Strongly Correlated Electrons
Evolution of electron spin resonance through a metallic quantum critical phase diagram
Marc Scheffler, Jörg Sichelschmidt, Conrad Clauss et al. (+6 more)
In the heavy-
fermion metal YbRh2Si2,
quantum criticality at a suppressed antiferromagnetic order is governed by the interplay of local
magnetic moments and itinerant conduction electrons. We demonstrate how this can be investigated by a new experimental approach that enables the observation of electron
spin resonance (ESR) across a broad range of frequencies and fields at very low temperatures. This allowed us to cover a large part of the phase diagram from the paramagnetic Fermi-
liquid phase to the phase with antiferromagnetic order and including the
quantum-critical regime. Both the ESR g-factor and the linewidth present distinct behaviors in these three regimes, providing further insight into the physics across a
quantum critical point. Notably, when cooling down at a field directly towards the
quantum critical point, both g-factor and linewidth continuously decrease. Furthermore, we observe a very good matching of the g-factor behavior upon field-tuning and temperature-tuning towards the
quantum-critical point. We analyze and discuss the results in the context of present theories on ESR in strongly correlated electron systems.
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All authors Marc Scheffler, Jörg Sichelschmidt, Conrad Clauss, Mojtaba Javaheri Rahim, Boris I. Kochelaev, Cornelius Krellner, Christoph Geibel, Frank Steglich, Martin Dressel
Soft Condensed Matter
Boundary- and Screening-Induced Bubbly Phases in Autophoretic Active Matter
Kingshuk Panja, Günther Turk and Rajesh Singh
Spatial confinement and chemical screening fundamentally reshape the non-
equilibrium phase behavior of autophoretic active particles. Here, we present a systematic study mapping the collective dynamics of self-propelled particles governed by chemo-attractive translational forces ($\mu_t < 0$) and chemo-repulsive rotational torques ($\mu_r > 0$) across varying screening parameters $\kappa$, torque magnitudes $\mu_r$, and boundary condition coefficients $\Lambda^c$. Beyond standard chemotactic macro-phase separation and dynamic clustering, we report the emergence of novel boundary- and screening-induced bubbly phases, classified into boiling and bursting bubbles. Using a metric triad of steady-state cluster fraction $\langle S \rangle$, temporal fluctuation magnitude $\sigma_S$, and coordination number $\langle Q \rangle$, we draw phase diagrams to demarcate phases for no-flux boundaries ($\Lambda^c = 1$) and chemically permeable interfaces ($\Lambda^c = 0$) . Increasing chemical screening ($\kappa$) systematically suppresses long-range attraction, driving sequential phase transitions from macro-scale collapse toward bubbly states, dynamic micro-clusters, and homogeneous gas phases, while simultaneously inducing aggregate shape anisotropy. These findings provide predictive design rules for controlling active assembly and transport in microfluidic environments.
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Mesoscale and Nanoscale Physics
Strongly anisotropic non-Kramers electron spin as a quantum coherence probe of angular fluctuations
Achuthan Manoj Kumar, Remy Dassonneville, Guillaume Gerbaud et al. (+5 more)
Strongly anisotropic non-Kramers rare-earth ions combine giant longitudinal g-factors with a vanishing transverse component imposed by time-reversal
symmetry, a combination that makes their
spin transitions exquisitely sensitive to the orientation of the applied
magnetic field. We show that this sensitivity carries a dual identity: it is simultaneously an overlooked decoherence channel and the basis for a
spin-coherence-based angular probe. Using pulsed electron paramagnetic resonance at X-band, we report the first measurements of the
quantum coherence of Tb$^{3+}$ in a native-doped CaWO$_4$
crystal (15 ppb) and map the Hahn-echo coherence time $T_2$ as a function of temperature (2 to 10 K) and resonant field ($10^3$ to $10^4$ G). A parameter-free model combining
spin-
lattice relaxation, instantaneous
diffusion and spectral
diffusion from all independently quantified impurities overestimates $T_2$ by an order of magnitude at low temperature and wrongly predicts the field dependence of $T_2$, inconsistent with the observed monotonic decrease of $T_2$ with $B_r$. A two-parameter extension, including dynamical angular fluctuations of the
crystal axis, reproduces the full
dataset across multiple setups and laboratories. Two controlled experiments nominally identical except for different mechanical configuration of the setup establish the mechanical origin of the dominant contribution. The two-parameter extension corresponds to an angular amplitude noise spectral density of overall order 36 n{\deg}/$\sqrt{Hz}$ from global external vibrations (ranging from 10 to 66 n{\deg}/$\sqrt{Hz}$ depending on the exact setup mechanical configuration) estimated at $\sim$ 2.5 kHz plus a temperature-dependent contribution assumed to come from local
phonon-driven angular jitter. It identifies and highlights a decoherence pathway of practical relevance to any anisotropic solid-state
spin system.
