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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 26 November

Disordered Systems and Neural Networks

Local Geometric and Transport Properties of Networks that are Generated from Hyperuniform Point Patterns

James V. Raj, Xiaohan Sun, Charles Emmett Maher et al. (+2 more)

Hyperuniformity, which is a type of order that is characterized by the suppression of long-range density fluctuations in comparison to the fluctuations in standard disordered systems, has emerged as a powerful concept in many natural and engineered phenomena. In this paper, we harness hyperuniform point patterns to generate disordered, spatially-embedded networks that are distinct from both perfectly ordered lattices and uniformly random spatial networks. We refer to this class of disordered networks as hyperuniform-point-pattern-induced (HuPPI) networks, and we compare them to counterpart Poisson-point-pattern-induced (PoPPI) networks and networks that we generate from random-sequential-adsorption (RSA) packings (which have local order but are not hyperuniform). We examine HuPPI, PoPPI, and RSA networks that we generate using Gabriel, Delaunay, Delaunay-centroidal, and Voronoi network-generation methods. We show that HuPPI networks have smaller mean normalized total effective resistances (TERs) than PoPPI networks in Gabriel, Delaunay-centroidal, and Voronoi networks and have shorter mean random-walk mixing times than PoPPI networks in Gabriel, Delaunay, and Delaunay-centroidal networks. For all four network-generation methods and for both HuPPI and PoPPI networks, we find that the Ollivier–Ricci curvature (ORC) of an edge is negatively correlated with its TER edge contribution (i.e., the increase in TER that results from removing that edge). Collectively, our results (1) illustrate how the local network geometry that ORC measures is related to transport and network connectivity and (2) demonstrate that the network-generation method provides an additional design lever for spatial networks beyond the choice of their underlying point pattern. [This abstract is abridged significantly from the full abstract.]
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All authors James V. Raj, Xiaohan Sun, Charles Emmett Maher, Katherine A. Newhall, Mason A. Porter

Soft Condensed Matter

Relation between extensional viscosity and polymer conformation in dilute polymer solutions

Yusuke Koide, Takato Ishida, Takashi Uneyama et al. (+1 more)

We investigate extensional viscosity and polymer conformation in dilute polymer solutions under uniaxial extensional flow using dissipative particle dynamics simulations. At high extension rates, polymers are significantly stretched by extensional flows, and the extensional viscosity growth function exhibits strain hardening. To reveal their quantitative relation, we adopt an analysis method based on the Rouse-type model. We demonstrate that the extensional viscosity growth function is determined by the instantaneous gyration radii in the parallel and perpendicular directions to the extensional direction and their time derivatives. Our approach also provides a unified description of the steady-state extensional viscosity of dilute polymer solutions for various chain lengths and concentrations in terms of the polymer gyration radius.
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All authors Yusuke Koide, Takato Ishida, Takashi Uneyama, Yuichi Masubuchi

Mesoscale and Nanoscale Physics

Non-uniform Thermal Conductivity in Nanoscale Multiple Hotspot Systems

Yu He, Zhihao Zhou, Lina Yang et al. (+1 more)

Understanding nanoscale hotspot thermal transport is crucial in electronic devices. Contrary to common perception, recent experiments show that closely spaced nanoscale multiple hotspots can enhance heat dissipation. Here, the thermal transport in nanoscale multiple hotspot systems is investigated by solving the phonon Boltzmann transport equation. The local thermal conductivity is proposed to describe the non-uniform spatial distribution of heat transport capability in nanoscale multiple hotspot systems. The maximum value exceeds the uniform heating case by up to 27%, which is attributed to the spatially varying fraction of unscattered phonons emitted from hotspots. Moreover, the effects and mechanisms of hotspot spacing on thermal transport are investigated, showing that reducing the hotspot spacing can enhance the heat flux by up to 40%. This work challenges the conventional view that thermal transport capability is spatially uniform throughout the system and provides fundamental insights for thermal management in high-power-density integrated circuits.
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All authors Yu He, Zhihao Zhou, Lina Yang, Nuo Yang

Mesoscale and Nanoscale Physics

Edge-state transport in gapped bilayer graphene

Jesús Arturo Sánchez-Sánchez and Thomas Stegmann

We investigate electronic transport in gapped bilayer graphene (gBLG) devices. For certain edge terminations -typically a combination of zigzag, armchair, and bearded types - we observe edge state conduction within the band gap, which is opened by a potential bias between the two layers. The edge states can generate a non-local resistance, in line with recent experiments [1]. Band structure calculations of gBLG nanoribbons corroborate the existence of the edge states, whose edge localization can be switched by tuning the electron energy. Their existence strongly depends on the edge termination and does not originate from a topological bulk-boundary correspondence.
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Strongly Correlated Electrons

