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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 18 April

Mesoscale and Nanoscale Physics

Wave Packet Propagation in Tilted Weyl Semimetals for Black Hole Analog Systems

M. A. Lozande and E. A. Fajardo

We explore the realization of distinct analog black hole horizons within tilted Weyl semimetals by comparing two models with contrasting spectral properties. We demonstrate that a spatially varying tilt in the Weyl cone structure creates an effect analogous to the tilting of light cones near a gravitational black hole horizon. By analyzing wave packet dynamics in both models, we reveal two fundamentally different types of analog horizons. The first model exhibits complete wave packet reflection, effectively mimicking an impenetrable barrier. In contrast, the second model permits wave packet transmission across the horizon. Critically, for both models, wave packets initialized with zero momentum ($k_0=0.0$) experience the strongest horizon effects, characterized by a dramatic slowing and significantly longer dwell times at the horizon region. Finally, we find that both systems exhibit substantial probability loss, which we demonstrate is directly correlated with the wave packet's dwell time near the horizon. Our findings establish tilted Weyl semimetals as a rich, tunable platform for investigating non-trivial quantum effects and information dynamics associated with analog black hole horizons.
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Materials Science

Crystal Anisotropy Implications on the Magneto-Optical Properties of van der Waals FePS3

Ellenor Geraffy, Kusha Sharma, Shahar Zuri et al. (+10 more)

Antiferromagnetic FePS3 has recently gained significant interest in its potential applications in spin-related devices. Here, we show that in-plane structural anisotropy has a major impact in shaping the optical responses of FePS3 single-crystals from the bulk form down to the monolayer limit. X-ray diffraction on a bulk FePS3 crystal confirms a distorted FeS6 octahedron causing inequivalent Fe-Fe distances and consequently resulting in a higher a/b lattice parameter ratio. Micro-photoluminescence observations on bulk and monolayer FePS3 reveal four emissions: one intra-atomic d-d transition (band A, centered at ~1.24 eV) and three p-d charge transfer transitions (bands B, C, and D, centered around ~1.79 eV, ~2.3 eV, and ~2.56 eV, respectively). These bands exhibit different polarization behaviors, which persist down to the monolayer limit. Density functional theory calculations from bulk to monolayer FePS3 reveal the underlying electronic structure, assign the observed emissions, and indicate why these peaks have contrasting linear and circular polarization responses. These results establish a direct structure-optics relation in FePS3, highlighting the strong coupling between lattice anisotropy, electronic transitions, and symmetry-selective optical selection rules.
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All authors Ellenor Geraffy, Kusha Sharma, Shahar Zuri, Faris Horani, Adam K. Budniak, Muhamed Dawod, Yaron Amouyal, Thomas Brumme, Andrea Maricel León, Thomas Heine, Rajesh Kumar, Doron Naveh, Efrat Lifshitz

Materials Science

Quantum Computing of Phonon Spectra and Thermal Properties of Crystalline Solids

Naman Khandelwal, Bikash K. Behera, Ashok Kumar et al. (+1 more)

Variational quantum algorithms offer a promising framework for solving eigenvalue problems on near-term quantum hardware, yet their applicability beyond electronic structure calculations remains relatively unexplored. In this work, we investigate the quantum computing of lattice vibrational and thermodynamical properties by applying the variational quantum eigensolver and variational quantum deflation to phonon Hamiltonians derived from first-principles force constants obtained using density functional theory. The mass-weighted dynamical matrix is mapped onto a qubit-encoded Hermitian operator, enabling computation of the full set of acoustic and optical phonon branches of crystalline silicon and graphene using a reduced qubit register and direct benchmarking against classical diagonalization. The quantum-computed phonon spectrum is further used to evaluate vibrational entropy, constant-volume specific heat, and thermal expansion coefficient, reproducing expected low-temperature quantum behavior and the high-temperature Dulong-Petit limit. We further demonstrate that combined error mitigation strategies help recover phonon dispersions and thermodynamic behavior consistent with expected trends on near-term quantum hardware. Although classical phonon methods remain computationally superior, our results establish phonon-based thermodynamics as a stringent and physically transparent benchmark for assessing variational quantum algorithms on near-term quantum devices.
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All authors Naman Khandelwal, Bikash K. Behera, Ashok Kumar, Prasanta K. Panigrahi

Mesoscale and Nanoscale Physics

Evolution of topological phases in atomically thin WTe2 films

Changcang Qiao, Chen-Chia Hsu, Tao Zhang et al. (+4 more)

Topological materials ranging from topological insulators to semimetals host many novel quantum phenomena including quantum spin Hall effect and topological Fermi arcs. Transitions between these topological phases have attracted much research interest. We performed angle-resolved photoemission spectroscopy (ARPES) on WTe2 ranging from a monolayer to the bulk and reveal the evolution of the electronic structure and the band gap. Notably, the gap observed in the monolayer system is suppressed in the three layers, where the film becomes metallic. Variations in the topological properties with thickness are demonstrated by the first-principles calculations. Topological Z2 invariant is shown to oscillate between 1 and 0 with the addition of layers, originating from the interlayer coupling-induced change in band crossing. The system evolves into a Weyl semimetal when the conduction and valence bands touch near the Fermi level and the topological nature is described by the Chern number. Our findings demonstrate the non-monotonic dependence of topological states on dimensionality and how layer-driven electronic band reconfiguration leads to phase transitions in solids.
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All authors Changcang Qiao, Chen-Chia Hsu, Tao Zhang, Zhiming Sun, Dong Qian, Yang-hao Chan, Peng Chen

