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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 18 March

Superconductivity

Extended Hubbard model on fractals: d-Wave superconductivity and competing pairing channels

Robert Canyellas, Mikhail I. Katsnelson and Andrey Bagrov

Fractal structures such as the Sierpiński gasket have been predicted to enhance the critical temperature of s-wave superconductivity compared to regular crystals while maintaining macroscopic phase coherence of Cooper pairs. Here we extend this analysis to order parameters with non-trivial symmetry by studying the extended Hubbard model with nearest-neighbor attraction on fractal lattices. Using Bogoliubov-de Gennes mean-field theory, we find that the Sierpiński carpet dramatically alters the competition between pairing channels: the predominant d-wave superconducting dome at half filling of the square lattice becomes unstable for the carpet, while at high and low fillings extended s-wave pairing gets strongly enhanced. We attribute this to geometric frustration of sign-changing order parameters by the fractal boundary structure. On the triangular Sierpiński gasket, hybrid s+d+id states show critical temperature enhancement comparable to that previously observed for pure s-wave pairing. Our results demonstrate that fractal geometry acts as a selective filter for pairing symmetries, with the compatibility between order parameter structure and lattice topology determining which channels are stabilized or suppressed.
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Strongly Correlated Electrons

Novel Magnetoacoustic Resonance Technique for Exploring Hidden Quadrupoles in a Crystal Field Quartet

Mikito Koga and Masashige Matsumoto

Crystal field quartets with quadrupole degrees of freedom play a crucial role in hidden ordering systems, as exemplified by CeB$_6$. We present a novel magnetoacoustic resonance technique that combines acoustically induced strain fields with a linearly polarized high-frequency microwave field to probe quadrupoles inherent in the quartet hidden behind magnetic properties. This method offers the advantage of enabling quantum quadrupole resonance transitions for large excitation energy gaps within quartet sublevels under a strong magnetic field, which cannot be achieved by acoustic experiments alone. Formulating a simultaneous single-phonon-single-photon absorption transition process using Floquet theory, we demonstrate how the transition probabilities are affected by changing the propagation direction of a bulk acoustic wave. The key result is that distinct maxima in transition probabilities, attributed to specific propagation directions, indicate a characteristic of quadrupole physics and exhibit an abrupt change owing to an induced ordered moment. This photon-assisted magnetoacoustic resonance technique will promote a broader range of applications of acoustic experiments for the study of quadrupole physics.
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Materials Science

Single-pair charge-2 Weyl-Dirac composite semimetals

Hui-Jing Zheng, Ke-Xin Pang, Yun-Yun Bai et al. (+2 more)

The Nielsen–Ninomiya theorem requires that the total topological chiral charges in a crystal vanish, a constraint typically satisfied by identical nodes like Weyl–Weyl pairs. Whether a minimal heterogeneous configuration – comprising a single Weyl point (WP) and a single Dirac point (DP) – can exist in an electronic system has remained unresolved. Here, by systematically classifying all 1651 magnetic space groups (MSGs), we reveal that only 14 MSGs without spin-orbit coupling (SOC) and 10 MSGs with SOC are compatible with this exotic state. Furthermore, for nonmagnetic crystals, this configuration is uniquely realized in the spinless limit of chiral space groups 92 and 96. Guided by this principle, we predict an ideal realization in chiral three-dimensional boron allotropes (SDHBN-B$_{28}$ enantiomers). First-principles calculations unveil a $|C|=2$ WP at the $\Gamma$ point and a $|C|=2$ DP at the $A$ point, which constitute the only fermions near the Fermi level within a large $2$ eV energy window. Strikingly, the structural chirality rigidly dictates the sign of the topological charges, yielding two ultralong Fermi arcs spanning the surface Brillouin zone. Our work provides a complete crystallographic classification and a definitive material platform for exploring minimal heterogeneous chiral fermions.
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All authors Hui-Jing Zheng, Ke-Xin Pang, Yun-Yun Bai, Yanfeng Ge, Yan Gao

Soft Condensed Matter

Hexatic Order Coupled with Thermal Noise Produces Bubbles in Two-Dimensional Active Matter

Luke Langford and Ahmad K. Omar

The phase separation of purely-repulsive particles induced by self-propulsion is among the most well-studied non-equilibrium phase transitions. However, some notable features of this transition remain open questions, including the origin of bubbles within the dense phase in two dimensions. Various explanations have been proposed, ranging from a reversal of the Ostwald ripening process to topological defects at the borders of hexatic domains. We present particle-based simulations that disentangle the effect of hexatic domains on the bubble size and number distribution through the introduction of polydispersity. While hexatic order is found to be necessary for bubble formation, we also identify thermal translational noise is required for bubble generation. Intriguingly, the magnitude of the thermal noise needed for bubble formation can be remarkably small in comparison with the particle activity but cannot be identically zero. The cooperative motion evidenced within the dense phase of the thermal hexatic domains may may be necessary for bubble production.
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Materials Science

Symmetry-Driven Electrical Switching of Anisotropic Skyrmion Hall Effect in Altermagnets