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All authors Achuthan Manoj Kumar, Remy Dassonneville, Guillaume Gerbaud, Nolwenn Le Breton, Athanassios K. Boudalis, Patrice Bertet, Philippe Goldner, Sylvain Bertaina
Quantum Gases
Three-observable measurement of the critical velocity in a paraxial superfluid of light flowing past a mobile impurity
T. Aladjidi, M. Baker-Rasooli, T. D. Ferreira et al. (+4 more)
We report the measurement of the critical velocity of a paraxial superfluid of light flowing past a mobile impurity, realized using a dual-wavelength optical scheme in a warm vapor of $^{87}\text{Rb}$. The superflow is two-dimensional by nature, while the impurity features a highly repulsive potential, a large tunable radius, and a finite mass. The critical velocity is evaluated by simultaneously monitoring three complementary observables: the number of
vortices nucleated in the wake of the impurity, the hydrodynamic force exerted on it, and its displacement velocity relative to the flow. These independent methods yield consistent values for the critical velocity, which remain systematically below the Landau criterion and decrease with the impurity radius, in qualitative agreement with theoretical expectations. Our results demonstrate the reliability of these combined diagnostics, establishing paraxial superfluids of light as a versatile platform for exploring the impurity problem in
quantum hydrodynamics.
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All authors T. Aladjidi, M. Baker-Rasooli, T. D. Ferreira, A. Bramati, M. Albert, Q. Glorieux, P.-É. Larré
Soft Condensed Matter
Electromechanical Domain Wall Propagation in Dielectric Elastomers: An Exact Geometric Resolution via Conformal Mapping
Yu-Xin Xie
The localized electromechanical phase transition in dielectric elastomers involves complex moving boundaries and severe electrostatic fringe fields driven by high-
curvature interfaces. Traditional phenomenological models fundamentally underestimate the configurational forces by completely ignoring the in-plane electric field components and
geometric singularities. Here, we present a asymptotically exact
geometric framework to resolve the domain wall propagation. By mapping the highly deformed current configuration to a regular parametric strip via conformal mapping, the field singularities are algebraically eliminated. An exact integration by parts directly translates the higher-order
geometric metric into a rigorous topological mass term, projecting the global conformal electrostatics into a non-linear $\sigma$-model Lagrangian density. Incorporating the Gent strain-stiffening model, the continuous translation
symmetry yields a
Hamiltonian first integral.
Eigenvalue analysis and Bogomol'nyi-Prasad-Sommerfield (BPS) bound calculations prove that the domain wall emerges strictly as an asymmetric heteroclinic orbit connecting two saddle points. This
geometric resolution provides exact analytical scalings for the localized interface energy, domain wall thickness, and asymptotic decay lengths, eliminating all phenomenological parameters and offering a deterministic paradigm for
geometric instabilities in active soft matter.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Spin-to-polarization mapping with a coherent quantum dot-cavity receiver
Adrià Medeiros, Vincent Vinel, Eliott Rambeau et al. (+12 more)
Coherent light-matter interfaces controllably modifying the state of a
photon upon interaction with a stationary
qubit are a key resource for implementing deterministic entangling gates for optical
quantum technologies. This requires a one-to-one mapping between the state of the scattered
photon and that of the embedded
qubit. Here, we present an experimental signature of such a bijection by leveraging the
spin-induced Kerr rotation present in a low-noise charged
quantum dot-micropillar cavity device. Through time-resolved polarization measurements, we project the electron
spin to one of its eigenstates with $95\pm2\%$ fidelity with a single reflected
photon detection, and follow the subsequent
spin relaxation through the detection of a second reflected
photon. We demonstrate that, after a transient regime governed by the trion radiative lifetime, two orthogonal polarization states can be produced, each associated to a given
spin eigenstate. While the current results are limited by a timescale competition between electron
spin relaxation and trion radiative lifetime, they could be improved using hole
spins displaying increased relaxation times. Our work paves the way towards deterministic logic gates exploiting this one-to-one mapping between a
spin and the polarization of a scattered
photon.
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All authors Adrià Medeiros, Vincent Vinel, Eliott Rambeau, Petr Steindl, Elham Mehdi, Manuel Gundín, Clément Millet, Petr Stepanov, Niccolo Somaschi, Aristide Lemaître, Isabelle Sagnes, Olivier Krebs, Pascale Senellart, Dario A. Fioretto, Loïc Lanco
Mesoscale and Nanoscale Physics
Hierarchy of topological superconductivity generated via heterostructures of unconventional $p$-wave magnets
Koushik R. Das and Arijit Saha
A theoretical framework is proposed to engineer both first and second-order topological superconducting phases in a two-dimensional (2D)
heterostructure, consisting of a
quantum spin Hall
insulator (QSHI) and an unconventional $p$-wave magnet in presence of proximity-induced $s$-wave superconducting pairing. Our analysis establishes that the transitions between the trivial and topological superconducting (TSC) phases can be regulated though the parameters of $p$-wave magnet. Presence of chiral
symmetry leads to the characterization of both types of TSC phases by the respective invariants, one-dimensional winding number and quadrupolar winding number. These results are supplemented by an analytical effective low-energy edge theory that yields a deeper insight into the emergence of the different topological phases of the system. Bulk pairing analysis reveals the competition between the effective $(p_x+p_y)$ and $(p_x+ip_y)$ type pairings that are governed by the intrinsic
spin-orbit coupling inherited to the QSHI and
spin-split bands of the $p$-wave magnet, respectively.
