Strongly Correlated Electrons
Spin correlations, low-energy scales, and anisotropy scaling in kagome frustrated magnets
Phillip Popp, Stephan Rosenkranz, Arthur P. Ramirez et al. (+1 more)
Neutron scattering is central to identifying
quantum states of
magnetic materials. In the search for
quantum spin liquids, broad spectral features of inelastic spectra have been cited as evidence for spinon excitations, but can also arise from
magnon excitations excitations in the presence of quenched disorder and strong
magnon interactions. We develop a new approach to this problem, based on the adiabatic continuity in the $XXZ$ Heisenberg model on geometrically frustrating (GF)
lattices as a function of the model's anisotropy. Using this approach, we identify universal features and energies of finite-temperature
spin correlators. Focusing on the kagome
lattice, we show that the low-energy
spin spectral function contains robust, momentum-independent peaks with frequencies: $\omega_1 \approx 3.4 T^*$ and $\omega_2 \approx 6.3 T^*$, where the “hidden energy scale” $T^*$ is the characteristic scale of a low-temperature peak in the heat capacity, at which many GF magnets also display
spin-glass freezing. We show that the spectral features at low energies $\omega\lesssim T^*$ arise from single-
magnon scattering and identify the magnetizations of the respective excitations. We explore the
evolution of the spectral features with temperature and discuss extensions to other GF
lattices. Our results provide a sharp spectroscopic criterion for interpreting
neutron scattering in kagome and other GF
quantum magnets.
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All authors Phillip Popp, Stephan Rosenkranz, Arthur P. Ramirez, Sergey Syzranov
Strongly Correlated Electrons · Cross-listed from hep-th
Infinite-Order Lattice Chiral Anomalies and CPT
Elijah Lew-Smith, Salvatore D. Pace and Shu-Heng Shao
A key property of a global
symmetry's anomaly is its order: the smallest integer $n$ for which the diagonal
symmetry of the $n$-copy system is anomaly-free. While many familiar
lattice anomalies have finite order, perturbative anomalies in the continuum$-$those captured by Feynman diagrams$-$have infinite order. In this paper, we show that the Onsager
symmetry, a
lattice realization of the
chiral symmetry of a 1+1d massless Dirac
fermion, has an order-two anomaly. However, imposing
lattice CPT
symmetry enhances this anomaly from order two to infinite order, yielding a
lattice chiral symmetry structure that more faithfully matches the continuum
chiral anomaly. We also discuss the corresponding 2+1d
symmetry-protected topological phases for these infinite-order
lattice anomalies.
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Strongly Correlated Electrons
Mixed-dimensional quantum Monte Carlo studies of M-point moiré materials
Dumitru Călugăru, Konstantinos Vasiliou, Haoyu Hu et al. (+3 more)
A new moiré-material platform has recently been proposed based on twisting two-dimensional triangular-
lattice monolayers whose low-energy states lie at the three M points of the Brillouin zone. Continuum models derived from extensive ab initio simulations suggest that electrons in the conduction bands of one such M-point moiré material, twisted AA-stacked SnSe$_2$, realize a three-orbital Hubbard model with orbitally-selective, quasi-one-dimensional (quasi-1D) hopping, protected by a projective mirror
symmetry. Here, we show that the resulting "mixed-dimensional" limit – in which the hopping is exactly quasi-1D in each valley, while the valleys are coupled by interactions into a fully two-dimensional network – can be sampled with
Stochastic Series Expansion (SSE)
quantum Monte Carlo (QMC) without a sign problem at any filling. We develop an efficient new SSE QMC
algorithm that combines custom global updates with parallel tempering to overcome the equilibration challenges posed by the mixed-dimensional setting. We then use this
algorithm to explore the phase diagram of M-point twisted AA-stacked SnSe$_2$. Over extended and realistic ranges of twist angles and interaction strengths, we find that at integer fillings the system supports correlated
insulators whose nature and strength depend strongly on angle. At certain commensurate fractional fillings, we further find evidence for Wigner-Mott
insulators. We analytically account for the main features observed numerically using a strong-coupling description. Finally, we discuss perturbations away from the mixed-dimensional limit and the possibility of applying our method to other realizations of mixed-dimensional Hubbard models.
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All authors Dumitru Călugăru, Konstantinos Vasiliou, Haoyu Hu, B. Andrei Bernevig, Werner Krauth, S. A. Parameswaran
Statistical Mechanics · Cross-listed from cs.LG
Boltzmann Attention: Learnable Ising Couplings for Cooperative Attention
Gilhan Kim and Daniel K. Park
Attention mechanisms are central to modern sequence models, yet standard
attention computes relevance primarily through individual query–key similarities. Although softmax normalization introduces competition among positions, a standard
attention layer does not explicitly parameterize learnable interactions between
attention decisions. This limits its ability to directly model cooperative or antagonistic co-
attention structure within the
attention mechanism itself. We propose Boltzmann
attention, an energy-based generalization in which
attention patterns are governed by an interacting Ising model. The method augments the usual data-dependent local fields with learnable pairwise couplings, allowing the model to represent inter-position correlations beyond those captured by softmax or sigmoid
attention. Experiments on character-level
language modeling and synthetic bracket matching show that Boltzmann
attention consistently improves over standard softmax
attention within a standard
Transformer architecture, with the advantage becoming more pronounced as sequence length increases. A four-way ablation confirms that the improvement arises from the learnable pairwise couplings. These results suggest that explicit inter-position interactions provide a principled enhancement for
attention-based sequence modeling. Moreover, the Ising formulation opens a natural path toward
quantum-computing-based sampling strategies: we demonstrate that diabatic
quantum annealing provides a practical training method while maintaining competitive performance with exact Boltzmann computation.
