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Physics Condensed Matter

cond-mat Watch Condensed Matter

Monday 10 November

Quantum Gases

Broad Feshbach resonance with a large background scattering length in a fermionic atom-molecule mixture

Zhen Su, Tong-Hui Shou, Huan Yang et al. (+6 more)

We report the observation of a broad magnetic Feshbach resonance with a large background scattering length in an ultracold fermionic mixture of $^{23}$Na$^{40}$K molecules and $^{40}$K atoms, with both species prepared in their lowest hyperfine states. The Feshbach resonance is characterized by measuring resonantly enhanced loss rates and elastic scattering cross sections via cross-species thermalization. The large background scattering length can drive the atom-molecule mixture into the hydrodynamic regime when the magnetic field is far from the resonance. We observe that the center-of-mass motions of the atoms and molecules are phase-locked and oscillate with a common frequency due to hydrodynamic drag effects. This broad atom-molecule Feshbach resonance with its large background scattering length opens up a new avenue towards studying strongly interacting fermionic gases with mass imbalance.
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All authors Zhen Su, Tong-Hui Shou, Huan Yang, Jin Cao, Bo-Yuan Wang, Ting Xie, Jun Rui, Bo Zhao, Jian-Wei Pan

Mesoscale and Nanoscale Physics

Interface Roughness Scattering Processes in Quantum wells in a Tilted Quantizing Magnetic Field

M.P. Telenkov and Yu.A. Mityagin

Scattering processes by the interface roughness in a quantum well in a quantizing magnetic field are considered. An expression for the scattering rate is derived for a magnetic field tilted relative to the quantum well layers. By analyzing this expression, trends in the behavior of the scattering rate are established with variation in the magnetic field strength and orientation, the potential profile of the quantum well, and the interface roughness parameters.
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Strongly Correlated Electrons

Compression-induced magnetic obstructed atomic insulator and spin singlet state in antiferromagnetic KV2Se2O

Liucheng Chen, Jiayi Yue, Jingwen Cheng et al. (+8 more)

Among the complex many-body systems, the metal-insulator transition stands out as a cornerstone and a particularly fertile ground for scientific inquiry. The established models including Mott insulator, Anderson localization and Peierls transition, are still insufficient to capture the complex and intertwined phenomena observed in certain material systems. KV2Se2O, a newly discovered room-temperature altermagnetic candidate exhibiting a spin-density-wave transition below 100 K, provides a unique platform to investigate the interplay of many-body effects and unconventional magnetism, specifically the anticipated metal-insulator transition under extreme conditions. Here, we report a compression-induced insulator by suppressing the metallic behavior without structural phase transition. The newly opened gap is estimated to be 40 meV at around 43.5 GPa, given direct evidence for the insulating state. A concurrent switching of carrier type demonstrates the large Fermi surface reconstruction crossing the metal-insulator transition. The density functional theory calculations indicate that the discovered V+2.5-based insulator is a magnetic obstructed atomic insulator, being a spin-singlet state with bonding orbital order. This work not only presents an archetype of a pressure-driven metal-insulator transition decoupled from structural change but also delivers fundamental physical insights into the metal-insulator transition.
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All authors Liucheng Chen, Jiayi Yue, Jingwen Cheng, Jianli Bai, Zexiao Zhang, Xiaoli Ma, Fang Hong, Genfu Chen, Jian-Tao Wang, Zhijun Wang, Xiaohui Yu

Quantum Gases · Cross-listed from quant-ph

Dynamics of number entropy for free fermionic systems in presence of defects and stochastic processes

Atharva Naik, Bijay Kumar Agarwalla and Manas Kulkarni

We investigate the dynamics of number entropy in a chain of free fermions subjected to both defects and stochastic processes. For a special class of defects, namely conformal defects, we present analytical and numerical results for the temporal growth of number entropy, the time evolution of the number distribution, and the eigenvalue profile of the associated correlation matrix within a subsystem. We show that the number entropy exhibits logarithmic growth in time, originating from the Gaussian structure of the number distribution. We find that the eigenvalue dynamics reveal a profound connection to the reflection and transmission coefficients of the associated scattering problem for a broad range of defects. When stochastic processes are introduced, specifically Stochastic Unitary Processes (SUP) and Quantum State Diffusion (QSD), the number entropy scales as $\ln(t)$ in the SUP case and shows strong hints of $\ln [\ln(t)]$ scaling in the QSD case. These findings establish compelling evidence that number entropy grows logarithmically slower than the corresponding von Neumann entanglement entropy across a wide class of systems.
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Soft Condensed Matter

Colloidal rod dynamics under large amplitude oscillatory extensional flow

Steffen M. Recktenwald, Vincenzo Calabrese, Amy Q. Shen et al. (+2 more)

