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Critical superflows and thermodynamic instabilities in superfluids

Physical Review D 2023年第8期108卷 L081903-L081903页

作者： Blaise Goutéraux Filippo Sottovia Eric Mefford CPHT CNRS École Polytechnique Institut Polytechnique de Paris Palaiseau 91120 France Department of Physics and Astronomy University of Victoria Victoria V8W 3P6 BC Canada

In this work, we study the linear stability of superfluid phases of matter irrespective of the nature of microscopic degrees of freedom and the strength of interactions between them. Famously, assuming invariance under Galilean boosts and a phonon-roton single-particle dispersion relation, Landau predicted superfluid helium 4 would become unstable for large enough superfluid velocities. Here, we demonstrate that such instabilities generically follow from a change of sign of one of the eigenvalues of the matrix of second derivatives of the free energy. Our only assumption is the existence of static thermodynamic equilibrium, irrespective of any invariance under boosts or microscopic statistics. Turning on dissipation, we show that a linear dynamical instability also develops, leading to exponential growth in time of perturbations around equilibrium. Specializing to Galilean superfluids and assuming the existence of bosonic quasiparticles, our criterion reproduces Landau’s critical velocity for Bose-Einstein condensates. Our criterion also reduces to the well-known maximal supercurrent in weakly coupled superconductors described either by Landau-Ginzburg or Bardeen-Cooper-Schrieffer theory. Further, it correctly reproduces the onset of the instability in relativistic, strongly coupled superfluids without quasiparticles at zero as well as finite temperature, which we construct using gauge/gravity duality. As a less trivial application of our criterion, we show that in dirty superfluids the instability manifests itself first in the thermal diffusion mode instead of the superfluid sound mode. Our work provides a simple, comprehensive, and unified description of the large superflow instability of superfluids and superconductors at any temperature independent of the microscopic details of the system and the strength of interactions.

关键词： Gauge-gravity dualities Superfluidity Strongly correlated systems Superfluids Hydrodynamics string theory techniques in condensed matter

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T-linear resistivity, optical conductivity, and Planckian transport for a holographic local quantum critical metal in a periodic potential

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Physical Review B 2023年第12期108卷 125145-125145页

作者： F. Balm N. Chagnet S. Arend J. Aretz K. Grosvenor M. Janse O. Moors J. Post V. Ohanesjan D. Rodriguez-Fernandez K. Schalm J. Zaanen Instituut-Lorentz for Theoretical Physics Δ-ITP Leiden University 2333CA Leiden The Netherlands

High-Tc cuprate strange metals are characterized by a DC resistivity that scales linearly with T from the onset of superconductivity to the crystal melting temperature, characterized by a current life time τℏ≃ℏ/(kBT), the “Planckian dissipation”. At the same time, the optical conductivity ceases to be of the Drude form at high temperatures, suggesting a change of the underlying dynamics that surprisingly leaves the T-linear DC resistivity unaffected. We use the AdS/CFT correspondence that describes strongly coupled, densely many-body entangled metallic states of matter to study the DC thermoelectrical transport properties and the optical conductivities of the local quantum critical Gubser-Rocha holographic strange metal in 2+1 dimensions in the presence of a lattice potential, a prime candidate to compare with experiment. We find that the electrical DC resistivity is linear in T at low temperatures for a large range of potential strengths and wave vectors, even as it transitions between different dissipative regimes. At weak lattice potential the optical conductivity evolves as a function of increasing temperature from a Drude form to a “bad metal” characterized by a mid-IR resonance without changing the DC transport, similar to that seen in cuprate strange metals. This mid-IR peak and notably its temperature evolution can be fully understood as a consequence of umklapp hydrodynamics: i.e., hydrodynamic perturbations are Bloch modes in the presence of a lattice. At strong lattice potential an “incoherent metal” is realized instead where momentum conservation no longer plays a role in the transport. We confirm that in this regime the thermal diffusivity appears to be insensitive to the breaking of translations and can be explained by Planckian dissipation originating in universal microscopic chaos. A similar behavior has been found for holographic metals with strong homogeneous momentum relaxation. The charge diffusivity does not submit to this chaos explanation, eve

关键词： High-temperature superconductors Strongly correlated systems Hydrodynamics string theory techniques in condensed matter

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Massless graviton in a model of quantum gravity with emergent spacetime

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Physical Review D 2023年第2期108卷 024054-024054页

作者： Sung-Sik Lee Department of Physics and Astronomy McMaster University 1280 Main St. West Hamilton Ontario L8S 4M1 Canada Perimeter Institute for Theoretical Physics 31 Caroline St. North Waterloo Ontario N2L 2Y5 Canada

In the model of quantum gravity proposed in [J. High Energy Phys. 06 (2020) 70], dynamical spacetime arises as a collective phenomenon of underlying quantum matter. Without a preferred decomposition of the Hilbert space, the signature, topology and geometry of an emergent spacetime depend upon how the total Hilbert space is partitioned into local Hilbert spaces. In this paper, it is shown that the massless graviton emerges in the spacetime realized from a Hilbert space decomposition that supports a collection of largely unentangled local clocks.