Probing magnetic-field-induced multipolar ordering through field-angle-resolved magnetostriction and thermal expansion in PrIr$_2$Zn$_{20}$

Naoki Okamoto, Yohei Kono, Takahiro Onimaru et al. (+3 more)

We performed field-angle-resolved magnetostriction and thermal-expansion measurements on PrIr$_2$Zn$_{20}$, a cubic non-Kramers compound exhibiting antiferroquadrupolar order below $T_{\rm Q}=0.125$ K. Thermal expansion exhibits two qualitatively different anomalies under magnetic fields applied along the $[001]$ direction, providing experimental support for the existence of an intermediate A phase previously reported. Furthermore, comparison between the experimental results and theoretical modeling indicates a strong anisotropic coupling of the $O_{20}$ quadrupolar moment, which plays a key role in stabilizing the A phase. These findings demonstrate that multipolar states in non-Kramers systems can be effectively tuned by magnetic-field orientation, providing insights into the anisotropic nature of quadrupolar interactions.
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All authors Naoki Okamoto, Yohei Kono, Takahiro Onimaru, Keisuke T. Matsumoto, Kazumasa Hattori, Shunichiro Kittaka

Soft Condensed Matter

Self-avoiding walks pulled at an angle

C J Bradly, N R Beaton and A L Owczarek

We investigate polymers pulled away from an interacting surface, where the force is applied to the untethered endpoint and at an angle $\theta$ to the surface. We use the canonical self-avoiding walk model of polymers and obtain the phase diagram of the model using Monte Carlo simulations for a range of angles, temperatures and force magnitudes. The phase diagram of the model displays re-entrance at low temperatures for three-dimensional walks when the pulling is more vertical than horizontal. Our results agree with various exactly solvable lattice models that have been previously studied.
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Materials Science

Ion Jump Motion as the Background for Muon Diffusion in Battery Materials Research Using $\mu$SR

Ryosuke Kadono

Numerical simulations of muon spin relaxation ($\mu$SR) in ion diffusion were performed using the extended Kubo-Toyabe (KT) relaxation function $G_z^{\rm EA}(t)$ that incorporates an Edwards-Anderson type autocorrelation function for the jump motion of ions. The analysis of the generated $\mu$SR spectra using the conventional KT function $G_z^{\rm KT}(t;\Delta_{\rm KT},\nu_{\rm KT})$ (mimicking the previous analysis procedure) suggest that the anomalous peak in the fluctuation rate $\nu_{\rm KT}$ around a specific temperature $T^*$ and associated decrease of the linewidth $\Delta_{\rm KT}$ above $T^*$, often observed in the previous $\mu$SR studies on ion diffusion, originate from the sharp increase in the ion jump rate $\nu_{\rm i}$ against that of the muon $\nu_\mu$ with increasing temperature. This indicates that a more detailed reanalysis of the vintage data using $G_z^{\rm EA}(t)$ is useful for the proper evaluation of $\nu_{\rm i}$ and $\nu_\mu$. Meanwhile, it also suggests that the $\mu$SR results showing no such anomaly convey little information on ion diffusion.
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Statistical Mechanics

Anisotropic scale invariance and the uniaxial Lifshitz point from the nonperturbative renormalization group

Gonzalo De Polsi and Pawel Jakubczyk

We employ the derivative expansion of the nonperturbative renormalization group to address the phenomenon of anisotropic scale invariance and the associated functional fixed points, also known as Lifshitz points, in systems characterized by a scalar order parameter. We demonstrate the existence of the Lifshitz fixed point featuring a non-classical value of the anisotropy exponent $\theta<1/2$ and provide estimates for values of a set of critical exponents in the physically most relevant case of the three-dimensional uniaxial Lifshitz point $(d,m)=(3,1)$, $m$ denoting the anisotropy index. We compare our predictions with existing estimates from perturbative expansions around dimensionality $d=4+\frac{1}{2}$ as well as those from the $1/N$ expansion.
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Materials Science

Hierarchical high-throughput screening of alkaline-stable lithium-ion conductors combining machine learning and first-principles calculations

Zhuohan Li, KyuJung Jun, Bowen Deng et al. (+1 more)

Solid-state batteries require lithium-ion conductors that combine high ionic conductivity with stability under harsh electrochemical and chemical conditions. Here, we investigate the chemical factors governing the stability of NASICON-type and garnet-type Li-ion conductors in highly alkaline environments. This is particularly relevant to solid-state Li-air cells operated under humidified air where alkaline conditions arise due to the formation of LiOH discharge products. We implement a hierarchical high-throughput screening workflow that consists of a pre-screening step using a universal machine-learning interatomic potential and a more accurate DFT-based screening. This approach enables rapid evaluation of over 320,000 compositions, from which 209 alkaline-stable candidates are identified. We identify specific cation substitutions that improve alkaline stability in NASICON and garnet compounds and reveal the underlying mechanism. More importantly, we highlight design trade-offs that require careful composition optimization to simultaneously enhance synthesizability, operational stability, and Li-ion/electronic conductivities for practical humid Li-air battery applications.
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All authors Zhuohan Li, KyuJung Jun, Bowen Deng, Gerbrand Ceder