We perform a combined experimental and theoretical investigation of the orientational dynamics of rod-like colloidal particles in dilute suspension as they are subjected to a time-dependent homogeneous planar elongational flow. Our experimental approach involves the flow of dilute suspensions of cellulose nanocrystals (CNC) within a cross-slot-type stagnation point microfluidic device through which the extension rate is modulated sinusoidally over a wide range of Péclet number amplitudes ($Pe_0$) and Deborah numbers ($De$). The time-dependent orientation of the CNC is assessed via quantitative flow-induced birefringence measurements. For small $Pe_0 \lesssim 1$ and small $De \lesssim 0.03$, the birefringence response is sinusoidal and in phase with the strain rate, i.e., the response is linear. With increasing $Pe_0$, the response becomes non-sinusoidal (i.e., nonlinear) as the birefringence saturates due to the high degree of particle alignment at higher strain rates during the cycle. With increasing $De$, the CNC rods have insufficient time to respond to the rapidly changing strain rate, leading to asymmetry in the birefringence response around the minima and a residual effect as the strain rate passes through zero. These varied dynamical responses of the rod-like CNC are captured in a detailed series of Lissajous plots of the birefringence versus the strain rate. Experimental measurements are compared with simulations performed on both monodisperse and polydisperse systems, with rotational diffusion coefficients $D_r$ matched to the CNC. A semiquantitative agreement is found for simulations of a polydisperse system with $D_r$ heavily weighted to the longest rods in the measured CNC distribution. The results will be valuable for understanding, predicting, and optimizing the orientation of rod-like colloids during transient processing flows such as fiber spinning and film casting.
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All authors Steffen M. Recktenwald, Vincenzo Calabrese, Amy Q. Shen, Giovanniantonio Natale, Simon J. Haward

Disordered Systems and Neural Networks · Cross-listed from q-bio.PE

Emergent self-inhibition governs the landscape of stable states in complex ecosystems

Nitesh Kumar Patro, Washington Taylor and Akshit Goyal

Species-rich ecosystems often exhibit multiple stable states with distinct species compositions. Yet, the factors determining the likelihood of each state's occurrence remain poorly understood. Here, we characterize and explain the landscape of stable states in the random Generalized Lotka-Volterra (GLV) model, in which multistability is widespread. We find that the same pool of species with random initial abundances can result in different stable states, whose likelihoods typically differ by orders of magnitude. A state's likelihood increases sharply with its total biomass, or inverse self-inhibition. We develop a simplified model to predict and explain this behavior, by coarse-graining ecological interactions so that each stable state behaves as a unit. In this setting, we can accurately predict the entire landscape of stable states using only two macroscopic properties: the biomass of each state and species diversity. Our analyses also provide insight into the biomass-likelihood relationship: High-biomass states have low self-inhibition and thus grow faster, outcompete others, and become much more likely. These results reveal emergent self-inhibition as a fundamental organizing principle for the attractor landscape of complex ecosystems—and provide a path to predict ecosystem outcomes without knowing microscopic interactions.
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Disordered Systems and Neural Networks · Cross-listed from math-ph

Average Winding Number for Determinantal Curves associated with 2-Matrix Models in the Class AIII

Mathieu Yahiaoui and Mario Kieburg

To classify one-dimensional disordered quantum systems with chiral symmetry, we analyse the winding number of the determinant of a parametrized non-Hermitian random matrix field over the unit circle modelling the off-diagonal block of a disordered chiral Hamiltonian. The associated partition function is computed explicitly for a broad class of additive two-matrix models extending beyond the Ginibre Unitary Ensemble. In the large-dimension limit, we derive an asymptotic expansion of the average winding number whose leading term exhibits universal features, up to the tail behaviour of the underlying random matrix ensemble, and identify a new correction term absent in the previously studied Ginibre case.
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Superconductivity

KTaO3-based editable superconducting diode

Yishuai Wang, Wenze Pan, Meng Zhang et al. (+1 more)

Superconducting diodes, which enable dissipationless supercurrent flow in one direction while blocking it in the reverse direction, are emerging as pivotal components for superconducting electronics. The development of editable superconducting diodes could unlock transformative applications, including dynamically reconfigurable quantum circuits that adapt to operational requirements. Here, we report the first observation of the superconducting diode effect (SDE) in LaAlO3/KTaO3 heterostructures, a two-dimensional oxide interface superconductor with exceptional tunability. We observe a strong SDE in Hall-bar (or strip-shaped) devices under perpendicular magnetic fields (< 15 Oe), with efficiencies above 40% and rectification signals exceeding 10 mV. Through conductive atomic force microscope lithography, we demonstrate reversible nanoscale editing of the SDE's polarity and efficiency by locally modifying the superconducting channel edges. This approach enables multiple nonvolatile configurations within a single device, realizing an editable superconducting diode. Our work establishes LAO/KTO as a platform for vortex-based nonreciprocal transport and provides a pathway toward designer quantum circuits with on-demand functionalities.
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All authors Yishuai Wang, Wenze Pan, Meng Zhang, Yanwu Xie

