropically with a weak but massless Dirac dispersion along the confinement direction. The observed band crossings belong to topological nodal lines pinned to the mini-Brillouin zone boundaries. As such, they are enforced and robustly protected by the non-symmorphic
symmetry of the superlattice. Finally, we demonstrate that the topological excitations can be almost continuously controlled by tuning the moiré
lattice periodicity, directly unveiling moiré
heterostructures as a promising platform for creating and controlling topological moiré-Dirac states.
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All authors R. Ganser, M. P. T. Masilamani, B. Geldiyev, M. M. Hirschmann, A. Consiglio, J. Schusser, D. Di Sante, M. Ünzelmann, F. Reinert
Mesoscale and Nanoscale Physics
Magnomechanical Coupling in Suspended 2D van der Waals Ferromagnets
Ritesh Das, Alvaro Bermejillo-Seco, Herre S. J. van der Zant et al. (+2 more)
Magnomechanical systems provide a promising route for exploring coherent hybrid
magnon-
phonon interactions and hybrid information processing, but their realization has so far been limited by weak
magnon-
phonon coupling in conventional bulk platforms. We show that a suspended membrane of a two-dimensional van der Waals ferromagnet with in-plane magnetization and out-of-plane mechanical oscillations exhibits large magnomechanical coupling dominated by magnetoelastic interactions. The parametric single
magnon-
phonon coupling rate scales linearly with pre-strain and can reach hundreds of Hertz to low kiloHertz in suspended membranes of van der Waals ferromagnets such as CrGeTe_3 under experimentally realistic conditions. This rate exceeds typical values reported for YIG spheres by more than three orders of magnitude. Our results demonstrate that suspended membranes of van der Waals magnets provide a robust and highly tunable platform for magnomechanics.
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All authors Ritesh Das, Alvaro Bermejillo-Seco, Herre S. J. van der Zant, Peter G. Steeneken, Yaroslav M. Blanter
Strongly Correlated Electrons
Self-consistent vertex corrected $GW$ with static and dynamic screening using tensor hypercontraction: assessment of molecular charged excitations
Munkhorgil Wang, Ming Wen, Pavel Pokhilko et al. (+3 more)
We investigate self-consistent vertex corrections to the $GW$ self-energy for ionization potentials (IPs) and electron affinities (EAs). We
benchmark IPs against $\Delta$CCSD(T) references in the $G_0W_0\Gamma$29 and GW100 sets and compare GW100 EAs with EOM-CCSD references. Because many anions are metastable, these addition energies are model quantities and should not be interpreted as experimental EAs. Tensor hypercontraction (THC) of the Coulomb integrals enables efficient self-consistent $GW\Gamma_{\Sigma}$ implementations, where vertex corrections are included only in the self-energy. We establish a hierarchy of vertex-corrected self-energies relative to sc$GW$, ordered from least to most negative as SOX $>$ SOSEX $>$ G3W2 $>$ 2SOSEX $>$ sc$GW$. Equivalently, the absolute magnitude increases along this sequence. This trend follows an effective-screening picture, in which increasing screening progressively reduces exchange contributions. Static and dynamic variants show consistent differences due to the frequency dependence of the screened interaction. Across all methods, vertex corrections act as an approximately frequency-uniform self-energy renormalization rather than altering its spectral structure. In terms of accuracy, sc$GW\Gamma_{\Sigma}$ does not uniformly improve IPs or the EA model quantities over sc$GW$. For IPs, SOX and SOSEX usually degrade performance, whereas 2SOSEX and G3W2 remain close to sc$GW$, with only marginal improvements for selected systems at higher cost. Although the tested variants reduce EA MAEs, this should not be interpreted as a general improvement for physical anions because many nominal EA states are metastable. These results indicate that generic vertex insertions are insufficient to outperform sc$GW$; systematic improvements require designed diagrammatic approximations combined with efficient tensor factorization.
