arXiv subjects

Matteo Baggioli

Publications and source records attributed to Matteo Baggioli.

At least 37 records · Page 2Linked to original sources

arXiv2025

Dissipation induced elastic-mode instability with topological excitation in holographic non-equilibrium steady cnoidal wave supersolid

The possible existence of an exotic phase of matter rigid like a solid but able to sustain persistent and dissipation-less flow like a superfluid, a "supersolid", has been the subject of intense theoretical and experimental efforts since the discovery of superfluidity in Helium-4. Recently, it has been proposed that nonlinear periodic modulations known as cnoidal waves, that naturally emerge in Bose-Einstein condensates, provide a promising platform to find and study supersolidity in non-equilibrium phases of matter. Nevertheless, so far the analysis has been limited to a one-dimensional zero-temperature system. By combining the dissipative Gross-Pitaevskii equation with a finite temperature holographic model, we show that the proposed cnoidal wave supersolid phases of matter are dynamically unstable at finite temperature. We ascribe this instability to the dynamics of the "elastic" Goldstone mode, which arises as a direct consequence of translational order in the presence of dissipation, and establish a direct connection between the elastic-mode instability of the supersolid state and the nucleation of topological excitations during the relaxation towards a homogeneous equilibrium state, which resembles the Landau instability in superfluids. Finally, we numerically confirm the dominant role of the elastic-mode instability in the collision between cnoidal waves in the strong dissipation limit.

cond-mat.quant-gas↗

arXiv2025

Topological Magnetic Phases and Magnon-Phonon Hybridization in the Presence of Strong Dzyaloshinskii-Moriya Interaction

In recent years, the interplay between quantum magnetism and topology has attracted growing interest, both for its fundamental importance and its technological potential. Topological magnons, quantized spin excitations with nontrivial band topology, hold particular promise for spintronics, offering routes to robust, low-dissipation devices for next-generation information processing and storage. While topological magnons in honeycomb ferromagnets with weak next-nearest-neighbor Dzyaloshinskii-Moriya interactions (DMI) have been extensively investigated, the strong-DMI regime remains largely unexplored. In this work, we examine topological magnetic phases and magnon-phonon hybridization in a two-dimensional magnetic system with strong DMI. We show that strong DMI drives a transition from a ferromagnetic ground state to a 120$^\circ$ noncollinear order. An additional Zeeman field further induces noncoplanar spin textures, giving rise to a diverse set of topological phases. We demonstrate that these topological phases can be directly probed through the anomalous thermal Hall effect. Finally, we find that the spin-spin interactions in the strong-$D$ phase enable magnon-phonon coupling that yields hybridized topological bands, whereas such coupling vanishes in the weak-$D$ phase.

cond-mat.mes-hall↗

arXiv2025

Revealing the Geometrical and Vibrational Properties of the Defects Driving the Boson Peak

In amorphous solids, the vibrational density of states shows an excess of modes over the Debye model, known as the boson peak, whose origin remains unclear. Studies suggest a link to quasi-localized nonphononic vibrations or 'defects,' but identifying them is challenging due to hybridization with phonons that renders methods based on localization properties, such as the participation ratio, unreliable. We introduce a practical method to separate hybridized phonons from localized vibrations and find that boson peak phonons hybridize with compact, two-dimensional defects exhibiting oscillatory pure shear deformations. These two-dimensional defects are also exposed by the procedure recently employed to identify stringlets (Nature Physics volume 18, pages 669-677 (2022)), suggesting that these may not be one-dimensional objects as speculated. Our work demonstrates the presence of localized defects at the boson peak frequency and provides a comprehensive characterization of their vibrational and geometric properties, resolving the tension between the concepts of quasi-localized quadrupolar defects and stringlets.

cond-mat.soft↗

arXiv2025

Simple holographic dual of the Maxwell-Cattaneo model & the fate of KMS symmetry for non-hydrodynamic modes

