Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B24: Do strange metals exhibit Plankian dissipation?Invited
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Sponsoring Units: DCMP Chair: Joerg Schmalian, Karlsruhe Institute of Technology Room: Room 237 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B24.00001: Role of spatial disorder in strange metals Invited Speaker: Subir Sachdev We now have a reasonable theory for non-Fermi liquids without quasiparticles in two spatial dimensions: a Fermi surface coupled to a critical boson, with the boson representing a symmetry-breaking order or an emergent collective mode. It was initially proposed that such a non-Fermi liquid could describe the strange metal behavior of correlated electron compounds. But it has now been established that the transport properties of such a non-Fermi liquid are not very different from that of a Fermi liquid: the conservation of momentum in the singular low-energy processes prevents the decay of electrical currents. However, in the presence of spatial disorder, strange metal behavior is possible at low temperatures (T): I will review recent work showing how spatial disorder in the boson-fermion coupling leads to a metal with marginally defined quasiparticles, a T ln(1/T) specific heat, linear-in-T resistivity, an optical conductivity which scales as 1/frequency, and a Planckian scattering rate. |
Monday, March 6, 2023 12:06PM - 12:42PM |
B24.00002: A stability bound on the T-linear resistivity of conventional metals Invited Speaker: Chaitanya Murthy The electrical resistivity of conventional metals varies linearly with temperature T in the regime T > ω_0, where ω_0 is a characteristic phonon frequency. The corresponding transport scattering rate of electrons is 1/τ_tr = 2π λT, where λ is a dimensionless strength of the electron-phonon coupling. The fact that experimentally measured values satisfy λ <~ 1 is striking---especially because in the conventional theory of metals, λ is not a-priori bounded---and has been noted in the context of a conjectured "Planckian" bound on transport. The appeal of such a universal bound is that, if correct, it might also govern the strange metallic behavior observed in a variety of correlated electron materials, which exhibit T-linear resistivity extending down to low temperatures T << ω_0, the microscopic origin of which remains a matter of heated debate. |
Monday, March 6, 2023 12:42PM - 1:18PM |
B24.00003: Electron-electron and electron-phonon contributions to scattering in strange metals Invited Speaker: Andrew Mackenzie A central question in the analysis of strange metal transport is whether the scattering mechanism is dominantly elastic or inelastic [1]. In the high temperature region, this is essentially a question of whether electron-electron or electron-phonon scattering dominates. I will argue that this issue can be addressed by measurement and analysis of the temperature-dependent Lorenz ratio of correlated electron metals, and comparison with that of metals in which electron-phonon scattering is known to be very strong. |
Monday, March 6, 2023 1:18PM - 1:54PM |
B24.00004: Evidence of good quasiparticles with Plankian scattering Invited Speaker: Brad J Ramshaw Strange metals have strange resistivity: linear-in-temperature (T-linear) down to low temperature. Strange metals are found in many families of correlated electron materials, leading to the conjecture that a universal bound - the "Planckian" bound - limits the scattering rate of electrons to a value set by fundamental constants [1]. If the Planckian bound exists, it would provide a natural explanation for why a host of seemingly disparate systems, including high-temperature superconductors and twisted bilayer graphene, all have T-linear resistivity. Perhaps most dramatically, T-linear resistivity suggests that electron-electron interactions are so strong that conventional concepts such as quasiparticles and Boltzmann transport do not apply in strange metals [2]. We have measured the angle-dependent magnetoresistance (ADMR) of Nd-LSCO: a strange metal with perfectly T-linear resistivity down low temperature. We find two remarkable results: 1) we can model our entire data set using Boltzmann transport and a conventional Fermi surface [3]; and 2) we extract a transport scattering rate that saturates the Planckian bound [4]. We show that our extracted Fermi surface and scattering rate are quantitatively consistent with other transport properties, including the Hall effect and the high-field magnetoresistance. These results suggest that quasiparticles are alive and well in this strange metal, despite T-linear resistivity and a scattering rate that saturates the Planckian bound. We present a new idea involving "strange scatterers", originating from two-level systems, that can produce strange-metal behaviour in an otherwise conventional metal, pointing to a resolution of the apparent contraction of Planckian scattering in a metal where Boltzmann transport works. |
Monday, March 6, 2023 1:54PM - 2:30PM |
B24.00005: Electrons with Planckian scattering obey standard orbital motion in a magnetic field Invited Speaker: Gael Grissonnanche In various so-called strange metals, electrons undergo Planckian dissipation [1,2], a strong and anomalous scattering that grows linearly with temperature [3], in contrast to the quadratic temperature dependence expected from the standard theory of metals. In some cuprates [4,5] and pnictides [6], a linear dependence of the resistivity on magnetic field has also been considered anomalous – possibly an additional facet of Planckian dissipation. Here we show that the resistivity of the cuprate strange metals Nd0.4La1.6-xSrxCuO4 [7] and La2-xSrxCuO4 [8] is quantitatively consistent with the standard Boltzmann theory of electron motion in a magnetic field, in all aspects – field strength, field direction, temperature, and disorder level. The linear field dependence is found to be simply the consequence of scattering rate anisotropy. We conclude that Planckian dissipation is anomalous in its temperature dependence but not in its field dependence. The scattering rate in these cuprates does not depend on field, which means their Planckian dissipation is robust against fields up to at least 85 T. |
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