Wenhui Du, Kaiying Dou, Ying Dai et al. (+3 more)

Controlling the skyrmion Hall effect (SkHE) is pivotal for developing topological spintronics but typically relies on magnetic field reversal. Here, we demonstrate a general strategy for the purely electrical switching of the SkHE in two-dimensional altermagnets. Through symmetry and model analysis, we reveal that the intrinsic altermagnetic symmetry imposes sublattice-dependent anisotropic exchange and Dzyaloshinskii-Moriya interactions. These interactions induce a highly anisotropic SkHE, where the transverse velocity is strictly dictated by the current direction relative to the crystal axes. Crucially, we show that an external electric field can strongly modulate these interaction parameters by inversing the altermagnetic symmetry, allowing for the reversible inversion of the anisotropic SkHE. Using first-principles and atomistic spin model simulations, this mechanism is further demonstrated in monolayer CaMnSn. Our study establishes a unique strategy for realizing precise, electrically tunable skyrmion transport without magnetic fields.
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All authors Wenhui Du, Kaiying Dou, Ying Dai, Zeyan Wang, Baibiao Huang, Yandong Ma

Strongly Correlated Electrons

Generalized symmetry-protected topological phases in mixed states from gauging dualities

Linhao Li, Zhen Bi and Weiguang Cao

Decoherence in realistic quantum platforms motivates a mixed-state notion of topological phases of matter, including average symmetry-protected topological (ASPT) phases. Alongside this progress, generalized symmetries–notably noninvertible and dipole symmetries–have become powerful organizing principles for exotic quantum phases, yet their implications for mixed states remain less explored. In this work, we bridge these directions through a gauging correspondence between mixed-state phases with generalized symmetries and mixed-state phases with ordinary group symmetries, recasting the classification of noninvertible and dipole ASPT phases into familiar classifications of symmetry breaking and ASPT phases with dual symmetries. Using this approach, we classify and construct a subclass of ASPT phases with non-invertible and dipole symmetries in $(1+1)d$, including phases that are intrinsic to mixed states, and characterize them via string order parameters and protected edge modes.
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Strongly Correlated Electrons

Magnetic-field tuning of the spin dynamics in the quasi-2D van der Waals antiferromagnet CuCrP$_{2}$S$_{6}$

Joyal John Abraham, Yaqian Guo, Yuliia Shemerliuk et al. (+14 more)

The use of antiferromagnets in magnetoelectronic devices as counterparts of ferromagnets is a new, rapidly developing trend in spintronics that leverages antiferromagnetic (AFM) magnons for transmitting of spin currents. Van der Waals (vdW) antiferromagnets are particularly attractive in this respect as they possess tunable magnetic properties and can be easily integrated into spintronic devices. In this work we use electron spin resonance (ESR) spectroscopy to assess the potential of the vdW AFM compound CuCrP$_{2}$S$_{6}$ for magnonic applications by exploring the magnetic field ($H$) dependence of the spectrum of magnon excitations below its AFM ordering temperature $T_{\rm N} \approx 30$ K and the correlated spin dynamics above $T_{\rm N}$. ESR reveals prominent ferromagnetic (FM) spin correlations that persist far above $T_{\rm N}$ suggesting an intrinsically two-dimensional character of the spin dynamics in CuCrP$_{2}$S$_{6}$. Most interestingly, at $T < T_{\rm N}$, CuCrP$_{2}$S$_{6}$ features two non-degenerate, i.e., distinct in energy AFM magnon modes at $H = 0$ which can be tuned to the FM type of collective spin excitations with increasing $H$. These remarkable properties are favorable for the induction and control of unidirectional spin current in CuCrP$_{2}$S$_{6}$ and suggest it as a new functional material for magnetoelectronics.
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All authors Joyal John Abraham, Yaqian Guo, Yuliia Shemerliuk, Sebastian Selter, Saicharan Aswartham, Kranthi Kumar Bestha, Laura T. Corredor, Anja U. B. Wolter, Olga Kataeva, Luka Rogić, Noah Somun, Damjan Pelc, Oleg Janson, Jeroen van den Brink, Bernd Büchner, Vladislav Kataev, Alexey Alfonsov

Mesoscale and Nanoscale Physics

Phonon circular birefringence and polarization-filter in Magnetic Topological Insulators

Abhinava Chatterjee and Chao-Xing Liu

The surface phonon Hall viscosity (PHV)-an acoustic analog of axion electrodynamics-emerges from the strain response of magnetic topological insulators and gives rise to novel acoustic phenomena. In this work, we propose a previously unexplored effect: a phonon polarization-filter mechanism induced by the surface PHV, which generates an interface phonon mode with its frequency below the bulk mode frequency. This interface mode possesses a specific circular polarization and therefore acts as a polarization filter, confining only phonons with the matching polarization at the interface. Magnetic topological insulators can thus selectively transmit one type of circularly polarized phonon mode, enabling the manipulation of phonon polarization and angular momentum. In addition, we further develop a generalized scattering framework to study the effect of an injected acoustic wave from a trivial insulator to a magnetic topological insulator with both normal and oblique incidence, and discuss the phenomena of surface acoustic Faraday rotation and longitudinal-transverse mode conversion. Our results establish surface Hall viscosity as a powerful mechanism for engineering axial phonon states and open new avenues for topological phononic devices based on phonon angular momentum.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Engineering strong coupling with molecular coatings in optical nanocavities

