Strongly Correlated Electrons
Fermion condensation in a generalized Hatsugai-Kohmoto model with momentum-mixing Landau interactions
Jan Heinrich, Andreas Rückriegel and Peter Kopietz
The Hatsugai-Kohmoto (HK) model is an exactly solvable electronic
lattice model where the interaction between electrons with opposite
spin is diagonal in momentum space. We generalize the HK model by introducing momentum-mixing Landau interactions. Within a self-consistent mean-field analysis we find that the ground state of this model exhibits a partially flat energy band, in agreement with the
fermion condensation scenario proposed by Khodel and Shaginyan [JETP Lett. 51, 553 (1990)]. Inspired by Andersons pseudospin formulation of BCS theory, we show that the HK model with Landau interactions can be mapped onto a generalized Ising model where each site of the reciprocal
lattice hosts two Ising
spins. In the pseudospin picture the emergence of a partially flat electronic band corresponds to the smoothing of a
magnetic domain wall. Moreover, guided by the pseudospin picture, we propose an exactly solvable variant of the HK model which has a unique ground state for all densities.
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Disordered Systems and Neural Networks
Random Matrix Spectra from Boltzmann-Weighted Lattice Ensembles
Yaprak Önder, Abbas Ali Saberi and Roderich Moessner
We introduce a random
matrix framework for studying statistical-mechanical
lattice systems through spectral observables.
Equilibrium configurations sampled from a Boltzmann measure are mapped to
matrix ensembles whose covariance structure is inherited from the spatial correlations of the underlying model. This construction maps real-space correlation functions to a momentum-space variance profile, providing a direct bridge between statistical-mechanical correlations and correlated random
matrix ensembles. We derive this variance profile in finite-correlation-length and critical regimes, and compute spectral moments within a Wick-contraction expansion. A complementary self-consistent description of the bulk density is developed using the resolvent formalism. These analytical methods are benchmarked against Monte Carlo data for the two-dimensional Ising model and three-dimensional Edwards–Anderson
spin glasses. In both cases, the spectra evolve from the semicircle law at high temperature to model-dependent critical forms reflecting the structure of correlations. The framework, therefore, provides a quantitative spectral route to probing collective behavior in ordered and disordered statistical systems, while also defining a class of physically motivated correlated random
matrix ensembles.
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Mesoscale and Nanoscale Physics
Stacking-order-dependent electronic properties of MoTe2/WSe2 moiré bilayers
Zhongdong Han, Wenjin Zhao, Eegene Clara Chung et al. (+17 more)
Transition metal dichalcogenide (TMD) moiré
bilayers have realized a wide range of strongly correlated and topological phenomena. The physics in these materials is often sensitive to the interlayer stacking order. Polarization-resolved optical second harmonic generation (SHG) is the most used technique for stacking order characterization but unverified for most heterobilayers. Here we calibrate the optical SHG for angle-aligned MoTe2/WSe2
bilayers by the scanning transmission electron microscopy (STEM). We directly compare the transport and
magnetic properties and the electronic phase diagram for two distinct stacking orders. With the calibrated stacking order assignment, we clarify the interpretation of earlier results, including the nature of the Chern
insulator, mechanism of an electric-field-tuned metal-
insulator transition at half band filling, and the Kondo
lattice physics. Our work provides a consistent picture of the relation between the stacking order and the electronic properties of MoTe2/WSe2 moiré
bilayers.
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All authors Zhongdong Han, Wenjin Zhao, Eegene Clara Chung, Chia-Hao Lee, Zui Tao, Zhengchao Xia, Yichi Zhang, Yiyu Xia, Jekwan Lee, Bowen Shen, Ariana Ray, Yu-Tsun Shao, Tingxin Li, Shengwei Jiang, Yihang Zeng, Kenji Watanabe, Takashi Taniguchi, David Muller, Kin Fai Mak, Jie Shan
Mesoscale and Nanoscale Physics
Destructive interference of second harmonic generation in AA stacked MoTe$_2$/WSe$_2$
Yiduo Wang, Yao Lu, Changshen Chen et al. (+14 more)
The stacking configuration of two-dimensional materials critically governs their optical and electronic responses. Monolayer transition-metal dichalcogenides (TMDC) lack inversion
symmetry and exhibit
exciton-enhanced second-harmonic generation (SHG). In TMDC
bilayers, 60{\deg} (0{\deg}) stacking is conventionally expected to suppress (enhance) SHG owing to destructive (constructive) interference of the layer-resolved nonlinear polarizations. Here, we report an unconventional destructive SHG interference in nearly 0{\deg}-stacked (AA-stacked) MoTe2/WSe2 heterobilayers using two independent probes: atomic-resolution imaging and stacking-sensitive
exciton hybridization measurements. Supported by ab initio GW and Bethe-Salpeter equation calculations, we show that distinct two-
photon resonances associated with the WSe2 C
exciton and the MoTe2 D
exciton generate a nearly $\pi$ phase difference ($\Delta\phi$) in their second-order nonlinear susceptibilities $\chi^{(2)}$, leading to the anomalous destructive interference. We further demonstrate that in small-angle twisted MoTe2/WSe2, the SHG polarization state is governed by the interplay between twist angle $\alpha$ and phase difference $\Delta\phi$, and can be mapped onto trajectories on the Poincaré sphere. At excitation energies satisfying $\Delta\phi$ + 3$\alpha$ = 180{\deg}, the SHG output becomes nearly circularly polarized (ellipticity ~ 0.91) and undergoes an abrupt 90{\deg} azimuthal rotation, corresponding to a
geometric polarization singularity in the parameter space. Our findings open new routes for
exciton-resonance engineered nonlinear photonics and stacking-resolved optical functionality in moiré materials.
