Materials Science · Cross-listed from physics.chem-ph
Implementation of the multigrid Gaussian-Plane-Wave algorithm with GPU acceleration in PySCF
Rui Li, Xing Zhang, Qiming Sun et al. (+3 more)
We introduce a GPU-accelerated multigrid Gaussian-Plane-Wave density fitting (FFTDF) approach for efficient Fock builds and
nuclear gradient evaluations within Kohn-Sham density functional theory, as implemented in the GPU4PySCF module of PySCF. Our CUDA kernels employ a grid-based parallelization strategy for contracting Gaussian basis function pairs and achieve up to 80% of the FP64 peak performance on NVIDIA GPUs, with no loss of efficiency for high angular momentum (up to f-shell) functions.
Benchmark calculations on molecules and solids with up to 1536 atoms and 20480 basis functions show up to 25x speedup on an H100 GPU relative to the CPU implementation on a 28-core shared
memory node. For a 256-water cluster, the ground-state energy and
nuclear gradients can be computed in ~30 seconds on a single H100 GPU. This implementation serves as an open-source foundation for many applications, such as ab initio molecular dynamics and high-throughput calculations.
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All authors Rui Li, Xing Zhang, Qiming Sun, Yuanheng Wang, Junjie Yang, Garnet Kin-Lic Chan
Materials Science
Suppression of Metallic Transport in Nitrogen-rich Two-Dimensional Transition Metal Nitrides
Hongze Gao, Da Zhou, Nguyen Tuan Hung et al. (+12 more)
The recent experimental realization of two-dimensional (2D) transition metal nitrides (TMNs, e.g., Mo5N6, {\delta}-MoN, and W5N6) opens new opportunities for exploring their fundamental physical properties at the two-dimensional limit. In this work, we propose a unified picture of transport phenomena in the nitrogen-rich 2D W5N6 and Mo5N6, and the stoichiometric 2D {\delta}-MoN based on several observations and first-principles calculations. Temperature coefficient of resistance (TCR) and magnetoresistance (MR) from
Hall measurements consistently suggest disorder-induced transport mechanism at low temperatures (10-30 K). Notably, we observe a transition from metal to semimetal driven by the variation of nitrogen content in TMNs, supported by the suppressed density of states at the
Fermi energy in nitrogen-rich TMNs (e.g. Mo5N6) from first-principle calculations. Carrier density calculations of bulk TMNs and 2D TMNs with -NH termination groups further reveal the switching of majority carrier type of Mo5N6 at reduced thickness, which is in great agreement with
Hall measurement results. Our findings demonstrate that high nitrogen content in metallic molybdenum nitrides can induce the transition to a semimetallic phase at the 2D limit, shedding light on both the fundamental aspects of these materials and directions in future material design.
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All authors Hongze Gao, Da Zhou, Nguyen Tuan Hung, Chengdong Wang, Zifan Wang, Ruiqi Lu, Yuxuan Cosmi Lin, Jun Cao, Michael Geiwitz, Gabriel Natale, Kenneth S. Burch, Xiaofeng Qian, Riichiro Saito, Mauricio Terrone, Xi Ling
Mesoscale and Nanoscale Physics
Interplay of bound states in the continuum and Fano–Andreev interference in a hybrid triple quantum dot
Alejandro González I., Pedro A. Orellana and Vladimir Juricic
We investigate bound states in the continuum (BICs) in a hybrid normal–superconducting triple
quantum dot system, where the central dot is coupled to two normal leads and the lateral dots are proximity-coupled to superconducting electrodes. Local electron–electron interactions are treated within the Hubbard approximation. Finite bias, together with lateral-dot detuning and superconducting proximity, induces interference between elastic electron tunneling (ET) and Andreev reflection (AR) channels, mediated by BIC-related modes and proximity-induced Andreev bound states. As the bias is swept through the subgap resonances, ET exhibits sharp antiresonances that evolve into exact transport zeros, signaling the emergence of (quasi-)BICs. We further find a continuous crossover from a Fano–Andreev BIC-supported regime to a Fano–Andreev quasi-BIC regime as the detuning asymmetry increases. The formation of BICs and quasi-BICs is accompanied by a pronounced change in the occupation of the side
quantum dot, providing an internal diagnostic directly correlated with the transport signatures of the bound states.