Diffusion, as described by Fick's laws, governs the spreading of particles, information, data, and even financial fluctuations. However, due to its parabolic structure, the diffusion equation leads to an unphysical prediction: any localized disturbance instantaneously affects the entire system. The Maxwell-Cattaneo (MC) model, originally introduced to address relativistic heat conduction, refines the standard diffusion framework by incorporating a finite relaxation time $τ$, associated with the onset of local equilibrium. This modification yields physically relevant consequences, including the emergence of propagating shear waves in liquids and second sound in solids. Holographic methods have historically provided powerful tools for describing the hydrodynamics of strongly correlated systems. However, they have so far failed to capture the dynamics governed by the MC model, limiting their ability to model intermediate time-scale phenomena. In this work, we construct a simple holographic dual of the Maxwell-Cattaneo model and rigorously establish its equivalence through a combination of analytical and numerical techniques. As an important byproduct of our analysis, and contrary to previous ad-hoc assumptions, we find that effective field theories featuring non-hydrodynamic modes exhibit a generalized form of Kubo-Martin-Schwinger (KMS) symmetry, which reduces to the canonical form only in the hydrodynamic limit.

hep-th↗

arXiv2025

Burgers rings as topological signatures of Eshelby-like plastic events in glasses

Eshelby-like quadrupolar structures serve as the fundamental microscopic units for characterizing plastic instabilities in amorphous solids and play a crucial role in explaining their mechanical failure, including the formation of shear bands. However, identifying Eshelby-like plastic events in glasses remains challenging due to their inherent structural and dynamical complexity. In this work, we show that Eshelby-like structures can be precisely identified and localized using a topological invariant known as the continuous Burgers vector. By combining analytical and simulation techniques, we reveal the emergence of a topological Burgers ring around Eshelby plastic events, enabling the precise identification of their center of mass and capturing their orientation as well. This proposed method offers a clear and unambiguous framework to locate and characterize the plastic rearrangements that govern plasticity in glasses.

cond-mat.dis-nn↗

arXiv2025

Topological signatures of collective dynamics and turbulent-like energy cascades in apolar active granular

Active matter refers to a broad class of non-equilibrium systems where energy is continuously injected at the level of individual ``particles". These systems exhibit emergent collective behaviors that have no direct thermal-equilibrium counterpart. Their scale ranges from micrometer-sized swarms of bacteria to meter-scale human crowds. In recent years, the role of topology and self-propelled topological defects in active systems has garnered significant attention, particularly in polar and nematic active matter. Building on these ideas, we investigate emergent collective dynamics in apolar active granular fluids. Using isotropic granular vibrators as a model experimental system of apolar active Ornstein-Uhlenbeck particles in a dry environment, we uncover a distinctive three-stage time evolution arising from the intricate interplay between activity and inelastic interactions. By analyzing the statistics, spatial correlations, and dynamics of vortex-like topological defects in the displacement vector field, we demonstrate their ability to describe this intrinsic collective motion. Furthermore, associated to these topological defects, we reveal the onset of a turbulent-like inverse energy cascade, where kinetic energy transfers across different length scales over time. As the system evolves, the power scaling of the energy transfer increases with the duration of observation. Our findings show that topological concepts can be extended to the nonequilibrium dynamics of apolar active matter, revealing a direct link between microscopic topological processes and emergent large-scale behaviors in active granular fluids that lack both a well-defined direction of motion and an intrinsic axis of orientation at the particle scale.

cond-mat.soft↗

arXiv2025

Dissipative quantum phase transitions monitored by current fluctuations

Dissipative phase transitions (DPT) are defined by sudden changes in the physical properties of nonequilibrium open quantum systems and they present characteristics that have no analog in closed and thermal systems. Several methods to detect and characterize DPT have been suggested in the literature, the most famous of which -- the $\textit{Liouvillian gap}$ -- can be derived from a spectral analysis of the Liouvillian super-operator that governs the complex interplay between coherent and dissipative dynamics. Here, we consider the $\textit{output current}$, defined as the average total quantum jumps per unit time between the open quantum system and the environment. We propose that output current fluctuations, and in particular their dynamical correlations, their power spectrum, and their characteristic timescale can provide valuable information about DPT, confirming a dramatic change of behavior at the critical point. We validate our proposal using the dissipative XYZ model and the nonlinear driven-dissipative Kerr model, showing good agreement with previous estimates of the location of the critical point. Compared to previous approaches, our proposal could be already experimentally tested in optical systems, providing a practical method to detect criticality in quantum open systems.

