Strongly Correlated Electrons
$\alpha$-RuCl$_3$ intercalated into graphite: a new three-dimensional platform for exotic quantum phases
Aleksandar Razpopov, Shirin Mozaffari, Takahiro Matsuoka et al. (+5 more)
Multilayer
graphene with different stacking sequences has emerged as a powerful setting for correlated and topological phases. In parallel, progress in
graphene heterostructures with
magnetic or correlated materials-most notably the Kitaev candidate $\alpha$-RuCl$_3$-has demonstrated charge transfer,
magnetic proximity effects, and interfacial reconstruction, creating new opportunities for engineered
quantum systems. Motivated by these developments, we explore a three-dimensional analogue in which $\alpha$-RuCl$_3$ layers are inserted directly into the van der Waals gaps of graphite, forming an intercalated system. Here, we report the successful synthesis and comprehensive characterization of graphite intercalated with $\alpha$-RuCl$_3$. Using a combination of X-ray diffraction,
quantum oscillation measurements, and first-principles electronic structure calculations, we study the structural and electronic properties of these intercalated
crystals. Our results demonstrate that graphite intercalated with $\alpha$-RuCl$_3$ offers a robust route to develop three-dimensional materials with access to novel correlated and topological states.
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All authors Aleksandar Razpopov, Shirin Mozaffari, Takahiro Matsuoka, Matthew Cothrine, Nan Huang, Miaofang Chi, Roser Valentí, David Mandrus
Strongly Correlated Electrons
Strain Response as a Probe of Spinons in Quantum Spin Liquids
Penghao Zhu, Archisman Panigrahi, Leonid Levitov et al. (+1 more)
Quantum spin liquids (QSLs) host emergent, fractionalized fermionic excitations that are charge-neutral. Identifying clear experimental signatures of these excitations remains a central challenge in the field of strongly correlated systems, as they do not couple to conventional electromagnetic probes. Here, we propose
lattice strain as a powerful and tunable probe: Mechanical deformation of the
lattice generates large pseudomagnetic fields, inducing pseudo-Landau levels that serve as distinctive spectroscopic signatures of these excitations. Using the Kitaev model on the honeycomb
lattice, we show that distinct QSL phases exhibit strikingly different strain responses. The semimetallic Kitaev
spin liquid and the gapped
chiral spin liquid display pronounced Landau quantization and a diamagnetic-like response to strain, whereas the Majorana metal phase shows a paramagnetic-like response without forming Landau levels. These contrasting behaviors provide a direct route to experimentally identifying and distinguishing QSL phases hosting fractionalized excitations. We further outline how local resonant ultrasound spectroscopy can detect the strain-induced resonances associated with these responses, offering a practical pathway towards identifying fractionalized excitations in candidate materials.
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All authors Penghao Zhu, Archisman Panigrahi, Leonid Levitov, Nandini Trivedi
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Many-body symmetry-protected zero boundary modes of synthetic photo-magnonic crystals
Alan Gardin, Emilio Cobanera and Giuseppe C. Tettamanzi
The topological classification of
insulators and
superconductors, the "ten-fold way", is grounded on fermionic many-body
symmetries and has had a dramatic impact on many fields of physics. Therefore, it seems equally important to investigate a similar approach for
bosons as tightly analogous to the fermionic prototype as possible. There are, however, several obstacles coming from the fundamental physical differences between
fermions and
bosons. Here, we propose a theory of free
boson topology (topological classification and bulk-boundary correspondence) protected by bosonic many-body
symmetry operations, namely, squeezing transformations, particle number, and bosonic time reversal. We identify two
symmetry classes that are topologically non-trivial in one dimension. They include key models like the bosonic Kitaev chain, protected by a squeezing
symmetry within our framework, and the celebrated bosonic SSH model, protected by a squeezing
symmetry and particle number. To provide a robust experimental platform for testing our theory, we introduce a new
quantum meta-material: photo-magnonic
crystals. They are remarkable for their experimental flexibility and natural affinity for displaying band topological physics at microwave frequencies. We engineer a many-body
symmetry-protected topological photo-magnonic chain with boundary modes mandated by a Pfaffian invariant. Using an electromagnetic finite-element modelling, we simulate its reflection and transmission and identify experimental signatures of its boundary modes. The experimental tuning of the
crystal to its
symmetry-protected topological phase is also addressed. Our modelling of the photo-magnonic chain provides a thorough blueprint for its experimental realisation and the unambiguous observation of its exotic physics.