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Materials Science
Efficient all-electron Bethe-Salpeter implementation using crystal symmetries
Jörn Stöhler, Stefan Blügel and Christoph Friedrich
We describe an all-electron implementation of the Bethe-Salpeter equation (BSE) for the calculation of optical absorption spectra in the full-potential linearized augmented-plane-wave (FLAPW) method. So far, FLAPW implementations have resorted to a simple plane-wave basis for the bare and screened Coulomb potentials, thereby forgoing the all-electron description to some extent. In contrast, we expand the interaction potentials in the all-electron mixed basis. As in most implementations, the BSE is solved by the diagonalization of a two-particle
Hamiltonian matrix, whose dimension is proportional to the number of $\mathbf{k}$ points. Due to the large number of $\mathbf{k}$ points required to converge the BSE, the resulting
matrix becomes large even for small unit
cells. We describe a method that exploits the
crystal symmetries to accelerate the construction and diagonalization of the two-particle
Hamiltonian. In particular, we employ group theoretical tools to bring the
Hamiltonian into block-diagonal form. Furthermore, it is shown that often only one of the blocks needs to be taken into account for the optical absorption spectrum leading to a considerable speedup of the diagonalization step. The code allows for the inclusion of
spin-orbit coupling and is parallelized with the possibility of storing the
Hamiltonian in distributed
memory over many nodes, keeping the
memory demands low. To validate our implementation, we show optical absorption spectra and report
exciton binding energies for bulk Si, LiF, and MoS$_2$. By exploiting the
crystal symmetries, we can reduce the dimension of the
Hamiltonian matrix of Si by a factor of five, resulting in a 125-fold speedup in its diagonalization. The calculated
exciton binding energies of 22~meV and 76~meV for Si and MoS$_2$ are closer to experimental values than in previous BSE studies.
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Mesoscale and Nanoscale Physics
Josephson effect in graphene Corbino disks
Adam Rycerz
Peculiar features of the Josephson effect in
graphene were described theoretically by Titov and Beenakker [Phys. Rev. B 74, 041401(R) (2006)], who solved the Dirac-Bogoliubov-de-Gennes equation for a
superconductor-
graphene-
superconductor junction with rectangular geometry. Here, we adopt the analysis for
graphene Corbino disks, finding out that - for the outer to inner radii ratio $r_2/r_1\gtrsim{}5$ - such systems may demonstrate, when varying the electrochemical potential and the spatial profile of the electrostatic barrier, crossover from standard Josephson tunneling (SJT), via
graphene-specific multimode Dirac-Josephson tunneling (MDJT), towards the ballistic Josephson effect (BJE). Signatures of SJT appear only near the Dirac point when the barrier shape is close to rectangular, MDJT appears in the tripolar range and is very robust against varying the barrier shape, and BJE is restored in the unipolar range when smoothing the barrier shape. A comparison with the results of a numerical simulation of
quantum transport on the honeycomb
lattice is also given.
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Mesoscale and Nanoscale Physics
Second-order Skin Effect in a Brick-Wall Lattice
Dipendu Halder, Srijata Lahiri and Saurabh Basu
Non-Hermitian skin effect, which is a unique feature of non-Hermitian systems, exhibits the formation of an extensive number of boundary modes under open boundary conditions. However, its manifestation in higher dimensions remains elusive. In our work, we demonstrate a hybrid skin-topological effect arising from the interplay between first-order band
topology and non-reciprocal hopping in an engineered two-dimensional brick-wall geometry. The non-Hermitian brick-wall
lattice under open boundary conditions in both directions exhibits several unconventional spectral features. Notably, the
eigenvalues associated with the corner skin modes do not exhibit non-trivial windings in the complex energy plane; instead, they exhibit dynamically stable exceptional point-like features that do not originate from eigenvector coalescence. In contrast, the remaining modes accumulate at the opposite pair. Of all the corner skin modes, only the two that originate from the topological corner states of the Hermitian brick-wall
lattice remain localized at individual corners, while the rest accumulate at the pair of opposite corners. This spatial distribution contrasts sharply with the second-order skin effect, where corner skin modes are more uniformly distributed. Finally, for the non-Hermitian Brick-wall
lattice, we design and implement the corresponding topolectrical
circuit (
circuit for a square
lattice is included for comparison) to directly visualize the hybrid skin-topological modes.
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Materials Science
Engineering Nonlinear Optical Responses via Inversion Symmetry Breaking in Bilayer Bi2Se3
Vineet Kumar Sharma, Alana Okullo, Barun Ghosh et al. (+2 more)
Paucity of naturally occurring noncentrosymmetric materials is stimulating growing interest in engineered two-dimensional systems for nonlinear optical applications. Here, we show that breaking inversion
symmetry in centrosymmetric
bilayer Bi$_2$Se$_3$ through twisting, point-defect insertion, or the application of an external electric field unlocks rich nonlinear optical responses. In twisted
bilayer Bi$_2$Se$_3$ at the first commensurate angle of 21.78$^\circ$, we find peak shift and injection current conductivities of -14 $ nm.\mu AV^{-2}$ and 104 $\times 10^8$ $nm.A V^{-2}s^{-1}$, respectively, which lie in the visible spectrum and enable efficient THz applications. The external electric field and point-defect insertion both transform the
bilayer into C$_ {3v}$
symmetry, with the selenium vacancy (V$_{Se}$) achieving peak shift and injection current conductivities of -190 nm.$\mu AV^{-2}$ and -170 $\times 10^8$ $nm.A V^{-2}s^{-1}$. In all three cases, the peak nonlinear optical responses are found to be comparable to those of
benchmark 2D materials such as GeS, and the broadband responses, including helicity-dependent current generation, make these engineered
bilayers viable candidates for next-generation 2D photovoltaics.