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Quantum Gases
Joyce Kwan, Perrin Segura, Yanfei Li et al. (+7 more)
Fractional
quantum Hall states are a cornerstone of topological physics, hosting fractionally charged quasiparticles with exotic statistics that promise to enable topologically protected
quantum information processing. Among these, the Pfaffian state introduced by Moore and Read implements a p-wave pairing structure that supports excitations with non-Abelian exchange statistics. Despite extensive study in electronic systems, direct access to its pairing structure has remained limited. Here we realize a three-particle bosonic Pfaffian state of ultracold $^{87}\mathrm{Rb}$ atoms in an optical
lattice subject to a Floquet-engineered synthetic
magnetic field. Using a
Bayesian-optimized adiabatic protocol, we prepare a state exhibiting Pfaffian pairing correlations. Site-resolved measurements of multi-point density correlations reveal a pronounced suppression of short-range three-body coincidences, reflecting the underlying pairing structure. We further probe the state's transport response through
Hall drift measurements. Our results establish a bottom-up approach to engineering non-Abelian topological order and lay the groundwork for future explorations of anyonic braiding in synthetic matter.
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All authors Joyce Kwan, Perrin Segura, Yanfei Li, Tizian Blatz, Annie Zhi, Brice Bakkali-Hassani, Annabelle Bohrdt, Martin Greiter, Fabian Grusdt, Markus Greiner
Materials Science · Cross-listed from physics.optics
Quantifying the Distribution of Biexciton Emission Efficiencies in Colloidal Quantum Shells
Tjom Arens, Dulanjan Harankahage, Divesh Nazar et al. (+2 more)
The efficiency of multi-
photon emission is an important characteristic of
quantum light sources. Bright multi-
photon emission is desirable for high-power lighting and
lasers, while its complete suppression is required for high-purity single-
photon generation. In colloidal
quantum emitters, multi-
photon emission can vary significantly between individual particles. Resolving this heterogeneity remains challenging with conventional particle-by-particle approaches. Here, we introduce a crosstalk-suppressed SPAD-array
photon-correlation approach for high-throughput quantification of multi-
photon emission from more than 1000 colloidal
quantum shells. By projecting two images of the same sample onto distant regions of the detector array, we avoid short-range crosstalk between detector pixels. Time gating suppresses dark-count coincidences and distinguishes individual emitters from clusters. Applying this method to
quantum shells reveals a near-Gaussian distribution of biexciton emission efficiencies, with a mean of 0.55 and an estimated intrinsic standard deviation of 0.12. Intra-batch correlations between the biexciton efficiency and the particle brightness are consistent with the volume scaling of Auger quenching. These results establish SPAD-array
photon correlation as a scalable route to resolve multi-
photon heterogeneities in nanoparticle ensembles.
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All authors Tjom Arens, Dulanjan Harankahage, Divesh Nazar, Mikhail Zamkov, Freddy T. Rabouw
Statistical Mechanics · Cross-listed from hep-th
Nonadditivity in Quantum Field Theory: Replica Energies, Scaling Filters, and the Renormalization Group
Giacomo Santoni and Francesco Scardino
Extensive systems have a simple thermodynamic signature: the dimensionless canonical free energy scales homogeneously with the size of the system. We show that the failure of this scaling, measured by the replica energy ${\cal E}$, provides a useful bridge between statistical mechanics and
quantum field theory. The associated differential operator $(1-\frac1d L\partial_L)$ removes the leading bulk contribution to $\mathcal{F}=\beta F_{\rm can}=-\log Z$ and isolates the part that is sensitive to boundaries,
topology, defects, long-range forces, or other sources of nonadditivity. In
quantum field theory this thermodynamic idea has two closely related uses. For ordinary finite-volume or spherical partition functions, suitable higher-order versions of the same filter remove local counterterms and extract universal fixed-point data such as the central charge, the sphere free energy $F$, and the Euler anomaly coefficient $a$. For replica geometries with entangling defects, the same filtering principle gives the renormalized defect free energy. In $2+1$ dimensions, its $n\to1$ limit gives the entropic $F$-function, with the sign fixed below by the standard free-energy convention. We use this perspective to distinguish ordinary finite-size corrections,
topology-dependent constants in gapped phases, subextensive fracton degeneracies, and genuinely nonextensive systems with long-range interactions such as self-gravitating thermal matter. Replica energy therefore offers a common thermodynamic
language for additivity, defect free energies, and renormalization-group irreversibility.