Strongly Correlated Electrons

Band mixing and particle-hole asymmetry in moiré fractional Chern insulators

Nicolás Morales-Durán, Jingtian Shi, Cristian Voinea et al. (+2 more)

We investigate the effect of remote band mixing on the stability of fractional Chern insulators in a family of models that approximate continuum descriptions of moiré materials. Our results suggest that the experimentally observed asymmetry between filling fractions $\nu=1/3$ and $\nu=2/3$ in twisted MoTe$_2$ originates from a competition between a fractional Chern insulator, an electron Wigner crystal, and a hole Wigner crystal. In the absence of band mixing, the leading instability at $\nu = 1/3$ is the electron crystal, whereas at $\nu = 2/3$ the main competing phase is the hole crystal. Remote band mixing substantially lowers the energy of the electron crystal but has only a weak effect on the hole crystal. Consequently, it destabilizes the fractional Chern insulator at $\nu=1/3$ more strongly than at $\nu=2/3$. This mechanism also provides an explanation for the emergence of re-entrant integer quantum anomalous Hall states in moiré MoTe$_2$ for fillings $\nu>1/2$.
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All authors Nicolás Morales-Durán, Jingtian Shi, Cristian Voinea, Paweł Potasz, Jennifer Cano

Strongly Correlated Electrons

UCd$_{11}$: A strongly localized 5$f^3$ material

Martin Sundermann, Naoki Ito, Daisuke Takegami et al. (+11 more)

UCd$_{11}$ is an antiferromagnetic uranium intermetallic compound ($T_{\rm N}$ = 5.3K) with enhanced electron mass and uranium-uranium spacings nearly twice the Hill limit, suggesting a weakly hybridized 5$f$ electronic character. Various x-ray spectroscopy techniques indicate that uranium in UCd$_{11}$ adopts the formal U$^{3+}$ 5$f^3$ configuration, while core-level photoemission spectroscopy (PES) data of UCd$_{11}$ reveal only a weak satellite feature, typically interpreted as a signature of itinerancy. In this work, we present density functional theory (DFT) combined with dynamical mean-field theory (DMFT) calculations of UCd$_{11}$, using material-specific parameters tuned to reproduce valence-band PES spectra at different photon energies, thereby exploiting the energy dependence of photoionization cross sections. Our results demonstrate that UCd$_{11}$ is a highly localized uranium 5$f^3$ system. Furthermore, core-level spectra obtained from a DFT+DMFT Anderson impurity model reveal that, contrary to common assumptions, the presence or absence of satellite structures is not a reliable indicator of strong correlations or itinerant 5$f$ behavior.
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All authors Martin Sundermann, Naoki Ito, Daisuke Takegami, Chun-Fu Chang, Sheng-Huai Chen, Chang-Yang Kuo, Simone G. Altendorf, Andrei Gloskovskii, Hlynur Gretarsson, Eric D. Bauer, Jan Kuneš, Liu Hao Tjeng, Andrea Severing, Atsushi Hariki

Mesoscale and Nanoscale Physics

Charge-Density Waves of Single and Double NbS$_{3}$ Chains

S. Tanda, S. Kashimoto, H. Yamamoto et al. (+3 more)

The physics of a genuine one-dimensional system in which electrons are confined in one direction remains unclear. The actual electronic state of such a genuinely one-dimensional system has not been investigated in previous experiments, for they have all been conducted on quasi-one-dimensional specimens, namely in strongly anisotropic bulk crystals. Conventionally, charge-density waves (CDWs) driven by Fermi surface nesting have been considered to appear in one-dimensional electron-lattice systems. However, the CDW transitions actually observed to date have all occurred in quasi-one-dimensional systems and therefore do not directly indicate a genuine one-dimensional electronic state. We investigated, for the first time, isolated single and double-chain NbS$_{3}$ samples using the carbon-nanotube-sheath method and discovered CDWs in both systems. In the single-chain, surprisingly, a $(1/4)b^*$ CDW was observed, in contrast to the $(1/3)b^*$ CDW that has been observed in bulk samples. In the double-chain, the coexistence of a $(1/2)b^*$ dimer structure and a $(1/3)b^*$ CDW was confirmed. This discovery represents a significant advancement in the field of low-dimensional physics, surpassing the limitations of previous studies on bulk systems.
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All authors S. Tanda, S. Kashimoto, H. Yamamoto, K. Inagaki, H. Nobukane, Y. Fukuda

Materials Science

On the complementary roles of anisotropic crack density and anisotropic crack driving force in phase-field modeling of mixed-mode fracture