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All authors Vineet Kumar Sharma, Alana Okullo, Barun Ghosh, Arun Bansil, Sugata Chowdhury
Quantum Gases
Soliton turbulence of a strongly driven one-dimensional Bose gas
Manon Ballu, Romain Dubessy, Aurélien Perrin et al. (+2 more)
We study the out-of-
equilibrium dynamics of a weakly interacting one-dimensional Bose gas in a box trap, subjected to a drive realized by a periodically oscillating linear potential. After a transient regime, the gas reaches a quasi-steady state, characterized by the presence of several
solitons. At weak driving amplitude, the
solitons are only weakly perturbed by one another, while at strong driving amplitude a regime analogous to
turbulence is reached, where the
solitons are strongly intertwined with each other. We show that a hallmark of both regimes can be found in the momentum distribution, which displays a power-law decay $n(k) \sim k^{-2}$ at weak driving amplitude and $n(k) \sim k^{-\alpha}$ with a power-law exponent $\alpha\in [7,9]$ at large amplitude. We further characterize each of the two regimes by following the space-time maps and characterizing the
solitons using the inverse scattering transform. The protocol analyzed in this study is amenable to experimental realization in current experimental setups.
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All authors Manon Ballu, Romain Dubessy, Aurélien Perrin, Hélène Perrin, Anna Minguzzi
Strongly Correlated Electrons
Topological properties of gapless phases in an interacting spinful wire
Polina Matveeva, Dmitri Gutman and Sam T. Carr
We study
topology in gapless phases of an interacting spinful model with
spin-charge separation. We focus on the gapless boundaries between $\mathbb{Z}_2$
symmetry-breaking phases. We find two topologically non-trivial gapless states that occur at the boundary between a non-trivial and a trivial
insulator. They correspond to topological Luther-Emery
liquid and topological Mott
insulator. The Luther-Emery
liquid is characterized by gapless charge excitations and features topological edge modes that carry fractional
spin, while the topological Mott
insulator has gapless
spin sector and features edge states that carry fractional charge. Surprisingly, even though there is no mean-field description of the interacting gapless phases, as there is no local order parameter, we show that they can be adiabatically connected to a non-interacting topological metal. This non-interacting state is a phase boundary between decoupled Su-Schrieffer-Heeger chains with the winding number $\nu=2$ and chains with $\nu=1$.
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Materials Science · Cross-listed from physics.chem-ph
Permeation of hydrogen across graphdiyne: molecular dynamics vs. quantum simulations and role of membrane motion
Mateo Rodríguez, José Campos-Martínez and Marta I. Hernández
Previous research based on electronic structure calculations and molecular dynamics (MD) simulations have demonstrated that graphdiyne (GDY) is a very suitable two-dimensional membrane for the separation of small molecules in a gas mixture of different species. However,
quantum effects may play a role in the dynamics of these permeation processes when light molecules are the ones involved in the crossing of the GDY subnanometric pores. In this work we report rigorous
quantum-mechanical calculations together with equivalent MD simulations of the transport of H2 molecules through a static GDY membrane, as a case study for the validity of the application to these problems of classical dynamics. The force fields employed are based on an improved Lennard-Jones formulation, with parameters optimized by means of accurate ab initio calculations. It is found that, although
quantum effects are still significant at the temperatures of interest (between 250 and 350 K), MD simulations are able to reasonably reproduce the dependence of the
quantum permeances with the temperature. Moreover, MD permeances computed with
quantum corrections through Feynman-Hibbs effective potentials provide a lower bound to
quantum permeances, while the pure classical counterpart gives an upper bound, thus leading to a well delimited range of confidence of the permeation results. Furthermore, within MD simulations it is possible to incorporate the thermal motion of the GDY layer and in this situation it is observed an enhancement of the permeances with respect to the fixed membrane case, due to a significant reduction of the permeation barriers when the GDY atoms are allowed to vibrate. It seems apparent therefore, that modeling the membrane motion is crucial to provide reliable simulations of the gas transport features.
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Materials Science
Concerted Electron-Ion Transport by Polyacrylonitrile Elucidated with Reactive Deep Learning Potentials
Rajni Chahal-Crockett, Michael D. Toomey, Logan T. Kearney et al. (+4 more)
Charge transport in
polymers, such as polyacrylonitrile (PAN), is crucial for electronics and energy storage. For instance, PAN can transport cations e.g., Li+, by facilitating dynamic cation-nitrile coordination in batteries. However, little is known regarding the underlying role of complex reactive
polymer configurations. Herein, we develop a deep-learning potential, trained on ab initio energies and forces of nonequilibrium reactive PAN configurations, to unravel the kinetics of PAN cyclization initiated by a nucleophile (OH- dissociated from LiOH) attacking the terminal nitrile carbon. We find, based on the reaction free-energetics, rates, and charge analysis, that the nucleophile attack producing the first ring is the rate-limiting step, which subsequently triggers Li+-coupled electron transfer along the PAN backbone, causing ~10,000 times faster sequential ring-formation of the remaining nitriles. PAN's extended configurations, where dipolar and H-bonding interactions are minimal, enable such rapid kinetics. By validating our computational findings with IR and NMR experiments, we establish a pathway for designing reactive
polymers with enhanced charge transport for energy applications.