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Mesoscale and Nanoscale Physics
Gate-tunable spin-valley transport via carrier velocity in monolayer WSe$_2$
Otman Bouladiane, Hocine Bahlouli, Clarence Cortes et al. (+2 more)
We theoretically investigate
spin- and valley-resolved
quantum transport in monolayer tungsten diselenide (WSe$_2$) described by an effective massive Dirac
Hamiltonian. Particular
attention is devoted to a finite barrier region characterized by simultaneously modulated
Fermi velocity and scalar potential. The barrier velocity $v_2$ is related to the external velocity $v_1$ through a velocity ratio $\xi=v_2/v_1$, motivated by an optical analogy with the Snell-Descartes law. The exact refraction condition depends on the full
spin- and valley-resolved dispersion, and the simple ratio $\xi=v_2/v_1$ is recovered only in the massless, symmetric limit. The interplay of intrinsic
spin-orbit coupling in the conduction and valence bands, quantified by $\lambda_c$ and $\lambda_v$, with
spin- and valley-dependent Zeeman fields, $M_s$ and $M_v$, gives rise to substantial changes in the quasiparticle dispersion, leading to pronounced modifications of the transport characteristics. By solving the Dirac equation and enforcing current-conserving matching conditions at the interfaces, we compute the
spin- and valley-dependent transmission probability and conductance. Our results demonstrate that the barrier velocity, scalar potential, incidence angle, incident energy, and barrier width serve as effective control parameters for transport, giving rise to strong anisotropy and resonant tunneling features. Furthermore, we show that both the magnitude and orientation of
spin- and valley-polarized currents can be continuously tuned via velocity and potential modulation. These findings establish combined velocity and potential engineering as a powerful theoretical framework for controlling
spin-valley physics in two-dimensional transition-metal dichalcogenides.
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All authors Otman Bouladiane, Hocine Bahlouli, Clarence Cortes, David Laroze, Ahmed Jellal
Materials Science
Effect of polar distortions on the linear and nonlinear anomalous Hall conductivity of altermagnetic $\alpha$-MnTe
Mathews Benny, Sahar Izadi Vishkayi, Amar Fakhredine et al. (+2 more)
Altermagnetic $\alpha$-MnTe with Néel vector along the $y$-axis exhibits a finite anomalous
Hall conductivity (AHC) and weak ferromagnetism along the $z$-axis. As already demonstrated in the bulk, there is the breaking of the C$_6$
symmetry by the in-plane Néel vector, leaving a C$_2$-type
magnetic symmetry. The surface of $\alpha$-MnTe breaks the C$_2$, leaving only a time-reversed mirror
symmetry with respect to the $x=0$ plane. Therefore, we demonstrate that on the surface, the interplay between breaking of the
crystal symmetry and Néel vector orientation produces a reduction of the space group from hexagonal P6$_3$/mmc to orthorhombic Amm2. As a result, the surface exhibits not only a polar distortion along the $z$-axis, but also a polar distortion and a weak ferrimagnetism along the $y$-axis. To describe the surface of MnTe in an accessible way, we simplify the problem and examine the effect of the in-plane electric field in bulk MnTe. Moreover, as a doped ionic
semiconductor, the properties of MnTe can be influenced by
lattice polarization under an applied electric field. We investigate the interplay between the intrinsic anomalous
Hall effect and
lattice polarization, showing that polarization effects can substantially affect the AHC. Since the electric field breaks inversion
symmetry, this contribution from the
lattice polarization coexists with the non-linear anomalous
Hall effect, highlighting the rich transport phenomenology of altermagnets.
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All authors Mathews Benny, Sahar Izadi Vishkayi, Amar Fakhredine, Chanchal K. Barman, Carmine Autieri
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Deterministic Single-Photon Emitter Arrays in Hexagonal Boron Nitride by Carbon-Assisted Focused Ion Beam Engineering
Mangababu Akkanaboina, Rohit Kumar, Brijesh Kumar et al. (+4 more)
The realization of on-chip photonic
circuits requires scalable and deterministic single-
photon emitters (SPEs) at room temperature, which remain a challenge in van der Waals materials. In this work, we report a novel three-step fabrication process for the generation of spatially controlled SPE arrays in hexagonal boron nitride (hBN). The process comprises site-selective gallium (Ga) focused ion beam milling, nanoscale conformal carbon deposition over the patterned regions, and subsequent thermal annealing. The synergistic combination of these steps resulted in a site-correlated emitter yield of ($\sim 89\%$) across 100 fabrication sites. Second-order autocorrelation measurements revealed pronounced three-level emitter dynamics where the best emitters exhibited high purity ($g^{(2)}(0)=0.15 \pm 0.09$).To the best of our knowledge, this is the first lithography-free, direct-write approach combining Ga-ion milling, selective carbon engineering, and thermal annealing to deterministically generate \hBN{} \SPE{}s. The reproducibility of the method is validated across multiple independently fabricated samples. These results establish a scalable, lithography-free pathway toward on-demand SPE arrays relevant to integrated
quantum photonics.