Strongly Correlated Electrons

Exploring the Anomalous Nernst Effect in SrRuO$_3$

Anna Merin Francis, Avirup De, Abhijit Biswas et al. (+3 more)

We investigate the anomalous Nernst effect in epitaxial SrRuO$_3$ thin films grown on c-cut Al$_2$O$_3$ substrates, and in a polycrystalline SrRuO$_3$ slab. Through comprehensive measurements of the transverse thermoelectric response as a function of temperature and magnetic field, we observe a pronounced Nernst signal near $T_c$ in the (111) oriented SrRuO$_3$ thin films. The strong temperature and nontrivial field dependence underscore the pivotal role of the magnetic anisotropy in tuning the Berry curvature and, consequently, the anomalous Nernst effect in SrRuO$_3$.
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All authors Anna Merin Francis, Avirup De, Abhijit Biswas, Lily Mandal, Pallavi Kushwaha, Sunil Nair

Materials Science

Optical contrast-based determination of number of layers for two-dimensional van der Waals magnet Fe$_3$GeTe$_2$

Neesha Yadav, Sandeep and Pintu Das

Recent advances in revealing intrinsic magnetism in two-dimensional (2D) materials have highlighted their potential for future spintronic applications, driven by their novel physical properties, promising for future spintronic devices. In order to explore layer dependent magnetic behavior, in general, mechanically exfoliated flakes from high-quality single crystals are used. It is crucial to determine the number of layers of these materials accurately. In the absence of an efficient and quick method, researchers often rely on atomic force microscopy (AFM) imaging to identify their number of layers. In this work, we report an optical contrast study as a quick and cost-effective technique to determine the number of layers of Fe$_3$GeTe$_2$ (FGT). Here, we observed a linear relationship between the optical contrast (derived from optical microscopic images) observed for mechanically exfoliated FGT nano-flakes and their thickness, as measured by the AFM imaging method. This technique requires no additional equipment; it relies solely on a conventional optical microscope. Additionally, our results reveal a thickness-dependent evolution of the intensity; in contrast, the Raman frequency demonstrates no significant dependence on layer thickness. Also, our studies reveal two additional Raman modes of FGT, at the frequency of 129\,cm$^-1$ & 190\,cm$^-1$. Both modes show the intensity dependence on the thickness of FGT, same as out-of-plane (A$_{1g}$) Raman modes.
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Tuesday 25 November

Soft Condensed Matter

Gravitational aggregation regimes: critical dissipation threshold, optimal rigidity and fractal transition

Yohann Trivino

I present a three-dimensional Discrete Element Method study of self-gravitation and contact mechanics in cold granular assemblies. The model couples direct Newtonian attraction between every particle pair with a linear visco-elastic normal contact law. Particles are treated as non-cohesive spheres; the normal force is parameterized to reproduce a prescribed restitution coefficient. Rotations are integrated using quaternions to avoid singularities. By normalizing the stiffness kn by kstar = G*m^2/R^3 and time by the free-fall time t_ff, I perform systematic parameter campaigns over dissipation (gamma) and normalized stiffness ktilde = kn/kstar. Results reveal three aggregation regimes. For low gamma the particles remain largely dispersive; above a critical gamma of about 5e2 aggregation accelerates until plateaus are reached in the aggregation time T_agg divided by t_ff. For stiffness ktilde on the order of 1e6 the aggregation time reaches a clear minimum. The cluster fraction C/Ntot shows a non-monotonic dependence on ktilde, with optimal cohesion at intermediate rigidity and peripheral isolation at extreme stiffness. Mapping the fractal dimension F across (gamma, ktilde) demonstrates transitions from compact structures (F about 3) to ramified structures (F below 2). These findings quantify how microscopic contact laws govern both the kinetics and microstructure of gravity-driven aggregation, providing a predictive framework for planetesimal formation and for calibrating DEM models against laboratory and micro-gravity experiments.
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Statistical Mechanics

Hardware Acceleration of Frustrated Lattice Systems using Convolutional Restricted Boltzmann Machine

Pratik Brahma, Junghoon Han, Tamzid Razzaque et al. (+2 more)