Athul S. Rema, Adrián E. Rubio López and Felipe Herrera

Quantum emitters near the surface of silver nanoparticles undergo Rabi oscillations in electronic population dynamics due to strong coupling with near-field multipole modes that are not radiative. Low-frequency nanoparticle dipole modes are radiative but do not couple strong enough to quantum emitters. These features limit the observation of strong coupling. Using macroscopic quantum electrodynamics theory within a Lorentzian pseudo-mode approximation for the non-Markovian interaction kernel, we demonstrate that by coating spherical silver nanoparticles with a thin molecular J-aggregate layer, the resulting core-shell plexciton resonance restructures the local electromagnetic vacuum at dipole-mode frequencies to enable Rabi oscillations for quantum emitters that otherwise would only undergo exponential population decay. Specifically, we show for quantum dot emitters in the near field of silver nanospheres of 20 nm radius, that weak-to-strong coupling crossovers can be induced using 2 nm J-aggregate shells. Our work demonstrates the potential of molecular aggregates to enable deep sub-wavelength structuring of the vacuum field for the observation of coherent quantum dynamics in optical nanocavities.
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Materials Science

Thermodynamic accessibility of Li-Mn-Ti-O cation disordered rock-salt phases

Ronald L. Kam, Shilong Wang and Gerbrand Ceder

Disordered rock-salt with Li-excess (DRX) cathode phases within the Li-Mn-Ti-O (LMTO) composition space have recently been extensively studied, as they promise to deliver exceptional energy density at low cost in Li-ion batteries. The continued development of LMTO DRX with improved power density and cycling stability requires optimization of the composition and particle size/morphology, which are determined by synthesis conditions such as annealing temperatures and hold times. These challenges motivate our investigation of the phase diagram of the LMTO rock-salt phase space, with a focus on understanding the stability of DRX by quantifying the order-disorder transition temperature ($T_\text{disord}$) as a function of composition. We harness first-principles calculations and X-ray diffraction experiments to establish the LMTO phase diagram, which lies within the LiMnO$_2$ – Li$_2$MnO$_3$ – Li$_2$TiO$_3$ pseudo-ternary. Our calculations predict that the LMTO phase diagram at elevated temperature ($700 - 1300$ C) is composed of three phases: DRX, orthorhombic LiMnO$_2$, and layered Li$_2$Mn$_\text{1-y}$Ti$_\text{y}$O$_3$ ($0 < \text{y} < 1$). $T_\text{disord}$ decreases significantly as off-stoichiometry is introduced to the end-point compositions, resulting in a eutectoid phase diagram. Importantly, a significant range of LMTO compositions containing small to moderate fractions of Li-excess and Ti doping (relative to LiMnO$_2$) have $T_\text{disord}$ spanning $700 - 900$ C. These temperatures are substantially lower than conventional DRX synthesis temperatures ($\geq 1000$ C), suggesting the promise of decreasing synthesis temperatures for specific DRX compositions. The compositions containing moderate to high fractions of Mn$^{4+}$ instead have much greater $T_\text{disord}$ and phase separation to layered Li$_2$MnO$_3$ becomes highly favored.
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Superconductivity

Field-angle dependence of magnetoresistance in UTe2

Jun Ishizuka and Youichi Yanase

We theoretically study angle-resolved magnetoresistance under rotated magnetic field in the normal state of a spin-triplet superconductor UTe$_2$. The Wannier model derived from a GGA+$U$ calculation shows quasi-two-dimensional Fermi surfaces with warping in the $k_z$ direction, consistent with quantum oscillation measurements in the high magnetic field regime. Solving the semiclassical Boltzmann equation, we show that the Fermi surface geometry gives rise to oscillations in the magnetoresistance when the field is tilted from the $c$ axis toward the $a$ or $b$ axis. By assuming a band-dependent relaxation time, the calculated angle-resolved magnetoresistance is in good agreement with the recent transport experiment. This is direct evidence for the warped Fermi surface revealed by ordinary intraband transport. It suggests that the hole band with long relaxation time dominates electron transport. The field angle dependence of the Hall resistivity is calculated for further experimental verification.
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Statistical Mechanics

Crossover effects on the phase transitions phenomena translated by arborecences and spectral properties

Roberto da Silva

This study investigates how visibility graphs constructed from Monte Carlo Markov Chain time series of spin models capture the critical behavior of the system. More precisely, we show that this approach identifies continuous phase transitions as well as important nuances, such as crossover effects occurring in the transition from a critical line to a first-order line through a tricritical point, as observed, for example, in the Blume–Emery–Griffiths model or, in a simpler setting, in the Blume–Capel model. By applying Kirchhoff's theorem, we show that the number of spanning trees of the resulting graphs serves as a sensitive indicator of these phase transitions. Furthermore, a qualitative analysis of the adjacency matrices based on random matrix theory provides additional evidence for these phenomena. The methodology developed here can potentially be extended to the analysis of criticality in empirical time series from complex systems, such as climate, financial, and epidemiological data, where the Hamiltonian governing the dynamics is not necessarily known.
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Tuesday 17 March

