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Physics Condensed Matter

cond-mat Watch Condensed Matter

Tuesday 6 January

Strongly Correlated Electrons

Possible inverse magnetic melting effect in vdW-like Kondo lattice CeSn$_{0.75}$Sb$_2$

Hai Zeng, Yiwei Chen, Zhuo Wang et al. (+5 more)

Given the intimate connection between magnetic orders and the interplay among multiple degrees of freedom in heavy-fermion systems, controlling and understanding the associated inverse melting effect is crucial for unveiling novel condensed-matter states and their potential applications. Here, we report the growth of single crystalline quasi-two-dimensional van-der-Waals-like (vdW-like) Kondo lattice CeSn$_{0.75}$Sb$_2$, and its physical properties by a combination of transport / magnetic / thermodynamic measurements. We find that it hosts a fragile antiferromagnetic (AFM) order and a cluster glass (CG) ground state, both of which are highly sensitive to external fields. Upon cooling under low in-plane magnetic fields, the AFM phase evolves into a polarized paramagnetic phase, either directly or indirectly through the intermediate CG phase. This process constitutes a possible inverse magnetic melting effect that restores the broken translational / rotational symmetries. Our work provides a rare paradigm of inverse magnetic melting effect in vdW-like heavy-fermion materials, and enriches the physics in conventional Kondo-lattice models.
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All authors Hai Zeng, Yiwei Chen, Zhuo Wang, Shuo Zou, Kangjian Luo, Yang Yuan, Meng Zhang, Yongkang Luo

Materials Science

Transformation Journey of Zr-based MOFs: Study on Mechanics and Hydrogen Storage under Doping Regulation

Yanhuai Ding, Dan Qian and Zhipeng Liu

This study delves into the transformation journey of Zr-based Metal-Organic Frameworks (MOFs), focusing on enhancing their mechanical properties and hydrogen storage capacities through doping regulation. MOFs, a versatile class of crystalline porous materials, have garnered significant attention due to their unique properties and broad potential applications in gas storage, separation, catalysis, and sensing. Among them, Zr-based MOFs stand out for their exceptional stability and high surface area. This research systematically investigates six key Zr-based MOFs (UIO-66, UIO-67, UIO-68, MOF-801, MOF-802, and MOF-841) using multiscale computational methods, including molecular dynamics (MD) simulations, grand canonical Monte Carlo (GCMC) simulations, and density functional theory (DFT). The study explores the impact of metal ion substitution (Fe, Co, Ni, Cu, Zn) on the mechanical and hydrogen storage properties of these MOFs. Our findings reveal that metal ion substitution significantly influences the mechanical stability and hydrogen adsorption capacity of Zr-based MOFs, providing valuable insights for the design and optimization of high-performance MOF materials.
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Materials Science

Anisotropic Kinetics of Ion-Irradiation-Induced Phase Transition in Gallium Oxide

Taiqiao Liu, Tongtong Wang, Zeyuan Li et al. (+8 more)

Radiation-tolerant semiconductors have traditionally been engineered by the principle of suppressing defect accumulation and amorphization, based on the assumption that radiation damage is inherently stochastic. Here we show that, in monoclinic $\beta$-\ce{Ga2O3}, a promising ultrawide-bandgap semiconductor, surface crystallographic orientation deterministically governs radiation tolerance through highly anisotropic kinetics of the $\beta$-to-$\gamma$ phase transition. Using machine-learning molecular dynamics coupled with a local configurational-entropy descriptor, we quantitatively map anisotropic $\beta$-to-$\gamma$ transition kinetics, showing that the critical dose, transition-layer depth, and kinetic stability of the $\gamma$-phase are fundamentally governed by surface orientation. Under ion irradiation, non-channeling surfaces such as (100), (001), and (-201) undergo severe surface amorphization, whereas the strongly channeling (010) surface resists damage accumulation and promotes subsurface $\gamma$-phase nucleation. During thermal annealing recovery process, these initial states follow two distinct recovery pathways: the channeling (010) surface reverts directly from $\gamma$-to-$\beta$, whereas non-channeling surfaces follow a sequential amorphous-to-$\gamma$-to-$\beta$ transition pathway. This work establishes surface orientation as a fundamental design principle for achieving radiation tolerance through controlled polymorphic transitions, providing a universal framework for engineering functional materials capable of withstanding extreme irradiation environments.
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All authors Taiqiao Liu, Tongtong Wang, Zeyuan Li, E Zhou, Junlei Zhao, Jiaren Feng, Xiaoyu Fei, Yuzheng Guo, Flyura Djurabekova, Sheng Liu, Zhaofu Zhang

Mesoscale and Nanoscale Physics

Intrinsic Step Jamming in Nanometer-Scale KPZ-like Rough Surfaces under Interface-Limited Crystal Growth and Retreat