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All authors Mangababu Akkanaboina, Rohit Kumar, Brijesh Kumar, Hrushikesh Gawali, Parul Sharma, Ikshvaku Shyam, Anshuman Kumar
Soft Condensed Matter
Approximate additivity in the solvent-mediated potential of mean force for ultrasoft particle systems
Joshua F. Robinson, Gary Yu and Patrick B. Warren
Recently an approximate additivity principle has been successfully applied to molecular chemical potentials in ultrasoft particle systems [R. L. Hendrikse, C. Amador and M. R. Wilson, Phys. Chem. Chem. Phys. 27, 1554 (2025)]. We articulate this additivity principle as one of two ansätze and apply these to dimers in the infinite dilution limit. In this limit, we show that the solvent-mediated potential of mean force (PMF) between solutes, extracted from the hypernetted-chain (HNC) closure of the Ornstein-Zernike equations, can be expressed as a convolution between solute-specific generalised excluded volume functions. In the limit of a structureless solvent of point particles and hard core solutes, this recovers the exact Asakura-Oosawa depletion potential as the overlap between excluded volume spheres. The theory extends to the opposite limit of ultrasoft particle solvents and solutes, such as those encountered in dissipative particle dynamics (DPD), where the solvent-mediated PMF can be recovered with considerable accuracy. These results confirm that in coarse-grained molecular DPD simulations the parametrisation of the solute-solvent interactions is sensitive to the intramolecular bond lengths if they are smaller than the range of the solvent-solvent interaction potential, due to the overlap of the soft excluded volume functions.
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Materials Science
Plasmonic properties and correlation energies from a compact multipole representation of the dielectric response in 2D metals
Dario A. Leon, Claudia Cardoso and Kristian Berland
Multipole-Padé approximants provide a compact representation of dynamical response functions in terms of a small number of collective modes. Here, we generalize this framework to incorporate momentum dependence across the full Brillouin zone of 2D metals by constructing a
symmetry-conserving, anisotropic representation of the inverse dielectric function. This analytic form enables efficient and accurate evaluation of quantities involving dynamical screening, including spectral features and correlation energies. We construct such compact representations for a set of seven two dimensional metals spanning distinct electronic regimes, and show that a small number of dispersive plasmonic modes suffices to accurately describe the dielectric response across the full Brillouin zone, while also yielding accurate correlation energies. The proposed representation therefore establishes a direct bridge between ab initio calculations and analytical models of screening, opening new avenues for applications in condensed matter systems.
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Statistical Mechanics
Mass generation at a fixed point: A Functional Renormalization Group Study of the tricritical O($N$) model in $d=3$ and $N=\infty$
Shunsuke Yabunaka and Bertrand Delamotte
Renormalization group (RG) fixed points are commonly associated with scale invariance and a divergent correlation length. We show that this connection can fail in the tricritical $O(N)$ model in three dimensions in the limit $N\to\infty$. Revisiting the line of fixed points identified by Bardeen, Moshe, and Bander, we use the functional renormalization group to clarify the mechanism leading to mass generation at its singular endpoint (the BMB fixed point). We demonstrate that the generated mass is nonuniversal and originates from the nonanalytic structure of the effective potential. We show that the critical exponent $\nu$ which takes the value $\nu = 1/2$ along the regular part of the BMB line, that is, for $0 \leq \lambda < \lambda_{\rm BMB}$, jumps to $\nu = 1/3$ on the singular part of this line with the BMB FP, corresponding to $\lambda = \lambda_{\rm BMB}$, being the pivotal point between these two regimes. We also show how its singular potential emerges dynamically along the renormalization flow.
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Superconductivity
Substrate insulated Josephson junctions for superconducting quantum circuits
U. Strobel, L. Radtke, L. Kamps et al. (+7 more)
We have developed a fabrication technique for Josephson junctions that employs a three-dimensional patterned, low-loss substrate instead of commonly used organic resists. The technique enables the fabrication of high-quality trilayer junctions from a wide range of geometries and materials, including high-melting-point
superconductors such as tantalum or niobium. The junction electrodes are free from intentionally introduced
oxides and organic materials, which are known sources of decoherence. We fabricate and characterize underdamped Nb/AlOx/Nb junctions of different sizes in several geometries. Such junctions enable manufacturing of
quantum circuits operating at higher speeds and elevated temperatures.
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All authors U. Strobel, L. Radtke, L. Kamps, J. N. Voss, J. Lisenfeld, J. Luo-Hofmann, D. Reuter, S. Masis, A. V. Ustinov, H. Rotzinger
Superconductivity
Superconductivity in the pressure-amorphized topological insulator CrP$_4$
Chutong Zhang, Xiangzhuo Xing, Na Zuo et al. (+12 more)
The interplay among superconductivity, magnetism, and nontrivial band
topology represents one of the most compelling frontiers in condensed matter physics. The exploration of novel superconductivity in 3d transition-metal compounds, particularly the rare Cr-based systems containing strongly
magnetic Cr ions, has long attracted
attention owing to their unconventional pairing mechanisms that challenge conventional wisdom. Yet, Cr-based
superconductors remain scarce, especially those possessing nontrivial topological character, underscoring the urgent need to uncover new members. Here we report the observation of superconductivity in pressure-amorphized Cr-based topological
insulator CrP$_4$. Upon compression, CrP$_4$ undergoes an anomalous
quantum phase transition from a metallic to a semiconducting-like state at around 15 GPa, driven by significant changes in the electronic structure. At approximately 70 GPa, re-metallization with superconductivity occurs alongside an irreversible amorphization. The superconducting transition temperature Tc increases monotonically with pressure, reaching 4.8 K at 141.3 GPa. Furthermore, theoretical calculations predict multiple topological phase transitions from a strong topological
insulator to a trivial state and finally back to a strong topological state under pressure. Our study not only establishes CrP$_4$ as the first Cr-based amorphous
superconductor but also opens a new paradigm for exploring superconducting and topological properties in amorphous materials.