quant-ph↗

arXiv2025

Atomistic mechanisms of viscosity in 2D liquid-like fluids

Shear viscosity plays a fundamental role in fluid dynamics from heavy-ion collisions to biological processes. Still, its microscopic mechanisms at the individual particle kinetic level remain a subject of ongoing research, specially in dense systems. In this work, we systematically investigate the shear viscosity ($η$) of two-dimensional (2D) simple fluids using computer simulations of Lennard-Jones, Yukawa, and one-component plasma systems. By combining Frenkel's liquid description, consisting of solid-like quasi-harmonic vibrations interrupted by thermally activated hops, with the concept of lifetime of local atomic connectivity $τ_{LC}$, we find a surprisingly simple formula for the kinematic viscosity that is solely determined by $τ_{LC}$ and the average kinetic particle speed $\bar{v}_p$. The derived analytical expression provides a direct link between macroscopic and microscopic dynamics, which shows excellent agreement with the simulation data in the dense liquid-like regime in all the 2D fluids considered. Moreover, it is discovered that, $τ_{LC}$ in 2D fluids is universally determined by the effective potential difference between the first peak and valley of the pair correlation function, implying a direct connection between macroscopic shear transport and microscopic structure. Finally, we demonstrate that the characteristic length scale $l_p= \bar{v}_p τ_{LC}$, which governs the macroscopic shear viscosity, aligns with the elastic length-scale that defines the propagation limit of collective shear waves in liquids. These findings establish that shear viscosity in 2D fluids arises from the diffusive transport of average particle momentum across the elastic length scale. Moreover, they highlight that shear dynamics are fundamentally governed by localized configurational excitations within the atomic connectivity network.

cond-mat.soft↗

arXiv2025

Topological defects govern plasticity and shear band formation in two-dimensional amorphous solids

Understanding the fundamental mechanisms behind plastic instabilities and shear band formation in amorphous media under applied deformation remains a long-standing challenge. Leveraging on the mathematical concept of topology, we revisit this problem using two-dimensional experimental amorphous granular packings subjected to pure shear. We demonstrate that topological defects (TDs) in the displacement vector field act as carriers of plasticity, enabling the prediction of both the onset of plastic flow and the global mechanical response of the system. At the microscopic level, we show that these TDs are responsible for the dynamical breakdown of local orientational order, thereby linking topological excitations to short-range structural changes. Finally, we establish that the spatial localization and cooperative alignment of TDs underlie the formation of macroscopic shear bands, which drive plastic flow under large shear loads. This process is mediated by the quasi-periodic annihilation of large defect clusters and their geometric transformation from an approximately isotropic to a strongly anisotropic shape. Our results provide a unified framework for understanding plastic deformation and shear band formation in two-dimensional amorphous systems by connecting topology, short-range order, and mechanical response.

cond-mat.soft↗

arXiv2025

Holographic D-brane constructions with dynamical gauge fields

Holographic D-brane constructions, governed by the Dirac-Born-Infeld (DBI) action, play a central role in the AdS/CFT correspondence, particularly in applications to quantum chromodynamics and condensed matter systems. In this work, we demonstrate how to equip these bottom-up holographic models with dynamical boundary gauge fields, thereby introducing electromagnetic interactions into their dual field theory descriptions. As a direct application of this formalism, we compute the dispersion relations of the lowest quasinormal modes around both equilibrium and nonequilibrium steady states, and show that their behavior matches the predictions from hydrodynamics with dynamical $U(1)$ symmetry.