Noriko Akutsu and Yoshihiro Kangawa

We investigate an intrinsic step-jamming phenomenon at the nanometer scale on Kardar-Parisi-Zhang (KPZ)-like kinetically roughened crystal surfaces that arises during interface-limited steady crystal growth or retreat. Monte Carlo simulations using the Metropolis algorithm on a restricted solid-on-solid (RSOS) lattice model demonstrate that intrinsic step jamming persists on surfaces below 20 nm. In the present model, transport processes such as surface and volume diffusion are excluded, as are elastic interactions, step-step repulsion or attraction, and stoichiometric effects. We show that intrinsic step jamming arises from asymmetric fluctuations in atomic attachment and detachment driven by biased transition probabilities under the SOS restriction, leading to collective step congestion. Asymmetric fluctuations also determine whether adatom or hole clusters grow or recede. This mechanism bears close similarity to jamming phenomena in the asymmetric simple exclusion process (ASEP), including multi-lane variants. In contrast, symmetric thermal fluctuations generate adatom or hole clusters on terraces, thereby suppressing intrinsic step jamming. Possible routes to suppress intrinsic step jamming, including experimentally accessible strategies, are also discussed.
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Statistical Mechanics · Cross-listed from math-ph

Boundary operators in the Brownian loop soup

Federico Camia and Rongvoram Nivesvivat

We obtain infinitely many boundary operators in the Brownian loop soup in the subcritical phase by analyzing the conformal block expansion of the two-point function that computes the probability of having two marked points on the upper half-plane being separated by Brownian loops. The resulting boundary operators are primary operators in a 2D CFT with central charge $c\leq1$ and have conformal dimensions that are non-negative integers. By comparing the above-mentioned conformal block expansion with probabilities in the Brownian loop soup, we provide a physical interpretation of the boundary operators of even dimensions as operators that insert multiple outer boundaries of Brownian loops at points on the real axis.
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Superconductivity

Energy-Resolved Real-Space Imaging of Orbital Nematicity in an Fe-Based Superconductor

Asato Onishi, Zifan Xu, Cédric Bareille et al. (+7 more)

Electronic nematicity in Fe-based superconductors is manifested by spontaneous rotational symmetry breaking and the formation of nematic domains with mutually orthogonal directions of $d_{xz}$/$d_{yz}$ orbital anisotropy. However, its energy dependence has remained largely unexplored in real space. Using 5.82-eV laser-excited photoemission electron microscopy (laser-PEEM) with an energy-selective slit, we visualize the evolution of linear dichroic (LD) contrast within individual nematic domains of Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ ($x\approx0.08$). We discover a sign reversal of the LD contrast at an energy $\sim0.4$ eV below the Fermi level, directly revealing an inversion of orbital anisotropy inside each domain. This behavior reflects a different energy-dependent redistribution of spectral weight between the $d_{xz}$ and $d_{yz}$ states, highlighting the crucial role of orbital-selective coherence in the nematic phase of Fe-based superconductors.
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All authors Asato Onishi, Zifan Xu, Cédric Bareille, Yoichi Kageyama, Shigeyuki Ishida, Hiroshi Eisaki, Kota Ishihara, Kenichiro Hashimoto, Toshiyuki Taniuchi, Takasada Shibauchi

Soft Condensed Matter

Protein-Water Energy Transfer via Anharmonic Low-Frequency Vibrations

Brandon Neff and Matthias Heyden

Heat dissipation is ubiquitous in living systems, which constantly convert distinct forms of energy into each other. The transport of thermal energy in liquids and even within proteins is well understood but kinetic energy transfer across a heterogeneous molecular boundary provides additional challenges. Here, we use atomistic molecular dynamics simulations under steady-state conditions to analyze how a protein dissipates surplus thermal energy into the surrounding solvent. We specifically focus on collective degrees of freedom that govern the dynamics of the system from the diffusive regime to mid-infrared frequencies. Using a fully anharmonic analysis of molecular vibrations, we analyzed their vibrational spectra, temperatures, and heat transport efficiencies. We find that the most efficient energy transfer mechanisms are associated with solvent-mediated friction. However, this mechanism only applies to a small number of degrees of freedom of a protein. Instead, less efficient vibrational energy transfer in the far-infrared dominates heat transfer overall due to a large number of vibrations in this frequency range. A notable by-product of this work is a highly sensitive measure of deviations from energy equi-partition in equilibrium systems, which can be used to analyze non-ergodic properties.
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Quantum Gases

Universal coarsening of a two-dimensional Bose gas under conservative evolution

Andrew J. Groszek and Thomas P. Billam

We investigate the phase ordering dynamics of a uniform two-dimensional Bose gas quenched to a finite temperature in the superfluid phase. Starting from a defect-rich, far-from-equilibrium state, we model the subsequent evolution with the projected Gross-Pitaevskii equation, which conserves both energy and particle number. By tuning the initial energy, we control the effective post-quench temperature and examine its role in the equilibration dynamics. We find that the gas exhibits universal behaviour at all temperatures, evidenced by spatio-temporal scaling of correlation functions and power-law growth of the correlation length $\sim t^{1/z}$, with $z$ the dynamical critical exponent. We find $z$ to be temperature dependent, with $z \approx 1.5$ for post-quench temperatures just below the Berezinskii-Kosterlitz-Thouless (BKT) transition, and $z \approx 1.9$ for quenches to near-zero temperature. Analysis of the Porod tail of the momentum distribution suggests a temperature-dependent competition between vortices and sound waves in the coarsening process. The two-time correlation function also exhibits universal scaling, decaying as $\sim t^{-\lambda/z}$, with autocorrelation exponent $\lambda$. Near the BKT transition we obtain $\lambda \approx 2$, whereas $\lambda$ is found to diverge as the effective temperature approaches zero.
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Statistical Mechanics · Cross-listed from hep-lat