Statistical Mechanics

Fractional epidemics from quantum loops

Jose Jesus Bernal-Alvarado and David Delepine

Classical compartmental models of epidemiology rely on well-mixed, local interaction approximations that fail to capture the heavy-tailed burst dynamics and long-range spatial correlations observed in real-world outbreaks. While fractional calculus is frequently employed to model these anomalous behaviors, fractional operators are introduced phenomenologically. In this work, we demonstrate that fractional space-time epidemic dynamics emerge naturally and rigorously from first principles using a non-equilibrium quantum field theory model. By mapping the stochastic contagion process to a gauge-mediated field theory via the Doi-Peliti formalism, we go beyond the static mean-field approximation to compute the full dynamical one-loop vacuum polarization. We prove that integrating out a dynamically fluctuating host vacuum generates anomalous momentum and frequency scaling. Transitioning back to coordinate space, this derives a coupled space-time fractional integro-differential equations, where the non-linear transmission vertex is governed by parabolic Riesz potentials and Riemann-Liouville time derivatives. We show that in the anomalous regime ($\alpha < 2$), local Debye screening is modified, facilitating Lévy flight super-spreading and temporal avalanches. Consequently, the effective reproductive number ($R_{eff}$) ceases to be a scalar, transforming into a spectral dispersion relation bounded strictly by the ultraviolet spatial cutoff.
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Statistical Mechanics

Transient Thermodynamic Efficiency of Adaptive Inference in Continuously Nonstationary Environments

Aditya Gupta

Adaptive physical and biological systems continually process fluctuating information from their environments. When the environment is nonstationary, inference itself becomes a nonequilibrium process with thermodynamic cost. We analyse a minimal stochastic model which is an overdamped particle in an adaptive double well potential whose control parameter tracks a drifting Ornstein Uhlenbeck signal. Using stochastic energetics, we derive explicit expressions for entropy production, mutual information rate, and a time dependent learning efficiency. High precision Langevin simulations reveal transient peaks in learning efficiency during rapid environmental shifts, absent in steady state averages. These results identify transient adaptive regimes as moments of maximal information to energy conversion, highlighting that maximal thermodynamic learning performance arises transiently rather than in steady state. Throughout this work, the environment is treated as an externally driven stochastic signal rather than a thermodynamic subsystem under control, and its intrinsic entropy production is therefore excluded from the thermodynamic accounting.
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Mesoscale and Nanoscale Physics

Spontaneous Polarization Suppression of Exciton-Exciton Annihilation in 3R-Stacked MoS$_2$ Bilayers

Tae Gwan Park, Xufan Li, Kyungnam Kang et al. (+4 more)

Rapid exciton-exciton annihilation (EEA) in two-dimensional semiconductors limits access to high-density excitonic regimes essential for efficient optoelectronic operation under strong excitation. Here, we show that EEA is suppressed by repulsive dipole-dipole interactions between interlayer excitons polarized by the spontaneous polarization intrinsic to rhombohedral (3R)-stacked MoS$_2$ bilayers. Using ultrafast pump-probe spectroscopy, we measure an EEA rate of $\gamma_{\rm EEA}=(5.03\pm0.99)\times10^{-3}$ cm$^2$ s$^{-1}$ in 3R bilayers, which is approximately 18.2-fold smaller than that in monolayers and 2.9-fold smaller than that in nonpolar 2H bilayers. Despite the higher exciton diffusivity recently reported for 3R relative to 2H bilayers, the reduced EEA rate in 3R indicates a rate-limited regime governed by the close-encounter annihilation probability rather than diffusion. A rate-limited annihilation model incorporating a dipole-dipole repulsive potential captures the observed ratio $\gamma_{{\rm EEA},3{\rm R}}/\gamma_{{\rm EEA},2{\rm H}}\approx0.35$ for an exciton-exciton encounter distance of $\sim$1.3 nm, consistent with the bilayer exciton Bohr radius. These results show that spontaneous polarization in 3R-stacked bilayers suppresses nonlinear excitonic losses and provides a route toward high-density excitonics.
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All authors Tae Gwan Park, Xufan Li, Kyungnam Kang, David B. Geohegan, Christopher M. Rouleau, Alexander A. Puretzky, Kai Xiao