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All authors Rajni Chahal-Crockett, Michael D. Toomey, Logan T. Kearney, Yawei Gao, Joshua T. Damron, Amit K. Naskar, Santanu Roy
Materials Science
Visualizing Millisecond Atomic Dynamics of Nanocrystals in Liquid
Sungsu Kang, Jinho Rhee, Joodeok Kim et al. (+11 more)
Atomic structures of nanomaterials are inherently dynamic, continuously reshaped through interactions with chemical species and external stimuli. Such dynamics are further amplified as the size and dimensionality of nanomaterials are reduced. Despite advances in analytical methods, it remains challenging to capture structural dynamics of nanomaterials in reactive environments with both atomic spatial resolution and commensurate temporal resolution. Here, we directly visualize atomic-scale dynamics of gold (Au) nanocrystals in reactive
liquid environments with millisecond-speed
liquid cell electron microscopy (EM) and deep-learning denoising. We uncover reversible fluctuations in local crystallinity of Au nanocrystals dependent on the surrounding chemical environment. These transient fluctuations, driven by interactions at nanocrystal-
liquid interfaces, critically influence dissolution kinetics and grain boundary relaxation. By overcoming the spatiotemporal limitations in conventional
liquid cell EM, our findings provide insights into how transient nanoscale structures dictate the stability and reactivity of nanomaterials.
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All authors Sungsu Kang, Jinho Rhee, Joodeok Kim, Sam Oaks-Leaf, Minwoo Kim, Shengsong Yang, Chang Liu, Dongsu Kim, Sungin Kim, Binyu Wu, Won Bo Lee, David T. Limmer, A. Paul Alivisatos, Peter Ercius Jungwon Park
Superconductivity
Electrodynamic Signatures of Bogoliubov Fermi Surfaces in Moiré Graphene
Ke Wang, Qijin Chen, Rufus Boyack et al. (+1 more)
Understanding the superfluid stiffness \(D_s\) is a central problem in flat-band superconductivity. It is often interpreted together with spectroscopic probes such as tunneling, since both ultimately reflect the same superconducting quasiparticles. Their relationship is nevertheless complicated in flat bands, where
quantum-
geometric contributions to \(D_s\) must be included. The situation in moiré
graphene is particularly complex: tunneling experiments in some cases reveal an
evolution between V- and U-shaped spectra together with a quite universal finite zero-bias conductance (ZBC). These two phenomena along with others have been argued to suggest the presence of a Bogoliubov
Fermi surface (BFS), often generated by finite-momentum pair-density-wave (PDW) superconductivity. In this paper we calculate the superfluid stiffness in the presence of such a PDW. Virtual interband processes provide the familiar positive
geometric contribution that gives phase
rigidity to the flat-band condensate, allowing superconductivity to survive even in the presence of a BFS. At the same time, the multiband PDW pair structure enables the gapless BFS quasiparticles to respond to a phase gradient despite the negligible ordinary flat-band velocity. Their resulting counterflow reduces the stiffness even at zero temperature. As an experimentally accessible consequence, we predict a correlated
evolution of the residual ZBC and the low-temperature stiffness: enhanced zero-bias spectral weight should accompany reduced phase
rigidity. Observation of this correlation would support the presence of a BFS and indicate that the residual zero-energy states are intrinsic.
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All authors Ke Wang, Qijin Chen, Rufus Boyack, K. Levin
Materials Science
Chalcogen Doping Effect on the Insulator-to-Metal Transition in GdPS
Gokul Acharya, Rabindra Basnet, Santosh Karki Chhetri et al. (+5 more)
Topological semimetals offer a rich platform for exploring massless
fermion physics and realizing exotic properties with potential technological applications. GdPS, a
magnetic semiconductor derived from the nodal-line semimetal ZrSiS family, exhibits a field-induced
insulator-to-metal transition driven by exchange splitting. This transition is accompanied by an unusual, isotropic, and gigantic negative magnetoresistance, attributed to negligible
magnetic anisotropy resulting from the weak
spin-orbit coupling of half-filled Gd3+ 4f orbitals and light S atoms. In this work, we investigate Se substitution, which is expected to enhance
spin-orbit coupling. Indeed, we observe slightly increased
magnetic anisotropy in magnetotransport. Moreover, Se substitution suppresses the field-induced
insulator-to-metal transition, likely due to an enlarged band gap that demands a higher exchange splitting to close. These findings provide deeper insights into the interplay between
spin-orbit coupling,
magnetic anisotropy, and transport behavior in GdPS, offering guidance for future materials design for desired functionalities.
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All authors Gokul Acharya, Rabindra Basnet, Santosh Karki Chhetri, Dinesh Upreti, M. M. Sharma, Jian Wang, David Graf, Jin Hu
Statistical Mechanics · Cross-listed from cs.LG
Grokking as a Falsifiable Finite-Size Transition
Yuda Bi, Chenyu Zhang, Qiheng Wang et al. (+1 more)
Grokking – the delayed onset of generalization after early memorization – is often described with phase-transition
language, but that claim has lacked falsifiable finite-size inputs. Here we supply those inputs by treating the group order $p$ of $\mathbb{Z}_p$ as an admissible extensive variable and a held-out spectral head-tail contrast as a representation-level order parameter, then apply a condensed-matter-style diagnostic chain to coarse-grid sweeps and a dense near-critical addition audit. Binder-like crossings reveal a shared finite-size boundary, and susceptibility comparison strongly disfavors a smooth-crossover interpretation ($\Delta\mathrm{AIC}=16.8$ in the near-critical audit). Phase-transition
language in grokking can therefore be tested as a quantitative finite-size claim rather than invoked as analogy alone, although the transition order remains unresolved at present.