Materials Science · Cross-listed from physics.app-ph

Local metamaterials and transition layers

Kimya Yadollahpour, Hossein Khodavirdi and Ankit Srivastava

In this paper, we elucidate the concept of local acoustic metamaterials. These are composites which exhibit equi-frequency contours (EFC) which correspond to those expected of homogeneous local acoustic media. We show that EFCs for local acoustic media are conics in 2-dimension and quadrics in 3-dimension. In 2-D, the sure signature of negative properties is if the conic is a hyperbola and in 3-D, the sure signature is the presence of hyperboloids. We note that metamaterial coupling (Willis coupling) has the potential of translating these conics and quadrics in the wave-vector plane but that it does not fundamentally change the shape of these geometries. The local effective properties assigned to a composite in such cases are dispersive (frequency dependent) and they satisfy causality considerations. We finally also show that such properties truly characterize the composite in the sense that they can be used to solve scattering problems involving different samples of the composite. We show that this is made possible through the consideration of transition layers. While the sharp-interface model incurs scattering errors exceeding 20% at oblique angles, the Drude-layer model restores agreement to within 2% without requiring integral-equation or multi-mode expansions, thereby offering a simple yet highly efficient route to accurate scattering predictions in resonant local acoustic metamaterials.
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Superconductivity

Quantum Monte Carlo study of magnetism and chiral d+id-wave superconductivity in twisted bilayer graphene

Shi-Chao Fang and Xin-Yi Liao

We employ a large-scale, unbiased constrained-path quantum Monte Carlo method to systematically simulate the effective two-orbital Hubbard model for twisted bilayer graphene in order to gain deeper insight into the relationship between correlated states and the superconducting pairing mechanism in twisted bilayer graphene, as well as the influence of the twist angle on superconductivity. Initially, we investigate the modulation of superconductivity by nearest-neighbor attractive Coulomb interactions, demonstrating that electron-phonon coupling plays a significant role in the system. Our numerical results reveal that the superconducting state is dominated by chiral NN-d+id superconducting electron pairing symmetry, and that such nearest-neighbor attractive Coulomb interactions significantly enhance the effective long-range pairing correlation function of chiral NN-d+id wave. Then, we explore how the twist angle affects the superconducting state. Our results show that as the twist angle deviates downward from 1.08{\deg}, the effective pairing correlation function of the chiral NN-d+id wave increases substantially. Through these investigations, our numerical findings not only contribute to a more comprehensive understanding of strongly correlated systems such as twisted bilayer graphene, but also provide guidance for identifying twist-angle systems with potentially higher superconducting transition temperatures.
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Soft Condensed Matter

Shape-controlled growth of two-dimensional kagome-lattice colloidal crystals through nanoparticle capping

Rui Huang, Jordan Austin-Frank Wilson, Allen Sun et al. (+2 more)

Organic capping ligands can selectively bind to crystal facets to modulate growth kinetics and are important in chemical synthesis of inorganic nanocrystals. Using the capping ligands for shape-controlled growth of colloidal crystals is challenging due to the size mismatch of molecules and nanoparticle building blocks. In existing synthetic pathways, colloidal crystal shapes are determined by their thermodynamically favored phases yet controlling their shapes independent of lattice symmetry is vital to study many solid-state properties. Here, we develop a nanoparticle capping strategy to control colloidal crystal shapes and structural heterogeneity. Au bipyramids were used as building blocks and assembled into rhombohedral colloidal crystals driven by DNA hybridization. In (111) planes of the crystals, bipyramids assembled into kagome lattices, featuring structure cavities organized in a hexagonal lattice. The rhombohedral crystals have truncated tetrahedral crystal habits, and the degree of truncation defines the exposed facets and crystal shapes. Our surface capping strategy is to introduce DNA-modified nanospheres as effective capping agents, which selectively register on the surface vacancies of the kagome facets and resemble the role of organic ligands in classic nanocrystal growth. Such selective capping is driven by maximizing DNA hybridization and leads to slower growth of the (111) kagome facets, changing the crystal shape from three-dimensional truncated tetrahedra to two-dimensional layered microplates with structural heterogeneity and shape anisotropy. This study underpins the importance of capping agents in colloidal crystal growth and inspires effective ways to control the growth kinetics and heterostructures of colloidal crystals.
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All authors Rui Huang, Jordan Austin-Frank Wilson, Allen Sun, Artemis Harlow, Zhiwei Li

Strongly Correlated Electrons · Cross-listed from quant-ph

Quantum algorithm for one-quasiparticle excitations in the thermodynamic limit via cluster-additive block diagonalization