hep-th↗

arXiv2025

Stress-stress correlations in two-dimensional amorphous and crystalline solids

Stress-stress correlations in crystalline solids with long-range order can be straightforwardly derived using elasticity theory. In contrast, the `emergent elasticity' of amorphous solids, rigid materials characterized by an underlying disordered structure, defies direct explanation within traditional theoretical frameworks. To address this challenge, tensor gauge theories have been recently proposed as a promising approach to describe the emergent elasticity of disordered solids and predict their stress-stress correlations. In this work, we revisit this problem in two-dimensional amorphous and crystalline solids by employing a canonical elasticity theory approach, supported by experimental and simulation data. We demonstrate that, with respect to static stress-stress correlations, the response of a 2D disordered solid is indistinguishable from that of a 2D isotropic crystalline solid and it is well predicted by vanilla elasticity theory. Moreover, we show that the presence of pinch-point singularities in the stress response is not an exclusive feature of amorphous solids. Our results confirm previous observations about the universal character of static stress-stress correlations in crystalline and amorphous packings.

cond-mat.soft↗

arXiv2025

Singular Value Decomposition and Its Blind Spot for Quantum Chaos in Non-Hermitian Sachdev-Ye-Kitaev Models

The study of chaos and complexity in non-Hermitian quantum systems poses significant challenges due to the emergence of complex eigenvalues in their spectra. Recently, the singular value decomposition (SVD) method was proposed to address these challenges. In this work, we identify two critical shortcomings of the SVD approach when analyzing Krylov complexity and spectral statistics in non-Hermitian settings. First, we show that SVD fails to reproduce conventional eigenvalue statistics in the Hermitian limit for systems with non-positive definite spectra, as exemplified by a variant of the Sachdev-Ye-Kitaev (SYK) model. Second, and more fundamentally, Krylov complexity and spectral statistics derived via SVD cannot distinguish chaotic from integrable non-Hermitian dynamics, leading to results that conflict with complex spacing ratio analysis. Our findings reveal that SVD is inadequate for probing quantum chaos in non-Hermitian systems, and we advocate employing more robust methods, such as the bi-Lanczos algorithm, for future research in this direction.

hep-th↗

arXiv2025

A new scale anomaly in Dirac matter

The dynamics of Dirac semimetals is modeled at low energies by the massless Dirac Hamiltonian with the Fermi velocity replacing the velocity of light. The classical action is scale invariant. In 3D materials, Coulomb interactions induce a conformal anomaly associated to the charge renormalization already known in quantum field theory. In this work, we describe a new conformal anomaly induced by the running of the Fermi velocity that applies to Dirac semimetals in two and three dimensions. The case of graphene is particularly interesting. We analyze the anomaly and explore its thermodynamic and hydrodynamic consequences. The anomaly modifies the propagation speed of hydrodynamic sound waves, alters the thermodynamic equation of state, and induces a non-vanishing bulk viscosity proportional to the beta function of the Fermi velocity.

hep-th↗

arXiv2025

Atomistic mechanisms of dynamics in a two-dimensional dodecagonal quasicrystal

Quasicrystals have been observed in a variety of materials ranging from metal alloys to block copolymers. However, their structural and dynamical properties cannot be readily described in terms of conventional solid-state models of liquids and solids. We may expect the dynamics of this specific class of quasicrystalline materials to be more like glass-forming liquids in the sense of exhibiting large fluctuations in the local mobility ("dynamic heterogeneity") and non-Arrhenius temperature dependence of relaxation and diffusion. In this work, we investigate a model dodecagonal quasicrystal material in two dimensions (2D) using molecular dynamics (MD) simulations, with a focus on heterogeneous dynamics and non-Arrhenius relaxation and diffusion. As observed in glass-forming liquids and heated crystals, we observe a two-stage relaxation dynamics in the self-intermediate scattering function $F_s(k,t)$ of our quasicrystal material. It involves a fast $β$-relaxation and $α$ relaxation process having a highly temperature dependent relaxation time whose activation energy varies in concert with the extent of string-like collective motion, a phenomenon recognized to occur in glass-forming liquids at low temperatures and crystalline materials at elevated temperatures. After examining the dynamics of our dodecagonal quasicrystalline material in great detail, we conclude that the dynamics of these materials more closely resembles observations on metallic glass-forming liquids than crystalline materials.

cond-mat.mtrl-sci↗

arXiv2025

Chiral Anomalous Magnetohydrodynamics in action: effective field theory and holography