Superconductivity

A Dayem Loop Qubit Based on Interfering Superconducting Nanowires

Cliff Sun and Alexey Bezryadin

We propose a qubit design based on two parallel superconducting nanowires (i.e., a "Dayem loop qubit"). The inclusion of two nanowires instead of one leads to the Little-Parks effect, which provides an oscillator behavior for the qubit frequency as well as anharmonicity. Our key result is that even if the nanowires have an increasingly linear CPR at low supercurrents, the quantum interference between two condensates, induced by a magnetic field, leads to a restoration of cubic nonlinearity, which is predicted to be sufficient to create a functional transmon qubit based on thin superconducting wires. We consider both generic (cubic) current-phase relationships (CPR) as well as more realistic microscopic CPR, having higher-order nonlinearities. For higher-order CPRs, we propose a simple power-law phenomenological approximation valid at very low temperatures, at which superconducting qubits normally operate.
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Superconductivity

From Atomistic Impurity Landscapes to Two-Level-System Distributions and Microwave Loss: Hydrogen-Induced Losses in Nb$_2$O$_{5-\delta}$ and Ta$_2$O$_{5-\delta}$

Cristóbal Méndez, Sarvesh Chaudhari and Tomás A. Arias

We introduce a first-principles-guided framework for predicting statistical TLS distributions from mobile impurities in disordered materials. Machine-learned interatomic potentials, with DFT and minimum-action-path validation, connect impurity landscapes to tunnel-splitting and asymmetry distributions, TLS densities, and dielectric loss. Applied to amorphous Nb$_2$O$_{5-\delta}$ and Ta$_2$O$_{5-\delta}$, the framework implicates interstitial hydrogen as a source of microwave loss. Loss tangents match Nb-pentoxide measurements at inferred H concentrations, while weaker H uptake in Ta reproduces the Nb/Ta TLS contrast.
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Soft Condensed Matter

Mesoscopic Modeling of Dynamic Tetra-PEG Hydrogel Networks

Pietro Miotti, Lucien Cousin, Mark W. Tibbitt et al. (+1 more)

We introduce a mesoscopic model of dynamic Tetra-PEG hydrogel networks based on a hybrid Dissipative Particle Dynamics/Monte Carlo (DPD/MC) approach. Polymer chains are described by Finite Extensible Nonlinear Elastic (FENE) potential, while reversible cross-links are modeled with Morse potential and Monte Carlo bond exchange governed by Bell's force-dependent kinetics. After systematic calibration against theory and experiments, the model reproduces the characteristic Maxwell-like viscoelastic response of these networks. In particular, the relaxation time follows the expected scaling, $\tau_R \propto \tau_b (p - p_{\text{gel}})$, and the simulated storage moduli agree with experimental rheology. The mesoscopic resolution allows for graph-based topological analysis, where Tetra-PEG molecules and cross-links are represented as nodes and edges, providing access to bond distributions, fraction of dangling chains, and size of percolating clusters that are challenging to measure experimentally. Comparison with permanent-network predictions further suggests that dynamic bond exchange can affect bond distributions and delay the formation of a system-spanning cluster. This model bridges macromolecular bond kinetics and macroscopic mechanical properties, providing a complementary tool for rational design of dynamic polymer networks.
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All authors Pietro Miotti, Lucien Cousin, Mark W. Tibbitt, Igor V. Pivkin

Other Condensed Matter · Cross-listed from cs.CR

Synchronized DNA sources for unconditionally secure cryptography

Sandra Jaudou, Hélène Gasnier, Elias Boudjella et al. (+11 more)

Secure communication is the cornerstone of modern infrastructures, yet achieving unconditional security -resistant to any computational attack- remains a fundamental challenge. The One-Time Pad (OTP), proven by Shannon to offer perfect secrecy, requires a shared random key as long as the message, used only once. However, distributing large keys over long distances has been impractical due to the lack of secure and scalable sharing options. Here, we introduce a DNA-based cryptographic primitive that leverages random pools of synthetic DNA to install a synchronized entropy source between distant parties. Our approach uses duplicated DNA molecules -comprising random index-payload pairs- as a shared secret. These molecules are locally sequenced and digitized to generate a common binary mask for OTP encryption, achieving unconditional security without relying on computational assumptions. We experimentally demonstrate this protocol between Tokyo and Paris, using in-house sequencing, generating a shared secret mask of $\sim$ 400 Mb with a residual error rate to achieve the usual overall decryption failure rate of $2^{-128}$. The min-entropy of the binary mask meets the most recent National Institute of Standards and Technology requirements (SP 800-90B), and is comparable to that of approved cryptographic random number generators. Critically, our system can resist two types of adversarial interference through molecular copy-number statistics, providing an additional layer of security reminiscent of Quantum Key Distribution, but without distance limitations. This work establishes DNA as a scalable entropy source for long-distance OTP, enabling high-throughput and secure communications in sensitive contexts. By bridging molecular biology and cryptography, DNA-based key distribution opens a promising new route toward unconditional security in global communication networks.
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All authors Sandra Jaudou, Hélène Gasnier, Elias Boudjella, Marc Canève, Victoria Bloquert, Vasily Shenshin, Tilio Pilet, Sacha Gaucher, Soo Hyeon Kim, Philippe Gaborit, Gouenou Coatrieux, Matthieu Labousse, Anthony Genot, Yannick Rondelez

Materials Science · Cross-listed from quant-ph

Die to wafer direct bonding of (100) single-crystal diamond thin films for quantum optoelectronics