Sumeet, M. Hörmann and K.P. Schmidt

We propose a quantum algorithm for computing one-quasiparticle excitation energies in the thermodynamic limit by combining numerical linked-cluster expansions (NLCEs) and the variational quantum eigensolver (VQE). Our approach uses VQE to block-diagonalize the cluster Hamiltonian through a single-unitary transformation. This unitary is then postprocessed using the projective cluster-additive transformation (PCAT) to ensure cluster additivity, a key requirement for NLCE convergence. We benchmark our method on the transverse-field Ising model (TFIM) in one and two dimensions, and with longitudinal field, computing one-quasiparticle dispersions in the high-field polarized phase. We compare two cost function classes, trace minimization and variance based, demonstrating their effectiveness with the Hamiltonian variational ansatz (HVA). For pure TFIM, $\lceil N/2 \rceil$ layers of HVA suffice: NLCE+VQE matches exact diagonalization. For TFIM with longitudinal field, where parity symmetry breaks and PCAT becomes essential, both $\lceil N/2 \rceil$ and $N$ layers of HVA converge with increasing cluster size, with $N$ layers providing improved accuracy. Our results establish PCAT as a cluster-additive framework that extends variational quantum algorithms to excited-state calculations in the thermodynamic limit via NLCE. While demonstrated with VQE, the PCAT postprocessing approach, which requires only low-energy eigenspace information, applies to any quantum eigenstate preparation method.
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Quantum Gases

A passive atomtronics filter for Fermi gases

Jun Hao Hue, Martin-Isbjörn Trappe, Piotr T. Grochowski et al. (+2 more)

We design an atomtronic filter device that spatially separates the components of a two-component Fermi gas with repulsive contact interactions in a two-dimensional geometry. With the aid of density–potential functional theory (DPFT), which can accurately simulate Fermi gases in realistic settings, we propose and characterize a barbell-shaped trapping potential, where a bridge-shaped potential connects two ring-shaped potentials. In the strongly repulsive regime, each of the ring traps eventually stores one of the fermion species. Our simulations are a guide to designing component filters for initially mixed, weakly repulsive spin components. We demonstrate that the functioning of this barbell design is robust against variations in experimental settings, for example, across particle numbers, for small deformations of the trap geometry, or if interatomic interactions differ from the bare contact repulsion. Our investigation marks the first step in establishing DPFT as a comprehensive simulation framework for fermionic atomtronics.
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All authors Jun Hao Hue, Martin-Isbjörn Trappe, Piotr T. Grochowski, Jonathan Lau, Leong-Chuan Kwek

Soft Condensed Matter

Mechanical instability generates monodisperse colloidosomes

Seungwoo Shin, Federico Cao, Robert A. Pelcovits et al. (+2 more)

Formation and rupture of vesicles is a fundamental process underlying diverse phenomena in biology, materials science, and biomedical applications. Vesicles form when the area of a growing disk-like membrane exceeds a critical value at which the edge and bending energies balance each other. Observing such topological transitions in lipid bilayers is a challenge because of their nanoscale dimensions and rapid dynamics. We study a scaled-up model of colloidal membranes assembled from rod-shaped colloidal particles. The unique features of colloidal membranes enable the real-time visualization of spontaneous closure driven by instability relevant to all membrane-based materials. First-principles theory quantitatively predicts the instability point for vesicle formation and intermediate membrane conformations during the disk-to-vesicle transition. The instability generates monodisperse, selectively permeable colloidosomes with size controlled by gravity and membrane thickness, providing a scalable and programmable platform for diverse applications.
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All authors Seungwoo Shin, Federico Cao, Robert A. Pelcovits, Thomas R. Powers, Zvonimir Dogic

Sunday 9 November

Materials Science · Cross-listed from quant-ph

A Hierarchy of Fibonacci Forbidden-Word Hamiltonians: From the Golden Chain to the Plastic Chain and Aperiodic Order

Marcelo Maciel Amaral

We introduce an infinite, scale-aligned hierarchy of one-dimensional, frustration-free Hamiltonians by forbidding the minimal forbidden factors of the Fibonacci word up to length $F_K$, the $K$-th Fibonacci number. The ground-state languages have exponential growth constants $\lambda_K$ that decrease monotonically, starting from the value associated with the “golden chain” (approximately 1.618) and progressing toward 1. This process yields a staircase of topological-entropy plateaus that flows to an aperiodic fixed point, also known as the Fibonacci subshift. The first nontrivial rung ($K=4$) is the “Plastic chain,” which forbids SS and LLL. We prove its ground-state counts follow a specific four-term linear recurrence relation and provide a closed-form solution governed by the plastic constant $\rho\approx 1.3247$. We propose an energy-entropy scaling where the energy penalty for each new forbidden pattern is proportional to the logarithmic ratio of the growth constants from the previous and current rungs, turning the sequence of projectors into an explicit renormalization-group flow from the initial high-entropy phase to the zero-entropy aperiodic fixed point. Algebraically, exact Temperley-Lieb braiding compatibility holds only at the base rung, $K=3$ (which forbids only SS); higher rungs define constrained aperiodic Hamiltonian codes rather than Temperley-Lieb representations. Small instances realized on a D-Wave quantum annealer match these predictions: $K=3$ is trivial, $K=4$ resolves a unit gap with moderate success, and $K\ge 5$ instances require reverse annealing to exceed $99\%$ success, clarifying reduction penalties and embedding variability.
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Mesoscale and Nanoscale Physics