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All authors Yiduo Wang, Yao Lu, Changshen Chen, Xiaotong Liao, Siyu Fan, Zhenyu Wang, Yaotian Liu, Subi Du, Yingze Jia, Ye Zhu, Yingwei Wang, Jun He, Song Liu, Jiawei Ruan, Zhen Chen, Kai-Qiang Lin, Yang Xu
Mesoscale and Nanoscale Physics
Probing topological phase transitions via nonlinear Hall response in strained moiré dice lattice
Gourab Paul, Srijata Lahiri, Bilal Tanatar et al. (+1 more)
Valley polarized twisted
bilayer dice
lattice hosts topologically nontrivial flat bands far from charge neutrality due to broken time reversal
symmetry, whereas the ones in the vicinity of it remain topologically trivial. However, when both valleys are taken into consideration, the time reversal
symmetry is preserved, which poses a serious hindrance to enumerate the valley specific topological phases that rely on the detection of the Berry
curvature. In this work, we demonstrate that such a twisted structure with an applied uniaxial strain exhibits a nonlinear
Hall effect far from charge neutrality. We ascertain that the nonlinear anomalous
Hall signals can serve as a probe for topological phase transitions associated with a specific energy state that is constrained to reside at the lower edge of the middle subband and controlled via a staggered mass. Specifically, we show that the nonlinear anomalous
Hall response undergoes a sign reversal across the topological phase boundaries. By tuning the carrier density, we compute the nonlinear
Hall response obtained from the Berry
curvature dipole, both in the
chiral limit, and also when the
chiral symmetry is broken. It is further seen that the nonlinear
Hall effect is significantly enhanced in the broken
chiral symmetry regime.
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All authors Gourab Paul, Srijata Lahiri, Bilal Tanatar, Saurabh Basu
Materials Science
Shear-Mode Raman Imaging of Ferroelectric Switching in Multilayer 3$R$-MoS$_2$
Yulu Liu, Kenji Watanabe, Takashi Taniguchi et al. (+1 more)
We use shear-mode Raman imaging to track ferroelectric switching in multilayer 3$R$-MoS$_2$. Within a single flake, mechanically segmented regions respond independently and follow distinct pathways. Partially polarized end states indicate that domain walls can reside between selected layer pairs, producing partial stacking transformations. The dwell time of intermediate states varies widely, indicating that pinning sites strongly influence the dynamics. Second-harmonic generation measurements further reveal three characteristic sample-boundary and domain-wall orientations, including a prevalent
chiral direction near the zigzag-armchair bisector. These results provide a direct, noninvasive view of domain-wall-mediated switching in a prototypical sliding ferroelectric and identify pinning and exfoliation-created boundaries as key factors governing its dynamics.
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All authors Yulu Liu, Kenji Watanabe, Takashi Taniguchi, Xiaoxiang Xi
Materials Science
Oxygen-Pressure-Limited Recovery of the Hematite {\alpha}-Fe$_2$O$_3$(0001) Surface from a Reduced Fe$_3$O$_4$(111)-Like Layer
Nishant Kumar, Matthias Blatnik and Jan Čechal
The oxidation kinetics of hematite {\alpha}-Fe$_2$O$_3$(0001) surfaces are vital for its applications in catalysis, environmental remediation, and industrial processes. Despite prior studies, the roles of temperature, oxygen partial pressure, and oxygen chemical potential in controlling nucleation and growth kinetics are not fully understood. Using real-time Low Energy Electron Microscopy/Diffraction (LEEM/LEED), we systematically investigate the oxidation of a reduced Fe$_3$O$_4$(111)-like surface layer to hematite under controlled conditions. We show that complete recovery of the hematite surface termination is closely linked to the nucleation and lateral growth of a two-dimensional honeycomb (H) phase. While higher temperatures accelerate nucleation, they slow lateral growth at constant oxygen pressure, indicating that oxygen supply limits the oxidation rate. Below an oxygen partial pressure threshold (~2$\times$10$^{-6}$ mbar), growth dramatically slows, underscoring the critical role of oxygen availability. Below a certain oxygen pressure threshold, the growth time rapidly increases. Our study elucidates the interplay between thermodynamics and kinetics in hematite surface oxidation, informing strategies to optimize surface properties for catalytic and industrial processes.