Tensor renormalization group approach to critical phenomena via symmetry-twisted partition functions

Shinichiro Akiyama, Raghav G. Jha, Jun Maeda et al. (+2 more)

The locality of field theories strongly constrains the possible behaviors of symmetry-twisted partition functions, and thus they serve as order parameters to detect low-energy realizations of global symmetries, such as spontaneous symmetry breaking (SSB). We demonstrate that the tensor renormalization group (TRG) offers an efficient framework to compute the symmetry-twisted partition functions, which enables us to detect the symmetry-breaking transition and also to study associated critical phenomena. As concrete examples of SSB, we investigate the two-dimensional (2D) classical Ising model and the three-dimensional (3D) classical $O(2)$ nonlinear sigma model, and we identify their critical points solely from the twisted partition function. By employing the finite-size scaling argument, we find the critical temperature $T_c=2.2017(2)$ with the critical exponent $\nu = 0.663(33)$ for the 3D $O(2)$ model. In addition, we also study the Berezinskii-Kosterlitz-Thouless (BKT) criticality of the 2D classical $O(2)$ model by extracting the helicity modulus from the twisted partition functions, and we obtain the BKT transition temperature, $T_{\mathrm{BKT}}=0.8928(2)$.
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All authors Shinichiro Akiyama, Raghav G. Jha, Jun Maeda, Yuya Tanizaki, Judah Unmuth-Yockey

Mesoscale and Nanoscale Physics

Stable boundary modes for fragile topology from spontaneous PT-symmetry breaking

Kang Yang, Fei Song and Piet W. Brouwer

Two-dimensional topological insulators protected by nonlocal symmetries or with fragile topology usually do not admit robust in-gap edge modes due to the incompatibility between the symmetry and the boundary. Here, we show that in a parity-time (PT) symmetric system robust in-gap topological edge modes can be stably induced by non-Hermitian couplings that spontaneously break the PT symmetry of the eigenstates. The topological edge modes traverse the imaginary spectral gap between a pair of fragile topological bands, which is opened by the presence of the non-Hermitian perturbation. We demonstrate that the net number of resulting in-gap modes is protected by an operator version of anomaly cancellation that extends beyond the Hermitian limit. The results imply that loss and gain can in principle drive fragile topological phenomena to stable topological phenomena.
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Materials Science

Efficient Screening of Organic Singlet Fission Molecules Using Graph Neural Networks

Li Fu, Longfei Lv, Fan Zhang et al. (+3 more)

Singlet fission (SF) provides a promising strategy for surpassing the Shockley-Queisser limit in photovoltaics. However, the identification of efficient SF materials is hindered by the limited availability of suitable molecular candidates and the high computational costs associated with conventional quantum-chemical methods for excited states. In this study, we introduce a high-throughput screening framework that integrates a graph neural network (GNN) with multi-level validation to accelerate the discovery of SF-active molecules. Trained on a previously reported FORMED database, the GNN achieves state-of-the-art accuracy in predicting SF-relevant excited-state properties, demonstrating a mean absolute error of about 0.1 eV for S1, T1, and T2 excitation energies. This capability facilitates the efficient screening of over 20 million molecular structures from both OE62 and QO2Mol databases. Our framework significantly reduces the computational demand associated with Time-Dependent Density Functional Theory validation by four orders of magnitude and identifies 180 potential SF molecules along with more than 1000 conformers. Subsequent assessments regarding synthetic accessibility, GW approximation and Bethe-Salpeter equation calculations further highlight a subset of experimentally feasible candidates among these SF candidates. The approach presented herein exemplifies an effective strategy for accelerating the discovery of functional molecules with optoelectronic applications.
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All authors Li Fu, Longfei Lv, Fan Zhang, Si Zhou, Weiwei Gao, Jijun Zhao

Mesoscale and Nanoscale Physics

Realization of a universal topological waveguide by tuning adiabatic geometry

Keita Funayama, Jotaro J. Nakane and Ai Yamakage

Quantum valley Hall-based topological phases have been attracting attention across diverse fields as a robust platform for wave guidance due to their high compatibility with engineering frameworks. Combining three representative boundary types enables topological waveguides with flexible designability and enhanced functionality. However, one of the three, namely the armchair boundary, has long been limited by inter-valley scattering, resulting in weak topological protection and severely restricting its use in practical devices. This long-standing constraint is a major barrier to realizing broadly applicable topological waveguide systems. Here, to address this challenge toward a broadly applicable design framework for topological waveguides, we experimentally demonstrate that topological adiabatic geometry implemented in a micro electromechanical system suppresses valley mixing. We found that the adiabaticity enhances immunity to defects and increases the transmission efficiency of the armchair boundary. As the adiabaticity increases, topological protection is recovered over an increasingly broad portion of the bulk band gap, extending from low to high frequencies. Furthermore, we show that the recovery of protection in the adiabatic armchair boundary enables waves to propagate through 90^{\deg} and 150^{\deg}-bent waveguides by coupling with other interface geometries. Suppressing valley mixing via adiabaticity paves the way for a universal design framework for topological waveguides and for restoring robust topological characteristics across a wide range of wave phenomena.
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Soft Condensed Matter