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Materials Science
Experimentally constrained modeling of the Pockels response of KNbO3 and KTaNbO3
Virginie de Mestral, Lorenzo Bastonero, Petr Bednyakov et al. (+6 more)
The soft-mode of electro-optic (EO) metal-oxide perovskites plays a critical role in determining their Pockels responses. This is the case of potassium tantalate niobate (KTN), which exhibits an intrinsic Pockels response 2.5 times larger than that of state-of-the-art barium titanate (BTO), highlighting its potential for high-performance EO applications. By combining ab initio calculations at the density-functional theory level and far-IR measurements, we reveal that the harmonic approximation combined with semi-local exchange-correlation functionals fails to accurately capture the soft transverse optical (TO) Slater mode of both potassium niobate and KTN, which dominates the technologically relevant r51 Pockels coefficient. Replacing the calculated mode frequency with its measured value provides an experimentally constrained approach that substantially improves the predicted Pockels response. For that purpose, the previously unreported TO Slater-mode frequency of KTN is extracted from far-IR reflectivity measurements. The results emphasize the potential of KTN-based EO modulators as an alternative to standard lithium niobate and BTO technologies, with a potentially lower energy consumption and device footprint.
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All authors Virginie de Mestral, Lorenzo Bastonero, Petr Bednyakov, Fedir Borodavka, Simon Mellaerts, Tetyana Ostapchuk, Alex Pescaru, Jiri Hlinka, Mathieu Luisier
Materials Science
Performance of Nanoring-based Transparent Conductors: a Computational Investigation
Gijs Vanoppen, Jef Hooyberghs, Wim Deferme et al. (+1 more)
Metallic nanoring networks can serve as promising flexible transparent electrodes. These materials are crucial components in a wide range of applications, including solar
cells, touchscreens and displays. In this work, a computational investigation considers in detail (i) the electrical conductance and optical performance of nanoring networks and (ii) the breakdown of these networks due to electrical damage. The electrical resistance of both the nanorings and the contacts between the rings (junctions) is taken into account. In part (i), the effects of 5 parameters on the electrical sheet resistance and optical transparency are presented. It is shown that several parameter combinations achieve better performance in comparison to indium tin oxide, currently the most widely used transparent electrode. In part (ii), due to electrical damage, the nanoring systems display the formation of a crack, running parallel to the vertical terminals, where a voltage difference is applied. The network degradation is measured by its sheet resistance, and a universal effect is observed: networks with varying filling factors exhibit the same degradation profile.
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All authors Gijs Vanoppen, Jef Hooyberghs, Wim Deferme, Bart Cleuren
Superconductivity
Tunable Chern superconductivity of PtBi$_2$ in slab geometry
Luca Ketmaier, Jeroen van den Brink and Ion Cosma Fulga
Recent experiments indicate that PtBi$_2$ is a Weyl semimetal whose surfaces become topological
superconductors with i-wave gap
symmetry at low temperature. The bulk hosts 12 Weyl cones while in the superconducting state each of the two surfaces hosts in addition 6 Majorana cones. We study a simplified model in a slab geometry, where the finite thickness gaps out the bulk Weyl cones and leaves the surface Majorana cones as the low-energy degrees of freedom. We identify two competing mechanisms that gap these cones: inter-cone hybridization opens a trivial gap, whereas a Zeeman field opens a nontrivial one. In the nontrivial regime, chiral Majorana edge modes connect the gapped cones. We determine their wavefunction profile and relate it to the momentum-space distribution of the cones. Mapping out the phase diagram, we find both trivial and nontrivial regions in the quasi-two-dimensional limit.
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Statistical Mechanics
Equivalence classes of finite-time transitions in optimal control and non-equilibrium relaxation
Jan Meibohm, Samuel Monter, Clemens Bechinger et al. (+1 more)
We present a theory for the optimal control of
stochastic systems in structured environments, represented by penalty terms in the cost functional. We show that such control problems generically feature sharp finite-time transitions associated with a qualitative change in the control strategy at a critical time. Starting from an overdamped Langevin equation and a quadratic cost functional, we show that all resulting problems fall into three canonical equivalence classes (parabolic,
hyperbolic, and elliptic), distinguished by the sign of the determinant of the control
Hamiltonian. For each class, we obtain the optimal protocol, the cost function, and the critical time in closed form, and show that the transition exhibits features of a continuous phase transition at mean-field level. We then establish a mapping between the optimal control cost and the large-deviation rate function governing non-
equilibrium relaxation after a potential quench. The mapping covers the parabolic and
hyperbolic classes, while the elliptic class has no simple relaxation counterpart. This correspondence implies that recently discovered finite-time dynamical phase transitions, which are exponentially costly to sample directly, are accessible through ordinary averages over optimally controlled trajectories. To validate our theoretical findings, we report three experiments with optically trapped colloidal particles: a control transition for the mean
stochastic work, and the finite-time dynamical phase transitions in free
diffusion and in harmonic relaxation.
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All authors Jan Meibohm, Samuel Monter, Clemens Bechinger, Sarah A. M. Loos
Strongly Correlated Electrons
Universal Driven Critical Dynamics of Entanglement Entropy
Chang-Yu Shen, Shuai Yin and Zi-Xiang Li
The Kibble-Zurek mechanism (KZM) and finite-time scaling (FTS) provide a foundational framework for driven critical dynamics, yet their predictive power has been largely confined to local observables. Here, we establish a universal finite-time scaling theory for the nonequilibrium dynamics of
quantum entanglement. Using unbiased
quantum Monte Carlo simulations, we investigate the corner
entanglement entropy of (2+1)-dimensional interacting Dirac
fermions driven from ordered phases toward a
quantum critical point. We find that the corner
entanglement accurately obeys a universal driven scaling governed by the driving rate and system size, persisting whether the initial ordered state is fully gapped or hosts gapless Goldstone modes. Crucially, this dynamical
entanglement exhibits a logarithmic dependence on the driving rate, from which the universal corner coefficient of the underlying conformal field theory can be robustly extracted far from
equilibrium. These results generalize the KZM from local observables to the intrinsic nonlocal
quantum information measures, offering a practical blueprint for characterizing
quantum criticality and
entanglement on programmable
quantum simulators.