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All authors Chutong Zhang, Xiangzhuo Xing, Na Zuo, Bowen Zheng, Bin Li, Jiajia Feng, Xiaolei Yi, Yan Meng, Xiaoran Zhang, Bingchao Yang, Chao Wang, Xin Chen, Yongsheng Zhang, Xiaofeng Xu, Xiaobing Liu
Mesoscale and Nanoscale Physics
Stacking switching between correlation-protected radial Rashba field and persistent spin textures in graphene encapsulated by 1T-TaS$_2$ monolayers
Juraj Mnich, Marko Milivojević and Martin Gmitra
We investigate the electronic structure,
spin textures, and charge to
spin/orbital transport in
graphene encapsulated by 1T-TaS$_{2}$ monolayers in the charge density wave phase. Using first-principles calculations, tight-binding modeling, and the Kubo formalism, we show that the encapsulation stacking dictates fundamentally distinct transport regimes. In the asymmetrical (AA) stacking, proximity fields from both interfaces constructively interfere, yielding a cumulative Rashba phase of nearly $\pi/2$. This pure radial Rashba
spin pattern leads to the unconventional Rashba-Edelstein effect, which robustly dominates over the conventional response by a factor of 35 across a wide energy range. Conversely, the symmetrical (AA') stacking preserves a horizontal mirror
symmetry, establishing a stable, purely out-of-plane persistent
spin texture. Furthermore, the computed orbital
Hall effect is exceptionally efficient, surpassing the
spin Hall effect by three orders of magnitude. Within the proximity-induced spectral gaps, the orbital
Hall conductivity exhibits a finite plateau, whereas the
spin Hall conductivity vanishes. Our findings establish
graphene encapsulated
heterostructures as a promising system for realizing distinct charge to
spin and charge to orbital interconversion regimes determined by the choice of stacking order.
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Materials Science
Thermodynamically consistent phase field model for hydrogen-assisted cracking
G. F. Bouobda-Moladje, A. Ruffini, Y. Le Bouar et al. (+1 more)
We propose a phase field model able to simulate hydrogen-assisted cracking in polycrystalline materials. Within a variational framework, the model simultaneously describes crack propagation and hydrogen segregation on crack surfaces and grain boundaries together with the associated reduction in interfacial energies. In the context of hydrogen-enhanced decohesion (HEDE) mechanisms, we demonstrate the ability of the model to capture the transition from transgranular cracking to hydrogen-assisted intergranular cracking.
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All authors G. F. Bouobda-Moladje, A. Ruffini, Y. Le Bouar, A. Finel
Soft Condensed Matter
Tunable Snapping and Rigid Foldability in the Mars Origami Pattern
Menelaos Raptis and Thomas C. Hull
Origami-inspired metamaterials exploit the interplay between geometry and elasticity to achieve programmable mechanical responses. Yet the origin and tunability of snap-through instabilities in non-rigidly foldable patterns remain poorly understood. Here we show that the Mars tessellation, a degree-4 vertex origami pattern composed of alternating square and rhombic faces, is not rigidly foldable because the folding-speed ratios required for vertex compatibility cannot be propagated consistently across neighboring units. This
geometric incompatibility forces the facets to bend during folding, giving rise to a reproducible snap-through discontinuity in the force-displacement curve with a mean force drop of about 92.6 +/- 5.5 %, marking a transition between metastable states.
Laser scoring of additional diagonal creases, guided by strain-field simulations, enables continuous tuning of the snap magnitude. These results reveal a general mechanism by which
geometric frustration can be harnessed to program multistability in thin-sheet metamaterials.
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Mesoscale and Nanoscale Physics
Enhanced localization length in a disordered one-dimensional band via cavity coupling to delocalized states
Francesco Mattiotti, Guido Pupillo, Jérôme Dubail et al. (+1 more)
We investigate the localization properties of cavity-coupled electronic states in disordered systems, motivated by recent proposals of cavity-mediated hopping in
quantum Hall systems. We first introduce a minimal two-band model in which localized states in a disordered one-dimensional band are coupled, through a homogeneous cavity mode, to an excited band of delocalized states. Combining perturbation theory with a transfer-
matrix approach, we show that cavity-assisted hopping between localized states decays exponentially with distance, implying that the eigenstates remain localized even beyond the perturbative regime. Nevertheless, the corresponding localization length increases with the light-matter coupling strength and can extend over several
lattice sites in the single-electron ultrastrong-coupling regime. We then study a disordered Landau band coupled to a cavity mode within the framework developed in Refs.[1,2]. We find that the effective cavity-mediated coupling between edge states also decays exponentially with distance, but with a localization length that can reach micrometer scales for experimentally realistic parameters. By analyzing the inverse participation ratio, we show that this enhanced coupling is predominantly mediated by the most extended states of the upper Landau band. Our results demonstrate that, while cavity-induced hopping in disordered
quantum Hall systems remains exponentially localized, the associated localization length can become sufficiently large for the corresponding states to exhibit effectively delocalized behavior on mesoscopic length scales.