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All authors Munkhorgil Wang, Ming Wen, Pavel Pokhilko, Chia-Nan Yeh, Miguel A. Morales, Dominika Zgid
Materials Science
Tuning magnitude and direction of lattice thermal conductivity in transition metal dichalcogenide heterobilayers
Elliot Perviz and Antonio Cammarata
We investigate the nanoscale mechanisms determining
lattice thermal conductivity (LTC) of pristine and W-doped MX$_2$-M$^\prime$X$^\prime_2$ transition metal dichalcogenide heterobilayers from first principles, using the exact solution of the linearised Boltzmann transport equation in both
phonon and relaxon bases. Pristine heterobilayers exhibit isotropic in-plane LTC with preserved ordering across temperature. Relaxon analysis identifies descriptors linking LTC to
phonon properties such as the
phonon group velocity and layer localisation. While systems with lighter atoms generally favour higher LTC, a sufficiently large mass contrast is required to induce layer localisation of the transport-relevant vibrational modes. Further, we show through the thermal viscosity that the relative distribution of vibrational states between metal/non-metal sublattices influences the balance between Normal and Umklapp scattering processes. On the other hand, doped systems exhibit reduced and anisotropic in-plane LTC, retain a well-defined layer character, but are strongly affected by enhanced
phonon-
phonon scattering due to mass disorder. Notably, we find that both configuration and temperature dictate the direction of maximum thermal transport, which opens the possibility to tune the direction of maximum (and minimum) conductivity via doping in novel 2D functional materials. Thanks to its general formulation, the analysis protocol can be readily extended to other van der Waals
heterostructures, and the descriptors may be implemented in high-throughput engines to identify promising layered materials with tailored thermal transport characteristics.
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Strongly Correlated Electrons
Topochemical Fluorination of La$_2$NiO$_{4+\delta}$ Single Crystals
Hasan Yilmaz, Masahiko Isobe, Oliver Clemens et al. (+1 more)
Topochemical fluorination offers a low–temperature route for modifying the anion chemistry and electronic ground states of layered transition-metal
oxides, providing access to metastable phases and functionalities that are not able to be achieved through conventional solid–state synthesis. Despite extensive work on polycrystalline samples and thin films, topochemical fluorination of bulk single
crystals has not been studied, limiting insights into intrinsic structure property relationships. Here, we investigate the topochemical fluorination of optical float zone grown (OFZ) La$_2$NiO$_{4+\delta}$ single
crystals using
polymer-based PTFE, PVDF and inorganic CuF$_{2}$ fluorination
agents and compare it to our topochemical pathways of reduction of LaNiO$_{3-x}$. By systematically investigating direct and indirect contact reaction pathways, we can understand fluorination mechanisms, quantify the degree of fluorine incorporation, and evaluate the resulting structural and
magnetic modifications in a detail that was not possible in powder and thin films. Powder and single–
crystal X-ray diffraction reveal that fluorination proceeds without destroying the Ruddlesden–Popper framework, while inducing
lattice parameter changes consistent with anion intercalation in the bulk and ion exchange on the surface. This even induces a clear superstructure, which was not reported before and extends the understanding of anion insertion reactions beyond what is known on stage ordering in nickelates. Energy-dispersive X–ray spectroscopy confirms strong fluorine incorporation on the surface and reduced homogeneity in the bulk.
Magnetic susceptibility measurements demonstrate a change in
antiferromagnetic ordering upon fluorination.
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All authors Hasan Yilmaz, Masahiko Isobe, Oliver Clemens, Pascal Puphal
Materials Science
Benchmarking bandgap prediction in semiconductors under experimental and realistic evaluation settings
Haolin Wang, Xianyuan Liu, Anna Jungbluth et al. (+3 more)
Accurate bandgap prediction is crucial for
semiconductor applications, yet machine learning models trained on computational data often struggle to generalize to experimental bandgap measurements. Challenges related to data fidelity, domain generalization, and model interpretability remain insufficiently addressed in existing evaluation frameworks. To bridge this gap, we introduce RealMat-BaG, a
benchmark for assessing model reliability under experimentally relevant conditions. We curate an open-access
dataset of experimental bandgaps with aligned
crystal structures and compare graph neural networks as well as classical machine learning baselines. Our framework evaluates performance across statistical and domain-based splits, examines transfer from DFT-computed to experimental bandgaps, and analyzes interpretability at both elemental-property and structural levels. Our results reveal the fundamental generalization limitations of current bandgap prediction models and establish a
benchmark aligned with experimental measurements for developing more reliable learning strategies for materials discovery.