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Disordered Systems and Neural Networks
Design Principles for Reproducible Networks
Jasper van der Kolk, Cory Glover and Albert-Lásló Barabási
From
protein complexes to electronic
circuits, many natural and engineered systems function only if assembled in an exact, reproducible fashion. The structure of each of these systems can be understood as a network, yet network science lacks the mechanisms to consistently reproduce exact
topologies, focusing instead on generating network ensembles. We introduce the framework of network design where we encode the local constraints obeyed by a system's building blocks in a design set, and derive the Unigraphical Design
Theorem, which determines when these constraints guarantee reproducible assembly into a unique structure, a process we call unigraphical assembly. For systems whose design sets do not specify a unique outcome, we identify guided assembly as a second route to reproducibility, in which temporal ordering decomposes construction into unigraphical steps. Applying these results to 3,618 reproducible systems, including
protein complexes, molecules, and
robots, we classify those that undergo unigraphical assembly and those that require guided assembly. We further identify a diversity-redundancy boundary that explains how systems trade component variety for structurally interchangeable parts while retaining unique assembly. Finally, we experimentally test the theory using 3D-printed components to re-engineer generative construction sets into systems that assemble unigraphically into prescribed
topologies. Network design thus reframes reproducibility as a mathematically testable property of real networks, opening a route to the rational engineering of complex systems.
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Mesoscale and Nanoscale Physics
The Casimir free energy of peptide films on a silicon substrate: Impact of dielectric-to-metal transition in silicon and nanoparticles in peptide
G. L. Klimchitskaya and V. M. Mostepanenko
Using the Lifshitz theory of the van der Waals and Casimir forces, we calculate the Casimir free energy of thin peptide films deposited on silicon substrates. The Casimir free energy is found as a function of film thickness for different fractions of water in the film, in the presence of either nonmagnetic or
magnetic nanoparticles, and under the impact of irradiation of a silicon substrate with
laser pulses or dopants resulting in the dielectric-to-metal phase transition. It is shown that for a dielectric silicon there is the borderline value of the film thickness, such that the Casimir free energy is negative and contributes to the film stability for thicker films, but is positive and makes the film less stable for thinner ones. According to our results, the borderline value of peptide film thickness decreases with increasing volume fractions of water and in the film. This decrease is more pronounced for the
magnetic nanoparticles and becomes stronger with increasing their radius. The borderline value of peptide film thickness is found as a function of the fraction of water in the film. If the silicon substrate is in metallic state, the Casimir free energy of peptide coating is always positive, which makes it less stable. Possible applications of the obtained results in organic electronics and biomedicine are discussed.
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Soft Condensed Matter
Tailoring Mechanical and Acoustic Properties of Liquid-Filled Elastomers as Reusable Ultrasound Couplants
Surojit Ranoo, Romain Fayolle, Jean Baudry et al. (+1 more)
Couplants are indispensable for ultrasound-based applications to ensure seamless propagation of the acoustic waves between the transducer and targets. Existing hydro/oil-based gel couplants provide excellent acoustic coupling but are single-use and therefore not suitable for emerging applications such as wearable health monitoring, ultrasound-based biometric devices, and prolonged sonodynamic therapy. Alternatively,
polymer-based solid couplants have been explored as reusable solutions but generally fail to simultaneously provide effective mechanical conformability and efficient acoustic transmission. Here, we propose an innovative composite material design based on a silicone elastomer
matrix, in which mechanical and acoustic properties are tailored independently through the microencapsulation of diols and triols. An emulsion-based material formulation strategy is employed to produce a family of high-
liquid droplet content elastomeric composites containing up to 75 volume fraction (%) of
liquid. A robust material formulation strategy is established that enables independent parametric control over the resulting mechanical and acoustic properties. A specific composition containing 70 % glycerol has been identified and explored for biomedical applications, exhibiting mechanical softness comparable to that of skin and acoustic properties matching those of soft tissues. The material has been integrated into a functional ultrasound characterization device, demonstrating structural homogeneity and applicability of the proposed couplant. Furthermore, the composites exhibit mechanical conformability to stiff substrates with surface irregularities, making them also promising candidates for industrial applications.
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All authors Surojit Ranoo, Romain Fayolle, Jean Baudry, Nicolas Bremond
Mesoscale and Nanoscale Physics
Unravelling the Li-Haldane Conjecture with the Projected Ensemble
Daniel Spasic-Mlacak, Qi Camm Huang, Wen Wei Ho et al. (+1 more)
The
entanglement spectra of fractional
quantum Hall states contain universal fingerprints of their underlying topological order, as posited by the Li-Haldane
conjecture. In this work, we uncover a finer universal structure within the
entanglement spectra unravelled by projective measurements. Concretely, we study the projected ensemble of fractional
quantum Hall states, defined as the collection of
quantum states on a subsystem conditioned on measurement outcomes of its complement. We find that this ensemble exhibits a hidden hierarchy inside the Li-Haldane edge
manifold: by conditioning on measurement outcomes, the
entanglement spectrum's support is split into measurement-dependent sectors whose ranks we demonstrate are fixed by conformal field theory counting, an observation we dub the measurement-resolved Li-Haldane
conjecture. For the non-Abelian Moore-Read state, this hierarchy is particularly rich: each parity-resolved edge
manifold contains internal subspaces whose dimensions reproduce the conformal field theory counting of the opposite-parity sector. This structure persists even in realistic Coulomb-interacting ground states, establishing the projected ensemble as a sharp new probe of topological order beyond what the
entanglement spectrum alone can detect.