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Materials Science
Observation of spin-free interatomic orbital angular momentum in a chiral crystal
Dongjin Oh, Sungsoo Hahn, Chiara Pacella et al. (+4 more)
The inherent
spin-orbit interaction of electrons inevitably couples
spin to the orbital angular momentum (OAM), posing a fundamental challenge to
spin-free orbital transport. Here, we propose a novel strategy to achieve
spin-decoupled OAM states in crystalline solids. Using angle-resolved photoemission spectroscopy (ARPES), we resolve well-isolated s-orbital bands in a
chiral Te
crystal, clearly separated from the p-orbital
manifold. Combined circular dichroism ARPES and first-principles calculations reveal that these bands host OAM arising exclusively from interatomic hopping, with no intra-atomic contribution.
Spin-resolved ARPES further confirms the absence of
spin angular momentum (SAM), providing decisive evidence of
spin-free OAM states. These findings establish the existence of OAM without
spin polarization in crystalline solids and highlight the essential role of inter-atomic OAM. This work provides a general framework for designing spinless OAM states, opening an opportunity toward pure orbital currents for orbitronics.
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All authors Dongjin Oh, Sungsoo Hahn, Chiara Pacella, Junseo Yoo, Angel Rubio, Domenico Di Sante, Changyoung Kim
Strongly Correlated Electrons
Magnetism of single crystalline breathing pyrochlore spinel AgInCr4S8
Andrew F. May, Christopher M. Pasco, V. O. Garlea et al. (+5 more)
Single
crystals of \ce{AgInCr4S8} were grown by chemical vapor transport and crystallographic ordering of Ag/In that results in a breathing pyrochlore motif of Cr$^{3+}$ was verified by x-ray and
neutron diffraction. Long-range
antiferromagnetic order is observed below a Néel temperature of $T_{\mathrm N}$ $\approx$ 9.6 K. The
magnetic properties are characterized using ac and dc magnetization, specific heat capacity, and single
crystal neutron diffraction measurements. The specific heat data are characterized by a small lambda anomaly near 9.5 K and the estimated
magnetic entropy reaches $\approx$ $\frac{1}{3}$ of the expected value by 3$T_{\mathrm N}$, suggesting significant short-range order in the paramagnetic phase. Single
crystal neutron diffraction evidences an incommensurate
spin structure with propagation vector $\textbf{\textit{k}}$ = (0,0,$\delta$) and $\delta$ = 0.343 at 5 K. The minimal model that accounts for the data consists of
ferromagnetic layers of Cr atoms, with
magnetic moments lying in the plane of the layers and modulating in the perpendicular direction to form a helical structure propagating along $\textbf{\textit{k}}$. This study represents a rare investigation of single
crystals within the family of breathing pyrochlore materials.
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All authors Andrew F. May, Christopher M. Pasco, V. O. Garlea, Karolina Gornicka, Matthias D. Frontzek, Xiaoping Wang, Pyeongjae Park, Andrew D. Christianson
Mesoscale and Nanoscale Physics
Xin Theng Lee, Xin Hu, Yuya Ominato et al. (+3 more)
In this work, we theoretically investigate the
spin-Peltier effect in a
heterostructure composed of
graphene and a
ferromagnetic insulator (FI). Using a microscopic formalism based on the characteristic
spin-flip scattering length at the
graphene/FI interface, we analyze how
spin accumulation in
graphene gives rise to a temperature difference across the junction. We show that, in the presence of an external
magnetic field, the electronic spectrum of
graphene is quantized into Landau levels, which strongly modifies the available
spin-flip scattering channels. In particular, crossings between Landau levels significantly enhance the
spin-flip scattering amplitude, leading to a pronounced amplification of the
spin-Peltier response. Our results suggest that measurements of the
spin-induced temperature difference in
graphene-FI
heterostructures can serve as a sensitive probe of discrete electronic energy levels. More broadly, this work provides a theoretical framework for understanding
spin-driven thermal effects in hybrid systems combining Dirac materials and
magnetic insulators.
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All authors Xin Theng Lee, Xin Hu, Yuya Ominato, Masahiro Tatsuno, Takeo Kato, Mamoru Matsuo
Statistical Mechanics · Cross-listed from gr-qc
Thermodynamics of homogeneous Universes: de Sitter, Bonnor-Melvin and static Einstein
G.E. Volovik
In the theories, in which dynamic gravitational field emerges from the underlying matter fields, the gravitational field can be considered as a part of matter. Using this approach, we construct the thermodynamics of the homogeneous Universes – the de Sitter Universe, the Bonnor-Melvin-$\Lambda$ Universe and the static Einstein Universe. It is demonstrated that although these three Universes have different types of matter fields (ordinary matter,
magnetic field, gravitational field and
vacuum energy), they have the same thermodynamic properties. Their energy densities obey the same equation, which contains the corresponding matter densities and the pairs of the thermodynamically conjugate variables. In Minkowski
vacuum, where the ordinary matter and
magnetic and gravitational fields are absent, this thermodynamic approach automatically leads to zero cosmological constant.