Guk Heon Kim, Minseo Kim, Kwangsan Chun et al. (+1 more)

Phase-field models for anisotropic fracture employ two complementary mechanisms: (i) the anisotropic crack density function, controlling direction-dependent fracture resistance, and (ii) the anisotropic strain energy, governing the fracture driving force. Although the unified framework was presented in Pranavi et al.[Comput. Mech., 73 (2024)], the distinct roles of these mechanisms and their interaction remain uninvestigated. This work addresses this gap by first validating the formulation against mixed-mode fracture experiments on a soft elastomer (Lu et al. [Extreme Mech. Lett., 48 (2021)]), and then conducting systematic parametric studies on single-edge-notched (SEN) and open-hole tension (OHT) specimens to isolate each mechanism. The SEN studies show that the crack density anisotropy controls the crack path and toughness while leaving the elastic response unchanged, whereas the anisotropic strain energy deflects the crack but saturates rapidly. The OHT studies reveal a geometry-dependent role expansion: the anisotropic strain energy governs fiber-orientation-dependent stiffness, peak force, and fracture displacement. When both mechanisms act together, the combined response exhibits nonlinear synergistic interaction exceeding the linear sum of the individual contributions. These results establish that the crack density anisotropy governs the crack path (fracture resistance), while the anisotropic strain energy governs the driving force and, in stress-concentration geometries, additionally controls the elastic strain energy distribution around the stress concentrator.
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All authors Guk Heon Kim, Minseo Kim, Kwangsan Chun, Jaemin Kim

Strongly Correlated Electrons

An integrated theoretical and numerical approach to understand modern experiments on quantum magnetism

Zi Yang Meng, Cristian D. Batista and Shiliang Li

In recent decades, the study of quantum magnets, which feature unconventional behaviour such as exotic quantum phase transitions and quantum spin liquids, and unconventional magnetic states of matter, has made remarkable progress. However, each of the three foundational pillars – numerical simulations, analytical methods and, to a lesser extent, materials synthesis and experiments – often tends to view itself as the primary driver of the field. Even though the need for collaboration among theory, numerics and experiment to understand the complex phases of quantum magnets is well established, in our view there remains a persistent perception from experts in one area that the other two serve merely as supporting tools, primarily useful for validating the dominant ideas of one speciality, and less relevant to shaping the underlying scientific narrative. We refer to this mindset as the "pride and prejudice" in modeling and understanding modern quantum magnetism. In this Perspective, we advocate for a different, more integrated approach to overcome the challenges faced by quantum magnetism researchers. We argue that this alternative mindset has already started to advance the understanding of several important quantum magnetic models and their materials realizations.
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Soft Condensed Matter

Impact dynamics of flexible hydrogels on solid substrates of different wettabilities

Akash Chowdhury, Surjyasish Mitra and Sushanta K. Mitra

In this work, we perform experiments with spherical polyacrylamide (PAAm) hydrogel drops/spheres, spanning a broad range of shear moduli and impact velocities on hydrophilic (plasma-treated glass) and hydrophobic (silane-coated) substrates, yielding an elastic number El variation of five orders of magnitude. Transient spreading morphology and impact force were simultaneously resolved using synchronized high-speed imaging and piezoelectric force sensing. At low elastic numbers ($El < 1$), impacting hydrogels exhibit a hybrid poroelastic response: a liquid-rich contact foot is expelled from the polymer network and spreads independently, while the bulk drop undergoes viscoelastic contact-line pinning into a pancake geometry at maximum deformation. At high elastic numbers ($El > 1$), contact foot spreading is suppressed, and deformation is accurately described by a neo-Hookean energy balance, yielding a maximum spreading factor independent of substrate wettability. Further, we show that the normalized peak impact force $F^*$ collapses to a constant value consistent with the Wagner limit for $El < 1$ and follows a power-law scaling $F^* \sim El^{0.38}$ for $El > 1$, in close agreement with both Hertzian and neo-Hookean predictions, and independent of substrate wettability. Furthermore, we highlight that post-impact retraction is suppressed across nearly the entire parameter space due to adsorbed polymer chains anchoring the receding gel network to the substrate, producing circumferential ridge instabilities; rebound occurs only when elastic restoring forces overcome the work of adhesion.
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Soft Condensed Matter

A new thermodynamic language for colloid systems

Junfeng Zhou, Geliang Zhu and Lei Xu

A simple framework is presented for unified applications in various fields of colloidal research, with minimal additional concepts & definitions. Several case studies concerning glass transition & crystallization are provided under the minimalist version, upon which adaptations can be made to suit more complicated topics. Major factors influencing accuracy are also discussed.
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Strongly Correlated Electrons