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All authors Daniel Spasic-Mlacak, Qi Camm Huang, Wen Wei Ho, Nigel R. Cooper
Mesoscale and Nanoscale Physics · Cross-listed from math-ph
The conductivity matrix at the topological phase transition
Simone Fabbri, Giovanna Marcelli and Alessandro Giuliani
For a general class of two-dimensional non-interacting semi-metallic electron systems on a
lattice, we derive an explicit formula for the whole conductivity
matrix, by using Euclidean many-body formalism. The semi-metallic phase takes place whenever two Bloch bands touch at the Fermi energy with conical intersections and generally occurs at the transition between distinct integer
quantum Hall phases. Unlike the longitudinal conductivity (which depends solely on the shape of the cones at the Fermi level), the transverse conductivity is remarkably determined both by the conical structures of the bands and by the nature of the two nearby topological phases. Generically, in the semi-metallic state, neither the longitudinal nor the transverse conductivities are quantized in integer multiples of a universal conductivity
quantum; however, universality of the conductivity
matrix is restored under the assumption of emergent rotational
symmetry of the linearized
Hamiltonian at the Fermi points. Using our formula, we compute the conductivity
matrix for several physically relevant models of
quantum Hall fluids at the topological phase transition, exhibiting cases where the transverse conductivity is quantized in half-integer multiples of $e^2/h$ and cases where it depends continuously on an external strain parameter, thus shedding light on its universality or non-universality features.
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Soft Condensed Matter
Peeling threshold for removal of an adhered elastic sheet by a shear flow
Hugo Perrin and Lorenzo Botto
Fluid shear can induce detachment of a thin elastic sheet adhered to a flat substrate. This peeling process is important in a variety of environmental and technological systems. The condition for peeling depends on: the shear rate $\dot{\gamma}$, the fluid viscosity $\eta$, the length of the detached portion of the sheet $L$, the bending rigidity $B$ and the adhesion energy $\Gamma$. What are the laws governing the detachment? We address this question experimentally in the regime of intermediate adhesion, using macroscopic sheets bonded to a substrate and immersed in a shear
cell containing a viscous fluid. The experiments indicate a critical shear rate for peeling of the order of $\dot{\gamma} \sim B/(\eta L^3)$. This threshold is, unexpectedly, independent of adhesion. We rationalise this result by applying Griffith's fracture theory to optical measurement data of the shape of the sheet, under conditions of freely moving peeling front or clamped boundary. The results indicate that the large
curvature of the sheet for $\dot{\gamma} \sim B/(\eta L^3)$ yields a nearly diverging strain energy release rate at this threshold. This approximate divergence in turn yields a peeling threshold that depends at most weakly on $\Gamma$, confirming a theory that was proposed recently (Salussolia et al., J. Mech. Phys. Solids, 2020, 134). Among other applications, our work provides a quantitative formula that can aid the production at scale of 2D materials such as
graphene.
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Materials Science
Exciton multipolarity controls coherent and squeezed phonons in van der Waals heterostructures
Indrajit Maity, Arash A. Mostofi, Johannes Lischner et al. (+1 more)
Photoexcitation-driven changes in the electronic distribution displace atoms, generating coherent
phonons on ultrafast timescales. Two-dimensional (2D) materials and their
heterostructures offer a powerful platform for engineering these
phonons. Yet, despite the widespread observation of photoexcited coherent
phonons, a design principle for controlling their character remains elusive. Here, using detailed atomistic simulations of multilayers of alternating MoSe$_2$ and WSe$_2$, we reveal
exciton multipolarity as a design principle for tuning photoinduced
phonons from coherent to squeezed. These
phonons are interlayer breathing modes, with dipolar
excitons coupling linearly to generate coherent states and quadrupolar
excitons coupling quadratically to produce squeezed states. Moreover, an out-of-plane electric field enables switch-like control, converting quadrupolar
excitons into dipolar
excitons and switching the
phonon state from squeezed to coherent. For example, in trilayer WSe$_2$/MoSe$_2$/WSe$_2$, the photoexcited 1.04-THz breathing mode switches from a squeezed state at zero field to a coherent state under an applied vertical field. Experimentally, these
phonon states can be directly probed by ultrafast X-ray or electron diffraction and indirectly through transient reflectivity. Our results open new avenues for ultrafast control of
lattice and electronic dynamics on picosecond timescales, with implications for THz
quantum phononics, nanophotonic technologies, and
quantum-noise-limited sensing.