Cellular wrapping of elastic particles by a supported lipid membrane

Amir Khosravanizadeh, Pierre Sens and Farshid Mohammad-Rafiee

Constancy of life vitally depends on the internalization of particles through biomembranes. Of particular interest, cellular uptake, including phagocytosis, receptor-mediated endocytosis, and membrane fusion, critically depends on the elasticity of particles. Cellular membranes are strongly linked to a supporting cytoskeleton. However, in most previous studies, the effect of this cortical network somehow is overlooked. In this paper, we study the cellular wrapping of a membrane around a 2D elastic particle in the presence of a substrate mimicking cytoskeleton. Our simulations show that the impact of particle flexibility on the wrapping process depends on the magnitude of the membrane particle adhesion. In contrast, the extent of membrane protrusions formed around the target always increases with target stiffness. Since the extension of membrane protrusions is an essential step in the phagocytosis process, this result may indicate a selective behavior of macrophages in the phagocytosis of aged red blood cells.
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Statistical Mechanics

Thermalized buckling of extensible, semiflexible polymers

Richard Huang, David R. Nelson and Suraj Shankar

The Euler buckling of rods is a long-studied mechanical instability, and it remains relevant to this day, as the constituent components in many biological and physical systems are linear polymers, such as microtubules or carbon nanotubes. At finite temperature, if a polymer is shorter than its persistence length, the polymer is semiflexible, and its elasticity remains rod-like. But polymers can also stretch due to their finite extensibility, which can couple to energetically cheap bending deformations in nonlinear ways when a load is applied to the system. We show how the interplay between thermal fluctuations and nonlinear elasticity dramatically modifies the Euler buckling instability for compressed semiflexible polymers in a fixed strain ensemble. We identify a Ginzburg-like length scale beyond which thermally excited undulations lead to a softened Young's modulus, while the polymer nevertheless remains semiflexible. Both perturbative calculations and numerical Monte Carlo simulations suggest a qualitative change in several scaling properties of the buckling transition. The critical compressional strain for thermal buckling now increases with system size, in contrast to athermal buckling, where it decreases with system size. Renormalization group calculations confirm this picture, and also show that thermal buckling is controlled by a new fixed point with different critical exponents compared to classical Euler buckling.
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Strongly Correlated Electrons

Electronic band structure reconstruction in Ni intercalated ZrTe$_2$

Pedro H. A. Moya, Marli R. Cantarino, Lucas E. Correa et al. (+6 more)

The filling of the large van der Waals gap in Transition Metal Dichalcogenides (TMDs) often leads to lattice and electronic instabilities, which prelude the onset of a rich phenomenology. Motivated by previous results from macroscopic measurements, we investigate the electronic structure of the TMDs ZrTe$_2$ and Ni intercalated ZrTe$_2$ (Ni$_x$ZrTe$_2$, $x\approx 0.05$) employing angle-resolved photoemission spectroscopy (ARPES). We readily identify in Ni$_x$ZrTe$_2$ two flat bands, most likely associated with localized Ni-derived 3$d$-states, at about $\approx-0.7$ eV and $\approx-1.2$ eV in binding energy. More significantly, at low $T$, we identify an electronic structure reconstruction in Ni$_x$ZrTe$_2$, which halves the electronic periodicity along the $k_{z}$ direction. This is reminiscent of a commensurate band folding with wave-vector $q=(0,0,\pi)$. A mean-field model for a charge density wave (CDW) transition driven by interband hole-hole interactions is solved with inputs from the experimentally determined electronic band structure. Comparison between theory and experiments unveils a CDW transition in Ni$_x$ZrTe$_2$, for which the gap opens above the Fermi level. Our findings invite further investigation into the structural properties of intercalated ZrTe$_2$.
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All authors Pedro H. A. Moya, Marli R. Cantarino, Lucas E. Correa, Leandro R. de Faria, Rodrigo M. C. Huamani, Wendell S. Silva, Claude Monney, Antonio J. S. Machado, Fernando A. Garcia

Materials Science

Integrated magnonic chip using cascaded logic

Mengying Guo, Xudong Jing, Kristýna Davídková et al. (+10 more)