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All authors Francesco Mattiotti, Guido Pupillo, Jérôme Dubail, David Hagenmüller
Strongly Correlated Electrons
Structural responses incipient to pressure-driven antiferromagnetic quantum critical point of van der Waals heavy-fermion metal CeSiI
Hanming Ma, Tong Shi, Wenhao Li et al. (+12 more)
CeSiI is a van der Waals heavy-
fermion metal recently found to exhibit unconventional superconductivity near a pressure-induced
antiferromagnetic quantum critical point (QCP) at Pc =6 GPa. Here, we report a comprehensive single-
crystal X-ray diffraction study of CeSiI under high pressures up to 8.3 GPa at room temperature, revealing subtle structural responses that precede pressure-driven QCP. We find that the unit-
cell volume decreases smoothly upon compression without showing any structural phase transition in the investigated pressure range. Intriguingly, we observe abrupt and concurrent anisotropic responses of the
lattice parameters around Pc =6 GPa, i.e., the a-axis contracts while the c-axis enlongated suddenly, with the unit-
cell volume smoothily varies with pressure. Structural refinements further show that these
lattice anomalies primarily originate from changes of Ce-Ce and Ce-Si bond lengths, as well as a flattening of the inner honeycomb Si layer within the CeSiI monolayer around Pc. Our findings establish an interesting case linking pressure-driven electronic transition of QCP at low temperatures to incipient structural responses at room temperature, thereby providing fresh insight into the pressure-temperature phase diagram of CeSiI.
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All authors Hanming Ma, Tong Shi, Wenhao Li, Qingxin Dong, Xiaoli Ma, Shaoheng Ruan, Zhongjin Wu, Pengtao Yang, Zhaoming Tian, Jianping Sun, Yoshiya Uwatoko, Xiaohui Yu, Hechang Lei, Bosen Wang, Jinguang Cheng
Materials Science
Quantum dynamic simulation of triplet formation in an effective model of Y6 (BTP-4F)
Isabel Creed, Lucy J. F. Hart, Pranay Venkatesh et al. (+2 more)
We construct a five-state model for photoexcitation in Y6 (BTP-4F) dimers, and then solve the non-adiabtic dynamics using the Hierarchical Equations of Motion (HEOM) method. We find that triplets are populated mainly via a transiently excited intermolecular charge-transfer singlet to triplet Frenkel
exciton route; this route is not available to the monomer. Analysis of one-particle transition density
matrices suggests that the charge-transfer states are spatially distinct to the Frenkel
exciton states, indicating that the large
spin-orbit-coupling for this transition is due to it being permitted by an associated change in orbital character. Aggregation in Y6 therefore directly enables fast and high-yield intersystem crossing. We selenise our model dimers, significantly enhancing
spin-orbit-coupling, which then accelerates this charge-transfer mediated route. Looking forwards to simulations on larger aggregates, we show that, though Marcus theory gives qualitatively correct dynamics, the long-time yields are incorrect due to it missing
quantum recurrences. Instead, we show that the recently developed
memory-kernel projector\cite{Gestsson2025-ez} method can produce semi-classical rates directly from the HEOM equations which lead to quantitatively correct dynamics and yields.
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All authors Isabel Creed, Lucy J. F. Hart, Pranay Venkatesh, Tom Ward, Jarvist Moore Frost
Quantum Gases
Weakly interacting Bose gases in the canonical ensemble
Jonata S. Soares, Axel Pelster and Arnaldo Gammal
Based on the canonical description of a non-interacting Bose gas, we work out how both thermodynamic and statistical properties change perturbatively with respect to weak two-particle interactions. Up to first order, we obtain a recursion formula for the canonical partition function, which consists of the same Feynman diagrams as the grand-canonical description but with different Feynman rules. Resumming this recursion formula for the canonical partition function allows one to characterize the statistics of the ground-state occupancy by its respective cumulants. We demonstrate the applicability of this approach by analyzing a dilute Bose gas with contact interaction in a box trap. To this end, we used Dirichlet boundary conditions in view of their relevance for current experiments with atomic gases, where the box trap is implemented, for instance, with digital mirror devices.