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All authors Indrajit Maity, Arash A. Mostofi, Johannes Lischner, Ángel Rubio
Soft Condensed Matter
Simultaneous measurements of enzyme propagation and biopolymer mobility elucidate the directional degradation of a dense biopolymer matrix
Vincenzo Ruzzi, Antoine Bouchoux, Carole Antoine-Assor et al. (+9 more)
Enzymatic degradation of biopolymers underpins critical processes in biotechnological applications and natural processes, such as food digestion and cancer development, yet the interplay between enzyme propagation in a dense substrate and substrate degradation remains unresolved. It remains especially unclear whether degradation of a dense
matrix facilitates or impedes enzyme propagation. We simultaneously track with spatiotemporal resolution unidirectional enzyme
diffusion and biopolymer degradation in a model system. We demonstrate that enzyme
diffusion is decoupled from catalytic activity, while the degradation front progression is dictated by enzyme
diffusion, reaction kinetics and slow enzyme deactivation. These findings establish a quantitative framework to optimize enzymatic processes for applications in biomedicine, biomass valorization, and nanotechnology.
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All authors Vincenzo Ruzzi, Antoine Bouchoux, Carole Antoine-Assor, Donna-Joe Bigot, Salma Menzeh, Maike Petermann, Laurent Leclercq, Hervé Cottet, Cédric Montanier, Claire Dumon, Luca Cipelletti, Laurence Ramos
Materials Science
Heesch Nodal Lines in Inadmissible Achiral Antiferromagnets
Xing-Yao Guo, Chung-Yuen Chan, Zi-Ting Sun et al. (+1 more)
Recently, a new class of Weyl semimetals in antiferromagnets named Heesch Weyl semimetals was discovered, which have inadmissible chiral
magnetic point group
symmetries (inadmissible
magnetic point groups are incompatible with ferromagnetic order) and distinctive surface Fermi arcs. In Heesch Weyl semimetals, the Weyl points are pinned at high
symmetry momenta with two-dimensional irreducible corepresentations in the Brillouin zone. As the Weyl points are pinned, the Weyl points with opposite topological charges cannot emerge or be brought together for creation and annihilation as in conventional Weyl semimetals. In this work, we show that when mirror or rotoinversion
symmetries are restored so that the point group becomes achiral, long doubly degenerate lines connecting Weyl points with opposite topological charges emerge. We call these lines the Heesch nodal lines (HNLs) and their host materials the Heesch nodal line antiferromagnets. HNLs result in a large number of two-dimensional massless Dirac cones for planes intercepting the HNLs in the Brillouin zone. Moreover, a large subset of the HNL antiferromagnets has the special property that the lowest nonvanishing order of the nonlinear anomalous Hall effect starts with the third order. First-principles calculations on representative collinear and noncollinear antiferromagnets, such as MnTe, CrSb, and Mn$_3$GaN, confirm our predictions on the presence of HNLs. When the inadmissible
symmetry is broken by strain, the double degeneracy of the HNLs is lifted and the associated massless Dirac cones are gapped out, providing a route to realizing sizable anomalous Hall effects in antiferromagnetic
crystals. We conclude that all inadmissible antiferromagnets without parity-time
symmetry are topological. They are either Heesch Weyl antiferromagnets or Heesch nodal line antiferromagnets.
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All authors Xing-Yao Guo, Chung-Yuen Chan, Zi-Ting Sun, Kam Tuen Law
Strongly Correlated Electrons
Ground-State Phase Diagram, Higher-Winding Topology, and Lifshitz Criticality in an Anisotropic Four-Spin XX Chain
Mohammad Abbasi, Faraz Valeh and Saeed Mahdavifar
We investigate the
quantum critical and topological properties of a
spin-$1/2$ XX chain with anisotropic four-
spin cluster interactions in a transverse
magnetic field. The interplay of exchange anisotropy, cluster interactions, and the external field produces a rich phase diagram with multiple gapped topological phases and distinct
quantum critical boundaries. We identify several Lifshitz-type transitions arising from reconstructions of the low-energy Fermi-point structure, including an unconventional multicritical point where distinct critical branches intersect and the momentum-space
topology undergoes a singular reorganization. In the isotropic limit, a conventional Lifshitz transition emerges through the merging and annihilation of Fermi points, revealing distinct mechanisms of Fermi-point reconstruction within the same model. The gapped phases are characterized by quantized winding numbers $\nu=0,\pm1,-2,$ and $\pm3$, with the higher-winding phases induced by the extended cluster interactions. The $\nu=\pm3$ phases exhibit a richer topological structure than conventional short-range Kitaev-type chains and are separated from other sectors by field- and interaction-driven gap closings. These topological distinctions are further reflected in characteristic degeneracy patterns of the lowest levels of the bulk
entanglement spectrum. Our results demonstrate that anisotropic multispin interactions provide a versatile route to realizing higher-winding topological phases and unconventional multicriticality in one-dimensional
quantum systems.
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Mesoscale and Nanoscale Physics
Coherent interaction of WS$_2$ and quasi-2D perovskite excitons over micrometer distances via a cavity field
Marti Struve, Hamid Pashaei Adl, Jamie M. Fitzgerald et al. (+13 more)
The coherent coupling of cavity-confined
photons and excitonic matter resonances leads to the formation of cavity polaritons, hybrid light-matter quasi-particles. If multiple
exciton resonances couple to the same photonic mode, the resulting polariton constitutes a coherent interaction between matter resonances that can be spatially separated without any direct electronic coupling. In this work, we demonstrate the formation of such a coherent coupling at room temperature using an open optical cavity containing two distinct van der Waals materials - monolayer WS2 and layered quasi-2D halide perovskites (HaPs) - separated by $1.5 \mu\rm m$. The system forms three polariton branches, with the middle branch possessing nearly equal fractions of both
excitons and the photonic mode. White-light reflectivity and luminescence measurements are in good agreement with simulations using a coupled harmonic oscillator and a microscopic Wannier-Hopfield framework. Our results lay the foundation to combine highly complementary degrees of freedom in 2D materials in an in-situ tunable fashion to enable new polaritonic functionalities.