The transistor transformed not only electronics but everyday life, and the integrated circuit - now simply the "chip" - made computation scalable and ubiquitous. Magnonics has long promised a parallel path to low-energy information processing by using spin waves instead of charge. Progress, however, has been limited by two fundamental obstacles: intrinsic attenuation of spin waves and the requirement for precisely normalised output intensity and input phase to ensure reliable logic operation - conditions that are difficult to maintain in large-scale circuits owing to inevitable imperfections. Here, we report an integrated magnonic circuit that overcomes both limitations through engineered nonlinearity in nanoscale yttrium iron garnet waveguides. Nonlinear self-adjustment of the spin wave phase renders logic operation insensitive to the relative phases of the inputs, while a deeply nonlinear, threshold-activated self-normalised excitation restores and standardises the output intensity. Using space-resolved micro-focused Brillouin light scattering, we demonstrate reconfigurable AND, OR and three-input majority gates and realise deterministic cascading across sequential stages, establishing a scalable on-chip logic primitive. The architecture operates with gigahertz frequencies, supports dynamic threshold control for functional reconfiguration, and is compatible with scalable integration, making it attractive for adaptive and neuromorphic computing. By resolving phase-independent operation and signal restoration at the level of device physics, this work advances magnonics from isolated proof-of-concept devices towards integrated magnonic chips that can complement advanced CMOS in energy-constrained computing tasks.
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All authors Mengying Guo, Xudong Jing, Kristýna Davídková, Roman Verba, Zhenyu Zhou, Xueyu Guo, Carsten Dubs, Yiheng Rao, Kaiming Cai, Jing Li, Philipp Pirro, Andrii V. Chumak, Qi Wang

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

Acoustic Analogy of Quantum Baldin Sum Rule for Optimal Causal Scattering

Sichao Qu, Zixiong Yu, Erqian Dong et al. (+2 more)

The mass law is a cornerstone in predicting sound transmission loss, yet it neglects the constraints of causal dispersion. Current causality-based theories, such as the Rozanov limit, are applicable only to one-port reflective absorbers. Here, we derive a universal sum rule governing causal scattering in acoustic systems, establishing a rigorous analogy to the Baldin sum rule in quantum field theory. This relation reveals that the integral of the extinction cross-section is fundamentally locked by the scatterer's static effective mass and stiffness, which is validated numerically using seminal examples of underwater metamaterials. Furthermore, the proposed sum rule predicts an optimal condition for an anomalously broadened transmission loss bandwidth, as experimentally observed through the spectral shaping effect of an acoustic Fano resonator. Our findings open up an unexplored avenue for enhancing the scattering bandwidth of passive metamaterials.
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All authors Sichao Qu, Zixiong Yu, Erqian Dong, Min Yang, Nicholas X. Fang

Materials Science

Contact resistance and interfacial engineering: Advances in high-performance 2D-TMD based devices

Xiongfang Liu, Kaijian Xing, Chi Sin Tang et al. (+7 more)

The development of advanced electronic devices is contingent upon sustainable material development and pioneering research breakthroughs. Traditional semiconductor-based electronic technology faces constraints in material thickness scaling and energy efficiency. Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising candidates for next-generation nanoelectronics and optoelectronic applications, boasting high electron mobility, mechanical strength, and a customizable band gap. Despite these merits, the Fermi level pinning effect introduces uncontrollable Schottky barriers at metal-2D-TMD contacts, challenging prediction through the Schottky-Mott rule. These barriers fundamentally lead to elevated contact resistance and limited current-delivery capability, impeding the enhancement of 2D-TMD transistor and integrated circuit properties. In this review, we succinctly outline the Fermi pinning effect mechanism and peculiar contact resistance behavior at metal/2D-TMD interfaces. Subsequently, highlights on the recent advances in overcoming contact resistance in 2D-TMDs devices, encompassing interface interaction and hybridization, van der Waals (vdW) contacts, prefabricated metal transfer and charge-transfer doping will be addressed. Finally, the discussion extends to challenges and offers insights into future developmental prospects.
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All authors Xiongfang Liu, Kaijian Xing, Chi Sin Tang, Shuo Sun, Pan Chen, Dong-Chen Qi, Mark B. H. Breese, Michael S. Fuhrer, Andrew T. S. Wee, Xinmao Yin

Materials Science

Wafer-scale High-k SrTiO3 Dielectrics with Rational Barrier-layer Design for Low Leakage and High Charge Density

Majid Mohseni, Shivasheesh Varshney, Seung Gyo Jeong et al. (+3 more)

High-k oxides such as SrTiO3 promise large capacitance, but their dielectric response is often limited by leakage currents due to reduced bandgaps. We show that introducing a thin barrier layer beneath SrTiO3 is a simple and effective way to suppress leakage and increase charge density. Using hybrid molecular beam epitaxy, we grew uniform SrTiO3 films on Nb:SrTiO3, CaSnO3/Nb:SrTiO3, and 2-inch SiO2/p-Si stacks to directly compare how different barrier layers influence device behavior. Both CaSnO3 and SiO2 reduce leakage, but the ultra-wide-bandgap SiO2 layer enables much higher operating voltages, yielding charge densities exceeding 5x10^13 cm^-2 at room temperature - more than a fivefold enhancement compared to devices without a barrier layer. This improvement comes with a predictable trade-off: the lower dielectric constant of SiO2 reduces overall capacitance, making its thickness an important design parameter. Together, these results demonstrate that rational barrier-layer engineering - including wafer-scale integration on Si - provides a clear pathway to achieving higher charge densities in SrTiO3-based dielectric devices.
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All authors Majid Mohseni, Shivasheesh Varshney, Seung Gyo Jeong, Amber Walton, C. Daniel Frisbie, Bharat Jalan