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All authors Yuda Bi, Chenyu Zhang, Qiheng Wang, Vince D Calhoun
Superconductivity
Probing picosecond depairing currents in type-II superconductors
E. Wang, M. Chavez-Cervantes, J. Satapathy et al. (+8 more)
Accessing the intrinsic critical current density (Jc*) in type II
superconductors has significant fundamental and technological potential, both as a probe of the microscopic superconducting properties and as a means to increase current limits in high
magnetic field devices and in electrical power systems. Yet, the experimental critical current density in type II
superconductors (Jc), when measured with DC currents, is generally lower than the intrinsic limit, mostly due to
vortex motion and self-heating. Here, we show that ultrafast picosecond electrical pulses, which interact with the material on timescales over which
vortices are inertially immobile, carry supercurrents up to the intrinsic depairing limit Jc* >> Jc. We probe picosecond critical currents in NbN and YBa2Cu3O7 (YBCO), as representative s-wave and d-wave
superconductors, respectively. In NbN, we find a sharp onset of the picosecond depairing at a current density as large as Jc*=2.2 Jc, a limit that is well described by microscopic dynamics based on BCS theory. In contrast, YBCO exhibits a gradual suppression of superconductivity as a function of the picosecond current, reflecting its d-wave
symmetry. These results offer a powerful new probe of
superconductors beyond the reach of conventional transport measurements. The ability to reach the depairing current may also lead to robust new platforms for superconducting electronics.
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All authors E. Wang, M. Chavez-Cervantes, J. Satapathy, T. Matsuyama, G. Meier, X. Zhang, L. You, F. Marijanovic, J.B. Curtis, E. Demler, A. Cavalleri
Strongly Correlated Electrons
Bound states of anyons: a geometric quantization approach
Qingchen Li, Pavel A. Nosov, Taige Wang et al. (+1 more)
The question of anyon interactions and their possible binding plays a key role in the physics of fractional
quantum Hall states. Here, we introduce a controlled and scalable approach to study anyon binding by working entirely within the
Hilbert space of anyons. The resulting theory is characterized by an effective potential, which captures the electrostatic energy of classical anyon configurations, and a Kähler potential, which simultaneously encodes the anyon Berry phase and the structure of their
Hilbert space; both quantities are readily computed using Monte Carlo methods for large systems, enabling reliable extrapolation to the thermodynamic limit. By applying the formalism of
geometric quantization on Kähler
manifolds, we construct the anyon
Hamiltonian, which can be exactly diagonalized in the few-anyon
Hilbert space. Applying our approach to the quasiholes of the $\nu=1/3$ Laughlin state with screened Coulomb interaction, we find that Laughlin quasiholes form bound states for screening lengths comparable or smaller than the
magnetic length. Remarkably, binding occurs despite both the bare electron-electron interaction and the quasihole electrostatic potential being purely repulsive. The bound-state formation is a Berry phase effect, driven by oscillations in the quasihole density profile on the $\ell_B$ scale that are invisible in the quasihole electrostatic potential alone. For multiple quasiholes, we identify a sequence of phases as the screening length is reduced: free $e/3$ anyons, paired $2e/3$ bound states, three-anyon charge-$e$ clusters, and larger composite objects. Finally, we discuss possible signatures in charge imaging experiments on
quantum Hall systems and the relevance to the phase diagram of itinerant anyon phases in fractional
quantum anomalous
Hall materials.
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All authors Qingchen Li, Pavel A. Nosov, Taige Wang, Eslam Khalaf
Disordered Systems and Neural Networks · Cross-listed from cs.AI
When Is Collective Intelligence a Lottery? Multi-Agent Scaling Laws for Memetic Drift in LLMs
Hidenori Tanaka
Multi-
agent systems powered by large
language models (LLMs) are increasingly deployed in settings that shape consequential decisions, both directly and indirectly. Yet it remains unclear whether their outcomes reflect collective
reasoning, systematic bias, or mere chance. Recent work has sharpened this question with naming games, showing that even when no individual
agent favors any label a priori, populations rapidly break
symmetry and reach consensus. Here, we reveal the mechanism by introducing a minimal model, Quantized Simplex Gossip (QSG), and trace the microscopic origin of this agreement to mutual in-context learning. In QSG,
agents maintain internal belief states but learn from one another's sampled outputs, so one
agent's arbitrary choice becomes the next
agent's evidence and can compound toward agreement. By analogy with neutral
evolution, we call this sampling-driven regime memetic drift. QSG predicts a crossover from a drift-dominated regime, where consensus is effectively a lottery, to a selection regime, where weak biases are amplified and shape the outcome. We derive scaling laws for drift-induced polarization as a function of population size, communication bandwidth, in-context adaptation rate, and
agents' internal uncertainty, and we validate them in both QSG simulations and naming-game experiments with LLM populations. Together, these results provide a framework for studying the collective mechanisms of social representation formation in multi-
agent systems.