High-quality nanostructured diamond membranes for nanoscale quantum sensing

Alexander Pakpour Tabrizi, Artur Lozovoi, Sean Karg et al. (+4 more)

Deploying nitrogen vacancy (NV) centers in diamond as nanoscale quantum sensors for condensed matter and materials physics requires placing the NV centers close to the sensing target. One solution is to fabricate diamond nanostructures and integrate them with materials and devices. However, diamond etching and ion milling can introduce subsurface damage and surface defects that degrade the charge stability and spin coherence of NV centers near the surface. Here we report a procedure for fabricating low-damage nanostructured diamond membranes, and we show that this fabrication scheme preserves the optical and spin properties of state-of-the-art shallow NV center quantum sensors, within nanometers of the diamond surface, while providing significant photonic enhancement. Furthermore, we demonstrate a pick-and-place transfer method, which enables integration with diverse sensing targets.
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All authors Alexander Pakpour Tabrizi, Artur Lozovoi, Sean Karg, Tecla Bottinelli Mondandon, Melody Leung, Kai-Hung Cheng, Nathalie P. de Leon

Statistical Mechanics · Cross-listed from hep-th

Comment on CFT in AdS and boundary RG flows: O(1/N) Result

Kaoru Ohno and Yutaka Okabe

In a recent paper [JHEP 11 (2020) 118], S. Giombi and H. Khanchandani studied the 1/N expansion of the O(N) model in semi-infinite space within the framework of conformal field theory in anti-de Sitter space. They presented a series expansion for the O(1/N) correction to the boundary anomalous dimension in the case of the ordinary transition. Although they were unable to sum the series or simplify its form analytically, they demonstrated numerically that their result matches our earlier, simple analytic expression given in Prog. Theor. Phys. 70 (1983) 1226. In this paper, we show that their series expansion is in fact exactly equivalent to our original expression. However, since the final formula in eq. (4.57) of their paper, which is expressed in terms of two different 3F2 functions, cannot produce the correct values, we derive the correct formulae involving two 3F2 functions in the Appendices. We comment on the similarity and difference between their analysis and ours in the cases of the ordinary and special transitions, and present full details of deriving the anomalous dimension for all the cases including the extraordinary transition, which were not written in our earlier paper.
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Soft Condensed Matter

Thermal conductivity of commodity polymers under high pressures

Otavio Higino Moura de Alencar, James Mu, Marcus Müller et al. (+1 more)

Understanding the thermal conductivity of polymers under high-pressure conditions is essential for a range of applications, from aerospace and deep-sea engineering to common lubricants. However, the complex relationship between pressure, $P$, the thermal transport coefficient, $\kappa$, and polymer architecture poses substantial challenges to both experimental and theoretical investigations. In this work, we study the pressur-dependent thermal transport properties of a widely used commodity polymer – poly(methyl methacrylate) (PMMA) – using a combination of all-atom molecular dynamics simulations and semi-analytical approaches. While we report both classical and quantum-corrected estimates of $\kappa$, the latter approach reveals that as the pressure increases from 1 atm to 10 GPa, $\kappa$ rises by up to a factor of four – from 0.21 W m$^{-1}$ K$^{-1}$ to 0.80 W m$^{-1}$ K$^{-1}$. To better understand the mechanisms behind this increase, we disentangle the contributions from bonded and nonbonded monomer interactions. Our analysis shows that nonbonded energy-transfer rates increase by a factor of six over the pressure range, while bonded interactions show a more modest increase – about a factor of three. This observation further consolidates the fact that the nonbonded interactions play the dominant role in dictating the microscopic heat flow in polymers. These individual energy-transfer rates are also incorporated into a simplified heat diffusion model to predict $\kappa$. The results obtained from different approaches show internal consistency and align well with available experimental data. Additionally, some data for polylactic acid (PLA) are presented.
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All authors Otavio Higino Moura de Alencar, James Mu, Marcus Müller, Debashish Mukherji

Disordered Systems and Neural Networks

Machine learning intermolecular transfer integrals with compact atomic cluster representations

Keerati Keeratikarn, Christoph Ortner and Jarvist Moore Frost

Calculating intermolecular charge transfer integrals in organic semiconductors requires substantial computer resource for each individual calculation. We might alternatively construct a machine learning model for transfer integrals, which model the full six-degrees of freedom for the relative position of dimer pairs, trained on representative calculations for the molecules of interest. Recent developments have produced effective machine learning force fields, which model the total energy of atomic assemblies. We extend the Atomic Cluster Expansion (ACE) with the correct symmetries for transfer (kinetic-energy) integrals. Combined with a spherical harmonic basis makes, this forms a strong inductive bias and makes for a data efficient model. We introduce coarse-grained and heavy-atom representations, and assess the methodology on representative conjugated semiconductors: ethylene, thiophene, and naphthalene.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Flux-modulated tunable interaction regimes in two strongly nonlinear oscillators