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All authors Haolin Wang, Xianyuan Liu, Anna Jungbluth, Alexandra J. Ramadan, Robert D. J. Oliver, Haiping Lu
Mesoscale and Nanoscale Physics
Doping-Induced Brightening of Dark Excitons and Trions in a WSe$_2$ Monolayer
Grzegorz Krasucki, Artur O. Slobodeniuk, Kacper Walczyk et al. (+5 more)
Optically dark excitonic states play a critical role in the valleytronic, electronic, and optical properties of monolayer semiconducting transition metal dichalcogenides. Here, we investigate how electrostatic doping affects the in-plane
magnetic-field-induced activation of dark excitonic complexes in a gated WSe$_2$ monolayer. By continuously tuning the carrier density via gate voltage, we access $n$-type, charge-neutral, and $p$-type regimes and track the corresponding brightening dynamics. We find that the brightening rates of the dark negative trion ($T^{D-}$), dark neutral
exciton ($X^{D}$), and dark positive trion ($T^{D+}$) exhibit a strong and nontrivial dependence on doping. In particular, the pronounced asymmetry in the brightening behaviour of the neutral $X^{D}$ complex and the charged $T^{D-}$ and $T^{D+}$ trions reveals distinct underlying carrier interactions, which we describe using a rate-equation model for their steady-state populations. These findings highlight the key role of dark excitonic complexes in governing the optical response and carrier dynamics of doped S-TMD monolayers.
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All authors Grzegorz Krasucki, Artur O. Slobodeniuk, Kacper Walczyk, Katarzyna Olkowska-Pucko, Kenji Watanabe, Takashi Taniguchi, Adam Babiński, Maciej R. Molas
Other Condensed Matter
Control of relaxation properties of a macroscopic nuclear spin ensemble
János Ádám, Andrew J. Winter, Deniz Aybas et al. (+4 more)
Macroscopic
spin ensembles in solids are powerful platforms for
quantum sensing and precision metrology. A key challenge is controlling the
nuclear spin population relaxation time $T_1$, which can become prohibitively long at cryogenic temperatures due to
phonon freeze-out. We demonstrate optical control of the $T_1$ relaxation time of the $^{207}$Pb
nuclear spin ensemble in lead-containing ferroelectric
crystals PbTiO$_3$ (PT) and (PbMg$_{1/3}$Nb$_{2/3}$O$_3$)$_{2/3}$-(PbTiO$_3$)$_{1/3}$ (PMN-PT). Using X-band electron paramagnetic resonance (EPR) spectroscopy at 10 K, we characterize light-induced paramagnetic centers created by 405 nm
laser illumination. In PT, we observe paramagnetic Pb$^{3+}$ centers and their hyperfine interaction with nearby
nuclear spins. In PMN-PT, we identify two populations: isotropic Pb$^{3+}$ centers and anisotropic Ti$^{3+}$ centers occupying $d$-orbitals, with
spin number densities of $(2.5 \pm 1.0) \times 10^{17}$ cm$^{-3}$ and $(4.1 \pm 1.7) \times 10^{17}$ cm$^{-3}$, respectively. Power-dependent EPR measurements enable extraction of
spin relaxation times. We investigate the ionization and recombination dynamics of these transient paramagnetic centers. Using saturation-recovery
nuclear magnetic resonance, we demonstrate that
laser illumination reduces the $^{207}$Pb
nuclear $T_1$ by approximately a factor of two, from $(17 \pm 2)$ s to $(7 \pm 1)$ s at 4.6 MHz, and from $(1550 \pm 40)$ s to $(850 \pm 70)$ s at 40 MHz. We develop a model relating the
nuclear relaxation rate to the density of photoinduced paramagnetic centers. This optical control of
nuclear spin relaxation provides a pathway toward accelerated thermal polarization and dynamic
nuclear polarization in solid-state NMR-based precision measurements, including searches for
axion-like dark matter.