Monday 5 January

Soft Condensed Matter · Cross-listed from physics.app-ph

The physics of cranberry bogs

Caroline M. Barotta and Jack-William Barotta

The common New England sight of a cranberry bog presents a rich tapestry of fluid dynamics and soft matter phenomena. Here, we present four connected problems exploring the behavior of cranberries in their stages of harvest: the buoyant rise of a cranberry in a flooded bog, the stable floating configuration of a cranberry on the surface, the aggregation and interaction between many floating cranberries collected with a boom, and the piling of cranberries onto a truck for transportation. We model these phenomena from first principles and develop simple computational simulations of their collective behaviors. Additionally, we describe tabletop experiments to accompany these problems, either as in-class demonstrations or lab activities. Throughout, we draw connections to broader physical principles in soft condensed matter and fluids, allowing the real-world example of the cranberry bog to serve as a bridge between the undergraduate curriculum and topics in soft matter research.
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Statistical Mechanics

Lévy walkers inside spherical shells with absorbing boundaries: Towards settling the optimal Lévy walk strategy for random searches

L.G.P. Caramês, Y.B. Matos, F. Bartumeus et al. (+5 more)

The Lévy flight foraging hypothesis states that organisms must have evolved adaptations to exploit Lévy walk search strategies. Indeed, it is widely accepted that inverse square Lévy walks optimize the search efficiency in foraging with unrestricted revisits (also known as non-destructive foraging). However, a mathematically rigorous demonstration of this for dimensions $D \geq 2$ is still lacking. Here we study the very closely related problem of a Lévy walker inside annuli or spherical shells with absorbing boundaries. In the limit that corresponds to the foraging with unrestricted revisits, we show that inverse square Lévy walks optimize the search. This constitutes the strongest formal result to date supporting the optimality of inverse square Lévy walks search strategies.
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All authors L.G.P. Caramês, Y.B. Matos, F. Bartumeus, C.G. Bezerra, T. Macrì, M.G.E. da Luz, E.P. Raposo, G.M. Viswanathan

Strongly Correlated Electrons

$\mathbb{Z}_L$ symmetry breaking in SU(N) Fermi-Hubbard dots at zero and finite temperature

Loïc Herviou, Elodie Campan and Pierre Nataf

We address the SU(N) Fermi-Hubbard model on a chain, with $N$ the number of degenerate orbitals, or colors, for each fermion. In the limit of both large number of colors $N$ and particles, and small number of sites $L \geq 2$, the model is proved to undergo a $\mathbb{Z}_L$ symmetry breaking for attractive local interaction amplitude $U$. Using a combination of Exact Diagonalization with full SU(N) symmetry, generalized L-levels Holstein-Primakoff transformation, Hartree-Fock method and large-N saddle point approximation of the partition function, we extend the results obtained in [PRA 111, L020201 (2025)] to $L \geq 3$ and finite temperature $T>0$. In particular, we show that at $T=0$ for $U<U_c\sim -1/N$, the ground state is L-fold degenerate, while for positive temperatures, the critical temperature is both proportional to $N$ and $U$, i.e. $T_c \propto -U N$, making this phase transition particularly suitable for large-N fermions.
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Materials Science

Tailoring phonon-driven responses in {\alpha}-MoO3 through isotopic enrichment

Thiago S. Arnaud, Ryan W. Spangler, Johnathan D. Georgaras et al. (+29 more)

The implementation of polaritonic materials into nanoscale devices requires selective tuning of parameters to realize desired spectral or thermal responses. One robust material is {\alpha}-MoO3, which as an orthorhombic crystal boasts three distinct phonon dispersions, providing three polaritonic dispersions of hyperbolic phonon polaritons (HPhPs) across the mid-infrared (MIR). Here, the tunability of both optical and thermal responses in isotopically enriched {\alpha}-MoO3 (98MoO3, Mo18O3 and 98Mo18O3) are explored. A uniform ~5 % spectral redshift from 18O enrichment is observed in both Raman- and IR-active TO phonons. Both the in- and out-of-plane thermal conductivities for the isotopic variations are reported. Ab initio calculations both replicate experimental findings and analyze the select-mode three-phonon scattering contributions. The HPhPs from each isotopic variation are probed with s-SNOM and their Q- factors are reported. A Q-factor maxima increase of ~50 % along the [100] in the RB2 and ~100 % along the [001] in the RB3 are reported for HPhPs supported in 98Mo18O3. Observations in both real and Fourier space of higher-order HPhP modes propagating in single slabs of isotopically enriched {\alpha}-MoO3 without the use of a subdiffractional surface scatterer are presented here. This work illustrates the tunability of {\alpha}-MoO3 for thermal and nanophotonic applications.
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All authors Thiago S. Arnaud, Ryan W. Spangler, Johnathan D. Georgaras, Jonah B. Haber, Daniel Hirt, Maximilian Obst, Gonzalo Álvarez-Pérez, Mackey Long III, Felix G. Kaps, Jakob Wetzel, Courtney Ragle, John E. Buchner, Youngji Kim, Aditha S. Senarath, Richarda Niemann, Mingze He, Giulia Carini, Unai Arregui-Leon, Akash C. Behera, Ramachandra Bangari, Nihar Sahoo, Niels C. Brumby, J. Michael Klopf, Martin Wolf, Lukas M. Eng, Susanne C. Kehr, Thomas G. Folland, Alexander Paarmann, Patrick E. Hopkins, Felipe Jornada, Jon-Paul Maria, Joshua D. Caldwell