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Materials Science · Cross-listed from quant-ph
Towards transistor-based quantum computing
Y.-D. Liu, X. Xu, Q.-R. Wang et al. (+1 more)
In this work, we propose and study in depth a universal
quantum computing architecture based on a
quantum construction of transistors. Our teleportation-based
quantum transistors, called “telesistors”, are ground states of systems with
symmetry-protected topological order, hence suppress certain noises and provide high-fidelity Clifford gates without the need for active error correction. This physical protection, quantified by the string order parameters, serves as a low-overhead foundation upon which conventional fault-tolerant encoding (e.g., with stabilizer codes) can be built to achieve universal
quantum computation. This architecture shows rich connections with current known architectures, and some desirable merits especially compared with the
qubit-based
circuits regarding modularity, integration, and program storage. Our study shows that it is plausible to realize it with current technology in the near future.
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All authors Y.-D. Liu, X. Xu, Q.-R. Wang, D.-S. Wang
Materials Science
Efficient purely organic phosphorescent emitters for programmable luminescent tags: from building blocks to donor-acceptor-donor structures
Uliana Tsiko, Sebastian Kaiser, Jannis Fidelius et al. (+4 more)
Purely organic room-temperature phosphorescence (RTP) emitters are key components of programmable luminescent tags (PLTs), photonic devices for rewritable information storage and UV dosimetry. In this work, we systematically explore the design space of donor-acceptor and donor-acceptor-donor organic phosphorescent emitters in symmetric and asymmetric architectures. Phenoxathiine (PX) is introduced as an alternative donor to thianthrene (TA), combined with benzophenone (BP) or pyridine (Py) as acceptors. Through photophysical characterization,
quantum chemical simulations, and PLT device testing, we identify structure-property relationships and, in particular, investigate the impact of the individual moieties on the emission properties and stability. The RTP emission wavelength is primarily tunable through the donor moiety: PX-based emitters emit sky-blue ({\lambda}_P = 480 nm), while TA-based emitters emit in the green ({\lambda}_P = 520 nm) due to an increased Stokes shift. The acceptor unit strongly influences the phosphorescence
quantum yield, with Py-based emitters systematically outperforming BP-based ones. All newly synthesized PX-containing emitters show sufficient performance in PLT devices, though with reduced photostability compared to TA-based counterparts. Together, these results demonstrate that systematic donor-acceptor design enables predictable control over RTP emission properties, advancing the rational development of high-performance RTP-based photonic devices.
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All authors Uliana Tsiko, Sebastian Kaiser, Jannis Fidelius, Tim Achenbach, Jan J. Weigand, Sebastian Reineke, Karl Sebastian Schellhammer
Soft Condensed Matter
Microscopic Nonaffine Deformation Theory of LAOS in Polymers
Dario Nichetti and Alessio Zaccone
We develop a molecularly motivated framework connecting large-amplitude oscillatory shear (LAOS) nonlinearities in entangled
polymers to frequency-dependent nonaffine relaxation in disordered solids. The central idea is that the first harmonic in LAOS measures the residual phase-locked elastic response, whereas the higher harmonics encode the
Fourier signature of strain-dependent nonaffine relaxation. The finite-amplitude modulus is interpreted as a local tangent stiffness of the evolving microstructure, in the spirit of elastoplastic and incremental nonaffine models. For entangled
polymers, the analogue of the decreasing coordination number in cage-breaking theories of glass mechanics is identified not with the tube-orientation tensor itself, but with the fraction of surviving tube constraints. This distinction leads naturally to a crossover description controlled by a characteristic strain amplitude $\gamma_c$, rather than by universal fixed power-law exponents. The fitted value $N_{\max}\simeq1.72$ indicates that the present experimental data approach a strong but not fully saturated nonlinear state, remaining below the ideal limiting value predicted for complete constraint collapse. Finally, a constraint-counting argument combining an eight-chain affine network representation with the central-force nonaffine isostatic threshold gives a limiting estimate $|\mathrm{NLI}|_{\max}=3$. The results support the interpretation of the NLI as a
Fourier-resolved dynamic nonaffinity parameter and establish a bridge between tube-based
polymer dynamics, LAOS harmonic analysis, elastoplastic rheology, and microscopic nonaffine
lattice dynamics.
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Materials Science · Cross-listed from physics.optics
A Universal Magnetoelectric Limit for Chiral and Tellegen Bi-Isotropic Scatterers
Jorge Olmos-Trigo
We reveal the existence of a universal upper bound on the magnetoelectric coupling of any bi-isotropic nanoparticle. The bound arises solely from energy conservation, making it independent of the specific material properties of the nanoparticle and illumination conditions. Moreover, the bound does not rely on reciprocity, being identical for reciprocal (
chiral) and non-reciprocal (Tellegen) nanoparticles. We further show that the
chiral Mie coefficient of spherical particles of arbitrary optical size obeys the same bound across all multipolar scattering channels. Our results introduce a universal metric on the magnetoelectric coupling of bi-isotropic objects, setting identical limits on
chiral and Tellegen light-matter interactions at the single particle level.