Geometric frustration gives rise to emergent quantum phenomena and exotic phases of matter. While Monte Carlo methods are traditionally used to simulate such systems, their sampling efficiency is limited by the complexity of interactions and ground-state properties. Restricted Boltzmann Machines (RBMs), a class of probabilistic neural networks, offer improved sampling by incorporating machine learning techniques. However, fully-connected bipartite RBMs are inefficient for representing physical lattices with sparse interactions. To address this, we implement Convolutional Restricted Boltzmann Machines (CRBMs) that leverage translational symmetry inherent to lattices. Using the classical Shastry-Sutherland (SS) Ising lattice, we demonstrate (i) CRBM formulation that captures SS interactions, and (ii) digital hardware accelerator to enhance sampling performance. We simulate lattices with up to 324 spins, recovering all known phases of the SS Ising model, including the long range ordered fractional plateau. Our hardware characterizes spin behavior at critical points and within spin liquid phases. This implementation achieves a speedup of 3 to 5 orders of magnitude (33 ns to 120 ms) over GPU-based implementations. Moreover, the time-to-solution is within two orders of magnitude of quantum annealers, while offering superior scalability, room-temperature operation and reprogrammability. This work paves a pathway for scalable digital hardware that embeds physical symmetries to enable large scale simulations of material systems.
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All authors Pratik Brahma, Junghoon Han, Tamzid Razzaque, Saavan Patel, Sayeef Salahuddin

Statistical Mechanics · Cross-listed from quant-ph

Restoring a Missing Meta-Symmetry of Quantum Mechanics

Sheng Ran

In conventional quantum mechanics, all unitary evolution takes place within the space-time Hilbert space $\mathcal H_{xt}=L^2(\mathcal M_{xt})$, with time as the sole evolution parameter. The momentum-energy representation $\phi(k,E)$ is treated merely as a Fourier re-expression of the same state-kinematically equivalent but dynamically inert. Here we restore the fundamental symmetry between the conjugate pairs $(x,t)$ and $(k,E)$ by extending the quantum theory to an enlarged Hilbert space $\mathcal H_{\text{total}} = \mathcal H_{xt} \oplus \mathcal H_{kE}$, within which the momentum-energy sector $\mathcal H_{kE}=L^2(\mathcal M_{kE})$ carries its own autonomous unitary evolution generated by a self-adjoint operator $\hat{\mathcal T}$. The resulting structure establishes a meta-symmetry: a symmetry between two conjugate dynamical projections of a single global quantum state. It produces a dual-manifold geometry in which each domain is locally complete yet globally open, with divergent limits in one mapping onto extended regions in the other. Remarkably, the dual-manifold symmetry alone reproduces both the uniform dark-energy background and the exponential boundary mapping near black-hole horizons that underlies Hawking radiation. This framework thus opens a quantum-theoretic route to cosmological phenomena that are ordinarily treated within general relativity.
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Materials Science

Photo-induced carrier dynamics in InSb probed with broadband THz spectroscopy based on BNA crystals

Elodie Iglesis, Alexandr Alekhin, Maximilien Cazayous et al. (+3 more)

We report an optical pump - terahertz (THz) probe study of the photoinduced transient carrier dynamics in the low bandgap semiconductor Indium Antimonide (InSb). Using an organic N-benzyl-2-methyl-nitroaniline (BNA) crystal as a broadband THz source, we access the full spectral response over more than 5 THz, for varying pump-probe delay following the optical excitation. Using the Drude-Lorentz model accounting for differences between the excited length in material and the penetration depth of THz beam in pumped InSb, we extract the absolute carrier density as a function of the pump-probe delay, and provide insights on the diffusion length at given carrier densities, for different pump fluences. The mismatch between the THz penetration depth and the actual excited sample depth after carrier diffusion is discussed, since their evolutions with time and pump fluence are not intuitive as both quantities depend on carrier density.
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All authors Elodie Iglesis, Alexandr Alekhin, Maximilien Cazayous, Alain Sacuto, Yann Gallais, Sarah Houver

Materials Science

Cr2O3/e̱ta}-Ga2O3 Heterojunction Diodes with Orientation-Dependent Breakdown Electric Field up to 12.9 MV/cm

Yizheng Liu, Haochen Wang, Carl Peterson et al. (+3 more)