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All authors Marti Struve, Hamid Pashaei Adl, Jamie M. Fitzgerald, Oliwia Janikowska, Maciej Śmiertka, Alessandro Surrente, Sven Stephan, Christoph Lienau, Falk Eilenberger, Zdeněk Sofer, Watcharaphol Paritmongkol, William A. Tisdale, Paulina Plochocka, Ermin Malic, Christian Schneider, Martin Esmann
Materials Science
Ion-Engineered Insulator-to-Semiconductor Transition in Natural 2D Biotite
Dipanwita Mitra, Raphael B. de Oliveira, Guilherme S. L. Fabris et al. (+7 more)
Naturally occurring layered silicates offer an abundant yet unexplored class of 2D materials, but their insulating nature limits their functional utility. Here, we demonstrate a chemical strategy that transforms
liquid-phase-exfoliated biotite nanosheets into a tunable 2D
semiconductor through controlled NaOH treatment. The resulting
insulator-to-
semiconductor transition originates from Na incorporation, defect generation, and local structural reconstruction while largely preserving the layered framework. Structural and chemical analyses reveal
lattice distortion, interlayer reorganization, hydroxylation, and partial Na+-K+ exchange, establishing the origin of the electronic restructuring. This transformation broadens the optical response, shifting the approximately 221 nm absorption toward approximately 280 and 975 nm, reducing the optical bandgap from approximately 5.2 to 3.2-3.5 eV, and introducing low-energy transitions at approximately 1.12-1.17 eV. Electrical measurements reveal nonlinear transport with currents reaching close to 10 microA, demonstrating activated carrier conduction. Ultrafast transient absorption reveals pronounced excited-state absorption, with carrier cooling (0.16-0.38 ps) followed by fast (35-60 ps) and long-lived (336-491 ps) relaxation associated with trap-mediated recombination. Fluence-dependent dynamics reveal a hot-
phonon bottleneck at elevated carrier densities. Together with density functional theory calculations, these results establish chemical defect and ion engineering as a powerful route for converting naturally abundant layered minerals into electronically tunable 2D materials for emerging optoelectronic and ultrafast photonic technologies.
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All authors Dipanwita Mitra, Raphael B. de Oliveira, Guilherme S. L. Fabris, Debkanta Ghosh, AyonJyoti Karmakar, Raphael M. Tromer, Marcelo L. Pereira Junior, Douglas S. Galvão, Chandra Sekhar Tiwary, Prasanta Kumar Datta
Mesoscale and Nanoscale Physics
Real-space Floquet topology written by the orbital angular momentum of light
Mohammad Shafiei and Milorad V. Milošević
Floquet engineering usually treats light as a uniform control field that changes the
topology of an entire driven material. Here we show that structured light carrying orbital angular momentum (OAM) enables a different regime, in which
topology is written directly in real space. For ultrathin topological
insulator films, circularly polarized Laguerre–Gaussian beams generate a radial Floquet mass whose sign changes define a topological annulus bounded by two concentric chiral ring modes. The transition is helicity selective: below a thickness-dependent critical frequency, left-circularly polarized light drives mass inversion, whereas right-circularly polarized light increases the gap and leaves the film trivial. Independently, the OAM
quantum number shifts and reshapes the annulus without changing the frequency, intensity, or helicity. In the decoupled-surfaces limit, the same mechanism produces a purely Floquet-induced topological mass and a
vortex-core zero mode. These results identify
photon OAM as a control parameter for nonequilibrium
topology and provide a route to programmable topological landscapes in
quantum materials.
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Mesoscale and Nanoscale Physics
Sonu Verma, Bashab Dey and Akashdeep Kamra
The recent discovery of
excitons coupled to the
magnetic order, and the consequent strong magneto-optic responses, in some van der Waals
magnetic semiconductors has triggered intense activity at the interface of magnetism and
semiconductor optics. Here, we present an analytically tractable minimal model that describes
magnetic order, electrons, holes, and
excitons within a unified framework, thereby capturing a wide range of phenomena. It treats the
magnetic order and itinerant carriers to be comprised by distinct electronic orbitals that are mutually coupled via orbital-dependent onsite exchange, similar to the treatment of metallic magnets using an s-d model. Investigating CrSBr bilayer as a case study, we
benchmark our model and its predictions against recent experimental and ab-initio results finding good agreement as well as new insights enabled by the model's simplicity. Examining the optical selection rules, we find the conservation of a
quantum number formed from a combination of
spin and layer pseudospin to be a useful guiding principle, even in noncollinear
magnetic configurations. Our analysis finds a series of bright and dark excitonic states in such layered A-type antiferromagnets. The presented framework should be valuable in achieving intuitive understanding of recently discovered excitonic phenomena and guiding the discovery of other excitonic states in layered
magnetic semiconductors.