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Materials Science
Fermi-liquid behavior and characteristic temperature-dependent susceptibility in clean RuO$_2$ crystal
Shubhankar Paul, Atsutoshi Ikeda, Hisakazu Matsuki et al. (+6 more)
The
magnetic nature of the altermagnet candidate RuO$_2$ remains under debate. It has been recently shown from
quantum oscillations and angle-resolved photoemission spectroscopy (ARPES) that the high-quality RuO$_2$ bulk single
crystal is a paramagnetic metal. Here we report the specific heat and
magnetic susceptibility in ultra-clean RuO$_2$ single
crystals with residual resistivity ratio up to 1200. The
magnetic susceptibility increases with temperature and is phenomenologically fitted with an inclusion of $T\textrm{ln}(T/T_0)$ over a wide temperature range up to 400 K. In contrast, the energy dependence of the density of states and thermal activation of quasiparticles lead to a decrease with temperature. Such characteristic temperature dependence, similar to that observed in other $d$-electron metals, is attributable to an enhanced orbital contribution arising from
lattice-expansion-induced changes in the band structure. The electronic specific heat, the
magnetic susceptibility, and the $T^2$ coefficient in resistivity point to a weakly-correlated 3D
Fermi-
liquid state with a modest electron correlation, as supported by the Wilson and Kadowaki-Woods ratios.
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All authors Shubhankar Paul, Atsutoshi Ikeda, Hisakazu Matsuki, Giordano Mattoni, Jörg Schmalian, Kunihiko Yamauchi, Chanchal Sow, Shingo Yonezawa, Yoshiteru Maeno
Mesoscale and Nanoscale Physics
On the Cutting Edge: Helical Liquids in Time-Reversal-Invariant Topological Materials
Chen-Hsuan Hsu, Jelena Klinovaja and Daniel Loss
In this perspective, we discuss the unique electronic properties of helical
liquids appearing at the boundaries of time-reversal-invariant topological materials and highlight the key challenges impeding progress in this field. We advocate for a deeper theoretical understanding of the many-body aspects of these systems to gain insights into helical
liquids and the potential stabilization of topological zero modes. Such advancements are crucial for extensively exploring
quantum phenomena and for the advancement of
quantum science and engineering.
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Statistical Mechanics
Konstantinos Chalas, Pasquale Calabrese and Colin Rylands
In a periodic
lattice system an entangled antipodal pair state, otherwise known as a crosscap state, is a simple two site product state in which
spins at antipodal sites are prepared in Bell pairs. Such states have maximal bipartite
entanglement and serve as a useful platform for studying the quench dynamics of systems which have large initial
entanglement. In this paper, we study a generalization of these states which we dub entangled mutipodal states. These states, which are defined for fermionic systems, generalize the crosscap states by having correlations among more than two sites, specifically, those which sit at the vertices of regular polygons. By construction, the states are Gaussian and translationally invariant allowing many of their properties to be understood. We study the bipartite
entanglement entropy of these states both in and out of
equilibrium. In
equilibrium, the
entanglement profile as a function of subsystem size exhibits two distinct regimes, a volume-law growth followed by a saturation to a constant value, thus generalizing the Page-curve profile of the crosscap state. In the non-
equilibrium setting, we study quenches from these initial states to the free-
fermion chain, whose ensuing dynamics displays a far richer structure compared to the crosscap case. We interpret our results in terms of the quasiparticle picture, which requires multiplets of quasiparticles to be excited non-locally around the system. This scenario is confirmed by the appearance of a post-quench, negative tripartite information.
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Statistical Mechanics · Cross-listed from quant-ph
Information dynamics and symmetry breaking in generic monitored $\mathbb{Z}_2$-symmetric open quantum systems
Jacob Hauser, Ali Lavasani, Sagar Vijay et al. (+1 more)
We investigate the steady-state phases of generic $\mathbb{Z}_2$-symmetric monitored, open
quantum dynamics. We describe the phases systematically in terms of both information-theoretic diagnostics and spontaneous breaking of strong and weak
symmetries of the dynamics. We find a completely broken phase where information is retained by the
quantum system, a strong-to-weak broken phase where information is leaked to the environment, and an unbroken phase where information is learned by the observer. We find that weak measurement and dephasing alone constitute a minimal model for generic open systems with $\mathbb{Z}_2$
symmetry, but we also explore perturbations by
unitary gates. For a 1d set of
qubits, we examine information-theoretic and
symmetry-breaking observables in the path integral of the doubled state. This path integral reduces to the standard classical 2d random-bond Ising model in certain limits but generically involves negative weights, enabling a special self-dual random-bond Ising model at the critical point when only measurements are present. We obtain numerical evidence for the steady-state phases using efficient tensor network simulations of the doubled state.
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All authors Jacob Hauser, Ali Lavasani, Sagar Vijay, Matthew P. A. Fisher
Disordered Systems and Neural Networks
Topological marker in three dimensions based on kernel polynomial method
Ranadeep Roy and Wei Chen
The atomic-scale influence of disorder on the topological order can be quantified by a universal topological marker, although the practical calculation of the marker becomes numerically very costly in higher dimensions. We propose that for any
symmetry class in higher dimensions, the topological marker can be calculated in a very efficient way by adopting the kernel
polynomial method. Using class AII in three dimensions as an example, which is relevant to realistic topological
insulators like Bi2Se3 and Bi2Te3, this method reveals the criteria for the invariance of topological order in the presence of disorder, as well as the possibility of a smooth cross over between two topological phases caused by disorder. In addition, the significantly enlarged system size in the numerical calculation implies that this method is capable of capturing the
quantum criticality much closer to topological phase transitions, as demonstrated by a nonlocal topological marker.