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All authors János Ádám, Andrew J. Winter, Deniz Aybas, Dmitry Budker, Derek F. Jackson Kimball, Arne Wickenbrock, Alexander O. Sushkov
Materials Science
Electronic structures of spin-orbit-coupled metal candidate PbRe$_2$O$_6$: one dimensionality and molecular orbital formation
Yuki Yanagi and Michi-To Suzuki
We present a first-principles investigation of the electronic structure of the inversion-
symmetry-broken
spin-orbit-coupled metal candidate PbRe$_2$O$_6$. Our calculations reveal that the
Fermi surfaces derived from the $d_{yz}$ and $d_{zx}$ orbitals exhibit pronounced one-dimensional characteristics, which naturally account for the highly anisotropic charge transport observed experimentally. In addition, the $d_{x^2-y^2}$ orbitals on each Re haxagon form molecular orbitals, where the resulting $E_g$ molecular states generate nearly dispersionless bands in close proximity to the
Fermi level. The coexistence of these quasi-1D
Fermi surfaces and molecular-orbital-induced flat bands provides a possible microscopic origin for the successive phase transitions observed in PbRe$_2$O$_6$.
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Strongly Correlated Electrons
The odd-parity altermagnetism induced reconstruction of the Chern-insulating phase in Haldane-Hubbard model
Minghuan Zeng, Zheng Qin, Ling Qin et al. (+4 more)
Odd-parity altermagnetism(ALM) extends compensated collinear magnetism beyond the even-parity
spin splitting of conventional altermagnets, but its role in correlated topological phases remains largely unexplored. Using the cluster slave-
spin method, we show that the odd-parity ALM appearing in the ALM Chern-insulating phase of Haldane-Hubbard model significantly reconstructs the local
topology in the conventional Chern-insulating phase, while the total Chern number remains unchanged compared to the Chern-insulating phase. The Berry
curvature becomes
spin and valley selective; zigzag ribbons develop
chiral-
symmetry-breaking edge states; while armchair ribbons remain inversion symmetric. The optical response mirrors this separation between the local reconstruction and the global
topology: low-energy spectra are governed by quasiparticles near the gap, whereas the low-frequency
Hall conductivity stays quantized, $\sigma_{\rm T\uparrow}(\Omega\to 0)=\sigma_{\rm T\downarrow}(\Omega\to 0)=e^2/h$. These results establish the Haldane-Hubbard model as a minimal correlated platform for odd-parity altermagnetic
topology.
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All authors Minghuan Zeng, Zheng Qin, Ling Qin, Shiping Feng, Jia-Cheng He, Dong-Hui Xu, Rui Wang
Mesoscale and Nanoscale Physics
Temporal hopping dynamics in exciton-polariton condensation
Elena Rozas, Wojciech Bukalski, Yannik Brune et al. (+9 more)
Polariton condensates provide a versatile platform for exploring non-
equilibrium phase transitions and collective phenomena in open
quantum systems. Near the condensation threshold, these systems are particularly sensitive to fluctuations and instabilities, which can strongly influence the condensate formation. Using optical trapping and homodyne detection, we directly access the
photon statistics and second-order correlation function $g^{(2)}(0)$ of the condensate. We show that polariton condensation near the threshold is not a purely static transition, but instead undergoes a dynamical regime characterized by
stochastic hopping between condensed and non-condensed states. These intermittent dynamics are accompanied by a gradual reduction of $g^{(2)}(0)$ towards unity, revealing the progressive build-up of coherence even in the presence of strong temporal fluctuations. Numerical simulations, based on a
stochastic Truncated Wigner description of the driven-dissipative polariton field, reproduce these dynamics and capture the essential role of noise and reservoir interactions. This work demonstrates that the observed temporal hopping is an intrinsic feature of polariton condensation, providing a dynamical perspective that goes beyond static descriptions of the condensation phase transition.
