Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G56: Strange Metals |
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Sponsoring Units: DCMP Chair: Yu He Room: Mile High Ballroom 2C |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G56.00001: Coexisting Strange Metal and Fermi Liquid Collective Excitations in Sr2RuO4 Ali Husain, Matteo Mitrano, Melinda S Rak, Samantha Rubeck, Hongbin Yang, Fumihiko Nakamura, Chanchal Sow, Yoshiteru Maeno, Philip Edward Batson, Peter Abbamonte The strange metal is an enigmatic phase found in numerous strongly correlated systems distinguished by violations of Fermi liquid and Boltzmann transport theories. Using momentum-resolved EELS (M-EELS), we previously showed that, while charge excitations of a Fermi liquid are known to propagate as plasmons with well-defined energy and momentum, the strange metal Bi2.1Sr1.9CaCu2O8+x (Bi-2212) exhibits a featureless continuum of non-propagating charge fluctuations exhibiting simple scaling laws. Here, we present M-EELS results on Sr2RuO4 showing that it exhibits both a strange metal continuum and a well-defined low-energy collective mode below 100 meV propagating at near the Fermi velocity. Strikingly, the dispersion of this mode is strongly renormalized at low temperature where transport measurements indicate the onset of Fermi liquid behavior. These results suggest that Sr2RuO4 exhibits a crossover between Fermi liquid-like behavior at low energy and strange metal behavior at high energy, with the two sectors in coexistence. We also present new transmission M-EELS experiments validating the bulk origin of these observations. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G56.00002: Classical Glasses, Black Holes, and Strange Quantum Liquids Davide Facoetti, Giulio Biroli, Jorge Kurchan, David Reichman From the dynamics of a broad class of classical mean-field glass models we construct a quantum model with finite zero-temperature entropy, a quantum transition at zero temperature, and a time-reparametrization (quasi-)invariance in the dynamical equations for correlations. The low eigenvalue spectrum of the resulting quantum model is directly related to the structure and exploration of metastable states in the landscape of the original classical glass model. This mapping reveals deep connections between classical glasses and the properties of SYK-like models. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G56.00003: A hydrodynamical description for transport in the strange metal phase of cuprates Andrea Amoretti High temperature superconductors are strongly coupled systems which present a complicated phase diagram with many intertwined phases appearing at the same time. This makes it difficult to understand the mechanism which generates their singular transport properties (see e.g. [1]). Hydrodynamics, which mostly relies on the symmetries of the system without referring to any specific microscopic mechanism, constitutes a promising framework to analyze these materials. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G56.00004: Strange metallic magnetotransport in electron-doped cuprates Nicholas Poniatowski, Tarapada Sarkar, Pampa R Mandal Sarkar, Richard Greene The infamous linear-in-T resistivity seen in hole-doped cuprates has become the hallmark of strange metallicity, but a more expansive strange metal phenomenology exists in the electron-doped compounds. Linear-in-T resistivity and linear-in-H magnetoresistivity are observed at low temperatures, in stark contrast to conventional Fermi-liquid behavior, and at high temperatures an anomalous T2 resistivity is observed. In this talk, we discuss other signatures of strange metallicity at higher temperatures (50-300 K) in these compounds as evidenced by magnetotransport experiments. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G56.00005: Ubiquitous power law behaviour in the self energy of Strange Metals Steef Smit The high temperature superconducting state in cuprates is born out of the strange metal phase, showing resistivity linear in temperature, contravening Fermi liquid theory for metals. Theoretical understanding of this phase is limited, despite decades of research. Recently, the Anti-de Sitter/Conformal Field Theory (AdS/CFT) approach has been proposed to hold the answer, something we set out to test. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G56.00006: Microscopic origin of the `strange' metal Kyungmin Lee, Aavishkar Patel, Nandini Trivedi, Subir Sachdev We study a disordered Anderson-Hubbard lattice model of strongly interacting fermions. We obtain the space and time dependent electron Green’s function by numerically summing the `melon’ diagrams. We show the emergence of two ``fluids'': (i) a fraction of sites, with weaker hopping than the background, hybridize with a constellation of neighboring sites and nucleate islands, and behave similar to the Sachdev-Ye-Kitaev model; (ii) the remaining background electrons scatter off SYK islands, and display strange metal transport with a linear-in-temperature resistivity, and singular spectral widths down to zero temperature with no coherence scale. |
Tuesday, March 3, 2020 12:27PM - 12:39PM |