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Strongly Correlated Electrons
Microscopic evidence of dominant excitonic instability in Ta2NiSe5
Seokjin Bae, Arjun Raghavan, Irena Feldman et al. (+2 more)
An excitonic
insulator (EI) is a charge-neutral bosonic condensate of spontaneously formed electron-hole pairs. Exotic
quantum phenomena such as dissipationless charge neutral transport and huge potential for optoelectronic applications have led to an extensive search for intrinsic bulk materials that are EIs at ambient pressure without sophisticated device fabrication. The narrow gap semimetal Ta2NiSe5 has been proposed as a rare example of an intrinsic EI, but its ground state has remained controversial since the EI phase transition is accompanied by a structural distortion. Here, we use scanning tunneling microscopy and spectroscopy to present microscopic evidence that supports an excitonic origin of the insulating phase in Ta2NiSe5. First, we find that the insulating gap persists at structural domain boundaries where the bulk structural distortion is absent suggesting that the structural distortion is not the primary origin of insulating ground state. Second, the insulating gap is suppressed at localized charge puddles which indicates that charge correlations are important in producing the insulating gap. Finally, the decay length of the in-gap states at the puddles shows similar value to the estimated size of the
exciton wavefunction from previous photoemission studies. Taken together, these findings suggest that Ta2NiSe5 is an EI and may be a versatile platform to study the physics of bosonic condensates in solid-state system at ambient conditions.
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All authors Seokjin Bae, Arjun Raghavan, Irena Feldman, Amit Kanigel, Vidya Madhavan
Quantum Gases · Cross-listed from physics.atom-ph
Generation of strong ultralow-phase-noise microwave fields with tunable ellipticity for ultracold polar molecules
Shrestha Biswas, Sebastian Eppelt, Christian Buchberger et al. (+6 more)
Microwave(MW) fields with strong field strength, ultralow phase-noise and tunable polarization are crucial for stabilizing and manipulating ultracold polar molecules, which have emerged as a promising platform for
quantum sciences. In this letter, we present the design, characterization, and performance of a robust MW setup tailored for precise control of molecular states. This setup achieves a high electric field intensity of 6.9 kV/m in the near-field from a dual-feed waveguide
antenna, enabling a Rabi frequency as high as 71 MHz for the rotational transition of sodium-potassium molecules. In addition, the low noise signal source and controlled electronics provide ultralow phase-noise and dynamically tunable polarization. Narrow-band filters within the MW circuitry further reduce phase-noise by more than 20 dB at 20 MHz offset frequency, ensuring prolonged one-body molecular lifetimes up to 10 seconds. We also show practical methods to measure the MW field strength and polarization using a simple homemade dipole probe, and to characterize phase-noise down to -170 dBc/Hz with a commercial spectrum analyser and a notch filter. Those capabilities allowed us to evaporatively cool our molecular sample to deep
quantum degeneracy. Furthermore, the polarization tunability enabled the observation of field-linked resonances and facilitated the creation of field-linked tetramers.These techniques advance the study of ultracold polar molecules and broaden the potential applications of MW tools in other platforms of
quantum sciences.
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All authors Shrestha Biswas, Sebastian Eppelt, Christian Buchberger, Xing-Yan Chen, Andreas Schindewolf, Michael Hani, Erwin Biebl, Immanuel Bloch, Xin-Yu Luo
Materials Science
Learning interpretable surface elasticity properties from bulk properties
Saaketh Desai, Prasad P. Iyer and Remi Dingreville
Surface elasticity is central to understanding the mechanics and stability of surfaces and interfaces. It is characterized by quantities such as surface tension, residual surface stress, and surface stiffness, however their analytical expressions are typically difficult to derive from atomistic data, and depend strongly on modeling choices. This work presents a neural network-based equation learner which combines customized activation functions and connection-based
pruning to discover parsimonious, closed-form equations for surface elasticity from atomistic simulations. Applying the method to seven face centered cubic (FCC) metals, our equation learner uncovers interpretable equations that describe both low-Miller index and high-Miller index surface properties, capturing long-tail property distributions accurately. The discovered expressions are decoupled into two components: a universal, geometry-driven orientation function, and material-specific baseline coefficients. We find that lower-order properties such as surface tension are fundamentally geometry dependent, while higher-order properties such as surface stress and elasticity show more complex geometry and material dependence. We also relate material dependent coefficients to bulk properties, forming a clear map from bulk material properties to surface elasticity. Overall, this approach demonstrates that interpretable neurosymbolic machine learning can bridge the gap between atomistic simulations and physical laws, enabling the discovery of generalizable structure-property relationships for materials science phenomena such as surface elasticity.