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Mesoscale and Nanoscale Physics
General Construction from Topological Loop States to Topological Invariants in Exactly Flat Bands
Rui-Heng Liu, Jiangping Hu and Chen Fang
Electronic flat bands have localized Wannier-like orbitals as zero modes. In the Lieb or the kagome models, the localized orbitals satisfy a topological condition that entails two non-contractible loop eigenstates along $x/y$-axis in real space, and one topological band touching point with other bands in momentum space. In these topological-flat bands, the Bloch state at the touching point is ill-defined, and so is any topological invariant for the entire band. We propose a new topological condition that the loop states in different directions be linearly dependent. Its satisfaction removes the singularity at the band touching point, and enforces nontrivial, well-defined topological invariants. Enforcing the new condition, we obtain topological-topological (top$^2$)-flat bands in 2D and 3D that have nontrivial invariants including the Chern numbers, the $\mathbb{Z}_2$ invariants, and the topological-crystalline invariants. Under small, generic interactions, top$^2$-flat bands flow to correlated topological
insulators with a symmetric mass term; and specially designed interacting models can have top$^2$-flat bands as exact zero modes.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Inequality for Strong-Weak Spontaneous Symmetry Breaking in Fermionic Open Quantum systems
Abhijat Sarma and Cenke Xu
Under decoherence, an initial Gaussian (free-
fermion) state evolves into a non-Gaussian mixed state, so the resulting decohered fermionic state is not exactly solvable in general. We show through an inequality that a class of Rényi-2 correlators of the decohered
fermion state are upper-bounded by the Rényi-2 correlator serving as a proximate diagnostic of strong-weak spontaneous
symmetry breaking (SW-SSB) of the charge-U(1)
symmetry. This inequality holds for arbitrary decoherence strength and suggests that decoherence drives fermionic
quantum matter toward U(1) SW-SSB. We also make connections between our inequality and other subjects such as projected
quantum spin Hall insulator and Dirac
spin liquid states.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Implementing non-Abelian Hatano-Nelson model in electric circuits
Xiangru Chen, Jien Wu, Xingyu Chen et al. (+6 more)
Non-Hermitian systems generally host complex spectra that bring unique spectral
topologies, leading to the spectral braiding and non-Hermitian skin effect. The experimental exploration of non-Hermitian physics is mainly concentrated in artificial systems due to the flexibility in the introduction of the non-Hermiticity, but to date has focused only on the systems without gauge fields or with Abelian gauge fields. Here, we propose a non-Abelian Hatano-Nelson model with a nonreciprocal U(2) gauge field. The gauge field induces two non-Hermitian phenomena: the first is the
Hopf-link-shaped complex energy braiding, and the second is the bipolar skin effect arising under the non-Abelian condition. The non-Abelian Hatano-Nelson model is implemented in electric
circuits, and the
Hopf-link-shaped admittance spectra and bipolar skin admittance modes are observed. Our work enriches the experimental non-Hermitian physics, and provides an approach to designing multifunctional non-Hermitian devices.
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All authors Xiangru Chen, Jien Wu, Xingyu Chen, Zhenhang Pu, Yejian Hu, Jiuyang Lu, Manzhu Ke, Weiyin Deng, Zhengyou Liu
Materials Science · Cross-listed from cs.LG
How unconstrained machine-learning models learn physical symmetries
Michelangelo Domina, Joseph William Abbott, Paolo Pegolo et al. (+2 more)
The requirement of generating predictions that exactly fulfill the fundamental
symmetry of the corresponding physical quantities has profoundly shaped the development of machine-learning models for physical simulations. In many cases, models are built using constrained mathematical forms that ensure that
symmetries are enforced exactly. However, unconstrained models that do not obey rotational
symmetries are often found to have competitive performance, and to be able to learn to a high level of accuracy an approximate equivariant behavior with a simple data augmentation strategy. In this paper, we introduce rigorous metrics to measure the
symmetry content of the learned representations in such models, and assess the accuracy by which the outputs fulfill the equivariant condition. We apply these metrics to two unconstrained,
transformer-based models operating on decorated point clouds (a graph neural network for atomistic simulations and a PointNet-style architecture for particle physics) to investigate how
symmetry information is processed across architectural layers and is learned during training. Based on these insights, we establish a rigorous framework for diagnosing spectral failure modes in ML models. Enabled by this analysis, we demonstrate that one can achieve superior stability and accuracy by strategically injecting the minimum required inductive biases, preserving the high expressivity and scalability of unconstrained architectures while guaranteeing physical fidelity.