Dominic Lepage, Amin Yaghoobi, Heidi Tremblay et al. (+1 more)

This work unlocks the manufacturing of nanophotonic quantum systems that exploit the unique material properties of single-crystal diamond (SCD). We achieve this by introducing a semiconductor-compatible process for the direct bonding of multiple high-quality, ultrathin diamond films onto a carrier wafer, enabling the subsequent parallel nanofabrication of optoelectronic integrated circuits. Central to this approach is a new diamond surface-preparation method that avoids boiling tri-acid mixtures while producing exceptionally clean 20 um thin single crystals. These platelets are bonded side-by-side to 100 mm silica wafers and exhibit a record shear strength of 45.1 MPa for (100)-oriented diamond, surpassing all previously reported bonding attempts. Evidence indicates that the bonding is dominated by van der Waals interactions, likely arising from mismatched protonation mechanisms between Si-OH and C-OH surface terminations, rather than from covalent-bond-driven mechanisms. Despite this non-molecular nature, the heterostructures remain stable through liquid immersions and standard nanofabrication steps. Because the method depends primarily on surface cleanliness and roughness rather than specific chemistries, it is broadly transferable across wafer materials. This capability to parallel-bond ultrathin SCD films onto large-area substrates provides a scalable route to high-performance platforms spanning nanophotonic quantum technologies, high-power electronics, MEMS, and biotechnology.
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All authors Dominic Lepage, Amin Yaghoobi, Heidi Tremblay, Dominique Drouin

Materials Science

Spin crossover in FeO under shock compression

Lélia Libon, Alessandra Ravasio, Silvia Pandolfi et al. (+17 more)

FeO (wüstite), which exhibits complex electronic and structural properties with increasing pressure and temperature, is a key mineralogical phase for understanding deep planetary interiors. However, direct measurements of its spin state at high-pressure and temperature remain challenging in static compression experiments. Here, we employ laser-driven shock compression to extend the FeO principal Hugoniot up to $\sim$900 GPa and perform in situ X-ray diffraction and X-ray emission spectroscopy up to 250 GPa, probing FeO's crystal structure and spin state. We demonstrate a continuous spin crossover of iron in FeO over a broad pressure range, with the high-spin state persisting beyond Earth's core-mantle boundary (CMB) conditions. These observations provide new experimental constraints on iron spin state at extreme conditions essential for geophysical models of (exo)planetary interiors.
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All authors Lélia Libon, Alessandra Ravasio, Silvia Pandolfi, Yanyao Zhang, Xuehui Wei, Jean-Alexis Hernandez, Hong Yang, Amanda J. Chen, Tommaso Vinci, Alessandra Benuzzi-Mounaix, Clemens Prescher, François Soubiran, Hae Ja Lee, Eric Galtier, Nick Czapla, Wendy L. Mao, Arianna E. Gleason, Sang Heon Shim, Roberto Alonso-Mori, Guillaume Morard

Materials Science

Engineering Quantum Phases in Two Dimensions via Vacancy-Induced Electronic Reconstruction

Emmanuel V. C. Lopes, Felipe Crasto de Lima, Caio Lewenkopf et al. (+1 more)

Topological phases of matter are commonly understood as emerging either from crystalline symmetry and intrinsic spin-orbit coupling or from disorder-driven electronic renormalization. In realistic materials, however, structural defects naturally combine both ingredients. Here, we demonstrate a general and material-independent mechanism by which atomic vacancies can induce topological phase transitions in two-dimensional semiconductors that are otherwise topologically trivial. Vacancies generate locally ordered dangling-bond states governed by well-defined hopping and spin-orbit interactions, while their spatial distribution and mutual coupling introduce long-range disorder. As vacancy concentration increases, the hybridization of these defect states forms an emergent electronic subspace that undergoes a topological transition. Using a tight-binding framework supported by large-scale density functional theory calculations, we show that this vacancy-induced electronic reconstruction can robustly stabilize quantum spin Hall, quantum anomalous Hall, and Weyl semimetal phases, depending on symmetry breaking and spin polarization. Our results establish vacancies not merely as perturbations, but as active design elements capable of transforming trivial insulators into topological quantum matter, opening realistic routes for defect-engineered topological devices.
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All authors Emmanuel V. C. Lopes, Felipe Crasto de Lima, Caio Lewenkopf, Adalberto Fazzio

Mesoscale and Nanoscale Physics

Magnetically tunable telecom emission from Er3+ ions in layered WS2

Guadalupe Garcia-Arellano, Gabriel I. Lopez-Morales, Johannes Flick et al. (+2 more)