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Materials Science
New insights into hydrogen-assisted intergranular cracking in nickel
S. Quan, A. Zafra, E. Martínez-Pañeda et al. (+3 more)
We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site
lattice value ($\Sigma$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and propagation was evaluated by separating cracks containing single GB or multiple GBs. A larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture indicated a higher degree of embrittlement at elevated hydrogen concentrations. The number of cracks was significantly higher on the surface than in the bulk for the most severe hydrogen charging conditions ($\geq$ 8 wppm), while a similar number was observed for lower concentrations. The propensity for hydrogen-assisted intergranular cracking at different types of GBs on the surface and in the bulk material was consistent, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the GBs relative susceptibility. The $\Sigma$-3 boundaries were the most resistant to cracking, as evidenced by the considerably lower fraction of these GBs exhibiting intergranular cracking at all hydrogen concentrations considered. This contrasts literature findings for Ni
alloys and can be explained by the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the $\Sigma$-3 boundaries. No evidence of plasticity-mediated cracking initiation was observed.
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All authors S. Quan, A. Zafra, E. Martínez-Pañeda, C. Wu, Z.D. Harris, L. Cupertino-Malheiros
Materials Science
Altermagnetoelectric Spin Field Effect Transistor
Ziye Zhu, Xianzhang Chen, Xunkai Duan et al. (+4 more)
Spin field-effect transistors (SFETs) are promising candidates for low-power
spin-based electronics, yet existing realizations that rely on
spin-orbit coupling are constrained by limited material choices and short
spin-coherence lengths. Here we propose a different operating principle based on multiferroic altermagnets, in which
spin splitting is tuned by an electric field through
symmetry control rather than conventional
spin-orbit physics. Using an effective model combined with
quantum transport simulations, we show that the conductance is determined by the degree of matching between the electrically controlled
spin texture of the channel and the fixed
spin polarization of
ferromagnetic contacts, enabling clear ON and OFF states. Remarkably, we also address a long-standing challenge in multiferroic device design: spintronic channels require metallic carriers, whereas ferroelectricity is usually suppressed in metals. We resolve this conflict by imprinting multiferroic altermagnetism into highly conductive materials via the proximity effect. First-principles calculations for
graphene on multiferroic vanadium sulfide halides confirm that
graphene acquires a ferroelectrically switchable
spin splitting while retaining its metallic character. These results establish a practical route to SFET implementation and identify multiferroic altermagnets as a versatile platform for next-generation spintronic devices.
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All authors Ziye Zhu, Xianzhang Chen, Xunkai Duan, Zhou Cui, Jiayong Zhang, Igor Zutic, Tong Zhou
Soft Condensed Matter
Probing the Microscopic Origin of Toughness in Multiple Polymer Networks
Nicholas H. P. Orr, Magali Le Goff, Burebi Yiming et al. (+6 more)
Multiple
polymer networks, such as double-network elastomers comprising a sacrificial and a
matrix network, exhibit exceptional mechanical resilience, commonly attributed to the formation of an extended damage zone before a crack can grow. However, the microscopic mechanisms underlying their toughness remain poorly understood. Here, we combine advanced light scattering methods and molecular dynamics simulations to explore the microscopic relaxation dynamics and stress redistribution at the
polymer strand scale of single-network and double-network elastomers under uni-axial loading. Dynamic light scattering experiments show that microscopic rearrangements and bond-breaking events are localized near the crack tip in single networks, readily causing the crack to advance. In contrast, double networks exhibit delocalized microscopic rearrangements well ahead of and not directly correlated with crack propagation, enabling the dissipation of energy over broader regions and timescales. Numerical simulations of the damage zone show that bond breaking in the
matrix network of double networks leads to widespread stress redistribution, mitigating catastrophic damage localization. This enhanced ability to redistribute stress in a non-local manner allows a much larger extension before localized macroscopic failure occurs, explaining the superior toughness of double networks. Our findings identify early, delocalized bond-breaking events combined with more efficient dissipation pathways through enhanced microscopic rearrangements as the key microscopic mechanisms responsible for the outstanding toughness and extensibility of multiple elastomer networks.
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All authors Nicholas H. P. Orr, Magali Le Goff, Burebi Yiming, Jean-Louis Barrat, Mehdi Bouzid, Laurence Ramos, Costantino Creton, Kirsten Martens, Luca Cipelletti
Strongly Correlated Electrons
Spinons and Spin-Charge Separation at the Deconfined Quantum Critical Point
Sibin Yang and Anders W. Sandvik
Using
quantum Monte Carlo and numerical analytic continuation methods, we study the dynamic
spin structure factor and the single-hole spectral function of a two-dimensional
quantum magnet ($J$-$Q$ model) at its
quantum phase transition separating Néel
antiferromagnetic and spontaneously dimerized ground states. At this putative deconfined
quantum-critical point, we find a broad continuum of spinon excitations that can be accounted for by the fermionic $\pi$-flux state; a known mean-field model for deconfined
quantum criticality. We find that the best description of the two-spinon continuum is with a version of the model with a $2\times 2$ unit
cell, reflecting non-trivial mutual statistics of spinons and anti-spinons. The single-hole spectral function can be described by the same spinon dispersion relation and an independently propagating holon. Thus, the system exhibits
spin-charge separation and will likely evolve into an extended holon metal phase at finite doping.