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Other Condensed Matter
Properties of the skyrmion crystal SkX-2 in the Heisenberg triangular lattice with scalar chirality
H. Bocquet, C. J. Ganahl, M. Scheurer et al. (+2 more)
Skyrmion
crystals have been primarily discovered under a
magnetic field for materials with non-centrosymmetric interactions. More recent developments have investigated the stability of skyrmion
crystals in itinerant magnets without
magnetic field. In this study, we find that a type of skyrmion
crystal with two topological charges per unit
cell and no magnetization at the
ferromagnetic point in reciprocal space, SkX-2, is naturally stabilized in an $SO(3)$-symmetric model with short-range interactions realized by the Heisenberg model on the triangular
lattice with scalar chirality. We complement our numerical results with a theoretical analysis that quantitatively describes the transition from the
ferromagnetic ground state to the SkX-2 and the
evolution of the topological charge density. Despite the constraints given by the Mermin-Wagner
theorem at finite temperature, the SkX-2 exhibits both a first-order phase transition associated with translation
symmetry breaking and a continuous transition to a floating solid, depending on the charge density controlled by the model parameters. Finally, the tetrahedral phase supported by an
antiferromagnetic interaction in our model is found to host $\mathbb{Z}_2$-
vortices at finite temperature, suggesting the existence of an additional
vortex topological transition.
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All authors H. Bocquet, C. J. Ganahl, M. Scheurer, P. M. Derlet, A. M. Läuchli
Materials Science
Attached Split Ring Resonator Cavity for Magnon Photon Coupling
Aram Akoi, Liubov Ivzhenko and Maciej Krawczyk
We present a chip scale planar cavity platform based on an attached split ring resonator (ASRR) integrated with yttrium iron garnet (YIG) structures to achieve strong
magnon photon coupling in a compact hybrid system. The ASRR geometry was numerically optimized by tuning inter ring spacing, gap width, substrate thickness, and permittivity, resulting in a quality factor of Q = 190 at 5.48 GHz, enabling strong microwave
magnetic field confinement and reduced radiative losses. The optimized cavity was coupled to YIG elements of three geometries: full ring, half ring, and disk. Full electromagnetic simulations show that the full ring geometry exhibits balanced performance with coupling strength 115 MHz and cooperativity 13.10, while the half ring shows a comparable coupling strength of 108 MHz and slightly higher cooperativity 13.50, despite edge induced demagnetizing effects. In contrast, the disk geometry couples at lower bias
magnetic fields and achieves the strongest interaction (135 MHz, 25.30), enabled by improved microwave
magnetic field overlap. These results demonstrate that geometry, rather than
magnetic volume alone, is a key design parameter for tailoring
magnon photon coupling, providing a practical framework for lithography compatible, on chip hybrid magnonic and
quantum devices.
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Soft Condensed Matter
Thermodynamic and structural behavior of one-dimensional divalent patchy hard rods: Wertheim's first-order thermodynamic perturbation theory vs exact results
Ana M. Montero, Andrés Santos, Péter Gurin et al. (+1 more)
We investigate the thermodynamic and structural properties of divalent patchy hard rods confined to a one-dimensional channel by modeling the bonding sites as attractive square-well (SW) patches located at the rod tips. The zero-range sticky limit is recovered by letting the well width vanish while keeping the stickiness parameter finite. While Wertheim's first-order thermodynamic perturbation theory becomes exact in this sticky limit, it fails for finite-range site–site interactions. Because the present model is mathematically equivalent to an exactly solvable one-dimensional nearest-neighbor fluid, we use the exact solution to reformulate the thermodynamics in terms of association-theory variables, including the fraction of unbonded sites and a generalized law of mass action. Finite-range SW sites produce a richer structural behavior than sticky sites, including monotonic and oscillatory asymptotic decay of the pair correlation function, separated by the Fisher–Widom line. In the monotonic regime, the correlation length exhibits an absolute maximum defining the Widom line, while in the oscillatory regime it may display a local maximum and minimum, whose locus defines the “Extrema of the Correlation length under Oscillatory decay” line. These features disappear in the sticky limit, where the system remains entirely in the oscillatory regime. We also show that the high-pressure behavior of the correlation length changes from $\xi\sim p^2$ for finite-range SW sites to $\xi\sim p^3$ in the sticky limit.
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All authors Ana M. Montero, Andrés Santos, Péter Gurin, Szabolcs Varga
Statistical Mechanics
Competing anisotropies and phase transitions in the $q$-state clock model with a $p$-fold crystalline field
Milan Žukovič
We study the two-dimensional $q$-state clock model in the presence of an additional $p$-fold
symmetry-breaking crystalline field using Monte Carlo simulations. While the pure clock model exhibits Berezinskii–Kosterlitz–Thouless (BKT) transitions for sufficiently large $q$, the effect of competing discrete anisotropies on this topological phase remains nontrivial. We show that even weak crystalline fields qualitatively modify the phase diagram by suppressing the BKT phase and inducing transitions to states with true long-range order. The resulting behavior depends sensitively on the interplay between the intrinsic $\mathbb{Z}_q$
symmetry and the imposed $\mathbb{Z}_p$ anisotropy. In particular, in the six-state clock model for $p=2$ we observe qualitatively different scenarios depending on the sign of the field: a single transition for $h_2>0$ and a two-step ordering process for $h_2<0$ with an intermediate ordered phase. For $p=3$, the system exhibits a direct transition consistent with three-state Potts criticality. These results demonstrate that the phase structure cannot be inferred from
symmetry considerations alone, but is governed by the competition between distinct locking mechanisms. Our findings provide a discrete counterpart to the multi-frequency sine-Gordon description of generalized $XY$ models and illustrate how additional anisotropies reshape topological phase transitions in two dimensions.
