Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B50: Strange Metal PhysicsInvited Live
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Sponsoring Units: DCMP Chair: Subir Sachdev, Harvard University |
Monday, March 15, 2021 11:30AM - 12:06PM Live |
B50.00001: T-linear resistivity and Planckian dissipation in cuprates Invited Speaker: Anaelle Legros The perfectly linear temperature dependence of the resistivity observed as T→0 in a variety of metals close to a quantum critical point is a major puzzle of condensed matter physics. I will present high-field magneto-transport measurements of two hole-doped cuprates, near their pseudogap critical point p*, supporting that T-linear resistivity as T→0 is a generic property of cuprates, associated with a universal scattering rate. We measured the low-T resistivity of the bilayer cuprate Bi2212 just above p* [1] and found that it exhibits a T-linear dependence with the same slope as in the single-layer cuprate Nd-LSCO close to its own p* and in the low-T limit, despite their very different Fermi surfaces and structural, superconducting and magnetic properties. We also observed, using the Drude formula, that in various cuprates showing this low-T phenomenon (hole-doped and electron-doped) the slope of this T-linear resistivity is given by a universal relation implying a specific scattering rate for charge carriers: 1τ= αh/2πkB T, where h is Planck’s constant, k B is the Boltzmann constant and α a constant of order unity. This specific scattering rate corresponds to what is called the Planckian limit [2], and has been attributed to other metals showing a T-linear resistivity [3]. Finally, we directly measured the scattering rate in the single-layer cuprate Nd- LSCO, just above p* and in the low-T limit, using angle-dependent magneto-resistance measurements [4]: these experiments reveal an inelastic scattering rate which is isotropic and linear in temperature, and whose magnitude is consistent with Planckian dissipation. |
Monday, March 15, 2021 12:06PM - 12:42PM Live |
B50.00002: Theories of Planckian dissipation in strange metals Invited Speaker: Aavishkar Patel Metallic non-Fermi liquid phases above putative quantum critical points in a wide variety of materials with strongly correlated electrons display linear-in-temperature resistivity ("strange metallic" behavior) over a wide range of temperatures, down to temperatures approaching absolute zero. Furthermore, when expressed in terms of a Drude formula using the electron effective mass obtained from nearby Fermi liquid phases with well-defined quasiparticles, the temperature dependence of the resistivity implies a "universal" electron transport lifetime τtr ~ α h/(2π kBT), where α ~ 1 across different materials with very different electron-electron interaction strengths. I will describe two types of exactly solvable effective field theories, constructed along the lines of the Sachdev-Ye-Kitaev models, that can describe such universal behavior. The first kind realizes a "marginal Fermi liquid" phase as a quantum critical point between metallic Fermi liquid phases involving "small" and "large" carrier densitites. The second kind is an exotic state of matter that is very far from having well-defined quasiparticles, which lacks a sharp Fermi surface but nonetheless has a strong momentum dependence of the electron spectral function that significes a "remnant" Fermi surface. |
Monday, March 15, 2021 12:42PM - 1:18PM Live |
B50.00003: Anomalous Dimensions for Conserved Currents in Strange Metals Invited Speaker: Philip Phillips For the past 30 years, the transport properties in the unusual metallic phase seen in the cuprate superconductors and many other quantum critical metals have defied an explanation in terms of the standard building blocks of modern physics --- particles with local interactions and conservation laws. A recent proposal suggests that all of the properties of such `strange metals' can be understood if the current has an anomalous dimension not determined simply by dimensional analysis. My talk will focus on trying to understand this claim. To demystify this claim, I will first show that even in the standard formulation of electricity and magnetism, there is an extra degree of freedom, which has remained unnoticed until now, that can allow, in principle, for the current to have any allowable dimension. This extra degree of freedom is a consequence of Noether's Second Theorem. However, I will show that the only quantum theories to date which exhibit such odd behaviour are holographic models that are derived from a gravity theory that lives in higher dimensions. The existence of currents having anomalous dimensions, a direct probe of the existence of extra `hidden' dimensions, can be tested with the Aharonov-Bohm effect. I will describe this effect and its potential impact for unlocking the secret of the strange metal in the cuprates. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B50.00004: Incoherent strange metal sharply bounded by the pseudogap critical doping in Bi2212 Invited Speaker: Sudi Chen In normal metals, macroscopic properties are understood using the concept of quasiparticles. In the cuprate high-temperature superconductors, the metallic state above the highest Tc is found to be very different and called the “strange metal”. In this talk, I will present a comprehensive angle-resolved photoemission study of its spectral function in Bi2212 [1]. With increasing doping across a temperature-independent critical value pc ~ 0.19, we observe a dramatic change near the Brillouin zone boundary where the strange metal characterized by incoherent spectral function abruptly reconstructs into a more conventional metal with quasiparticle-like excitations. Furthermore, above the temperature scale of superconducting fluctuations, we find that the pseudogap—the anomalous suppression of low-energy spectral intensity with decreasing temperature—also sharply collapses at the very same pc. These observations suggest that the incoherent strange metal is a prerequisite for the pseudogap and challenge presumptions associating the pseudogap with a quantum critical point. |
Monday, March 15, 2021 1:54PM - 2:30PM Live |
B50.00005: Investigation of strange metallicity from numerical simulations of the doped Hubbard model Invited Speaker: Thomas Devereaux Strange or bad metallic transport, defined by its incompatibility with conventional quasiparticle pictures, is a theme common to strongly correlated materials and ubiquitous in many high temperature superconductors. The Hubbard model represents a minimal starting point for modeling strongly correlated systems. Here we demonstrate strange metallic transport in the doped two-dimensional Hubbard model using determinantal quantum Monte Carlo calculations. Over a wide range of doping, we observe resistivities exceeding the Mott-Ioffe-Regel limit with linear temperature dependence. The temperatures of our calculations extend to as low as 1/40 the non-interacting bandwidth, placing our findings in the degenerate regime relevant to experimental observations of strange metallicity. Our results provide a foundation for connecting theories of strange metals to models of strongly correlated materials. |
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