Reevaluating Quantum Geometric Criteria for Itinerant Magnetic Instabilities

Min-Fong Yang

The interplay between quantum geometry and electron correlation has emerged as a compelling paradigm in quantum many-body physics. Recent studies have highlighted the diagnostic utility of quantum geometry in identifying magnetic instabilities within itinerant electron systems. In the present work, we critically re-examine these theoretical proposals, which are commonly formulated within the random phase approximation (RPA). To this end, we reformulate the matrix-based RPA instability criterion in the channel representation for generic two-orbital systems, explicitly accounting for multiple channels of magnetic ordering. Our results demonstrate that magnetic phase transitions are intricately governed by the interplay between the bare susceptibility tensor and the spin interaction matrix. Consequently, prior assertions that instabilities can be predicted solely from the quantum geometric structure of a single-channel susceptibility are valid only under complete channel decoupling in both the interaction and susceptibility matrices. By adopting the channel representation, our formulation achieves greater physical transparency and computational tractability compared to the conventional orbital-space approach, thereby furnishing a promising alternative for advancing theoretical studies of complex multiorbital systems.
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Friday 17 April

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

Resonance Statistics -Informed Fitting Applied to Automated Cross Section Evaluation

William Fritsch, Noah Walton, Justin Loring et al. (+5 more)

This work investigates the use of resonance statistics for resonance evaluation to inform spin group assignment and an alternative fitting objective function beyond the commonly used chi-squared statistic. Resonance statistics -informed methods are applied to the automated resonance fitting framework, developed by N. Walton et al. In this automated framework, the utility of resonance statistics is largely unexplored. The new resonance statistics -informed spin group shuffling algorithm reduces spin group frequency bias seen in the base fitting algorithm. Although resonance statistics -informed optimization produces negligible changes in pointwise cross section agreement, it significantly improves consistency with Wigner level-spacing statistics and stabilizes the fitted resonance density in the presence of model imperfections.
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All authors William Fritsch, Noah Walton, Justin Loring, Jacob Forbes, Oleksii Zivenko, Aaron Clark, Elan Park-Bernstein, Vladimir Sobes

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

From Code to Figure: A FAIR-Aligned Data Provenance Chain for Reproducible Simulation Research in Numerical Physics

Markus Uehlein, Tobias Held, Christopher Seibel et al. (+3 more)

Computational physics increasingly depends on large simulation datasets generated by software that remains under active development for many years. In such settings, reproducibility requires not only well documented data but also explicit links between code versions, simulation inputs, generated outputs, analysis steps, and published figures. Here, we present an integrated workflow for reproducible and FAIR-aligned simulation research in numerical physics. We describe how version control, code review, automated testing, structured logging, metadata-rich output, and standardized post-processing can be combined to support traceability from software development to publication. The presented concepts demonstrated for one particular simulation framework are broadly applicable to computational physics and other data-intensive areas of scientific computing.
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All authors Markus Uehlein, Tobias Held, Christopher Seibel, Lukas G. Jonda, Baerbel Rethfeld, Sebastian T. Weber

Materials Science

Intrinsic grain-size gradients upon grain growth near a free surface

Jing Tang, Runlu Yan, Donglan Zhang et al. (+5 more)

Grain growth fundamentally shapes the microstructure of crystalline materials upon annealing, affecting their overall mechanical and functional properties. Recently, it has been rationalized that grain growth in polycrystals does not result solely from weighted curvature flow, but elastic effects (intrinsic stress) arised from shear coupling also need to be taken into account. We characterize and examine the effect of free surfaces on grain growth kinetics of high-purity, bulk polycrystalline nickel. By analyzing the microstructural evolution on cross sections of 1 mm thick specimens from the surface to the interior, as well as through in-plane investigations on specimens with varying thickness (1 mm, 40 $\mu$m, and 10 $\mu$m), an intrinsic grain-size gradient was identified, characterized by a gradual increase in grain size towards the interior. Interestingly, this grading was not restricted to the very surface but continued to depths of five to ten layers of grains, where effects from thermal grooves are considered negligible. We demonstrate that this behavior is significantly affected by elastic relaxation at the free surface, which alters the internal stress fields generated by shear-coupled grain boundary migration. These findings emphasize the relevance of free surfaces to the microstructural evolution of polycrystal.
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All authors Jing Tang, Runlu Yan, Donglan Zhang, Ronald Schnitzer, Lorenz Romaner, Marlene Kapp, Marco Salvalaglio, Oliver Renk

Quantum Gases

Dynamics of spinor Bose-Einstein condensates close to spin-spatial resonances

W. Wills, D. Blume and Q. Guan

We develop a coupled-channel framework to describe the dynamics of spinor Bose-Einstein condensates (BECs), with particular emphasis on the behavior near resonances between spin dynamics and spatial excitations. Taking advantage of the disparity between the spin-dependent and spin-independent scattering lengths in typical spinor BECs, the Bogoliubov modes of the spin-independent part of the full system Hamiltonian provide an efficient set of basis functions for describing the system dynamics in a coupled-channel framework. For quadratic Zeeman shifts far from any resonance, the system can be described by a single spatial wavefunction during the spin dynamics, i.e., the so-called single-mode approximation holds. By tuning the quadratic Zeeman shift, we find resonant excitations of the Bogoliubov modes, which can be classified into two categories: those with particle-hole correlations and those without particle-hole correlations. We show that the beyond-quadratic-order terms that are neglected in standard Bogoliubov theories become increasingly important for capturing the long-time dynamics of the system near resonances. The coupled-channel framework is benchmarked against results from 1D Gross-Pitaevskii equation simulations. The framework developed in this work not only provides a numerically efficient tool for describing spinor BEC dynamics governed by different length scales, but also provides a clean physical interpretation of resonance phenomena in spinor BECs. Applications of this approach to other systems and extensions to the beyond-mean-field regime are also discussed.
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Statistical Mechanics