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Materials Science
Multimodal and Multiscale Interrogation of a Mechanically Tough Glass Forming Copper-Based Metal-Organic Framework
Mounir El Skafi, Guo-Qiang Li, Sophie R. Thomas et al. (+8 more)
A copper-based metal-organic framework, Cu(Im)2, was synthesized using a sol-gel process and subsequently melt-quenched into glass upon heating above 240 {\deg}C. In this paper, we present a
multimodal, multiscale interrogation of the MOF nanocrystals and the resulting glasses. Structural characterization using X-ray diffraction, atomic force microscopy, and electron microscopy was performed to understand the morphology and size of the synthesized nanocrystals and glasses. Thermogravimetric analysis and differential scanning calorimetry were employed to understand the melting process of the
crystals to form the glass. Synchrotron pair distribution function analysis was performed to verify that the framework structure is maintained upon melting, and nearfield infrared nanospectroscopy provided insight into the local chemical structure of the materials. The mechanical characterization via nanoindentation revealed that the resulting glasses exhibit an appreciably high elastic modulus (~10 GPa) and the highest fracture toughness (K_1c ~ 0.5 MPa m^1/2) yet reported for MOF glasses. This development is central to the emerging field of MOF-based materials processing and shaping, while upholding mechanical robustness and resistance to cracking.
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All authors Mounir El Skafi, Guo-Qiang Li, Sophie R. Thomas, James D. Taylor, Mark Frogley, Gianfelice Cinque, Marc Pignitter, Michael Reithofer, Jia-Min Chin, Sebastian Henke, Jin-Chong Tan
Materials Science
Gd-4f Exchange Splitting and Mo-4d Crystal-Field Redistribution in Gd/W Co-doped La2Mo2O9: A DFT+U Study
Amogh U. Lanjewar, Saurabh Shiwankar and Smita Acharya
La2Mo2O9 (LAMOX) is a promising oxide-ion conductor for intermediate-temperature solid oxide fuel
cells, but its practical application is limited by a first-order monoclinic-to-cubic (alpha to beta) phase transition. Here, we investigate the electronic structure of pristine La2Mo2O9 and the Gd/W co-doped composition La1.6Gd0.4Mo1.7W0.3O9 using
spin-polarized density functional theory with an on-site Hubbard correction for the localized Gd-4f states. The projected density of states reveals that pristine La2Mo2O9 is an O-2p/Mo-4d charge-transfer oxide in which La contributes negligibly near the band edges. Gd/W co-doping introduces a strongly exchange-split Gd-4f
manifold with a majority-minority separation of approximately 1011 eV, substantially redistributes the Mo-4d electronic states through a threefold increase in
crystal-field splitting, and reduces the O-2p contribution near the valence-band maximum from 78% to 66%. These electronic signatures are consistent with the experimentally observed
lattice contraction, MoO Raman-mode softening, and the non-monotonic
evolution of oxide-ion conductivity across the co-doped series. In particular, the pronounced
crystal-field splitting and localized Gd magnetism at the highest doping level provide a microscopic electronic explanation for the observed suppression of ionic conductivity. The present results establish an atomistic electronic-structure framework for understanding dopant-induced phase stabilization and oxide- ion transport in Gd/W co-doped LAMOX electrolytes, providing design principles for improved solid oxide fuel
cell materials.
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Strongly Correlated Electrons
Fermi-Point Topology Determines Emergent Conformal Criticality in Extended Quantum Spin Chains
Mohammad Abbasi and Saeed Mahdavifar
Quantum criticality in one-dimensional
quantum systems is characterized by emergent conformal field theories (CFTs), whose central charge counts independent gapless degrees of freedom. Establishing a microscopic connection between this universal conformal structure and the momentum-space
topology of the underlying quasiparticle spectrum remains challenging. Here, we uncover a direct correspondence between Fermi-point
topology, conformal criticality, and
quantum entanglement in an extended
quantum spin chain with competing cluster interactions, exchange anisotropy, and a transverse
magnetic field. We show that interaction- and field-driven Lifshitz transitions generate conformal critical phases with effective central charges $c_{\rm eff}=1/2$, $1$, $3/2$, $2$, and $3$, including a multicritical point where Ising and Luttinger-
liquid sectors coexist. Importantly, the central charge is not determined simply by the number of
lattice gap closings or Fermi points, but by the number and conformal content of independent low-energy continuum sectors after accounting for
lattice symmetries, reciprocal-
lattice identifications, and mode equivalences. Thus, Lifshitz transitions may leave the conformal anomaly unchanged or modify the central charge depending on whether spectral reconstruction generates new independent continuum sectors. Real- and momentum-space
entanglement spectra provide complementary microscopic signatures, revealing both the conformal content and momentum-space organization of critical modes. Our results establish a microscopic framework linking Fermi-point
topology to emergent CFTs and show how interaction-driven spectral reconstruction can generate higher-central-charge criticality and unconventional multicritical behavior.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Fractalizing spacetime: Floquet codes with fractonic excitations that are immobile in space and time
Juliette Soule and Dominic J. Williamson
We generalize fractalization, a procedure for the construction of fracton models, from space to spacetime. We apply spacetime fractalization to construct fracton floquet codes with syndrome excitations that have limited mobility in space and time. This extends the notion of fracton order to intrinsically dynamical
quantum phases of matter that are inequivalent to static fracton phases. We find spacetime type-II fracton floquet codes which have no topological excitations that are mobile in space or time. These codes exhibit an extreme form of
quantum discrete time
crystal order with response periods that scale exponentially in their linear system sizes. In this context, the no-strings rule that characterizes type-II fractons leads to a superlinear scaling of the floquet code fault-distance with time, potentially lowering the time overhead required for
quantum error correction.
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