J. D. Koenig, G. Barbieri, F. Fani Sani et al. (+3 more)

The ability to efficiently simulate a variety of interacting quantum systems on a single device is an overarching goal for digital and analog quantum simulators. In circuit quantum electrodynamical systems, strongly nonlinear superconducting oscillators are typically realized using transmon qubits, featuring a wide range of tunable couplings that are mainly achieved via flux-dependent inductive elements. Such controllability is highly desirable both for digital quantum information processing and for analog quantum simulations of various physical phenomena, such as arbitrary spin-spin interactions. Furthermore, broad tunability facilitates the study of driven-dissipative oscillator dynamics in previously unexplored parameter regimes. In this work, we demonstrate the ability to selectively activate different dynamical regimes between two strongly nonlinear oscillators using parametric modulation. In particular, our scheme enables access to regimes that are dominated by photon-hopping, two-mode squeezing, or cross-Kerr interactions. Finally, we observe level repulsion and attraction between Kerr-nonlinear oscillators in regimes where the nonlinearities exceed the coupling strengths and decay rates of the system. Our results could be used for realizing purely analog quantum simulators to study arbitrary spin systems as well as for exploring strongly nonlinear oscillator dynamics in previously unexplored interaction regimes.
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All authors J. D. Koenig, G. Barbieri, F. Fani Sani, C. A. Potts, M. Kounalakis, G. A. Steele

Strongly Correlated Electrons

Resonating valence bond pairing energy in graphene by quantum Monte Carlo

S. Azadi, A. Principi, T.D. Kühne et al. (+1 more)

We determine the resonating-valence-bond (RVB) state in graphene using real-space quantum Monte Carlo with correlated variational wave functions. Variational and diffusion quantum Monte Carlo (DMC) calculations with Jastrow-Slater-determinant and Jastrow-antisymmetrized-geminal-power ansatze are employed to evaluate the RVB pairing energy. Using a rectangular graphene sample that lacks $\pi/3$ rotational symmetry, we found that the single-particle energy gap near the Fermi level depends on the system size along the $x$-direction. The gap vanishes when the length satisfies $L_x=3n\sqrt{3}d$, where $n$ is an integer and $d$ is the carbon-carbon bond length, otherwise, the system, exhibits a finite gap. Our DMC results show no stable RVB pairing in the zero-gap case, whereas the opening of a finite gap near the Fermi level stabilizes the electron pairing. The DMC predicted absolute value of pairing energy at the thermodynamic limit for a finite-gap system is $\sim 0.48(1)$ mHa/atom. Our results reveal a feometry-driven electron pairing mechanism in the confined graphene nanostructure.
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All authors S. Azadi, A. Principi, T.D. Kühne, M.S. Bahramy

Soft Condensed Matter

Enhanced Coalescence in Driven Foams

Alice Requier, Andrea Plati, Emmanuelle Rio et al. (+1 more)

External driving leads to the emergence of unique phenomena and properties in soft matter systems. We show that driving quasi-2D foams by mechanical vibration results in significant bubble coalescence, which is enhanced by the continuous phase yield stress. The competition between coarsening and coalescence can be modulated through vibration amplitude and foam liquid fraction, which can be used to create unusual structural motifs. The combined effect of coarsening and coalescence is captured through a statistical model that quantitatively describes the time evolution of the number of bubbles.
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All authors Alice Requier, Andrea Plati, Emmanuelle Rio, Anniina Salonen

Mesoscale and Nanoscale Physics

Facile Salt-Assisted Hydrothermal Synthesis of Nanodiamonds from CHO Precursors: Atomic-Scale Mechanistic Insights

Soumya Pratap Tripathy, Sayan Saha, Saurabh Kumar Gupta et al. (+14 more)

Hydrothermal synthesis offers an economical and scalable way to produce nanodiamonds under relatively mild, low-pressure and low-temperature conditions. However,its sustainability and the detailed mechanisms behind diamond formation in such environments are still not fully understood. In this work, we designed ten hydrothermal synthesis protocols using different CHO-based molecular precursors containing COOH and OH groups, such as organic acids, polyols, sugars, and polysaccharides.The reactions were carried out at 190 degrees Centigrade in chlorinated, strongly alkaline aqueous solutions with alkali and alkaline-earth metal ions. Using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we confirmed the presence of diamond-specific lattice planes and sp3-hybridized carbon structures. Our results show that the type of precursor, its molecular size, and the ionic composition of the solution play key roles in determining the defect patterns and polymorph distribution in the resulting nanodiamonds. Atomic-scale imaging showed both coherent and incoherent transitions from graphite to diamond, along with gradual lattice compression and complex twinning patterns. These observations provide direct insight into how interfacial crystallography and defect dynamics drive diamond formation in aqueous systems. Overall, the study positions hydrothermal synthesis as a sustainable, chemistry-driven, and tunable approach for creating nanodiamonds tailored for applications in quantum technologies, biomedicine, catalysis, and advanced materials.
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All authors Soumya Pratap Tripathy, Sayan Saha, Saurabh Kumar Gupta, Pallavee Das, Binay Priyadarsan Nayak, Anup Routray, Priya Choudhary, Srihari V, Bitop Maitra, Ashna Reyaz, Anushka Samant, Debopriya Sinha, Kritideepan Parida, Kuna Das, Abhijeet Sahoo, Kunal Pal, Sirsendu Sekhar Ray