Quantum many-body operator cascade as a route to chaos

Urban Duh and Marko Žnidarič

We describe a chaos scenario valid for chaotic many-body quantum systems, the simulation of which is one of the prime candidates for demonstrating quantum advantage, and clarify its importance for classical truncation-based simulations. By studying the spectral properties of the truncated propagator, we, for the first time, identify fractal structures responsible for many-body quantum chaos, analogous to the fractality in classical chaos emerging from the time evolution of initially smooth long-wavelength densities into ever finer short-wavelength densities. Namely, we show that the leading slowest-decaying Ruelle-Pollicott eigenoperators have a non-trivial fractal dimension quantifying their non-locality, visible also in the divergence of their condition numbers. Furthermore, we find that unitarity imposes an asymptotic equality between the temporal decay rate of local correlations and this many-body fractal dimension. With this insight, the scenario for many-body quantum chaos becomes clear: over time, local operators evolve toward increasingly non-local ones with a quantifiable fractal structure, thereby naturally leading to effective non-unitary relaxation on the subspace of local operators – a kind of many-body Kolmogorov cascade in the space of operators – which enables accurate truncation-based simulations. Our predictions are demonstrated numerically in various one- and two-dimensional quantum circuits, with and without conservation laws, as well as by exact results in dual-unitary circuits.
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Mesoscale and Nanoscale Physics

Anisotropic spin-valley coupling in SiMOS and Si/SiGe quantum dots

N. Tobias Jacobson, Natalie D. Foster, Ryan M. Jock et al. (+5 more)

While bulk silicon has long been understood to exhibit relatively weak spin-orbit coupling (SOC), confinement of electrons to quantum dots (QDs) at a silicon heterointerface results in significantly larger SOC. This is a concern for electron spin qubit performance, as intravalley and intervalley SOC can significantly perturb the operation of electron spin qubits. While these interactions can be harnessed to drive coherent rotations in a singlet-triplet qubit, coupling to low-lying excited valley states can lead to undesirable spin relaxation when valley splitting is on resonance with the Zeeman energy. In this work, we measure the angular dependence of the interfacial spin-orbit interaction as a function of the direction and magnitude of an applied external magnetic field in SiMOS and Si/SiGe heterostructures, two common material platforms for silicon spin qubits. We construct a physical model that accurately infers intra- and inter-valley SOC physics from fits to the data, allowing for a direct comparison between these two material systems. For the devices measured we find that, while the $g$-factor differences are comparable, the SiMOS QDs exhibit an order of magnitude larger spin-valley coupling than for Si/SiGe. Moreover, we find that the angular dependence of the spin-valley coupling is similar for both devices, with similar magnetic field orientations minimizing the spin-valley coupling. Our work points towards operational schemes for optimizing spin-valley coupling to avoid or exploit this mechanism for qubit operation.
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All authors N. Tobias Jacobson, Natalie D. Foster, Ryan M. Jock, Martin Rudolph, Andrew M. Mounce, Daniel R. Ward, Malcolm S. Carroll, Dwight R. Luhman

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

Continuum honeycomb Schrödinger operators with incommensurate line defects

Pierre Amenoagbadji and Michael I. Weinstein

We study wave propagation in 2D honeycomb structures with a non-commensurate or “irrational” line defect or edge. Our model is a Schrödinger operator which interpolates, across the edge, between two distinct bulk (asymptotic) Hamiltonians with a common spectral gap about the “Dirac point” of an unperturbed honeycomb operator. We seek edge states, eigenstates that are bounded and oscillatory parallel to the edge, and decaying in the transverse direction. For non-commensurate edges, the rigorous definition of these states is nontrivial due to the lack of translation invariance along the edge. To address this, we exploit quasiperiodicity along the edge by expressing the Hamiltonian as the restriction of a 3D (degenerate elliptic) Hamiltonian describing a 3D medium with a 2D interface within which there is periodicity. Via multiscale analysis, we construct approximate edge states in this 3D setting and obtain by restriction 2D edge states which are quasiperiodic along the irrational edge. These edge states are seeded by eigenfunctions of an effective Dirac operator, which has an infinite block-diagonal structure due to the non-commensurate geometry. A consequence is that infinitely many edge state eigenpairs arise, whose energies are dense in the perturbed bulk spectral gap. In a forthcoming paper, we rigorously construct these gap-filling edge states under a Diophantine condition. The main result here is a key tool in this construction: a resolvent expansion for the 3D Hamiltonian, whose leading term is the resolvent of the block-diagonal Dirac operator. The validity of this expansion requires an omnidirectional non-resonance (no-fold) condition on the dispersion functions of the unperturbed honeycomb Hamiltonian. This condition is satisfied in the strong binding regime. In contrast with earlier works on commensurate edges, the omnidirectional condition is independent of the edge.
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Statistical Mechanics

