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 G24: Experimental and theoretical advances on strange metalsInvited
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Sponsoring Units: DCMP Chair: Subir Sachdev, Harvard University Room: Room 237 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G24.00001: Gifts from anomalies: optical conductivity of metallic quantum critical points and other exact results Invited Speaker: Dominic Else The optical conductivity of strange metals appears to display a "scale-invariant'' form as a function of frequency and temperature. Although this is traditionally interpreted as a signature of quantum criticality, such an interpretation requires careful scrutiny, as it implies that the infrared renormalization group fixed-point theory that controls the quantum criticality must have a non-trivial frequency dependence of the optical conductivity. In this talk, I will present our results on optical transport in a model of a Landau ordering transition in metallic system, where strong fluctuations of a bosonic order parameter destroy the quasiparticles. We demonstrate that exact, non-perturbative results can be obtained for optical transport, and some other quantities, in such "Hertz-Millis" theories, by leveraging the large emergent symmetry and anomaly structure. In particular, we show that in the infrared limit, the boson self energy at zero wave vector, q=0, is a constant independent of frequency, and the real part of the optical conductivity, σ(ω), is purely a delta function Drude peak with no other corrections. Therefore, further frequency dependence in the boson self energy or optical conductivity can only come from irrelevant operators in a clean system. By contrast, in a modified version of the model with N flavors that has been discussed in past literature, we show that, in the large-N limit, there is a non-trivial optical conductivity in the infrared fixed point. |
Tuesday, March 7, 2023 12:06PM - 12:42PM |
G24.00002: Shot noise indicates the lack of quasiparticles in a strange metal Invited Speaker: Douglas Natelson Understanding of strange metal properties, observed in materials from the high-temperature superconductors to heavy fermion metals and van der Waals structures, is an outstanding challenge. In conventional metals, current is carried by quasiparticles with charge of magnitude e, and while it has been suggested that quasiparticles are absent in strange metals, direct experimental evidence is lacking. We examine short, diffusive nanowires of the heavy fermion strange metal YbRh2Si2 and discover strongly suppressed shot noise compared to conventional metals. In contrast, shot noise measurements in short, diffusive gold nanowires are consistent with theoretical expectations for Fermi liquids. Using Johnson-Nyquist noise measurements in long wires, we find an electron-phonon coupling in this material comparable to that of gold, confirming that the suppression of noise seen in the strange metal samples is not due to electron-phonon effects. Shot noise probes the effective charge, or the granularity of the current-carrying excitations. With no other known mechanism to suppress the shot noise, the experimentally observed suppression implies that the current is not carried by well-defined quasiparticles in YbRh2Si2. Our work sets the stage for similar studies on other strange metals to test the universality of this result, and for future experiments at lower temperatures to examine the shot noise as the material is field-tuned between the Fermi liquid and strange metal regimes. |
Tuesday, March 7, 2023 12:42PM - 1:18PM |
G24.00003: Universal theory of strange metals from spatially random interactions Invited Speaker: Aavishkar A Patel Non-Fermi liquid metallic phases (also known as strange metals) are widespread in two-dimensional or quasi two-dimensional materials with strongly correlated electrons, displaying electrical resistances that famously vary linearly with temperature (T) at low temperatures, in stark contrast to the higher powers of temperature predicted by Fermi liquid theory. This robust phenomenon, as well as other experimental observations, suggest that electrons must undergo inelastic collisions that do not conserve momentum, i.e. spatial disorder affects the interactions between electrons. I will describe a body of theoretical work on the controlled computation of the transport properties of non-Fermi liquids, allowing for the careful consideration of the role of interactions, disorder, and disordered interactions, culminating in a realistic and universal model for the ubiquitous T-linear resistivity. I will also present results from large scale sign-free hybrid quantum Monte Carlo simulations of the models studied theoretically, which support the theoretical results. Additionally, connections between these models and recent experiments on non-Fermi liquids involving phenomena such as cyclotron resonances and current shot noise will be discussed. |
Tuesday, March 7, 2023 1:18PM - 1:54PM |
G24.00004: Critical metallic phase in the overdoped random t-J model Invited Speaker: Maria Tikhanovskaya We investigate a model of electrons with random and all-to-all hopping and spin exchange interactions, with a constraint of no double occupancy. The model is studied in a Sachdev-Ye-Kitaev-like large-M limit with SU(M) spin symmetry. The saddle point equations of this model are similar to appoximate dynamic mean field equations of realistic, non-random, t-J models. |
Tuesday, March 7, 2023 1:54PM - 2:30PM |
G24.00005: Strange metals, from phenomenology to models: reconciling spectroscopy, thermodynamics and transport Invited Speaker: Antoine Georges I will discuss the remarkable implications of a `Planckian' T-linear scattering rate for optical spectroscopy and thermoelectric properties, and confront these predictions to measurements of the Seebeck coefficient and optical response of cuprates in the strange metal regime. I will show how the scaling of the optical conductivity can be reconciled with resistivity and specific heat measurements. I will also review recent works which support the existence of a quantum phase transition at a critical doping doping between two metallic phases in models of a doped Mott insulator with random exchange. At this quantum critical point, the Fermi surface undergoes a volume change and `Planckian' behaviour is found. |
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