Strongly Correlated Electrons

Influence of controlled disorder on the dipolar spin ice state of Ho-based pyrochlores

A.A. Aczel, B.R. Ortiz, Y. Luo et al. (+8 more)

Pyrochlore magnets of the form $R_2B_2$O$_7$, in which rare-earth ions on the $R$-site form a three-dimensional network of corner-sharing tetrahedra, provide a canonical setting for geometrical frustration. Ho-based pyrochlores host a dipolar spin-ice ground state, characterized by Ising moments constrained by the ice rules and elementary excitations analogous to magnetic monopoles. Here we examine how controlled chemical disorder influences this state by introducing site mixing on the non-magnetic $B$-site in two compounds. Ho$_2$GaSbO$_7$ contains only Ga$^{3+}$/Sb$^{5+}$ charge disorder, whereas Ho$_2$ScSbO$_7$ exhibits both charge and substantial size disorder arising from the large ionic-radius mismatch between Sc$^{3+}$ and Sb$^{5+}$. Although both materials retain the pyrochlore structure, neutron scattering measurements reveal a reduced correlation length for the $R/B$-site cation ordering and enhanced local structural distortions in Ho$_2$ScSbO$_7$. Despite these structural differences, bulk thermodynamic measurements and magnetic diffuse scattering demonstrate that both systems exhibit the defining signatures of a dipolar spin-ice state. Low-energy inelastic neutron spectroscopy further uncovers broad magnetic excitations that develop within the dipolar spin-ice regime, a feature absent in pristine Ho pyrochlores and indicative of disorder-induced splitting of the non-Kramers ground-state doublet. Together, these results show that controlled disorder generates tunable transverse-field-driven quantum fluctuations in Ho-based pyrochlores, although the dipolar spin-ice state is remarkably robust to this disorder.
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All authors A.A. Aczel, B.R. Ortiz, Y. Luo, G. Pokharel, P.M. Sarte, C. dela Cruz, J. Liu, G. Sala, S.D. Wilson, B.A. Frandsen, J.A.M. Paddison

Materials Science

X-ray photo-induced atomic motion in Phase Change Materials and conventional covalent chalcogenide glasses

Irene Festi, Antoine Cornet, Tomoki Fujita et al. (+10 more)

X-ray Photon Correlation Spectroscopy (XPCS) enables direct access to atomic-scale dynamics in disordered materials, revealing both spontaneous and X-ray-induced relaxation processes. Here, we study two compositionally similar alloy glasses near their glass transition temperatures: the phase change material (PCM) Ge15Sb85 and the non-PCM alloy Ge15Te85. Both exhibit X-ray induced atomic motion, yet with markedly different responses. Ge15Sb85 undergoes an immediate transition to a photo-induced yielding state, characterised by stationary dynamics governed solely by the absorbed dose. In contrast, Ge15Te85 shows a progressive slowing-down of the relaxation process, accompanied by a crossover from compressed to stretched exponential decay in the density autocorrelation functions. This behaviour is consistent with the emergence of liquid-like collective motion as supported by de Gennes narrowing in the wave-vector dependence of the dynamics at length scales comparable with the first sharp diffraction peak. Unlike Ge15Sb85, this alloy does not reach a stationary regime within experimental timescales, implying that the yielding transition occurs only after thousands of seconds with the available dose rate. Its response is also temperature dependent: at lower temperatures, the dynamics reflects intrinsic stress relaxation processes, whereas at higher temperatures becomes dose-controlled. These findings demonstrate that the dynamical response to X-ray excitation is not determined solely by chemical composition or bonding character, but results from the interplay between irradiation effects and structural relaxation pathways.
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All authors Irene Festi, Antoine Cornet, Tomoki Fujita, Jens Moesggard, Alberto Ronca, Jie Shen, Michael Sprung, Shuai Wei, Fabian Westermeier, Raphael Escalier, Andrea Piarristeguy, Giacomo Baldi, Beatrice Ruta

Soft Condensed Matter

Fluids at an electrostatically active surface: Optimum in interfacial friction and electrohydrodynamic drag