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Disordered Systems and Neural Networks · Cross-listed from cs.SE
The Evolutionary Ecology of Software: Constraints, Innovation, and the AI Disruption
Sergi Valverde, Blai Vidiella and Salva Duran-Nebreda
This chapter investigates the evolutionary ecology of software, focusing on the symbiotic relationship between software and innovation. An interplay between constraints, tinkering, and frequency-dependent selection drives the complex evolutionary trajectories of these socio-technological systems. Our approach integrates
agent-based modeling and case studies, drawing on complex network analysis and evolutionary theory to explore how software evolves under the competing forces of novelty generation and imitation. By examining the
evolution of programming
languages and their impact on developer practices, we illustrate how technological artifacts co-evolve with and shape societal norms, cultural dynamics, and human interactions. This ecological perspective also informs our analysis of the emerging role of AI-driven development tools in software
evolution. While large
language models (LLMs) provide unprecedented access to information, their widespread adoption introduces new evolutionary pressures that may contribute to cultural stagnation, much like the decline of diversity in past software ecosystems. Understanding the evolutionary pressures introduced by AI-mediated software production is critical for anticipating broader patterns of cultural change, technological adaptation, and the future of software innovation.
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Quantum Gases
Formation of bosonic $^{23}$Na$^{41}$K Feshbach molecules
Sungjun Lee, Younghoon Lim, Jongyeol Kim et al. (+2 more)
Ultracold Feshbach molecules are a crucial intermediate step for the creation of
quantum degenerate gases of strongly dipolar molecules. After coherent transfer to the rovibrational ground state, these dimers can realize stable dipolar gases with strong, tunable long-range interactions. Here, we report the creation of bosonic $^{23}$Na$^{41}$K Feshbach molecules by
radio-frequency (RF) association. An RF pulse applied on the molecular side of an interspecies Feshbach resonance at 73.6(1)~G associates up to $1.1(1)\times10^4$ molecules from a thermal mixture of $^{23}$Na and $^{41}$K atoms. Measurements of the binding energy reveal a broad resonance width of 5.1(2)~G, facilitating robust control over interspecies interactions. The molecule lifetime in the presence of background atoms exceeds 2~ms, extending to 7~ms after removal of $^{23}$Na. These results constitute a key step toward the production of ultracold $^{23}$Na$^{41}$K ground state molecules for the exploration of novel many-body phenomena in strongly dipolar Bose gases.
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All authors Sungjun Lee, Younghoon Lim, Jongyeol Kim, Jaeryeong Chang, Jee Woo Park
Statistical Mechanics
Universality Diagram of Phase Transitions in Long-range Statistical Systems
Tianning Xiao, Zhijie Fan and Youjin Deng
The percolation, Ising, and O($n$) models constitute fundamental systems in statistical and condensed matter physics. For short-range-interacting cases, the nature of their phase transitions is well established by renormalization-group theory. However, the universality of the transitions in these models remains elusive when algebraically decaying long-range interactions $\sim 1/r^{d+\sigma}$ are introduced, where $d$ is the dimensionality and $\sigma$ is the decay exponent. Building upon insights from Lévy flight, i.e., long-range simple random walk, we propose three universality diagrams in the $(d,\sigma)$ plane for the percolation model, the O($n$) model, and the Fortuin-Kasteleyn Ising model, respectively. The conjectured universality diagrams are consistent with recent high-precision numerical studies and rigorous mathematical results, offering a unified perspective on critical phenomena in systems with long-range interactions.
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Materials Science
Representation of Inorganic Synthesis Reactions and Prediction: Graphical Framework and Datasets
Samuel Andrello, Daniel Alabi and Simon J. L. Billinge
While machine learning has enabled the rapid prediction of inorganic materials with novel properties, the challenge of determining how to synthesize these materials remains largely unsolved. Previous work has largely focused on predicting precursors or reaction conditions, but only rarely on full synthesis pathways. We introduce the ActionGraph, a directed acyclic graph framework that encodes both the chemical and procedural structure, in terms of synthesis operations, of inorganic synthesis reactions. Using 13,017 text-mined solid-state synthesis reactions from the Materials Project, we show that incorporating PCA-reduced ActionGraph adjacency
matrices into a $k$-nearest neighbors
retrieval model significantly improves synthesis pathway prediction. While the ActionGraph framework only results in a 1.34% and 2.76% increase in precursor and operation F1 scores (average over varying numbers of PCA components) respectively, the operation length matching accuracy rises 3.4 times (from 15.8% to 53.3%). We observe an interesting trade-off where precursor prediction performance peaks at 10-11 PCA components while operation prediction continues improving up to 30 components. This suggests composition information dominates precursor selection while structural information is critical for operation sequencing. Overall, the ActionGraph framework demonstrates strong potential, and with further adoption, its full range of benefits can be effectively realized.