Mixed response geometry and critical crossover in the Ising model

Eric R. Bittner

We develop a geometric formulation of thermodynamic response in interacting spin systems and apply it to the two-dimensional Ising model. Treating inverse temperature and magnetic field as coordinates on a thermodynamic control manifold, we show that the mixed response field $\Omega_{\beta h} = -N\,\mathrm{cov}(m,e)$ arises naturally as a curvature-like quantity that measures correlations between magnetic and energetic fluctuations. Monte Carlo simulations reveal a strongly localized mixed-response ridge that emerges from the critical point and extends into the finite-field crossover regime. Analysis of the susceptibility, specific heat, and mixed-response maxima demonstrates distinct scaling behavior in the magnetic, energetic, and mixed fluctuation sectors. When represented in normalized response coordinates, trajectories obtained at different magnetic fields collapse onto a common curve, indicating that the evolution of the mixed response is strongly constrained by the susceptibility. This collapse suggests the emergence of a low-dimensional response manifold and points toward a geometric description of critical crossover based on relations among response functions rather than equilibrium states alone. The framework establishes a direct connection between fluctuation correlations, critical scaling, and geometric thermodynamic response.
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Materials Science · Cross-listed from physics.optics

Revealing full molecular orientation distributions in organic thin films by nonlinear polarimetry

Pierre-Luc Thériault, Emna Azek, Gabriel Juteau et al. (+7 more)

The performance of organic optoelectronic devices is critically dependent on how molecules orient within organic thin films. Yet, standard characterization techniques only reveal the first and second moments of the molecular orientation distribution. This limitation obscures the true molecular arrangement, as diverse distributions can yield identical low-order averages while exhibiting distinct functional properties. Here, we bridge this gap by combining multi-harmonic nonlinear polarimetry (second, third, and fourth harmonic) with the Maximum Entropy Method to reconstruct the probability distribution without any a priori assumptions. This allows us to resolve features in the distribution such as asymmetry and bimodality, that remain invisible to conventional probes. Furthermore, we use this method to benchmark molecular dynamics simulations, revealing that these simulations often fail to capture the complex distribution despite correctly predicting the first and second moments. This work transforms molecular orientation from an inferred average into a precise observable, establishing essential validation standards for predictive material design.
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All authors Pierre-Luc Thériault, Emna Azek, Gabriel Juteau, Anagh Mukherjee, Heorhii V. Humeniuk, Zhechang He, Alexandre Malinge, Dmytro F. Perepichka, Lena Simine, Stéphane Kéna-Cohen

Mesoscale and Nanoscale Physics

Nonequilibrium Cooper quartet generation in superconducting devices

Luca Chirolli, Alessandro Braggio and Michele Governale

Cooper quartets are aggregates of four electrons that generalize the concept of Cooper pairs, and their study can unfold unexplored perspectives in correlated matter and many-body physics. We propose a method to isolate them in a double-quantum-dot system coupled to conventional superconducting and normal leads. By driving the system out of equilibrium, we show that a resonance between the vacuum $|0\rangle$ and the four-electron state $|4e\rangle$ emerges in the high bias voltage regime, which involves a two-Cooper pair exchange process and is characterized by finite quartet correlations. We study the transport properties of the system and show that a peak in the Andreev current at high bias voltage has a width that scales with the magnitude of the quartet coupling $\Gamma_{4e}$, which can be tuned by the phase of additional superconducting leads, yielding distinctive signatures. By further studying the current-current correlations and the Fano factor, we establish a regime characterized by equal auto- and cross-correlations, which we interpret as a definitive signature of fast coherent two-Cooper-pair oscillations between the dots and the superconducting leads. The proposed platform, experimentally accessible in a quantum solid-state laboratory, enables exploration of quartet correlations and multifermion-correlated states of matter.
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Materials Science

Two New Molecular Nitrogen Phases near Megabar Pressures

Alexander F. Goncharov, Elena Bykova, Iskander Batyrev et al. (+7 more)

Molecular nitrogen exhibits remarkable structural diversity near the polymeric transition, where multiple phases are metastable. Here, we report two new molecular phases. The first, $t\zeta$-N$_2$, is a polytype of monoclinic $C2/c$ $\zeta$-N$_2$, characterized by a tripled $c$ axis and 96 atoms per unit cell. The second, $\xi$-N$_2$, is a previously unreported hexagonal phase ($P6cc$) containing 112 atoms per unit cell. Both phases were synthesized in a diamond anvil cell by laser heating $\zeta$-N$_2$ to 1800–2500~K at pressures of 78–98~GPa. Their crystal structures were determined using single-crystal X-ray diffraction, corroborated by Raman spectroscopy, and supported by first-principles calculations. The $t\zeta$-N$_2$ phase likely corresponds to the previously reported $\kappa$-N$_2$ phase.
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All authors Alexander F. Goncharov, Elena Bykova, Iskander Batyrev, Maxim Bykov, Huawei Chen, William Palfey, Mahmood Mohammad, Stella Chariton, Vitali Prakapenka, Jesse S. Smith