We report the fabrication of Cr2O3/e̱ta}-Ga2O3 heterojunction diodes using reactive magnetron sputtering of Cr2O3 on highly doped e̱ta}-Ga2O3 bulk substrates along (100), (010), (001), (110), and (011) orientation dependence of high electric field handling capability in e̱ta}-Ga2O3. Additional relative permittivity values in (110) and (011) orientations of e̱ta}-Ga2O3 were computed by using first-principles calculation methods for accurate apparent charge density (ND-NA) extraction and breakdown electric field analysis from capacitance-voltage measurements. The HJDs fabricated on n+ (110) exhibited breakdown electric fields >10 MV/cm up to 12.9 MV/cm, showing the highest experimentally observed parallel-plane junction electric field among e̱ta}-Ga2O3-based junctions. Breakdown electric fields among (100), (010), (001), and (011) orientations showed distinct distribution in the range of 5.13-5.26 MV/cm, 5.10-7.05 MV/cm, 2.70-3.33 MV/cm, and 3.88-4.38 MV/cm, respectively, validating the orientational dependence of parallel-plane junction electric field at breakdown in low-symmetry monoclinic e̱ta}-Ga2O3. The parallel-plane breakdown electric fields (EBr,||) reported in this work were extracted when the device experienced catastrophic breakdown at 100 mA/cm^2 current density compliance, and should not be confused with critical electric field (Ec) as a function of drift layer doping concentration, which accounts for electric-field dependent impact ionization coefficients in Si, SiC and GaN. This study can guide the choice of crystal orientation for high performance gallium oxide-based devices that require high electric field handling capability.
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All authors Yizheng Liu, Haochen Wang, Carl Peterson, James S. Speck, Chris Van De Walle, Sriram Krishnamoorthy

Superconductivity · Cross-listed from physics.ins-det

Tungsten Germanide Superconducting Nanowire Single-Photon Detectors with Saturated Internal Detection Efficiency at Wavelengths up to 29 {\mu}m

Benedikt Hampel, Daniel Kuznesof, Andrew S. Mueller et al. (+13 more)

Superconducting nanowire single-photon detectors (SNSPDs) are among the most sensitive single-photon detectors available and have the potential to transform fields ranging from infrared astrophysics to molecular spectroscopy. However, extending their performance into the mid-infrared spectral region - crucial for applications such as exoplanet transit spectroscopy and vibrational fingerprinting of molecules - has remained a major challenge, primarily due to material limitations and scalability constraints. Here, we report on the development of SNSPDs based on tungsten germanide, a novel material system that combines high mid-infrared sensitivity with compatibility for large-scale fabrication. Our detectors exhibit saturated internal detection efficiency at wavelengths up to 29 {\mu}m, while using 2.7x thicker films (8 nm vs 3 nm) and up to 4.5x wider nanowires (360 nm vs 80 nm) compared to mid-infrared-optimized SNSPDs fabricated from tungsten silicide. This advance will enable scalable, high-performance single-photon detection in a spectral region that was previously inaccessible, opening new frontiers in remote sensing, thermal imaging, environmental monitoring, molecular physics, and astronomy.
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All authors Benedikt Hampel, Daniel Kuznesof, Andrew S. Mueller, Sahil R. Patel, Robert H. Hadfield, Emma E. Wollman, Matthew D. Shaw, Dirk Schwarzer, Alec M. Wodtke, Khalid Hossain, Allison V. Mis, Alexana Roshko, Richard P. Mirin, Sae Woo Nam, Martin J. Stevens, Varun B. Verma

Strongly Correlated Electrons

Defect Bootstrap: Tight Ground State Bounds in Spontaneous Symmetry Breaking Phases

Michael G. Scheer, Nisarg Chadha, Da-Chuan Lu et al. (+1 more)

The recent development of bootstrap methods based on semidefinite relaxations of positivity constraints has enabled rigorous two-sided bounds on local observables directly in the thermodynamic limit. However, these bounds inevitably become loose in symmetry broken phases, where local constraints are insufficient to capture long-range order. In this work, we identify the origin of this looseness as order parameter defects which are difficult to remove using local operators. We introduce a $\textit{defect bootstrap}$ framework that resolves this limitation by embedding the system into an auxiliary $\textit{defect model}$ equipped with ancilla degrees of freedom. This construction effectively enables local operators to remove order parameter defects, yielding tighter bounds in phases with spontaneous symmetry breaking. This approach can be applied broadly to pairwise-interacting local lattice models with discrete or continuous internal symmetries that satisfy a property we call $\textit{defect diamagnetism}$, which requires that the ground state energy does not decrease upon adding any finite number of symmetry defects. Applying the method to the transverse field Ising models in 1D and 2D, we obtain significantly improved bounds on energy densities and spin correlation functions throughout the symmetry broken phase in 1D and deep within the phase in 2D. Our results demonstrate that physically motivated constraint sets can dramatically enhance the power of bootstrap methods for quantum many-body systems.
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All authors Michael G. Scheer, Nisarg Chadha, Da-Chuan Lu, Eslam Khalaf