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Materials Science
Magnetic field induced polarization enhancement in the photoluminescence of MBE-grown WSe$_2$ layers
Maksymilian Kuna, Mateusz Raczyński, Julia Kucharek et al. (+5 more)
We report an experimental study of the
magnetic-field dependence of the optically pumped valley polarization in an epitaxial tungsten diselenide (WSe$_2$) monolayer grown by molecular-beam epitaxy (MBE) on a hexagonal boron nitride (hBN) substrate. Circularly polarized photoluminescence (PL) measurements reveal that applying a weak out-of-plane
magnetic field, on the order of 0.1 T, dramatically increases the effectiveness of the optical orientation of the emission associated with defect-bound localized
excitons. We compare the obtained results with the earlier studies on the reference exfoliated monolayers, discussing both qualitative similarity as well as quantitative differences. Our observations are further supplemented by the results of time-resolved PL measurements, which confirm the pseudospin relaxation time of approximately 25 ps, a value significantly shorter than the $\approx$100 ps previously reported for mechanically exfoliated samples.
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All authors Maksymilian Kuna, Mateusz Raczyński, Julia Kucharek, Takashi Taniguchi, Kenji Watanabe, Tomasz Kazimierczuk, Wojciech Pacuski, Piotr Kossacki
Soft Condensed Matter
How Quorum Sensing Shapes Clustering in Active Matter
L. de Souza, E.F. Teixeira, G.M. Viswanathan et al. (+2 more)
Self-propelled particles undergoing persistent motion can accumulate either through excluded-volume interactions or through quorum sensing, where self-propulsion decreases at high local density. Using kinetic balance theory and simulations, we show that the interplay of these two mechanisms produces a reentrant, non-monotonic behavior in which clustering passes through a pronounced minimum as quorum-sensing strength or persistence time varies. Beyond a threshold quorum-sensing strength, we find long-lived transient states that retain
memory of initial conditions, including kinetically arrested active gels. Although quorum sensing can mimic attractive interactions, it also acts strongly in dilute regions, producing an effective cluster bistability that is captured by our theory. Our results explain collective states observed experimentally in synthetic and biological active systems.
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All authors L. de Souza, E.F. Teixeira, G.M. Viswanathan, P. Sollich, P. de Castro
Statistical Mechanics · Cross-listed from quant-ph
Stability of quantum chaos against weak non-unitarity
Yi-Cheng Wang, Ehud Altman and Samuel J. Garratt
We study the
quantum dynamics generated by the repeated action of a non-
unitary evolution operator on a system of
qubits. Breaking unitarity can lead to the purification of mixed initial states, which corresponds to the loss of sensitivity to initial conditions, and hence the absence of a key signature of dynamical chaos. However, the scrambling of
quantum information can delay purification to times that are exponential in system size. Here we study purification in systems whose
evolution operators are fixed in time, where all aspects of the dynamics are in principle encoded in spectral properties of the
evolution operator for a single time step. The operators that we study consist of global Haar random
unitary operators and non-
unitary single-
qubit operations. We show that exponentially slow purification arises from a distribution of
eigenvalues in the complex plane that forms a ring with sharp edges at large radii, with the
eigenvalue density exponentially large near these edges. We argue that the sharp edges of the
eigenvalue distribution arise from level attraction along the radial direction in the complex plane. By calculating the spectral form factor we also show that there is level repulsion around the azimuthal direction, even close to the outer edge of the ring of
eigenvalues. Our results connect this spectral signature of
quantum chaos to the sensitivity of the system to its initial conditions.
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Statistical Mechanics
Phase diagram of the one-dimensional three-state Potts model with an additional mean-field interaction
Alessandro Campa, Vahan Hovhannisyan, Stefano Ruffo et al. (+1 more)
We derive the phase diagram of the one-dimensional three-state Potts model with an additional mean-field interaction in the canonical ensemble. The free energy is obtained by mapping the model onto the
spin-$1$ Blume-Emery-Griffiths model and solving it by using an Hubbard-Stratonovich transformation combined with the transfer
matrix method. A complex structure with lines of first-order transitions, two triple points and a critical point appears at finite temperature. The phase diagram is two-dimensional, since there are two adjustable parameters, the nearest-neighbour coupling $K$ and the temperature $T$. We show that the phase diagram does not present second-order phase transition lines, due to the fact that the order parameter is not a
symmetry-breaking one. Quite remarkably, we are able to determine analytically one of the first-order phase-transition lines. We also prove that, when the nearest-neighbour coupling $K$ is large and negative, the first-order transition temperature becomes asymptotically independent of $K$.