关键词： Alternative gravity theories Quantum gravity string theory techniques in condensed matter Spacetime symmetries

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Holographic confining-deconfining gauge theories and entanglement measures with a magnetic field

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Physical Review D 2023年第8期107卷 086016-086016页

作者： Parul Jain Siddhi Swarupa Jena Subhash Mahapatra Asia Pacific Center for Theoretical Physics Pohang—37673 South Korea Department of Physics and Astronomy National Institute of Technology Rourkela Rourkela—769008 India

We study various holographic pure and mixed-state entanglement measures in the confined/deconfined phases of a bottom-up AdS/QCD model in the presence of a background magnetic field. We analyze the entanglement entropy, entanglement wedge cross section, mutual information, and entanglement negativity and investigate how a background magnetic field leaves its imprints on the entanglement structure of these measures. Due to the anisotropy introduced by the magnetic field, we find that the behavior of these measures depends nontrivially on the relative orientation of the strip with respect to the field. In the confining phase, the entanglement entropy and negativity undergo a phase transition at the same critical strip length, the magnitude of which increases/decreases for parallel/perpendicular orientation of the magnetic field. The entanglement wedge cross section similarly displays discontinuous behavior each time a phase transition between different entangling surfaces occurs, while further exhibiting anisotropic features with a magnetic field. We further find that the magnetic field also introduces substantial changes in the entanglement measures of the deconfined phase; however, these changes remain qualitatively similar for all orientations of the magnetic field. We further study the inequality involving the entanglement wedge and mutual information and find that the former always exceeds half of the latter everywhere in the parameter space of the confined/deconfined phases.

关键词： Gauge-gravity dualities string theory techniques in condensed matter

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Coulomb drag between two strange metals

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Physical Review B 2022年第20期106卷 205116-205116页

作者： E. Mauri H. T. C. Stoof Institute for Theoretical Physics Center for Extreme Matter and Emergent Phenomena Utrecht University Princentonplein 5 Utrecht 3584 CC Netherlands

We study the Coulomb drag between two strange-metal layers using the Einstein-Maxwell-Dilaton model from holography. We show that the low-temperature dependence of the drag resistivity is ρD∝T4, which strongly deviates from the quadratic dependence of Fermi liquids. We also present numerical results at room temperature, using typical parameters of the cuprates, to provide an estimate of the magnitude of this effect for future experiments. We find that the drag resistivity is enhanced by the plasmons characteristic of the two-layer system.

关键词： Gauge-gravity dualities Superconductivity Transport phenomena Cuprates string theory techniques in condensed matter

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Thermoelectric transport properties of gapless pinned charge density waves

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Physical Review B 2022年第4期106卷 L041118-L041118页

作者： Tomas Andrade Alexander Krikun Departament de Física Quàntica i Astrofísica Institut de Ciències del Cosmos Universitat de Barcelona Martí i Franquès 1 E-08028 Barcelona Spain Nordita KTH Royal Institute of Technology and Stockholm University Hannes Alfvéns väg 12 SE-106 91 Stockholm Sweden

Quantum strongly correlated matter exhibits properties which are not easily explainable in the conventional framework of Fermi liquids. Universal effective field theory tools are applicable in these cases regardless of the microscopic details of the quantum system, since they are based on symmetries. It is necessary, however, to construct these effective tools in full generality, avoiding restrictions coming from particular microscopic descriptions which may inadequately constrain the coefficients that enter in the effective theory. In this work we demonstrate with explicit examples how the hydrodynamic coefficients, which have been recently reinstated in the effective theory of pinned charge density waves (CDWs), can affect the phenomenology of the thermoelectric transport in strongly correlated quantum matter. Our examples, based on two classes of holographic models with pinned CDW, have microscopics which are conceptually different from Fermi liquids. Therefore, the above transport coefficients are nonzero, contrary to the conventional approach. We show how these coefficients allow one to take into account the change of sign of the Seebeck coefficient and the low resistivity of the CDW phase of the cuprate high temperature superconductors, without referring to the effects of Fermi surface reconstruction.