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Materials Science
Multiferroic Properties of Electrospun CFO-BCTSn Nanocomposites for Magnetoelectric and Magnetic Field Sensing Applications
Youness Hadouch, Nayad Abdallah, Daoud Mezzane et al. (+11 more)
Multiferroic CFO-BCTSn composite nanofibers were synthesized using a sol-gel electrospinning method. Electron microscopy revealed well-defined fibers with diameters of 120-150 nm. Structural analyses using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy confirmed the coexistence of the spinel CFO phase and the perovskite BCTSn phase without detectable secondary phases.
Magnetic hysteresis measurements demonstrated the
magnetic behavior of the nanofibers, while piezoresponse force microscopy confirmed their piezoelectric properties. Magnetoelectric coupling was evidenced by differences between the
magnetic hysteresis loops of electrically poled and unpoled samples. These lead-free composite nanofibers show potential for nanoscale magnetoelectric devices and
magnetic field sensing applications.
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All authors Youness Hadouch, Nayad Abdallah, Daoud Mezzane, Mbarek Amjoud, Voicu Dolocan, Khalid Hoummada, Nikola Novak, Anna Razumnaya, Brigita Rozic, Val Fisinger, Hana Ursic, Valentin Laguta, Zdravko Kutnjak, Mimoun El Marssi
Strongly Correlated Electrons
Hubbard-$U$-corrected electron-phonon interactions in strongly correlated materials via the finite-displacement method
Jiale Chen, Youyou Tu, Chengliang Xia et al. (+2 more)
Although the density functional theory plus Hubbard $U$ correction method (DFT+$U$) is broadly used to study electronic structure of strongly correlated materials, the extension of this method to electron-
phonon $g$
matrices has received limited
attention. Here, we implement an
algorithm that integrates DFT+$U$ method with the finite-displacement method for the calculations of
phonons and electron-
phonon $g$
matrices. The Hubbard $U$ corrections are applied not only to electronic and
phonon structures, but, more importantly, also to electron-
phonon $g$
matrices. We demonstrate our
algorithm in two prototypical correlated materials: infinite-layer nickelates LaNiO$_2$ and ruthenium dioxide RuO$_2$. We find that: i) While the Hubbard $U$ corrections weakly increase the electron-
phonon interaction of 20% hole-doped LaNiO$_2$, its total electron-
phonon coupling remains small and is insufficient to account for the observed superconducting transition temperature of about 10-30 K. Our results contrast with the recent work showing that the full GW corrections yield an elevated electron-
phonon coupling of 20% hole-doped LaNiO$_2$ five times larger than its DFT value. We attribute this discrepancy to the differences in the
Fermi surface
topology between DFT+$U$ and GW methods. ii) The inclusion of Hubbard $U$ corrections eliminates the imaginary
phonon modes of RuO$_2$ under strain on the TiO$_2$ substrate and substantially reduces the electron-
phonon coupling. Our results alleviate the discrepancy between the reported large theoretical electron-
phonon coupling and the low superconducting transition temperature observed experimentally. Our work provides an
algorithm that fully includes the Hubbard $U$ corrections on electron-
phonon properties of correlated materials, and highlights the importance of
Fermi surface shape and correlation effects on
phonon spectrum and electron-
phonon $g$
matrices.
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All authors Jiale Chen, Youyou Tu, Chengliang Xia, Jin Zhao, Hanghui Chen
Statistical Mechanics · Cross-listed from physics.soc-ph
Equilibrium and dynamics of a three-state opinion model on a network of networks
Irene Ferri, Albert Díaz-Guilera and Hiroki Sayama
Opinion formation models typically represent each individual as a single variable. However, in practice each individual holds interconnected beliefs whose internal organization may influence collective outcomes. To explore this dependence, we study a three-state opinion model on a network of networks in which each
agent has an internal belief graph and interacts with other
agents through an external social graph. Each belief can take two opposite polarized states or a neutral one and a neutrality parameter tunes the relative conviction of the neutral stance. We incorporate temperature into the model to account for external social agitation and for the tolerance of internal cognitive dissonance. We explore the stationary state and dynamics of the model using analytical approaches and Monte Carlo simulations on a fully connected external social graph, with internal belief
topologies given by one-dimensional chains, cliques, and
star-like structures, where there is a central core belief to which all other beliefs are connected. We find that the critical temperature at which the polarized consensus destabilizes increases with the addition of more beliefs to
star-like
agents but saturates in the case of ring- and clique-like internal
topologies. We also consider binary mixtures of
agents with different internal
topologies in equal proportions, showing that the interplay between
agents is regime-dependent, with the dominant
topology depending on the value of the neutrality parameter.