Statistical Mechanics

A new Fractal Mean-Field analysis in phase transition

Ismael S. S. Carrasco, Henrique A. de Lima and Fernando A. Oliveira

Understanding phase transitions requires not only identifying order parameters but also characterizing how their correlations behave across scales. By quantifying how fluctuations at distinct spatial or temporal points are related, correlation functions reveal the structural organization of complex systems. In this work, we reexamine the theoretical foundations of these correlations in systems undergoing second-order phase transitions, with emphasis on the Ising model extended to non-integer spatial dimensions. We revisit the hypothesis that, at criticality, the equilibrium dynamics become effectively confined to the fractal edge of spin clusters and redo the analysis using fractional calculus. Within this framework, the fractal dimension that governs the correlations in that subspace is directly related to Fisher's exponent $\eta$, which quantifies the singular behavior of the correlation function near criticality. Importantly, this correlation fractal dimension is distinct from the fractal dimension associated with the order parameter. The fractional approach allows us to directly compute the correlation fractal dimension and to establish an explicit geometrical relation connecting the two fractal dimensions. Moreover, the formulation naturally extends to non-integer spatial dimensions, remaining valid below the upper critical dimension and yielding the correct value of Fisher's exponent $\eta$ for a continuous spatial dimension $d$. Within this framework, we also provide empirical functions describing how the main critical exponents vary continuously as a function of the space dimension.
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Soft Condensed Matter

The metastability of lipid vesicle shapes in uniaxial extensional flow

M.A. Shishkin and E.S. Pikina

In this work, we investigate the elastic properties of deflated vesicles and their shape dynamics in uniaxial extensional flow. By analysing the Helfrich bending energy and viscous flow stresses in the limit of highly elongated shapes, we demonstrate that all stationary vesicle configurations are metastable. For vesicles with small reduced volume, we identify the type of bifurcation at which the stationary state is lost, leading to unbounded vesicle elongation in time. We show that the stationary vesicle length remains finite at the critical extension rate. The critical behaviour of the stationary vesicle length and of the growth rates of small perturbations is obtained analytically and confirmed by direct numerical computations. The beginning stage of the unbounded elongation dynamics is simulated numerically, in agreement with the analytical predictions.
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Soft Condensed Matter

Analytical Interaction Potentials for Disks in Two Dimensions

Binghan Liu, Junwen Wang, Gary S. Grest et al. (+1 more)

Compact analytical forms are derived for the interactions involving thin disks in two dimensions using an integration approach. These include interactions between a disk and a material point, between two disks, and between a disk and a wall. Each object is treated as a continuous medium of materials points interacting by the Lennard-Jones 12-6 potential. By integrating this potential in a pairwise manner, expressions for the potentials and resultant forces between extended objects are obtained. All the results are validated with numerical integrations. The analytical potentials are implemented in LAMMPS and used to simulate two-dimensional suspension of disks with an explicit solvent modeled as a Lennard-Jones liquid. In monodisperse disk suspensions, a disorder-to-order transition of disk packing is observed as the area fraction of disks is increased or as the solvent evaporates. In bidisperse disk suspensions being rapidly dried, stratification is found with the smaller disks enriched at the evaporation front. Such "small-on-top" stratification echoes the similar phenomenon occurring in three-dimensional polydisperse colloidal suspensions that undergo fast drying. These potentials can be applied to a wide range of two-dimensional systems involving disk-like objects.
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All authors Binghan Liu, Junwen Wang, Gary S. Grest, Shengfeng Cheng

Strongly Correlated Electrons

Hund-projected Kanamori model: an effective description of Hund's metals near the Mott insulating regime

Johan Carlström

Hund's coupling plays a decisive role in shaping electron correlations of multi-orbital systems, giving rise to a class of materials–Hund's metals–that combine local-moment physics with metallic transport. Here we derive an effective low-energy description of such a system near the Mott insulating regime, starting from the multi-orbital Hubbard-Kanamori Hamiltonian and projecting onto the high-spin manifold favored by Hund's first rule. The resulting Hund-projected Kanamori model captures the interplay between carrier motion and magnetic correlations in the presence of strong Hund's coupling. In the undoped limit, the model reduces to a spin-$N/2$ Heisenberg system with suppressed quantum fluctuations, approaching the classical limit for realistic five-band configurations. Upon doping, carrier motion couples strongly to the spin background and drives ferromagnetic correlations through a Hund-enhanced kinetic mechanism analogous to, but much stronger than, Nagaoka ferromagnetism. Owing to its reduced sign problem, the model can be addressed with advanced path-integral methods to determine quasiparticle structure and effective interactions between carriers-quantities that are challenging to obtain with other methods. This framework establishes a microscopic bridge between the Kanamori model and the emergent magnetic and transport phenomena characteristic of Hund's metals.
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Soft Condensed Matter