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All authors Alessandro Campa, Vahan Hovhannisyan, Stefano Ruffo, Andrea Trombettoni
Materials Science
Intervention Strategies for Polarization Switching in Hybrid Improper Ferroelectrics
Ayana Ghosh, Palanichamy Gayathri, Sathiyamoorthy Buvaneswaran et al. (+1 more)
The potential of hybrid improper ferroelectrics (HIFs) in electronic and spintronic devices hinges on their ability to switch polarization. Although the coupling between octahedral rotation and tilt is well established, the factors that govern switching barriers remain elusive. In this study, we explore this area to demonstrate the critical role of causal
reasoning in uncovering the mechanisms to control the ferroelectric switching barrier in HIFs. By combining causal discovery, causal interventions, and first-principles simulations, we identify tolerance factor, A-site cation radii mismatch, epitaxial strain, and octahedral rotation/tilt as key parameters and quantify how their interplay directly influences switching barrier. Three key insights emerge from our work: (a) the analysis identifies the structural descriptors controlling polarization reversal across a broad family of A-site-layered double perovskites and superlattices, (b) it uncovers non-trivial, material-specific rotation-tilt mechanisms, including a counterintuitive cooperative pathway where both rotation and tilt change while lowering the barrier, an effect mostly inaccessible to conventional Landau or first-principles-based approaches and (c) it maps these material-specific mechanisms to experimentally realizable parameters, showing that epitaxial strain from orthorhombic substrates (e.g., NdScO$_3$, NdGaO$_3$) selectively tunes octahedral distortions to achieve barrier reduction across varied compositions. These results establish actionable, materials-by-design principles linking composition, structure, and strain to polarization switching, while highlighting the potential of causal
reasoning to guide intelligent, mechanism-driven strategies for engineering complex functional
oxides.
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All authors Ayana Ghosh, Palanichamy Gayathri, Sathiyamoorthy Buvaneswaran, Saurabh Ghosh
Mesoscale and Nanoscale Physics
Electrically driven plasmon-polaritonic bistability in Dirac electron tunneling transistors
Shuai Zhang, Yang Xu, Junhe Zhang et al. (+12 more)
Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in
graphene/hexagonal-boron-nitride/
graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between
graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals
heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical
memory, sensing, and optoelectronic switching.
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All authors Shuai Zhang, Yang Xu, Junhe Zhang, Dihao Sun, Yinan Dong, Matthew Fu, Takashi Taniguchi, Kenji Watanabe, Cory R. Dean, Monica Allen, Jeffery Allen, F. Javier Garcia de Abajo, Antti J. Moilanen, Lukas Novotny, D. N. Basov
Mesoscale and Nanoscale Physics
Tunable giant Purcell enhancement of quantum light emitters by means of acoustic graphene plasmons
Justin Gruber, Mahtab A. Khan, Dirk R. Englund et al. (+1 more)
Inspired by the remarkable ability of plasmons to boost radiative emission rates, we propose leveraging acoustic
graphene plasmons (AGPs) to realize tunable,
giant Purcell enhancements for single-
photon, entangled-
photon, and multipolar
quantum emitters. These AGPs are localized inside a cavity defined by a
graphene sheet and a metallic nanocube and filled with a dielectric of thickness of a few nanometers and consisting of stacked layers of 2D materials, containing
impurities or defects that act as
quantum light emitters. Through finite-difference time domain (FDTD) calculations, we show that this geometry can achieve
giant Purcell enhancement factors over a large portion of the infrared (IR) spectrum, up to 6 orders of magnitude in the mid-IR and up to 4 orders of magnitude at telecommunications wavelengths, reaching
quantum efficiencies of 95% and 89%, respectively, with high-mobility
graphene. We obtain Purcell enhancement factors for single-
photon electric dipole (E1), electric quadrupole (E2), and electric octupole (E3) transitions and two-
photon spontaneous emission (2PSE) transitions, of the orders of $10^{4}$, $10^{7}$, $10^{9}$, and $10^9$, respectively, and a
quantum efficiency of 79% for entangled-
photon emission with high-mobility
graphene at a wavelength of $\lambda=1.55$ $\mu$m. Importantly, AGP mode frequencies depend on the
graphene Fermi energy, which can be tuned via electrostatic gating to modulate fluorescence enhancement in real time. As an example, we consider the Purcell enhancement of spontaneous single- and two-
photon emissions from an erbium atom inside single-layer (SL) WS$_2$. Our results could be useful for electrically tunable
quantum emitter devices with applications in
quantum communication and
quantum information processing.
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All authors Justin Gruber, Mahtab A. Khan, Dirk R. Englund, Michael N. Leuenberger
Materials Science
Exploring the Electronic Nature of Spinel Oxides: A Review of Their Electron Interactions and Prospects
Jagadis Prasad Nayak, Raju Saini, Sourav Dash et al. (+1 more)
This review discusses the multifaceted electronic properties of spinel
oxides with a particular focus on Lithium Vanadate (LiV2O4), Lithium Titanate (LiTi2O4), and Magnesium Titanate (MgTi2O4). We selected LiTi2O4, LiV2O4, and MgTi2O4 because they serve as quintessential examples of spinel
oxides' diverse and intriguing electronic phenomena. LiV2O4 heavy
fermion behaviour challenges traditional theories in d-electron systems, LiTi2O4 being the first
oxide superconductor provides critical insights into unconventional superconductivity driven by strong electron-
phonon interactions, and MgTi2O4 pronounced orbital ordering and metalinsulator transition offers a clear model for exploring electron-
lattice coupling. This shows how the inherent structural versatility of the spinel
lattice, characterised by its cubic close-packed oxygen network and variable cation distributions, enables a rich interplay of electron-electron correlations, electron-
lattice coupling, and orbital degrees of freedom. In LiV2O4, the combination of mixed-valence vanadium ions and a geometrically frustrated pyrochlore
lattice gives rise to heavy
fermion behaviour, whereas LiTi2O4 exhibits unconventional superconductivity driven by a high density of states at the
Fermi level and strong electronphonon interactions. MgTi2O4 undergoes a pronounced metal-
insulator transition, where orbital ordering triggers a Peierls-like distortion that stabilises a low-temperature insulating state through Ti-Ti dimerization. How the composition of these compounds affects their properties, based on both theoretical research and experimental findings, is illustrated by this review. It illustrates the promise of Spinels in practical technologies such as energy storage, electrocatalysis, and high-temperature lubrication.