Erbium ions (Er3+) provide a telecom-band optical transition with strong magnetic-dipole character, making them attractive for quantum communication and spin-photon interfaces. Identifying host environments that combine low decoherence with photonic compatibility, however, remains a central challenge. Here we investigate Er3+ emission in tungsten disulfide (WS2) flakes, a layered host offering low nuclear-spin density and narrow telecom emission. Using time- and polarization-resolved photoluminescence under modest magnetic fields (< 0.2 T), we observe pronounced dimming, lifetime extension, and rotation of the emission dipole when the field has an out-of-plane component, whereas in-plane fields produce little change. Effective model calculations of Er3+ in monolayer WS2 parametrized from density functional theory indicate that these effects arise primarily from Zeeman-induced mixing of near-degenerate crystal-field sublevels, which modifies the magnitude and orientation of the optical transition dipole moments. Comparative measurements in flakes of different thickness and numerical estimates of the local density of optical states further suggest a secondary contribution from dipole coupling to the anisotropic photonic environment of thin WS2 layers. These findings identify layered WS2 as a platform where magnetic fields can tune telecom emission through an interplay of crystal-field physics and anisotropic photonic coupling.
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All authors Guadalupe Garcia-Arellano, Gabriel I. Lopez-Morales, Johannes Flick, Cyrus E. Dreyer, Carlos A. Meriles

Superconductivity

Interplay of superconductivity and ferromagnetism in ferromagnetic semiconductor-based Josephson junctions

Hirotaka Hara, Lukas Baker, Axel Leblanc et al. (+8 more)

The interplay between superconductivity and ferromagnetism has long been pursued as a route to unconventional Josephson effects, yet suitable material platforms remain limited. Here we report Josephson junctions based on epitaxial Al/InAs/(Ga,Fe)Sb heterostructures grown by low-temperature molecular beam epitaxy, achieving atomically abrupt superconductor/semiconductor/ferromagnetic interfaces. The devices exhibit clear proximity-induced superconductivity, including multiple Andreev reflections and gate-tunable supercurrents, confirming transparent coupling across the hybrid structure. Under perpendicular magnetic fields, the junctions reveal highly unconventional Fraunhofer interference patterns with hysteresis, flux jumps, asymmetric lobe evolution, and clear nonreciprocity, providing strong evidence of induced ferromagnetism and broken time-reversal symmetry in the superconducting channel. Gate control further modulates the critical current, highlighting the semiconducting nature of the system. Our results demonstrate that ferromagnetic semiconductor heterostructures can serve as a highly tunable platform for exploring proximity-induced superconductivity and superconducting diode effects, and for advancing device concepts at the intersection of magnetism and quantum electronics.
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All authors Hirotaka Hara, Lukas Baker, Axel Leblanc, Shingen Miura, Keita Ishihara, Melissa Mikalsen, Patrick J. Strohbeen, Jacob Issokson, Masaaki Tanaka, Javad Shabani, Le Duc Anh

Soft Condensed Matter

Breakloose suppression in minimal friction models

Shubham Agarwal

Breakloose friction, the transient force peak at the onset of sliding, is often pronounced in nanoscale contacts but weak or absent in macroscopic systems. Although this behavior is commonly associated with rupture fronts and process-zone effects, how the stiction peak is controlled by system size, temperature, driving rate, and loading geometry, and what mechanisms underlie its emergence or suppression, remains incompletely understood. Here we investigate this problem using three minimal friction models with distinct loading geometries: a multi-particle Prandtl-Tomlinson system with independently driven particles, an end-driven Frenkel-Kontorova chain with elastic stress transmission along the interface, and a uniformly driven FK chain in which each site is coupled locally to the driving stage. We show that similar macroscopic suppression of breakloose friction can arise from fundamentally different mechanisms. In multi-particle PT systems, increasing system size or temperature promotes statistical dephasing of local depinning events, smoothing the global response. In end-driven FK chains, internal elasticity redistributes stress along the interface, delaying sliding onset and, together with higher temperature or slower driving, enabling progressive relaxation during loading. In uniformly-driven FK chains, the stiffness of the driving springs controls the synchronization of slip events and thereby the character of the sliding response. These results demonstrate that the presence or absence of a breakloose peak does not uniquely identify a single physical mechanism, but instead reflects the interplay of local pinning, elastic coupling, and contact architecture.
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Superconductivity

Real-space microscopic description of laser-pulse induced melting of superconductivity

Karl Bergson Hallberg, Guillermo Nava Antonio, Chiara Ciccarelli et al. (+1 more)

Quenching quantum order via laser pulses has proven a useful tool to access exotic physical effects in systems that are strongly perturbed out of equilibrium. However, theoretical modelling of experimental measurements is typically done phenomenologically or by assuming translational invariance due to the complexity of the problem. Here, we solve a microscopic real-space model of the time dynamics of a superconductor following an intense laser-pulse. We are able to reproduce recent experimental findings displaying a critical slowing-down of the melting of the order parameter for laser fluences close to the condensation energy. Moreover, we leverage the real-space resolution of our model to predict how phase fluctuations and currents in the system behave both spatially and temporally. We discover an unusual current flow in the superconductor after the pulse has subsided, resembling backward waves that normally require special engineering in metamaterials or wave guides. Our results predict a rich behavior of the superconducting order parameter at a microscopic level which is manifested in current textures that can be probed using radiation detection.
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All authors Karl Bergson Hallberg, Guillermo Nava Antonio, Chiara Ciccarelli, Jacob Linder