Memory Effects in Contact Line Friction

Niklas Wolf and Nico van der Vegt

When a drop of liquid comes into contact with a solid surface, it relaxes towards an equilibrium configuration, either wetting the surface or remaining in a droplet-like shape with a finite contact angle. The force driving the process towards equilibrium is the corresponding out-of-balance Young's force. However, the speed with which the liquid front advances depends strongly on an opposing friction force arising from dissipative processes due to the moving solid-liquid-gas contact line. In analogy to the treatment of hydrodynamic friction we present an exact method, based on the Mori-Zwanzig formalism, to extract this friction from equilibrium data. We find that the contact line exhibits long-lasting memory with a characteristic power-law decay due to coupling to the systems hydrodynamic modes. Within linear response regime, we obtain the frequency-dependent dissipative and elastic response of the contact line to an external perturbation, including a frequency-dependent friction coefficient. Similar to hydrodynamic friction in liquids, we find that the friction decreases beyond a characteristic frequency and the system exhibits predominantly elastic behavior.
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Strongly Correlated Electrons

Strong-coupling theory of bilayer plasmon excitations

Hiroyuki Yamase, Luciano Zinni, Matías Bejas et al. (+1 more)

Recently plasmon excitations in bilayer lattice systems were studied extensively in the weak-coupling regime. Unlike single-layer systems, these bilayers exhibit two distinct modes, $\omega_{\pm}$, which show characteristic dependences upon the momentum and hopping integrals along the $z$ direction. To apply them to cuprates, strong correlation effects should be considered, but a comprehensive analysis has not yet been investigated. In this work, we present a strong-coupling theory to analyze the charge dynamics of a bilayer system, utilizing the $t$-$J$-$V$ model, which includes the long-range Coulomb interaction, $V$, on a lattice. Although our theoretical framework is fundamentally different from the weak-coupling approach, we find that resulting plasmon excitations are similar to those of a weak-coupling theory. A key distinction is that our strong-coupling framework reveals a noticeable suppression of particle-hole excitations, which allows the plasmon modes to remain well-defined over a wider region of momentum. We suggest that the experimentally reported plasmon excitations in Y-based cuprates can be described by the $\omega_{-}$ mode, although we call for more systematic experiments to verify this.
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All authors Hiroyuki Yamase, Luciano Zinni, Matías Bejas, Andrés Greco

Strongly Correlated Electrons · Cross-listed from hep-th

Krylov Complexity of Supersymmetric SYK Models

James Chryssanthacopoulos and David Vegh

We study the effect of supersymmetry breaking on Krylov complexity in the $\mathcal{N}=2$ SYK model under irrelevant and mass deformations of the Hamiltonian. The irrelevant deformation breaks $\mathcal{N}=2$ supersymmetry down to $\mathcal{N}=1$, while the mass deformation breaks supersymmetry completely. Using Krylov subspace methods, we analyze the Lanczos sequence, Krylov dimension, complexity, and entropy of the undeformed model and both deformations at finite system size. Both deformations enlarge the Krylov space and raise the saturation complexity as the BPS degeneracy is lifted. For the system sizes explored, the irrelevant deformation drives the saturation complexity to roughly half the Krylov dimension, while the mass deformation decreases it over an intermediate range of deformation strengths as the system drifts toward integrability. These distinct behaviors reveal how the mechanism of supersymmetry breaking leaves an imprint on quantum complexity.
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Superconductivity

Light-induced Asymmetric Pseudogap below T$_\text{c}$ in cuprates

D. Armanno, O. Gingras, F. Goto et al. (+15 more)

To this day, high-temperature cuprate superconductors remain an unparalleled platform for studying the competition and coexistence of emergent, static and dynamic, quantum phases of matter exhibiting high transition temperature non-s-wave superconductivity, non-Fermi liquid transport and a still enigmatic pseudogap regime. However, how superconductivity emerges alongside and competes with the pseudogap regime remains an open question. Here, we present a high-resolution, time- and angle-resolved photoemission study of the near-antinodal region of optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. For a sufficiently high excitation fluence, we disrupt superconductivity and drive a transient change from a symmetric superconducting-like to an asymmetric pseudogap-like density of states, for electronic temperatures well below the equilibrium superconducting critical temperature. Conversely, when the superconductivity is fully restored, the pseudogap is suppressed, as signaled by a fully particle-hole symmetric density of states. A unique aspect of our experiments is that the pseudogap coexists with superconducting features at intermediate times or at intermediate fluence. Our findings challenge the paradigm that superconductivity emerges by establishing phase coherence in the pseudogap. Instead, our experimental results, supported by phenomenological theory, demonstrate that the two states compete, and that the low-temperature ground state of the cuprates originates from a competition between superconducting and pseudogap states.
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All authors D. Armanno, O. Gingras, F. Goto, J.-M. Parent, A. Longa, A. Jabed, B. Frimpong, R.D. Zhong, J. Schneeloch, G. D. Gu, G. Jargot, H. Ibrahim, F. Legare, B.J. Siwick, N. Gauthier, A. Georges, A.J. Millis, F. Boschini