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All authors Michelangelo Domina, Joseph William Abbott, Paolo Pegolo, Filippo Bigi, Michele Ceriotti
Strongly Correlated Electrons
Landau and fractionalized theories of periodically driven intertwined orders
Oriana K. Diessel, Subir Sachdev and Pietro M. Bonetti
We obtain the phase diagrams of field theories of intertwined orders in the presence of periodic driving by an external field which preserves all
symmetries. We consider both a conventional Landau theory of competing orders, and a fractionalized theory in which the order parameters are distinct composites of an underlying multi-component
Higgs field. We work in the large $N$ limit and couple to a Markovian bath. The long time limits are characterized by non-zero average values, oscillations with the drive period and/or half the drive period, quasi-periodic oscillations, or chaotic behavior.
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Materials Science
Chiral Epitaxy: Enantioselective Growth of Chiral Nanowires on Low-Symmetry Two-Dimensional Materials
Noya Ruth Itzhak, Kate Reidy, Maya Levy-Greenberg et al. (+20 more)
Chiral crystals exhibit useful handedness-dependent properties, including
spin selectivity and circularly polarized light sensitivity, yet controlling which enantiomer forms during synthesis remains a central challenge. Existing approaches utilize molecules in solution to template
crystal growth, which restricts processing conditions and introduces organic contaminants incompatible with device fabrication. Enantioselective growth of a
chiral crystal on a
chiral surface via vapor-phase synthesis (
chiral epitaxy) has not yet been demonstrated. Here, we show
chiral epitaxy of aligned tellurium nanowires on a low-
symmetry two-dimensional material, ReSe2. In situ electron microscopies suggest a mechanism where handedness is determined at nucleation by the interface energy difference between Te enantiomers and the
chiral substrate surface.
Chiral epitaxy provides a solvent-free, vapor-solid route to homochiral
crystals compatible with
semiconductor and
quantum manufacturing processes.
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All authors Noya Ruth Itzhak, Kate Reidy, Maya Levy-Greenberg, Paul Anthony Miller, Chen Wei, Juan Gomez Quispe, Raphael Tromer, Olle Hellman, Shahar Joselevich, Aliza Ashman, Lothar Houben, Ifat Kaplan-Ashiri, Xiao-Meng Sui, Olga Brontvein, Katya Rechav, Laurent Travers, Pedro A. S. Autreto, Douglas S. Galvão, Federico Panciera, Oded Hod, Leeor Kronik, Frances M. Ross, Ernesto Joselevich
Statistical Mechanics · Cross-listed from quant-ph
Eric R. Bittner
Classical thermodynamics admits a
geometric formulation in which work is associated with areas enclosed by cycles in state space. Whether an analogous structure persists in driven, dissipative
quantum systems remains an open question. Here we show that quasistatic work in open
quantum steady states is governed by an emergent
geometric curvature in control-parameter space arising from steady-state coherence. For a driven dissipative two-level system, we construct a work one-form whose
curvature determines the work produced in cyclic processes. The work vanishes under strong dephasing, identifying coherence as a necessary condition for nontrivial geometry. However, its magnitude is set not by the coherence itself but by the spatial structure of the
curvature: cycles enclosing comparable areas produce different work depending on their location in parameter space. Reversing the cycle orientation reverses the sign of the work, confirming its
geometric origin. These results establish a
geometric framework for open
quantum thermodynamics and identify
curvature as the organizing principle of thermodynamic response, with direct implications for driven light–matter systems in cavity
quantum electrodynamics.
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Mesoscale and Nanoscale Physics
Interlayer Coupling and Floquet-Driven Topological Phases in Bilayer Haldane Lattices
Imtiaz Khan, Muzamil Shah, Reza Asgari et al. (+1 more)
We investigate Floquet-driven topological phase transitions in an AB-stacked
bilayer Haldane
lattice with tunable intralayer hopping anisotropy. By combining interlayer hybridization, Haldane flux, and off-resonant circularly polarized light, we obtain controlled transitions among Dirac, semi-Dirac, and higher-Chern insulating phases. As the hopping anisotropy increases, the two inequivalent Dirac points move toward each other and merge at the Brillouin-zone $\mathbf{M}$ point, where a semi-Dirac dispersion emerges with linear and quadratic momentum dependence along orthogonal directions. In this regime, competition between the intrinsic Haldane mass and the Floquet-induced mass drives a sequence of sharp topological transitions with Chern numbers $C=0,\pm1,\pm2$. We further show that interlayer coupling qualitatively reshapes the Floquet band
topology by inducing helicity-dependent and valley-selective band inversions at the K and K$'$ points, thereby stabilizing higher-Chern phases in the valence bands. These changes are accompanied by redistribution of the Berry
curvature, bulk gap closings, and the collapse or sign reversal of quantized anomalous
Hall plateaus. As the system approaches the semi-Dirac limit, the topological phase space narrows and disappears at the critical merger point, beyond which the system becomes topologically trivial even when it remains gapped. Overall, the
bilayer geometry broadens the scope of Floquet topological control by enabling dynamically tunable higher-Chern phases and valley-dependent
Hall responses governed by interlayer coupling and light helicity.