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All authors Jagadis Prasad Nayak, Raju Saini, Sourav Dash, Gopi Nath Daptary
Other Condensed Matter
Vladimir L. Zhiliakov, Nataliia E. Kopteva, Irina A. Yugova et al. (+3 more)
We theoretically investigate the
spin structure and
spin dynamics of
excitons in bulk lead halide perovskite
semiconductors with cubic, tetragonal, and orthorhombic
crystal symmetry. The
exciton spin structure and its modification by an external
magnetic field are modeled for different regimes defined by the relative magnitude of the electron-hole exchange interaction (splitting between dark and bright states) and the Zeeman
spin splitting. The effects of
crystal symmetry and
magnetic field orientation with respect to the
crystal axes are considered for lead halide perovskite
crystals with band gaps in the range 1.4 - 3.5 eV, having different ratios of electron and hole g-factors. For cubic
symmetry, in a longitudinal
magnetic field, our theory predicts
quantum beats between the bright
exciton states under linearly polarized excitation and detection, while the dark
exciton remains optically inactive. In a transverse
magnetic field, all
exciton spin states become optically active and can be excited by circularly polarized light. Reduction of the
crystal symmetry leads to a zero-field offset of the
exciton Larmor precession frequencies, modifying the Zeeman splitting energy dependence on
magnetic field. This theoretical framework allows for the extraction of the strength of the exchange interaction and the
crystal symmetry. Experimentally, we measure the
exciton spin coherence via time-resolved photoluminescence at a temperature of 1.6 K in longitudinal and transverse
magnetic fields in orthorhombic MAPbI3
crystals. Polarization beats at the frequency of the bright
exciton are observed in both configurations. Comparison with theory indicates that the
excitons are in the strong exchange interaction regime, and the reduction of
symmetry does not lead to a significant splitting of the
exciton spin levels.
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All authors Vladimir L. Zhiliakov, Nataliia E. Kopteva, Irina A. Yugova, Dmitri R. Yakovlev, Ilya A. Akimov, Manfred Bayer
Mesoscale and Nanoscale Physics
Bruno Barton-Singer, Anusree Navallur and Stavros Komineas
We numerically and analytically study the transient dynamics of
magnetic skyrmions in synthetic antiferromagnets under a
magnetic field gradient. We consider skyrmions in a
bilayer with
antiferromagnetic coupling between the layers. The skyrmions in the two layers move almost perpendicular to the field gradient and the motion is eventually halted with the two skyrmions at a distance from each other. We find that the skyrmion displacement is proportional to the field gradient, while the time it takes to reach their final position is almost independent of it. Below a critical
magnetic field gradient strength, the system displays an unusual 'remembering' dynamics: when the
magnetic field gradient is removed, the skyrmions return to their original positions to a high degree of accuracy. We explain this observation and other quantitative features using a
moduli space dynamics approximation. We further provide an exact treatment of the dynamics that indicates that deviations from exact
memory of the skyrmion position can arise.
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Soft Condensed Matter
Modulation of DNA rheology by a transcription factor that forms aging microgels
Amandine Hong-Minh, Yair Augusto Gutiérrez Fosado, Abbie Guild et al. (+4 more)
Proteins and nucleic acids form non-Newtonian
liquids with complex rheological properties that contribute to their function in vivo. Here we investigate the rheology of the transcription factor NANOG, a key
protein in sustaining embryonic stem
cell self-renewal. We discover that at high concentrations NANOG forms macroscopic aging gels through its intrinsically disordered tryptophan-rich domain. By combining molecular dynamics simulations, mass photometry and Cryo-EM, we also discover that NANOG forms self-limiting micelle-like clusters which expose their DNA-binding domains. In dense solutions of DNA, NANOG micelle-like structures stabilize intermolecular entanglements and crosslinks, forming microgel-like structures. Our findings suggest that NANOG may contribute to regulate gene expression in a unconventional way: by restricting and stabilizing genome dynamics at key transcriptional sites through the formation of an aging microgel-like structure, potentially enabling mechanical
memory in the gene network.
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All authors Amandine Hong-Minh, Yair Augusto Gutiérrez Fosado, Abbie Guild, Nicholas Mullin, Laura Spagnolo, Ian Chambers, Davide Michieletto