Quantum Gases · Cross-listed from quant-ph

Scalable quantum resources with short-range interacting spin-$\frac12$ chains

Marcin Płodzień and Jan Chwedeńczuk

The dynamical generation of quantum resources, such as many-body entanglement, Bell correlations or spin squeezing, can be achieved via one-axis twisting (OAT) dynamics, which require all-to-all couplings. However, current digital and analog quantum simulation platforms natively provide short-range or power-law couplings that decay too quickly for this purpose. We demonstrate that two spin-$\tfrac12$ chain models – a staggered nearest-neighbor XXX chain and a long-range XXZ chain – develop an effective OAT nonlinearity when projected onto the symmetric sector. We show that these dynamics generate metrologically useful spin-squeezed states and Greenberger-Horne-Zeilinger coherences that ensure violation of many-body Bell inequalities. We confirm the accuracy of this mapping by comparing it to the exact dynamics and demonstrate that the generated correlations can be read out using a single probe qubit. The resulting dynamics can be simulated with analog and digital quantum simulators.
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Disordered Systems and Neural Networks · Cross-listed from physics.optics

Attractor-Keyed Memory

Natalia G. Berloff

Physical selectors (lasers choosing a mode, Ising machines settling on a ground state, condensates occupying a spin state) produce high-dimensional signatures at the moment of decision: full field amplitudes, multimode interference patterns, or scattering responses. These signatures are richer than the winner's index, yet they are routinely discarded. We show that when the signatures are repeatable across trials (stereotyped) and linearly independent across routes, a single linear decoder compiled from calibration data maps them to arbitrary payloads, merging selection and memory access into one event and eliminating the fetch that dominates latency and energy in sparse routing architectures. The construction requires one SVD of measured device responses, which certifies capability and bounds worst-case error for any downstream payload before the task is chosen. Runtime error separates into two independently diagnosable channels, decoding fidelity (controlled by dictionary conditioning $\sigma_{\min}(\Phi)$) and routing reliability (controlled by the margin-to-noise ratio $\Delta/T_{\mathrm{eff}}$), each with a distinct physical origin and targeted remedy. We derive the full error decomposition, give Ising-machine selector constructions, and validate the predicted scalings on synthetic speckle-signature simulations across three measurement modalities. No hardware demonstration exists; we provide a falsifiable four-step experimental protocol specifying what a first experiment must measure. Whether real device signatures satisfy stereotypy is the central open question.
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Strongly Correlated Electrons

Field-direction sensitivity of Kondo hybridization in UTe$_2$

Thomas Halloran, Gicela Saucedo Salas, Sylvia K. Lewin et al. (+6 more)

Neutron scattering experiments on the spin-triplet superconductor UTe$_2$ have established that the dominant low-energy magnetic response is along Brillouin zone boundaries, resembling the magnetic susceptibility of narrow-gap interband excitations. We report a study of the sensitivity of these excitations to magnetic field along the crystallographic $\hat{a}$-axis. Up to fields of $\mu_0 H$=13 T, the maximal inelastic neutron spectral weight increases in energy transfer, with a pronounced increase in $d\hbar\omega_{peak}/dH$ near $\mu_0 H$=7 T. This behavior parallels the field and temperature dependent features of the electrical resistivity that are associated with Kondo hybridization. Our measurements suggest that $\hat{a}$-axis fields near $\mu_0 H$=7~T induce a change in the hybridization between heavy $f$-electrons and the bare conduction band.
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All authors Thomas Halloran, Gicela Saucedo Salas, Sylvia K. Lewin, J.A. Rodriguez-Rivera, Colin L. Sarkis, Jakob Lass, Daniel G. Mazzone, Marc Janoschek, Nicholas P. Butch

Statistical Mechanics

Rejection-free Glauber Monte Carlo for the 2D Random Field Ising Model via Hierarchical Probabilistic Counters

Luca Cattaneo, Federico Ettori, Giovanni Cerri et al. (+2 more)

We present an efficient Monte Carlo algorithm for the simulation of the two-dimensional Random Field Ising Model (RFIM). The method combines the event-driven, rejection-free character of the Bortz Kalos-Lebowitz (BKL) algorithm with Glauber transition probabilities, introducing hierarchical probabilistic counters to perform spin selection in O(log N) operations. This enables efficient sampling of the system's dynamics, especially in the low-temperature and low-disorder regime, where traditional Metropolis updates suffer from critical slowing down. Furthermore, this approach allows a proper dynamical simulation of the Ising system's behavior even in the presence of a Random Field (RF), unlike the BKL method. RFIM simulations with Gaussian field distributions reproduce the expected reduction of the pseudo-critical temperature with increasing disorder. Benchmarking shows speedups exceeding two orders of magnitude compared to the Metropolis algorithm in the low-temperature regime. The proposed method provides an efficient and dynamically faithful tool for studying both equilibrium and non-equilibrium phenomena in disordered spin systems.
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All authors Luca Cattaneo, Federico Ettori, Giovanni Cerri, Paolo Biscari, Ezio Puppin