Strongly Correlated Electrons

Metamagnetic Transition in Low-Dimensional Site-Decorated Quantum Heisenberg Ferrimagnets

Weiguo Yin and A. M. Tsvelik

The prohibition of finite-temperature phase transition in one-dimensional (1D) Ising models and 1D/2D quantum Heisenberg models with short-range interactions fundamentally constrains the application potentials of low-dimensional magnetic materials. Recently, ultranarrow phase crossover (UNPC), which can approach a transition at a desirable finite temperature $T_0$ arbitrarily closely, was discovered in 1D decorated Ising chains and ladders. Here we present a theoretical study of similarly decorated, yet much more challenging, quantum Heisenberg ferrimagnets in a magnetic field, which features ferromagnetic backbone exchange $J$, antiferromagnetic site-decoration coupling $J_{AF}$, and different magnetic moments for the backbone and decorating spins $\mu_aS_a<\mu_bS_b$. We exactly solved the model in the large $J$ limit – as a central-macrospin model – and found two finite-temperature second-order transitions; just above $T_{c2}$ a “half-ice, half-fire” regime appears. Finite-$J$ weak-field results follow from an effective-field mapping, suggesting the emergence of UNPC at finite $T_0$ in 2D square lattices thanks to its exponentially strong initial magnetic susceptibility $\chi_0\propto e^{4\pi S_a^2 J/T_0}$, though less likely in 1D chains where $\chi_0\propto J/T_0$. These results may shed light on new technological applications of low-dimensional quantum spin systems and attract experimental and computational tests.
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Statistical Mechanics · Cross-listed from physics.flu-dyn

Geometric Intermittency in Turbulence

Ritwik Mukherjee, Siddhartha Mukherjee, I. V. Kolokolov et al. (+3 more)

Equal-time scaling exponents in fully developed turbulence typically exhibit non anomalous scaling in the inverse cascade of two-dimensional (2D) turbulence and anomalous scaling in three dimensions. We demonstrate that multiscaling is not confined to longitudinal, scalar velocity increments, but also emerges in increments associated with the magnitude and orientation of the velocity vector. This decomposition uncovers a multiscaling in the 2D inverse cascade, which remains obscured when using conventional structure functions. Our results highlight a decoupling between velocity amplitude and flow geometry, offering new insight into the statistical structure of turbulent cascades as well as showing how different classes of multiscaling emerge.
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All authors Ritwik Mukherjee, Siddhartha Mukherjee, I. V. Kolokolov, V. V. Lebedev, Takeshi Matsumoto, Samriddhi Sankar Ray

Strongly Correlated Electrons

Phase transitions in the spin-1/2 Heisenberg antiferromagnet on the square lattice

Jie Qiao, Shu-Hao Zhang, Jing-Bo Qin et al. (+2 more)

The nature of the intermediate ground-state phase in the spin-1/2 frustrated square lattice model has long been debated. Using cluster density matrix embedding theory, we investigate the phase diagram of this model. The Neel phase is directly identified for J2<0.45 and the collinear phase for J2>0.65 based on the ground state. Although no direct evidence of an internal phase transition is found within the intermediate phase from the ground state, analysis of the first excited state wave function reveals a continuous quantum phase transition in this region, with a critical point at J2=0.55. This critical point divides the intermediate phase into PVBS and CVBS.
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All authors Jie Qiao, Shu-Hao Zhang, Jing-Bo Qin, Xiao-Long Zhao, Qiang Cheng

Disordered Systems and Neural Networks

Exploring Replica Symmetry Breaking and Topological Collapse in Spin Glasses with Quantum Annealing