Chiral Anomalous Magnetohydrodynamics (CAMHD) provides a low-energy effective framework for describing chiral fluids in the presence of dynamical electromagnetic fields and axial anomaly. This theory finds applications across diverse physical systems, including heavy-ion collisions, the early universe, and Weyl/Dirac semimetals. Along with Schwinger-Keldysh (SK) effective theories, holographic models serve as a complementary tool to provide a systematic formulation of CAMHD that goes beyond the weak coupling regime. In this work, we explore holographic models with $U(1)_A \times U(1)$ symmetry, where the electromagnetic $U(1)$ field is rendered dynamical through mixed boundary conditions applied to the bulk gauge field and the axial anomaly is introduced via a Chern-Simons bulk term. Through a detailed holographic SK analysis, we demonstrate that the low-energy effective action derived from this model aligns precisely with the SK field theory proposed by Landry and Liu and, in fact, it generalizes it to scenarios with finite background axial field. This alignment not only validates the holographic model but also paves the way for its use in exploring unresolved aspects of CAMHD, such as the recently proposed chiral magnetic electric separation wave and nonlinear chiral instabilities.

hep-th↗

arXiv2025

Designing atomic-scale resistive circuits in topological insulators through vacancy-induced localized modes

We demonstrate that vacancies can induce topologically protected localized electronic excitations within the bulk of a topological insulator, and when sufficiently close, give rise to one-dimensional propagating chiral bulk modes. We show that the dynamics of these modes can be effectively described by a tight-binding Hamiltonian, with the hopping parameter determined by the overlap of electronic wave functions between adjacent vacancies, accurately predicting the low-energy spectrum. Building on this phenomenon, we propose that vacancies in topological materials can be utilized to design atomic-scale resistive circuits, and estimate the associated resistance as a function of the vacancy distribution's geometric properties.

cond-mat.mes-hall↗

arXiv2025

Experimental observation of gapped shear waves and liquid-like to gas-like dynamical crossover in active granular matter

Unlike crystalline solids, liquids lack long-range order, resulting in diffusive shear fluctuations rather than propagating waves. Simulations predict that liquids exhibit a $k$-gap in wave-vector space, where solid-like transverse waves reappear above this gap. Experimental evidence in classical liquids has been limited, observed only in 2D dusty plasmas. Here, we investigate this phenomenon using active Brownian vibrators and uncover distinct gas-like and liquid-like phases depending on the packing fraction. We measure key properties, including pair correlation functions, mean square displacements, velocity auto-correlation functions, and vibrational density of states. In the liquid-like phase, we confirm the $k$-gap in transverse excitations, whose size grows as the packing fraction decreases and eventually disappears in the gas phase. Our findings extend the concept of the $k$-gap to active granular systems and reveal striking parallels with supercritical fluids.

cond-mat.soft↗

arXiv2025

Hedgehog topological defects in 3D amorphous solids

The underlying structural disorder renders the concept of topological defects in amorphous solids difficult to apply and hinders a first-principle identification of the microscopic carriers of plasticity and of the regions more prone to structural rearrangements (``soft spots''). Recently, it has been proposed that well-defined topological defects can still be identified in glasses, and correlated to local and global plasticity, by looking at the eigenvector field or the particle displacement field. Nevertheless, all the existing proposals and analyses are only valid in two spatial dimensions. In this work, we propose the idea of using hedgehog topological defects to characterize the plasticity of 3D glasses and to geometrically predict the location of their soft spots. We corroborate our proposal by simulating a Kremer-Grest 3D polymer glass, and by using both the normal mode eigenvector field and the displacement field around large plastic events. Contrary to the 2D case, the sign of the topological charge defined from the eigenvector field is ambiguous and the geometry of the topological defects, whether radial or hyperbolic, plays a fundamental role in 3D. In fact, we find that the topological hedgehog defects relevant for plasticity are those exhibiting hyperbolic geometry, resembling the saddle-point structure of 2D topological defects with negative winding number (anti-vortices). Our results confirm that a topological characterization of plasticity in glasses is feasible and provide a concrete realization of this program in 3D amorphous systems.

cond-mat.soft↗