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Materials Science
In-Plane Ferromagnetism and Critical Dynamics in Alkali-Deficient K$_{1-x}$CrTe$_2$ (with $x \approx$ 0.3) Single Crystals
Catherine Witteveen, Felix Eder, Sara A. López-Paz et al. (+6 more)
Layered chromium tellurides are model systems for studying low-dimensional magnetism in van der Waals materials. We report the synthesis and characterization of K$_{1-x}$CrTe$_2$ single
crystals ($x \approx 0.3$), which crystallize in the $Cm$ space group with trigonal prismatic K$^+$ coordination, unlike the octahedral environments of more stoichiometric ACrX$_2$ compounds. Magnetization measurements show a sharp
ferromagnetic transition at $T_{\rm C}=117$ K and in-plane
magnetic anisotropy, supported by density functional theory.
Neutron diffraction reveals
ferromagnetic alignment of Cr
spins within and between layers. This contrasts with the out-of-plane A-type antiferromagnetism in LiCrTe$_2$ and NaCrTe$_2$, but resembles CrTe$_2$. These differences likely arise from changes in interlayer spacing, Cr oxidation state, or stacking. AC susceptibility and $\mu$SR indicate short-range order above $T_{\rm C}$ and dynamic behavior below. Overall, K$_{1-x}$CrTe$_2$ provides a tunable platform for studying
spin orientation and dimensionality in two-dimensional magnets.
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All authors Catherine Witteveen, Felix Eder, Sara A. López-Paz, Vladimir Pomjakushin, Jonas A. Krieger, Zurab Guguchia, Harald O. Jeschke, Martin Månsson, Fabian O. von Rohr
Superconductivity
Multiple Superconducting Phases in Palladium Deuteride Induced by Nuclear-Spin Isotope Effect
Ryoma Kato, Ten-ichiro Yoshida, Riku Iimori et al. (+5 more)
We study the superconducting properties of high-quality PdD$_{x}$ films. The resistivity shows a sharp drop at $T$ $\sim$1.7 K, marking the superconducting transition. However, a finite resistivity persists and vanishes at $\sim$0.6 K. The temperature and
magnetic-field dependences of the resistivity exhibit multiple anomalies within the superconducting state, revealing distinct superconducting phases. Such anomalies are absent in PdH$_{x}$ films. These results demonstrate a clear qualitative difference between the superconducting phase diagrams of PdD$_{x}$ and PdH$_{x}$, highlighting the role of
nuclear-
spin isotope effects.
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All authors Ryoma Kato, Ten-ichiro Yoshida, Riku Iimori, Masanobu Shiga, Yuji Inagaki, Takashi Kimura, Koichiro Ienaga, Tatsuya Kawae
Soft Condensed Matter
Origin of Persistent Boundary Motion in Confined Active Matter
Elsa Baby, Manoj Gopalakrishnan and Vishwas V. Vasisht
Active matter systems under confinement display persistent surface motion and a strong boundary affinity. However, despite extensive studies of their positional dynamics, much less
attention has been given to the corresponding orientational behavior. Here, using molecular simulations of an active Brownian particle confined within a hard circular boundary and the Fokker-Planck equation, we show that the positional distribution of the particle is directly coupled to orientational fluctuations, as characterized by the conditional orientational distribution. Confinement generates two preferred tangential orientational states connected by
stochastic flipping pathways: rapid boundary-localized switching and slower bulk-mediated excursions. Further, the positional distribution exhibits a nontrivial power-law decay with distance from the boundary that is closely linked to
curvature-induced bistable orientational states and the variance of the associated conditional distribution. The mean waiting time between flips exhibits power-law dependence on the confinement strength. Our results establish that the interplay between orientational fluctuations, bistability, positional accumulation, and
stochastic switching governs the observed dynamics of active particles under confinement, providing a framework for understanding transport, exploration, and escape processes in confined active systems.
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Quantum Gases · Cross-listed from quant-ph
Symmetry-Induced Relaxation Comb and Strong Quantum Mpemba Effect in Long-Range XXZ Spin Chains
Zijun Wei, Mingdi Xu, Yefeng Song et al. (+3 more)
We uncover a
symmetry-filtered mechanism for anomalous dissipative relaxation in a long-range XXZ
spin chain subject to local dephasing. At the isotropic point, the coherent
Hamiltonian has global $SU(2)$
symmetry, whereas the full Liouvillian retains only the $U(1)$
symmetry associated with total magnetization. This structure pins a family of spatially uniform zero-$U(1)$-charge left eigenoperators with exact
eigenvalues $\lambda=-2q$, forming a Liouvillian relaxation comb. For the
ferromagnetic Dicke ground state, the overlap envelope on this comb is known exactly at finite size and becomes Gaussian in the large-$S$ limit. Since higher-$q$ components decay rapidly, the $q=1$ comb tooth controls the long-time dynamics and yields universal $D(t)\sim e^{-2t}$ relaxation independent of system size and interaction range. This mode-accessibility filtering realizes a spectral strong
quantum Mpemba effect: an initially farther state relaxes faster than closer thermal states because slow non-steady Liouvillian modes are inaccessible. Weak breaking of the
Hamiltonian $SU(2)$
symmetry restores slow-mode overlap and suppresses this acceleration.