Kumar Ghosh

Replica symmetry breaking (RSB) underlies the complex organization of disordered systems, yet quantitative validation beyond $N \sim 100$ spins has remained computationally challenging. We use quantum annealing to access ground states of the Sherrington-Kirkpatrick model up to $N = 4000$ spins, enabling the most extensive test of Parisi's Nobel Prize-winning RSB solution to date. Five independent observables confirm RSB predictions: ground-state energies converge to Parisi's value with characteristic $N^{-2/3}$ corrections, energy fluctuations scale as $N^{-3/4}$ ($\gamma = 0.739 \pm 0.036$), the chaos exponent $\theta = 0.51 \pm 0.02$ ($R^2 = 0.989$) confirms mean-field universality, the overlap distribution exhibits hierarchical structure ($\sigma_q = 0.19$), and the complexity remains invariant under 36% network dilution. Beyond a critical threshold $0.8 < D_c < 0.9$, the hierarchy collapses discontinuously through a cooperative avalanche that converts the entire system to vacancies within a narrow parameter window $\Delta D = 0.1$. These findings establish quantum computation as a tool for probing emergent many-body phenomena and uncover the topological foundations of complexity in disordered systems, with implications for neural networks, optimization, and materials science.
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Strongly Correlated Electrons

Ultrafast symmetry modulation and induced magnetic excitation in the Kagome metal RbV3Sb5

Mengxue Guan, Xiaodong Zhou, Jingyi Duan et al. (+8 more)

Light-matter interaction in frustrated Kagome metals enables access to hidden quantum states, yet the microscopic origin of symmetry breaking under ultrafast excitation remains elusive. Here, we uncover a microscopic mechanism for laser-induced symmetry breaking in RbV3Sb5 through first-principles real-time simulations. Selective excitation of a single-QM phonon mode dynamically breaks both rotational and time-reversal symmetries within the 2X2X1 charge density wave (CDW) superlattice. The resulting anisotropic lattice distortion lifts geometric frustration and stabilizes a nonequilibrium ferrimagnetic phase, accompanied by a sizable intrinsic anomalous Hall effect. Distinct from prior interpretations based on orbital antiferromagnetism or extrinsic perturbations, our findings reveal a spin-driven pathway for symmetry breaking under strong optical fields. These results provide a microscopic foundation for exploring how spin, lattice and charge degrees of freedom are intertwined in nonequilibrium correlated states.
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All authors Mengxue Guan, Xiaodong Zhou, Jingyi Duan, Chaoxi Cui, Wei Jiang, Zeying Zhang, Binhua Zhang, Zhengwei Nie, Xun Shi, Zhiwei Wang, Yugui Yao

Mesoscale and Nanoscale Physics

Spin-valley 0.7 anomaly in bilayer graphene/WSe$_2$ quantum point contacts

Jonas D. Gerber, Efe Ersoy, Michele Masseroni et al. (+10 more)

We report a well-resolved 0.7 conductance anomaly at $G = 0.7\times(2e^2/h)$ in bilayer graphene/WSe$_2$ quantum point contacts. Proximity-enhanced spin-orbit coupling splits the four-fold ground state of bilayer graphene into well-separated spin-valley locked Kramers doublets. The anomaly emerges between these opposite spin-valley states. Despite fundamentally different band structure and wavefunction characteristics, the temperature and bias phenomenology closely mirror GaAs systems. In contrast, the parallel magnetic field response differs significantly, confirming the central role of valley degrees of freedom. This opens new pathways to study valley-exchange correlation physics in regimes inaccessible to conventional semiconductors.
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All authors Jonas D. Gerber, Efe Ersoy, Michele Masseroni, Markus Niese, Artem O. Denisov, Christoph Adam, Lara Ostertag, Jessica Richter, Takashi Taniguchi, Kenji Watanabe, Yigal Meir, Thomas Ihn, Klaus Ensslin

Materials Science

Decoupling interface and thickness effects on hydrogen absorption in V/MgO: experiments and DFT

Qiuxiang Zhang, Yan Zhu, Xiaofang Peng et al. (+3 more)

We report combined experimental and first principles investigations of hydrogen absorption in epitaxial vanadium films on MgO(001) with nominal thicknesses of 10 nm and 50 nm. In - situ optical transmission and four - probe resistance isotherms show that the 50 nm film reproduces bulk like behavior with a clear first order alpha-beta hydride transition, the formation enthalpy and entropy gradually decrease with increasing hydrogen concentration. The 10 nm film, by contrast, displays continuous uptake without plateaus, with formation enthalpies H that are relatively close in magnitude to the 50 nm film (both exhibiting exothermic behavior in the range of approximately 0.5 to 0.3 eV/H), but with a more negative entropy change S (larger S) indicating reduced configurational freedom for hydrogen in the ultrathin limit; the critical temperature for phase coexistence is suppressed below 400 K. Density functional theory calculations on MgO V superlattices (Vn/(MgO)n, n = 3,5,7) reveal pronounced V 3d and O 2p hybridization and interfacial charge redistribution that weaken hydrogen binding near the interface and recover toward bulk values with increasing V thickness. These results indicate that interfacial electronic structure, in addition to finite size energetics, governs hydride stability in ultrathin V films and that layer - thickness and interface engineering can tune reversible hydrogen uptake.
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All authors Qiuxiang Zhang, Yan Zhu, Xiaofang Peng, Weiguang Yang, Yuping Le, Xiao Xin