关键词： Charge density waves Electrical conductivity Heat transfer Seebeck effect string theory techniques in condensed matter

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Damping of Pseudo-Goldstone Fields

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Physical Review Letters 2022年第14期128卷 141601-141601页

作者： Luca V. Delacrétaz Blaise Goutéraux Vaios Ziogas Kadanoff Center for Theoretical Physics University of Chicago Chicago Illinois 60637 USA. CPHT CNRS École Polytechnique IP Paris F-91128 Palaiseau France.

Approximate symmetries abound in nature. If these symmetries are also spontaneously broken, the would-be Goldstone modes acquire a small mass, or inverse correlation length, and are referred to as pseudo-Goldstones. At nonzero temperature, the effects of dissipation can be captured by hydrodynamics at sufficiently long scales compared to the local equilibrium. Here, we show that, in the limit of weak explicit breaking, locality of hydrodynamics implies that the damping of pseudo-Goldstones is completely determined by their mass and diffusive transport coefficients. We present many applications: superfluids, QCD in the chiral limit, Wigner crystal and density wave phases in the presence of an external magnetic field or not, nematic phases, and (anti)ferromagnets. For electronic density wave phases, pseudo-Goldstone damping generates a contribution to the resistivity independent of the strength of disorder, which can have a linear temperature dependence provided the associated diffusivity saturates a bound. This is reminiscent of the phenomenology of strange metal high-Tc superconductors, where charge density waves are observed across the phase diagram.

关键词： Gauge-gravity dualities Goldstone bosons Hydrodynamics Nonequilibrium Green's function string theory techniques in condensed matter Symmetries in condensed matter

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string-like theory of quantum Hall interfaces

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Physical Review B 2022年第24期106卷 245138-245138页

作者： Oğuz Türker Kun Yang National High Magnetic Field Laboratory and Department of Physics Florida State University Tallahassee Florida 32306 USA

We derive the effective theories for quantum Hall droplets with attractive interaction among the constituent particles. In the absence of confining potentials, such droplets are defined by their freely moving interfaces (or boundaries) with the vacuum. We demonstrate that the effective theories take forms like string theories. Generalization to interfaces between different quantum Hall liquids is discussed.

关键词： Electronic structure Quantum Hall effect string theory techniques in condensed matter

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Analytic AC conductivities from holography

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Physical Review D 2022年第6期105卷 066013-066013页

作者： Jie Ren Wenni Zheng School of Physics Sun Yat-sen University Guangzhou 510275 China

We find exact, analytic solutions of the holographic ac conductivity at arbitrary frequency ω and temperature T, in contrast to previous works where the ac conductivity was analytically obtained usually at small ω and T. These solutions enable us to study the analyticity properties of the current-current correlator G(ω) in detail. The first system we study is the AdS5 planar black hole with momentum dissipation, whose extremal limit has an AdS2 factor. Then we study AdS4 and AdS5 Einstein-dilaton systems whose special cases are maximal gauged supergravities. The solutions show how the poles move and how branch cuts emerge as the temperature varies. As a by-product, we obtain an R-current correlator in N=4 super-Yang-Mills theory on a sphere at finite temperature in the large N and strong coupling limit.

关键词： Classical black holes Electrical conductivity Finite temperature field theory Gauge-gravity dualities Effective field theory string theory techniques in condensed matter

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Entropic force and real-time dynamics of holographic quarkonium in a magnetic field

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Physical Review D 2022年第8期105卷 086011-086011页

作者： Siddhi Swarupa Jena Bhaskar Shukla David Dudal Subhash Mahapatra Department of Physics and Astronomy National Institute of Technology Rourkela Rourkela—769008 India KU Leuven Campus Kortrijk–Kulak Department of Physics Etienne Sabbelaan 53 bus 7657 8500 Kortrijk Belgium Ghent University Department of Physics and Astronomy Krijgslaan 281-S9 9000 Gent Belgium

We continue the study of a recently constructed holographic QCD model supplemented with a magnetic field. We consider the holographic dual of a quark-antiquark pair and investigate its entropy beyond the deconfinement phase transition in terms of interquark distance, temperature and magnetic field. We obtain a clear magnetic field dependence in the strongly decreasing entropy near deconfinement and in the entropy variation for growing interquark separation. We uncover various supporting evidence for inverse magnetic catalysis. The emergent entropic force is found to become stronger with magnetic field, promoting the quarkonium dissociation. We also probe the dynamical dissociation of the quarkonium state, finding a faster dissociation with magnetic field. At least the static predictions should become amenable to a qualitative comparison with future lattice data.

关键词： Gauge-gravity dualities string theory techniques in condensed matter

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