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Strongly Correlated Electrons
Kinetic kagome magnetism: from self-trapping RVB polarons to semiclassical correlations
Yufei Pei, Shuai A. Chen, Claudio Castelnovo et al. (+1 more)
To gain deeper insight into the role of hole kinetics in determining magnetism in highly frustrated doped Mott
insulators, we consider the single-hole counter-Nagaoka problem on the kagome
lattice, using magnetization as a tuning parameter. Near full polarization, a doped hole delocalizes upon binding reversed
spins in a pattern of singlet bonds which we term resonating-valence-bond (RVB) polaron. These RVB polarons can have extremely small effective bandwidths, and hence exhibit self-trapping. By tuning the
spin polarization, we track the
evolution of these states toward the unpolarized sector, where we observe the emergence of $\sqrt{3}\times\sqrt{3}$
antiferromagnetic correlation reminiscent of the classical Potts and Heisenberg models on the kagome
lattice. These results provide a framework to understand how RVB physics at short scales evolves into conventional
magnetic correlations at long scales.
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All authors Yufei Pei, Shuai A. Chen, Claudio Castelnovo, Roderich Moessner
Disordered Systems and Neural Networks
Roughening of active nonlinear interfaces with broken tilt symmetry
Ailén M. Cámara, Alejandro B. Kolton and José Luis Iguaín
We study the roughening of an interface with nonlinear elasticity driven by temporally correlated noise, which breaks statistical tilt
symmetry. Using scaling arguments and a self-consistent Hartree approximation, we derive the crossover diagram and the steady-state structure factor. We identify three scaling regimes associated with the Larkin, anharmonic Larkin, and Edwards–Wilkinson universality classes, and obtain the crossover lengths separating them. Numerical simulations of large systems confirm the analytical predictions over the full parameter range. Our results provide a unified description of finite-size and crossover effects in a minimal nonlinear-elastic Ornstein–Uhlenbeck active interface.
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Mesoscale and Nanoscale Physics
Experimental straintronics in nanotube quantum dots
L. Huang, I. G. Rebollo and A. R. Champagne
Single-wall carbon nanotubes (SWCNTs) are narrow ribbons of
graphene with atomically precise edges and a single
quantum transport channel, at experimentally-relevant dopings. This makes them ideal systems to harness
quantum transport straintronics (QTS), i.e. using mechanical strain to control accurately
quantum transport. We present QTS data from three single-wall carbon nanotube
quantum dot (SWCNT-QD) transistors over a broad range of in-situ tunable and reversible uniaxial strain ($\Delta\varepsilon_\text{mech}\approx$ 0 to 3 %). We first present the nanofabrication of the suspended SWCNT transistors whose channel lengths are $\approx$ 30 nm. The channels are strained by moving gold clamps holding firmly the nanotubes. We present detailed charge transport data, $dI/dV_{\text{B}} - V_{\text{B}} - V_{\text{G}}$ and $dI/dV_{\text{B}} - V_{\text{B}} - \Delta\varepsilon_\text{mech}$, showing a large mechanical-gating effect of the SWCNT-QDs. The precise reversibility of the data, and their agreement with QTS theory, confirms that the tubes are strained elastically. We demonstrate that the mechanical control of the QD doping is not due to capacitive-gating effects, but to quantitatively predictable bandstructure changes including a strain-tunable bandgap. This precise mechanical control of the doping and bandgap of SWCNT-QDs could find applications in
qubits, condensed matter physics, and homojunction molecular transistors.
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Statistical Mechanics
Path convergence in diffusion models
Roi Holtzman, Roman Beauvallet and Werner Krauth
We discuss
diffusion-model paths interpolating between a target distribution known only through p patterns and a reference distribution that can be sampled. These interpolating paths can be constructed symmetrically or else in forward direction (often referred to as a "noising") from the target patterns to the reference distribution or in backward direction (as a "denoising") from the reference distribution to the patterns. For backward paths with identical
diffusion noise, we consider the path convergence in number of patterns p towards the path for infinitely many patterns. In a one-dimensional test case, we show that this convergence is on a scale 1/sqrt(p), but with infinite mean square deviation. We demonstrate that the path convergence allows for extrapolation towards the p=infinity path which samples the target distribution. We provide a proof-of-concept extrapolation
algorithm and propose the convergence and extrapolation of paths as a possible strategy for density estimation and generalization. We illustrate all our
algorithms through pseudo-codes and provide Python implementations.
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Quantum Gases
Grand-canonical phase diagram and chiral-current suppression at $\pi$ flux in a bosonic two-leg ladder
Meng Zhang, Qingyun Xu and Zhi Lin
We investigate the ground-state phase diagram of repulsively interacting
bosons on a two-leg ladder threaded by a uniform artificial
magnetic flux, using the cluster Gutzwiller mean-field method. In the strong-rung-coupling regime, self-consistent calculations are performed on a $2\times4$ cluster. By analyzing the superfluid order parameter, leg-resolved currents,
chiral current, the current ratio on adjacent legs, and the density imbalance between the two legs, we distinguish Mott-insulating from superfluid regimes and characterize the observed states as Meissner-like,
vortex-like (superfluid or Mott insulating), or biased-ladder. In regions overlapping with previous DMRG studies, our results qualitatively agree with the established phase structure, demonstrating that the cluster Gutzwiller approach balances computational efficiency and physical accuracy. We then construct the first grand-canonical $t$–$\mu$ phase diagrams for this system, revealing how the
magnetic flux modifies the shape, tilt, and extent of the Mott lobes. We further explore previously inaccessible regimes, including higher fillings $\rho\gtrsim1$ and the intermediate interaction window $U/t\in[7.69,9.09]$. Special
attention is paid to $\varphi=\pi$, where the effective triangular-ladder mapping becomes singular. Owing to the equivalence of $\varphi=\pi$ and $-\pi$ modulo $2\pi$, a combined
symmetry forbids net
chiral currents, leading to a nonchiral Mott-insulating state, in contrast to the
chiral-superfluid tendency expected away from $\varphi=\pi$. Our results offer a computationally efficient route for mapping the global phase structure of bosonic flux ladders and provide guidance for future ultracold-atom experiments in artificial gauge fields.