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Real-time Monitoring of Neon Film Growth for Electron-on-Neon Qubits

Sidharth Duthaluru, Kaiwen Zheng, Erik A. Henriksen et al. (+1 more)

Electron-on-neon (eNe) charge states coupled to superconducting circuits are a promising platform for quantum computing. Control over the formation of these charge states requires techniques to track and control the growth of solid Ne films on the circuit surface. We demonstrate a real-time Ne film-growth monitor using high-transition-temperature (high-$T_c$) YBCO microwave resonators. The high $T_c$ enables tracking of the film thickness near Ne's triple temperature and below. Across more than 300 solidification experiments, we find that the final Ne thickness varies stochastically from a few nm to a few $\mu$m for films solidified from the liquid phase. By increasing the driving power in the resonator, we consistently reduce the final thickness to below 100 nm. These results represent an important step toward controlled formation of Ne films for eNe qubits and highlight the broader utility of high-$T_c$ resonators for hybrid quantum systems.
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All authors Sidharth Duthaluru, Kaiwen Zheng, Erik A. Henriksen, Kater W. Murch

Strongly Correlated Electrons · Cross-listed from quant-ph

Multi-Field Relativistic Continuous Matrix Product States

Karan Tiwana and Antoine Tilloy

Relativistic continuous matrix product states (RCMPS) are a powerful variational ansatz for quantum field theories of a single field. However, they inherit a property of their non-relativistic counterpart that makes them divergent for models with multiple fields, unless a regularity condition is satisfied. This has so far restricted the use of RCMPS to toy models with a single self-interacting field. We address this long standing problem by introducing a Riemannian optimization framework, that allows to minimize the energy density over the regular submanifold of multi-field RCMPS, and thus to retain purely variational results. We demonstrate its power on a model of two interacting scalar fields in $1+1$ dimensions. The method captures distinct symmetry-breaking phases, and the signature of a Berezinskii-Kosterlitz-Thouless (BKT) transition along an $O(2)$-symmetric parameter line. This makes RCMPS usable for a far larger class of problems than before.
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Soft Condensed Matter · Cross-listed from physics.bio-ph

Rectification of stress by fiber networks: Manifestation of non-linear screening through self-organized buckling

Kanaya Malakar, Albert Countryman and Bulbul Chakraborty

Force transmission at large length scales is crucial for such biological functions as cell motility and morphogenesis. The networks that transmit these forces are malleable, patterned by active forces generated at the microscale by biological motors. In this paper we explore a simple model of a non-linear fiber network which has only two modes of deformation, but exhibits diverse mechanical phases with distinct large-scale response, tuned by the strength of a microscopic force dipole. We demonstrate, via numerical simulations, that the network is remodeled by organized patterns of buckling, which lead to a renormalization of the Poisson ratio. Finally, we show that the emergent behavior at large length scales can be ascribed to "mechanical screening" of the force dipole, analogous to dielectric screening of charges in electrostatics.
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Materials Science · Cross-listed from quant-ph

Elucidating the Inter-system Crossing of the Nitrogen-Vacancy Center up to Megabar Pressures

Benchen Huang, Srinivas V. Mandyam, Weijie Wu et al. (+12 more)

The integration of Nitrogen-Vacancy color centers into diamond anvil cells has opened the door to quantum sensing at megabar pressures. Despite a multitude of experimental demonstrations and applications ranging from quantum materials to geophysics, a detailed microscopic understanding of how stress affects the NV center remains lacking. In this work, using a combination of first principles calculations as well as high-pressure NV experiments, we develop a complete description of the NV's optical properties under general stress conditions. In particular, our ab initio calculations reveal the complex behavior of the NV's inter-system crossing rates under stresses that both preserve and break the defect's symmetry. Crucially, our proposed framework immediately resolves a number of open questions in the field, including: (i) the microscopic origin of the observed contrast-enhancement in (111)-oriented anvils, and (ii) the surprising observation of NV contrast-inversion in certain high-pressure regimes. Our work lays the foundation for optimizing the performance of NV high-pressure sensors by controlling the local stress environment, and more generally, suggests that symmetry-breaking stresses can be utilized as a novel tuning knob for generic solid-state spin defects.
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All authors Benchen Huang, Srinivas V. Mandyam, Weijie Wu, Bryce Kobrin, Prabudhya Bhattacharyya, Yu Jin, Bijuan Chen, Max Block, Esther Wang, Zhipan Wang, Satcher Hsieh, Chong Zu, Christopher R. Laumann, Norman Y. Yao, Giulia Galli