Cecilia Herrero, Lyderic Bocquet and Benoit Coasne

While fluids near a solid surface are at the core of applications in energy storage/conversion, electrochemistry/electrowetting and adsorption/catalysis, their nanoscale behavior remains only partially deciphered. Beyond conventional effects (e.g. adsorption/reaction, interfacial transport, phase transition shifts), recent experimental and theoretical studies on metallic surfaces have unraveled exotic peculiarities such as complex electrostatic screening, unexpected wetting transition, and interfacial quantum friction. These novel features require developing and embarking new tools to tackle the coupling between charge relaxation in the metal and molecular behavior in the vicinal fluid. Here, using the concept of Virtual Thomas-Fermi fluids, we employ a molecular simulation approach to investigate interfacial transport of fluid molecules and metal charge carriers at their interface–including the underlying electrostatically-driven dynamic friction and the coupling between charge current/hydrodynamic flow (the so-called electrohydrodynamic drag). While conventional numerical techniques consider either insulating materials or metallic materials described as polarizable, non-conducting media, our atom-scale strategy provides an effective yet realistic description of the solid excitation spectrum–including charge relaxation modes and conductivity. By applying this approach to water near metallic surfaces of various electrostatic screening lengths, we unveil a non-monotonous dependence of the fluid/solid friction on the metallicity with a maximum occurring as the charge dynamic structure factors of the solid and fluid strongly overlap. Moreover, we report a direct observation of the electrohydrodynamic drag which arises from the momentum transfer between the solid and liquid through dynamic electrostatic interactions and the underlying interfacial friction.
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Statistical Mechanics · Cross-listed from math.CO

Lee-Yang phenomena in edge-coloured graph counting

Maximilian Wiesmann

We study the accumulation of zeros of a polynomial arising from the enumeration of edge-coloured graphs along certain limit curves. The polynomial is a variant of an edge-chromatic polynomial, which specialises to the partition function of the ferromagnetic Ising model on a random regular graph. We call this accumulation behaviour a Lee-Yang phenomenon in analogy with the Lee-Yang theorem. The limiting loci are semialgebraic and arise from anti-Stokes curves of an exponential integral.
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Materials Science

Polymer-Iron Oxide Hybrid Films for Controlling Electrokinetic Properties

Austin Dick, Xiao Tong, Kim Kisslinger et al. (+2 more)

Electrokinetic phenomena at polymer-water interfaces are central to technologies for water purification, ion separations, and energy conversion, yet the ability to systematically control polymer surface charge and associated electrokinetic processes remains limited. Here, we demonstrate a simple liquid-phase infiltration (LPI) method to synthesize polymer-metal oxide hybrid films with controllable interfacial properties. Hydroxy-terminated poly(2-vinylpyridine) (P2VP-OH) brushes grafted to silicon substrates were infiltrated with iron nitrate from ethanolic solution, followed by low-temperature thermal treatment to convert the infiltrated precursor into iron oxide. Spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis confirmed oxide incorporation and hybrid film formation without polymer degradation. Electrokinetic flow characterization reveals that the hybrid films acquire the electrokinetic properties of the infiltrated oxide, with concentration-dependent streaming potentials and surface conductivities closely matching those of pure iron oxide films. These results establish metal oxide infiltration as a scalable and low-cost strategy for controlling interfacial charge in polymer surfaces. The approach introduces new materials and design parameters for tailoring ion selectivity, transport, and energy conversion, with broad implications for the development of advanced membranes, electrokinetic harvesting devices, and polymer-supported oxide electrodes.
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All authors Austin Dick, Xiao Tong, Kim Kisslinger, Carlos E. Colosqui, Gregory Doerk

Strongly Correlated Electrons

Fermi Sets: Universal and interpretable neural architectures for fermions

Liang Fu

We introduce Fermi Sets, a universal and physically interpretable neural architecture for fermionic many-body wavefunctions. Building on a “parity-graded” representation [1], we prove that any continuous fermionic wavefunction on a compact domain can be approximated to arbitrary accuracy by a linear combination of K antisymmetric basis functions–such as pairwise products or Slater determinants–multiplied by symmetric functions. A key result is that the number of required bases is provably small: K=1 suffices in one-dimensional continua (and on lattices in any dimension), K=2 suffices in two dimensions, and in higher dimensions K grows at most linearly with particle number. The antisymmetric bases can be learned by small neural networks, while the symmetric factors are implemented by permutation-invariant networks whose width scales only linearly with particle number. Thus, Fermi Sets achieve universal approximation of fermionic wavefunctions with minimal overhead while retaining clear physical interpretability. As a numerical illustration, a single Fermi Sets model applied to metallic solid hydrogen in three dimensions, trained simultaneously across multiple nuclear geometries, surpasses all diffusion Monte Carlo benchmarks.
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Statistical Mechanics

Exact critical-temperature bounds for two-dimensional Ising models

Davidson Noby Joseph and Igor Boettcher

We derive exact critical-temperature bounds for the classical ferromagnetic Ising model on two-dimensional periodic tessellations of the plane. For any such tessellation or lattice, the critical temperature is bounded from above by a universal number that is solely determined by the largest coordination number on the lattice. Crucially, these bounds are tight in some cases such as the Honeycomb, Square, and Triangular lattices. We prove the bounds using the Feynman–Kac–Ward formalism, confirm their validity for a selection of over two hundred lattices, and construct a two-dimensional lattice with 24-coordinated sites and high critical temperature.
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