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All authors Zijun Wei, Mingdi Xu, Yefeng Song, Xiang-Ping Jiang, Yangqian Yan, Lei Pan
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Spin-polarized lasing in a photonic lattice
A. Herrero Otermin, N. Carlon Zambon, A. Bieganowska et al. (+3 more)
We characterize
spin-polarized lasing in a two-dimensional photonic
lattice fabricated from a GaAs/InGaAs
semiconductor microcavity sample. The
lattice is defined by a staggered arrangement of rounded rectangular micrometric mesas that laterally confine and couple the optical modes. Polarization-, angle-, and energy-resolved micro-photoluminescence measurements reveal the transition from the strong-coupling regime to
photon lasing, accompanied by extended spatial coherence across several
lattice unit
cells. Under circularly polarized nonresonant excitation, the emitted light acquires a controllable circular polarization whose handedness follows that of the pump. These results establish photonic-
lattice VCSELs as a platform for
spin-controlled coherent emission in extended optical systems.
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All authors A. Herrero Otermin, N. Carlon Zambon, A. Bieganowska, F. Jabeen, L. Viña, C. Antón-Solanas
Materials Science
High-performance linear-scaling electronic structure method via chromatic superposition states
Zhikang Jiang, Zhizhi Xiao, Mingfa Tang et al. (+4 more)
We introduce a high-performance linear-scaling electronic structure method that employs chromatic superposition states (CSS) as a low-dimensional, high-fidelity representation, which can be orders of magnitude smaller than the full
Hilbert space. Grounded in the system's finite correlation length, the CSS representation aggregates the uncorrelated orbitals into a single basis via a graph-coloring scheme, and is independent of the system size yet accurately preserves all sparse operators in solving the Kohn-Sham equations. The projection onto CSSs is efficiently computed by employing the block-Lanczos Krylov method which features high hardware efficiency and linear-scaling cost, enabling fast calculation of large-scale Kohn-Sham density
matrix. We show that this method already outperforms previous linear-scaling density
matrix purification method by more than one order of magnitude in computational speed at even small scale, while preserving high accuracy. The practical utility of the CSS method is demonstrated through molecular dynamics simulation of a 10000 $H_2O$, and self-consistent calculation of a 1-million $H_2O$ with modest resources.
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All authors Zhikang Jiang, Zhizhi Xiao, Mingfa Tang, Weiyu Li, Zhaoru Sun, Ke Xia, Youqi Ke
Strongly Correlated Electrons · Cross-listed from hep-th
Chaos-Integrability Transition in the BPS Subspace of the $\mathcal{N}=2$ SYK Model
Leon Miyahara and Shono Shibuya
We study chaos-integrability transition purely within a BPS subspace of a specific supersymmetric model that interpolates between the chaotic $\mathcal{N}=2$ SYK model and an integrable $\mathcal{N}=2$ "commuting" SYK model. Using the framework of BPS chaos, we analyze the spectrum of an operator projected onto the BPS subspace. We numerically find that its spectral statistics exhibit random-
matrix behavior near the SYK limit and smoothly transitions to Poisson statistics near the integrable limit. Our results provide a direct example of a chaos-integrability crossover diagnosed solely from BPS states.
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Materials Science
Topological phononics
Zeguo Chen, Tiantian Zhang, Xulong Wang et al. (+12 more)
Topological phononics extends the foundational concepts of topological condensed matter physics to the realm of
lattice vibrations and classical mechanical waves, unlocking robust, defect-immune states and phenomena beyond the reach of conventional phononic engineering. This review provides a unified, systematic framework for understanding topological
phonons across natural and artificial systems, spanning solid-state materials, acoustic/mechanical metamaterials, and non-Hermitian platforms. We cover the core theoretical principles – from Berry
curvature and
symmetry-protected topological invariants to bulk-boundary correspondence – alongside experimental advances in probing topological
phonon states via inelastic scattering and momentum-resolved techniques for solid-state
phonons as well as pump-probe measurements in acoustic/mechanical metamaterials. Key topics include Weyl/Dirac/nodal-line
phonons in crystalline solids,
symmetry-engineered topological phases in metamaterials, non-Hermitian effects (exceptional points, skin effect), and emergent directions such as Floquet engineering, synthetic dimensions, and real-space topological textures (skyrmions, merons). We also highlight technological applications in robust waveguides, on-chip surface-acoustic-wave devices, and acoustofluidics, while outlining future challenges and opportunities in
quantum phononics, nonlinear topological phenomena, and interdisciplinary integration with photonics and electronics. This review serves as a comprehensive guide across physics, materials science, and engineering, bridging fundamental theory with cutting-edge experiments and innovations in topological phononics.
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All authors Zeguo Chen, Tiantian Zhang, Xulong Wang, Jiangxu Li, Zhi-Kang Lin, Feng Gao, Li-Wei Wang, Yizhou Liu, Qi Wang, Xiujuan Zhang, Guancong Ma, Xingqiu Chen, Minghui Lu, Yanfeng Chen, Jian-Hua Jiang