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All authors Imtiaz Khan, Muzamil Shah, Reza Asgari, Gao Xianlong
Mesoscale and Nanoscale Physics
Energy-gap–controlled current oscillations in graphene under periodic driving
Hasna Chnafa, Clarence Cortes, David Laroze et al. (+1 more)
We investigate the impact of an induced mass term $\Delta$ on the current density in
graphene subjected to a space- and time-dependent periodic potential $U(x,t)$. By solving the Dirac equation and deriving both the quasi-energy spectrum and the corresponding eigenspinors, we obtain explicit analytical expressions for the current density, which exhibits a clear dependence on $\Delta$. We show that $\Delta$ acts as a tunable control parameter that governs the amplitude, sign, and resonance structure of Josephson-like current oscillations. For normal incidence and a purely time-periodic potential, our results reveal that the oscillations within the energy gap gradually diminish as the mass term $\Delta$ increases. This suppression leads to a weakening of the Josephson-like effect typically observed in such systems. When the potential $U(x,t)$ is periodic in both space and time, the behavior becomes more complex. The current density can take either positive or negative values depending on the magnitude of the induced gap, and it generally decreases over time. As a result, the resonance phenomena–prominent at lower gap values–become progressively less significant as $\Delta$ increases. These findings underscore the tunable nature of light-matter interactions and
quantum transport in gapped
graphene, suggesting potential applications in terahertz (THz) nanoelectronic devices and optically controlled
quantum switches.
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All authors Hasna Chnafa, Clarence Cortes, David Laroze, Ahmed Jellal
Other Condensed Matter
Capturing thermal effects beyond the zero-temperature approximation using the uniform electron gas
Brianna Aguilar-Solis, Brittany P. Harding and Aurora Pribram-Jones
Density functional theory at finite temperatures often relies on the zero-temperature approximation, which uses a ground-state exchange-correlation functional with thermalized densities. This approach, however, neglects the explicit temperature dependence of the exchange-correlation free energy – a key factor in regimes such as warm dense matter, where both electronic and thermal effects are significant. In this work, we introduce the
entropy-corrected zero-temperature approach, in which the exchange-correlation
entropy is extracted using the generalized thermal adiabatic connection formula to construct a thermal correction to the standard zero-temperature approximation. Using a uniform electron gas parametrization, we compare this approach to the finite-temperature adiabatic connection and demonstrate that it performs best at lower densities. This provides a useful complement to zero-temperature density functional approximations, which generally perform better at moderate-to-large densities. We further identify a density-dependent intersection between the adiabatic connection curves, revealing a dependence on the ground state correlation energy and correlation potential. Additionally, extension of the
entropy corrected approach applied as a local density approximation–like temperature correction to the zero temperature approximation is discussed.
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Soft Condensed Matter
Radial Distribution Function in a Two Dimensional Core-Shoulder Particle System
Michael Wassermair, Gerhard Kahl, Andrew J Archer et al. (+1 more)
An important quantity in
liquid state theory is the radial distribution function $g(r)$. It can be calculated within the framework of classical density functional theory in two very distinct ways. In the test-particle route, one fixes a single fluid particle, turning it into an external potential in which the inhomogeneous structure of the fluid is calculated by minimising the functional. The second route to $g(r)$ in density functional theory employs the Ornstein-Zernike equation and the pair direct correlation function, that can be obtained from the second functional derivatives of the excess (over the ideal gas) free energy functional. Since typically an approximate excess free energy functional is employed, the test-particle route, which requires only one functional derivative, is more accurate than the Ornstein-Zernike route. Here we study a two dimensional core-shoulder particle system and find that in some circumstances the results from the Ornstein-Zernike route can be comparable in accuracy to the test-particle results for $r>\sigma$, the core diameter. We also examine in detail the asymptotic $r\to\infty$ decay of $g(r)$, finding a variety of possible decay wavelengths at different state points and state points where there is a crossover from one wavelength to a very different one. This behaviour is a signature pointing to the rich phase behaviour of the incipient solid phases.
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All authors Michael Wassermair, Gerhard Kahl, Andrew J Archer, Roland Roth
Materials Science
Controlled antivortex propagation at bifurcations in reconfigurable NdCo/NiFe racetracks
V.V. Fernandez, A.E. Herguedas-Alonso, C. Fernandez-Gonzalez et al. (+7 more)
The controlled propagation of
spin textures at bifurcations is a critical challenge for racetrack-based logic devices. Here, we investigate the effect of longitudinal and transverse
magnetic fields on the propagation of
magnetic antivortices at bifurcations within the stripe domain pattern of a reconfigurable NdCo/NiFe racetrack in order to control the preferred antivortex trajectory.
Magnetic Transmission X-ray Microscopy experiments were employed to correlate the observed propagation path with the local
magnetic configuration. We demonstrate that Zeeman coupling to the magnetization components at the bifurcation core enables switching of the preferred propagation branch using low-amplitude transverse
magnetic fields, without modifying the global stripe domain configuration that defines the guiding racetrack landscape. In-plane
magnetic anisotropy provides an additional mechanism to break the
symmetry between the upper and lower bifurcation branches by tuning the relative orientation between the stripe domain pattern and the longitudinal
magnetic fields.
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All authors V.V. Fernandez, A.E. Herguedas-Alonso, C. Fernandez-Gonzalez, R. Valcarcel, P. Suarez, A. G. Casero, C. Quiros, A. Sorrentino, A. Hierro-Rodriguez, M. Velez