Bulletin of the American Physical Society
APS March Meeting 2021
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: Tlinear 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 highfield magnetotransport measurements of two holedoped cuprates, near their pseudogap critical point p*, supporting that Tlinear resistivity as T→0 is a generic property of cuprates, associated with a universal scattering rate. We measured the lowT resistivity of the bilayer cuprate Bi2212 just above p* [1] and found that it exhibits a Tlinear dependence with the same slope as in the singlelayer cuprate NdLSCO close to its own p* and in the lowT 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 lowT phenomenon (holedoped and electrondoped) the slope of this Tlinear resistivity is given by a universal relation implying a specific scattering rate for charge carriers: 1τ= αh/2πk_{B }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 Tlinear resistivity [3]. Finally, we directly measured the scattering rate in the singlelayer cuprate Nd LSCO, just above p* and in the lowT limit, using angledependent magnetoresistance 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 nonFermi liquid phases above putative quantum critical points in a wide variety of materials with strongly correlated electrons display linearintemperature 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 welldefined quasiparticles, the temperature dependence of the resistivity implies a "universal" electron transport lifetime τ_{tr }~ α h/(2π k_{B}T), where α ~ 1 across different materials with very different electronelectron interaction strengths. I will describe two types of exactly solvable effective field theories, constructed along the lines of the SachdevYeKitaev 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 welldefined 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 AharonovBohm 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 hightemperature 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 angleresolved photoemission study of its spectral function in Bi2212 [1]. With increasing doping across a temperatureindependent 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 quasiparticlelike excitations. Furthermore, above the temperature scale of superconducting fluctuations, we find that the pseudogap—the anomalous suppression of lowenergy 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 
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 twodimensional Hubbard model using determinantal quantum Monte Carlo calculations. Over a wide range of doping, we observe resistivities exceeding the MottIoffeRegel limit with linear temperature dependence. The temperatures of our calculations extend to as low as 1/40 the noninteracting 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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