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

Continuous-wave laser absorption spectroscopy of the Thorium-229 nucleus

I. Morawetz, T. Riebner, L. Toscani De Col et al. (+17 more)

A low-energy nuclear transition in the isotope thorium-229 has been excited in thorium-doped crystals with laser light. This opens the perspective towards a highly stable and robust solid-state optical nuclear clock. The required laser radiation at 148 nm wavelength has so far been produced using pulsed laser systems where only a small fraction of the incident photons has been resonant with the narrow nuclear transition. Here we show that the nuclear resonance can be excited with a continuous-wave narrow-bandwidth laser source with a power of less than 1 nW, and that the resonance signal can be detected in absorption rather than in fluorescence. This eliminates the slow nuclear fluorescence decay from the detection process and offers a considerable advantage for clock operation through fast signal acquisition. The VUV laser source is based on three sequential frequency doublings, starting from a diode laser at 1187 nm that is well suited for linewidth narrowing and for frequency comparisons with optical atomic clocks. We use absorption spectroscopy for the quantitative characterization of two different Th-centers in calcium fluoride crystal and measure the isomeric shift between them. One of the centers shows a very small static electric crystal field gradient 0.1 V/$\r{A}^2$, to be compared to gradients in the range of 100 V/$\r{A}^2$ observed earlier. This indicates a center with high symmetry of the ions surrounding the Th nucleus, promising nuclear resonance lines that are nearly independent of the lattice spacing.
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All authors I. Morawetz, T. Riebner, L. Toscani De Col, F. Schneider, N. Sempelmann, F. Schaden, M. Bartokos, G. A. Kazakov, S. Lahs, K. Beeks, B. Gerstenecker, A. Grüneis, M. Pimon, T. Schumm, V. Lal, G. Zitzer, V. Petrov, J. Tiedau, M. V. Okhapkin, E. Peik

Soft Condensed Matter

Conformal Elastodynamics in 2D Dilational Metamaterials

Neel Singh, Audrey A. Watkins, Giovanni Bordiga et al. (+3 more)

Flexible mechanical structures can undergo large deformations under small loads, enabling large, complex, and nonlinear wave responses under finite-frequency driving. Here, we study a dynamically driven canonical flexible mechanical metamaterial composed of rigid squares connected at their corners by flexible hinges. This metamaterial supports a uniform dilational mechanism and, in the limit of ideal joints, exhibits a Poisson ratio of -1. The presence of this dilational mode of deformation gives rise to a conformal symmetry, in which the dynamics are approximately invariant under a wide class of physical transformations – conformal maps. We find that the low-frequency response of the system is dominated by conformal deformations consisting of spatially varying rotations and dilations concentrated at the boundary. Even at high frequencies, each conformal map implies a conserved spatially complex momentum. We explore how experimental parameters such as material stiffnesses and the geometry and number of unit cells allow experimental conformal momenta to approach this conservation, varying slowly compared to the non-conformal momenta of same order. These results constitute a new framework opening fundamental avenues for the study of conformal wave phenomena in dilational metamaterials as well as potential strategies for controlling nonlinear waves and vibrations.
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All authors Neel Singh, Audrey A. Watkins, Giovanni Bordiga, Vincent Tournat, Katia Bertoldi, Zeb Rocklin

Superconductivity

Ultrafast Magneto-Pressure Spectroscopy and Control of Correlated Phases in a Trilayer Nickelate

Zhi Xiang Chong, Joong-Mok Park, Shuyuan Huyan et al. (+10 more)

Ultrafast spectroscopy under simultaneous high pressure and magnetic field provides a versatile approach for investigating pressure-driven electronic instabilities and correlated phases, and for probing potential bulk superconducting behavior under extreme conditions. However, such an experimental platform has yet to be implemented, standing as a roadblock to a fuller understanding of nonequilibrium superconductivity and vortex-controlled quasi-particle (QP) dynamics. Here, we bridge this capability gap by developing high pressure (up to 40 GPa), high magnetic field (up to 7 T), cryogenic (down to 5 K) femtosecond spectroscopy, and using it to probe magneto-pressure evolution of quasiparticle dynamics in the trilayer nickelate $\mathrm{Pr}_4\mathrm{Ni}_3\mathrm{O}_{10}$. We observe pronounced critical slowing down of QP relaxation at the charge-density-wave transition, which collapses under applied pressure. At higher pressures, the relaxation instead lengthens at low temperature, consistent with incipient superconducting correlations. However, the negligibel magnetic-field-dependence up to 7~T and absence of vortex-induced pre-bottleneck dynamics–robust signatures observed in our controlled bulk superconducting samples–indicates that any superconducting state under the present pressure conditions is likely non-bulk, filamentary, or strongly inhomogeneous. The magneto-pressure ultrafast capability opens a new avenue for resolving outstanding questions surrounding pressure-induced superconductivity and intertwined orders in correlated quantum materials.
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All authors Zhi Xiang Chong, Joong-Mok Park, Shuyuan Huyan, Avinash Khatri, Martin Mootz, Xinglong Chen, Daniel P. Phelan, Liang Luo, Ilias E. Perakis, J. F. Mitchell, Sergey L. Bud'ko, Paul C. Canfield, Jigang Wang