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Materials Science
Tracking atomic-scale interdiffusion in immiscible bimetallic nanoparticles via four-dimensional electron tomography
Jisheng Xie, Dijin Jiang, Zhen Sun et al. (+4 more)
The interdiffusion of immiscible elements is generally considered both thermodynamically unfavorable and kinetically hindered. At the nanoscale, however, the mixing behavior of multielements materials often diverges from bulk
equilibrium, yet a quantitative, atomically resolved description of this transformation has remained challenging. Using ex situ four dimensional atomic resolution electron
tomography combined with in situ scanning transmission electron microscopy, here we reveal the atomic scale miscible transition driven by interdiffusion in immiscible PdIr nanoparticles at temperatures far below the melting point. The pathway involves surface reconstruction atom hopping at 200oC and surface flattening at 300oC, followed by a critical transition at 400oC where Ir interfacial
diffusion and discrete Ir intermediates drive miscible intermixing. Upon reaching the nanoscale melting point 900oC, collective inward Ir
diffusion yields the thermodynamically stable IrPd configuration. Our findings provide quantitative atomic scale insights into how metastable nanostructures evolve through distinct intermediates, offering a design framework for advanced multielement materials.
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All authors Jisheng Xie, Dijin Jiang, Zhen Sun, Yiheng Dai, Zezhou Li, Yao Zhang, Jihan Zhou
Superconductivity
Structural Changes and Transport Properties of $\mathrm{YBa_2Cu_3O_7}$ Locally Modified by a He$^+$ Focused Ion Beam
Ross Carter, Robin Hutt, Paul Zimmermann et al. (+9 more)
Irradiation of a material with ions can cause various defects that can lead to structural phase transitions and the modification of the material's properties. Here we study the irradiation of the epitaxyally grown thin films of the high-temperature
superconductor $\mathrm{YBa_2Cu_3O_7}$ with $30\,\mathrm{keV}$ He$^{+}$ ions which leads to the expansion of the
crystal lattice, decrease of the critical temperature $T_c$ and eventually transition to an
insulator. Fabrication of such insulating regions with a focused He-Ion beam with a spot size of $\sim 10\,\mathrm{nm}$ is a powerful technique for fabrication of superconducting nano-devices. Using low-temperature resistivity measurements, diffraction with a nanofocused X-ray beam and atomic force microscopy, we investigated how the structure and the electric transport properties of $\mathrm{YBa_2Cu_3O_7}$ depend on the irradiation dose in a range $10$–$100\,\mathrm{ions/nm^2}$ and on the lateral size of the irradiated area in a range $30$–$5000\,\mathrm{nm}$.
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All authors Ross Carter, Robin Hutt, Paul Zimmermann, Ainur Abukaev, Jan Ullmann, Simon Koch, Christoph Schmid, Manfred Burghammer, Reinhold Kleiner, Dieter Koelle, Edward Goldobin, Ivan A. Zaluzhnyy
Strongly Correlated Electrons
From Topological Order to Mixed-State Phases: A Ground-State Probe of Fractionalized Excitations
Yunlong Zang, Yu-Bin Li and Shenghan Jiang
How do we detect topological phases from a single ground state?
Entanglement entropy and spectrum have long been the standard tools – but the reduced density
matrix (RDM) itself contains far more information. We show that the RDM of a 2D topologically ordered system, expressed at the
entanglement cut, realizes a 1D mixed-state phase. For the $\mathbb{Z}_2$ toric code phase, it is a 1D $\mathbb{Z}_2$ strong-to-weak spontaneous
symmetry breaking (SW-SSB) phase, where deconfinement of anyons manifests as the short-range correlation of both $\mathbb{Z}_2$ charge and $\mathbb{Z}_2$ domain-wall in the RDM. The bulk $e$-$m$ duality translates into a Kramers–Wannier self-duality of the SW-SSB phase. Extending the framework to gapped $\mathbb{Z}_2$
spin liquids, the global
spin-rotation
symmetry manifests as an additional weak
symmetry for the 1D RDM.
Spin-$\frac{1}{2}$ spinons result in a cusp on the disorder parameter of
spin-rotation at $\theta=\pi$, providing a direct, ground-state signature of
symmetry fractionalization. We verify this prediction analytically using the
matrix product density operator formalism and numerically for the kagome-
lattice resonating valence bond state. The proposed observable requires only a single ground-state wavefunction, making it amenable to
quantum simulation platforms.
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