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All authors Elena Rozas, Wojciech Bukalski, Yannik Brune, Adbhut Gupta, Kirk Baldwin, Loren N. Pfeiffer, Hassan Alnatah, Jonathan Beaumariage, David W. Snoke, Paolo Comaron, Marzena H. Szymanska, Marc Aßmann
Superconductivity
Critical Role of Hydrogen in Unconventional Superconductors: The Case of Hydrogenated FeSe Layers
Lan-Lin Du, Yang Yang, Shiqi Hu et al. (+1 more)
Hydrogenation is known to tune superconductivity in a wide range of materials. While its microscopic role has been clarified in
phonon-mediated
superconductors such as hydrogenated MgB2, LaH10, and H3S, much less is known for hydrogenated cuprates and iron-based
superconductors, where even the underlying structural motifs remain elusive. Using hydrogenated FeSe as a prototypical example, we reveal how hydrogen affects superconductivity in the presence of strong electronic correlations: correlation-induced orbital renormalization shifts hydrogen-derived spectral weight from the high-energy region toward the
Fermi surface (FS), remarkably enhancing the electron-
phonon coupling (EPC). We predict a structurally stable FeSeH phase where, compared to bare FeSe, hydrogen incorporation reshapes the FS
topology and increases the number of channels for electron-
phonon scattering, while simultaneously introducing high-frequency
phonons that strengthen pairing. First-principles EPC calculations combined with dynamical mean field theory (DMFT) yield a superconducting transition temperature (Tc) exceeding 40 K. Fully anisotropic Eliashberg theory reveals a two-gap superconducting state, consistent with the gap structure experimentally observed in doped FeSe. Our findings identify correlation-enhanced EPC as a plausible microscopic mechanism for iron-based superconductivity and offer a new perspective on pairing in strongly correlated systems. In addition, this work establishes hydrogenated FeSe as a promising platform for engineering two-dimensional
superconductors and superconducting
quantum devices.
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All authors Lan-Lin Du, Yang Yang, Shiqi Hu, Sheng Meng
Soft Condensed Matter
Fundamental picture of the conduction mechanism in solid-state polymer electrolytes revealed by terahertz spectroscopy
Johanna Weidelt, Jijeesh Ravi Nair, Diddo Diddens et al. (+9 more)
Solid
polymer electrolytes (SPEs) based on cross-linked poly(ethylene
oxide) (PEO) encompassing lithium salts have gained significant
attention as separators in solid-state lithium metal batteries. Here, we employ terahertz time-domain spectroscopy (THz-TDS), as a noninvasive contact-free technique, to investigate the conduction properties of these cross-linked SPEs and unravel their dependencies on the added lithium salt and the sample temperature. The obtained THz conductivity spectra are dominated by THz absorption bands, which we attribute to resonant vibrations within the
polymer matrix of the electrolyte. By careful application of Lorentz model, the conductivity spectra have been analyzed, and the relevant
polymer vibration modes have been quantitatively assessed. Calculations based on the density functional theory (DFT) were performed to elucidate the possible microscopic mechanisms of these resonant vibrations. This study sheds light on the relevance of
polymer matrix vibrations validating the hopping transport of lithium ions in SPEs which ultimately leads to the technologically relevant ionic conduction in the solid-state
polymer-based electrolytes.
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All authors Johanna Weidelt, Jijeesh Ravi Nair, Diddo Diddens, Wentao Zhang, Felix Pfeiffer, Tiago de Oliveira Schneider, Markus Meinert, Tomoki Hiraoka, Linda Nesterov, Masoud Baghernejad, Dmitry Turchinovich, Hassan A. Hafez