Quantum Gases

Supersolid Rotation in an Annular Bose-Einstein Condensate coupled to a Ring Cavity

Gunjan Yadav, Nilamoni Daloi, Pardeep Kumar et al. (+2 more)

We theoretically investigate an annularly confined Bose-Einstein Condensate (BEC) coupled to a four-mirror ring cavity supporting traveling-wave optical modes. Under symmetric driving by counter-propagating Laguerre-Gaussian beams carrying equal and opposite orbital angular momenta, the system realizes supersolid phases coexisting with persistent superfluid circulation. Specifically, we obtain a supersolid state if we start with a BEC of winding number $L_p$ as well as supersolid packets with coherent superpositions of two different BEC $L_p$ values. Under asymmetric pumping, realized with Laguerre-Gaussian beams of different orbital angular momenta, chiral symmetry is broken in the system, resulting in asymmetric cavity field amplitudes, directional density modulations, and tunable rotational dynamics of the resulting supersolid lattice. This leads to rotating supersolid density structures for a single winding-number state, and rotating wave packets for an initial superposition of rotational eigenstates. Finally, we probe the presence of Goldstone and Higgs modes which can be observed using minimally destructive measurements of the cavity output spectrum. Our mean-field theory reveals interference-driven rotation without physical stirring, and distinguishes our work from prior static cavity supersolids. Our results establish the ring cavity annular BEC as a versatile platform for generating chiral quantum matter, implementing rotation-sensing devices and generating atomtronic circuits with supersolids.
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All authors Gunjan Yadav, Nilamoni Daloi, Pardeep Kumar, M. Bhattacharya, Tarak Nath Dey

Soft Condensed Matter

Emergent Information Formation in Prebiotic Protocell Clusters: A Computational Mechanics Framework of $\epsilon$-Machines and Attractor Memory

Michael Massoth

Casimir-Lifshitz forces generate an unavoidable, long-range attraction between protocells under prebiotically realistic conditions. This interaction stabilizes mesoscale clusters such as tetrahedra, octahedra, and 13-cell icosahedra. These highly symmetric assemblies act as persistent macrostates whose transitions remain reproducible despite microscopic noise. A physics-guided coarse-graining yields a well-defined mesodynamics that can be represented as an $\epsilon$-machine: a small deterministic automaton whose causal states correspond to cluster attractors and whose transitions encode ordered reconfiguration pathways. The theory of Rosas et al. (Software in the natural world) shows that such systems can become informationally, causally, and computationally closed, thereby forming an autonomous proto-software layer. In this framework, prebiotic information does not arise from polymers but from attractor-based memory and structured transition dynamics in a purely physical cluster process.
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Strongly Correlated Electrons

Fluctuating Pair Density Wave in Finite-temperature Phase Diagram of the $t$-$t^\prime$ Hubbard Model

Qiaoyi Li, Yang Qi and Wei Li

The Hubbard model and its extensions are canonical theoretical frameworks for understanding correlated electronic states, including those in high-$T_c$ cuprates. Here, we use state-of-the-art thermal tensor network method to map out the temperature-doping phase diagram of the $t$-$t^\prime$ Hubbard model. On the electron-doped side, we find a $d$-wave superconducting (dSC) regime, supporting the scenario of high-$T_c$ superconductivity. In contrast, on the hole-doped side, no robust dSC phase is detected. Instead, a finite-temperature regime dominated by strong pair-density-wave (PDW) fluctuations emerges, which may eventually give way to charge density wave order upon further cooling. The PDW state exhibits inter-arc pairing with net momentum near $(0, \pi)$, distinct from the zero-momentum pairing in conventional dSC. Furthermore, these fluctuating PDW states occupy the lower portion of the pseudogap regime on the hole-doped side. We provide a comprehensive finite-temperature perspective consistent with previous ground-state studies, shedding new light on pairing instabilities and exotic electronic states in high-$T_c$ superconductors.
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Quantum Gases

Renormalised thermodynamics for Bose gases from low to critical temperatures

Michael H. Heinrich, Alexander Wowchik and Jürgen Berges

We compute thermodynamic properties of dilute Bose gases using non-perturbative approximations of the two-particle irreducible (2PI) effective action. It is shown how to systematically renormalise the self-consistent descriptions beyond conventional Gaussian approximations such as Hartree-Fock-Bogoliubov theory. This allows us to determine the condensate depletion from low to high temperatures, including its critical behaviour at the phase transition. While the universal anomalous dimension at criticality is vanishing for Gaussian approximations, we determine its non-zero value at next-to-leading order of a self-consistent expansion in the number of field components.
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