G56.00007: Incoherent Strange Metal Sharply Bounded by a Critical Doping in Bi2212 Su-Di Chen, Makoto Hashimoto, Yu He, Dongjoon Song, Kejun Xu, Junfeng He, Thomas Devereaux, Hiroshi Eisaki, Donghui Lu, Jan Zaanen, Zhixun Shen 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”. To study this state, we use angle-resolved photoemission spectroscopy to directly measure its spectral function. 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. This sharp reconstruction signals the incoherent strange metal as a distinct state of matter. 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. This suggests that the pseudogap is a low-temperature phenomenon associated with the incoherent strange metal. |
Tuesday, March 3, 2020 12:39PM - 12:51PM |
G56.00008: The optical conductivity of (K,Rb,Cs)Fe2As2: hidden temperature behaviors and electronic correlations strength Ricardo Lobo We measured the temperature dependence of the optical reflectivity in undoped XFe2As2 iron pnictides, where X = K, Rb, and Cs. A two-Drude analysis of the data quantitatively describes the Kramers-Kronig obtained optical conductiity of all compositions. From this analysis, we extracted the scattering rate and effective mass for each Drude contribution. Both our parameters and the overall optical conductivity are compared to first principles DMFT calculations. We discuss the tempeature behavior of the scattering rate as a funciton of X and show that a hidden linear behavior emerges from the decomposition of the optical conductivity. The comparison of the full optical conductivity to DMFT caculations allows us to infer the evolution of the electronic correlations strength with ionic replacement. |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G56.00009: 13C NMR measurement of θ-(BEDT-TTF)2I3 in non-Fermi liquid region Kazuya Miyagawa, Hideaki Murase, Takuro Sato, Masafumi Tamura, Kazushi Kanoda The BEDT-TTF salts with θ-type molecular arrangement, θ-(BEDT-TTF)2X, which have a triangular lattice show a wide verity of electronic states (charge order insulator, charge glass state, metal) according to monovalent anion, X. Among them, the X=I3 salt is considered to be in a typical metal because quantum oscillations are observed at low temperatures [1]. On the other hand, in the optical spectrum, normal Drude response was not observed above 100 K. So the salt is different from a simple Fermi liquid picture at high temperature [2]. Recently, we report increase of resistance noise near 50 K-180 K, where the resistance exceeds the Mott limit [2,3]. In this study, the 13C NMR spectra and the 1/T2, which captures slow fluctuations in the order of kHz were measured. In the salt showing charged glass, the 1/T2 has a peak, which is thought to be associated with the glass formation process [4]. On the other hand, in X=I3 salt, the temperature dependence of 1/T2 is very weak and the absolute value remained small. There was also no significant increase in linewidth. This means that the spectral density of fluctuation in the kHz range is small. [1] M. Tamura et al., JPSJ (1994). [2] K. Takenaka et al., PRL (2005). [3] T. Sato et al., Nat. Mat. (2019). [4] K. Miyagawa et al., JPSJ (2019). |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G56.00010: Machine learning of non-Fermi liquid transport in quantum critical metals George Driskell, Samuel Lederer, Carsten Bauer, Simon Trebst, Eun-Ah Kim Anomalous transport, such as T-linear resistivity (a hallmark of non-Fermi liquid behavior), is a ubiquitous feature of strongly correlated metallic systems, but famously difficult to understand theoretically. For relevant simple models, the transport computations of even numerically exact Monte Carlo simulations are subject to enormous systematic errors and come at great additional computational cost. Building on earlier work, we apply quantum loop topography (QLT) and supervised learning on quantum Monte Carlo data to examine the Fermi liquid to non-Fermi liquid crossover in models of both Ising nematic and spin density wave quantum criticality. Previous work on these models has demonstrated this crossover using measurements of correlation functions at nonzero imaginary time separation. Our results, using only equal time measurements, show good agreement with these previous results at dramatically lower computational cost. Hence, QLT-based machine learning can accelerate the exploration of parameter space in search for non-Fermi liquid behavior by obviating the need for expensive dynamical measurements. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G56.00011: Normal state properties of quantum-critical metals at finite temperatures Avraham Klein, Yoni Schattner, Erez Berg, Andrey Chubukov Recent years have seen an intense effort to study models of fermionic quantum criticality and superconductivity via sign-problem-free quantum Monte Carlo. These studies found a number of puzzling features, which are in qualitative disagreement with quantum-critical-scaling theories and, in particular, cast doubt on the validity of Eliashberg-type approaches to quantum criticality. I will discuss how thermal fluctuations destroy the nice scaling properties of quantum-critical systems and show that after generalizing Eliashberg theory to account for thermal fluctuations many of the qualitative disagreements vanish. This work provides concrete guidelines for analyzing ongoing numerical work. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G56.00012: Supermetal Hiroki Isobe, Liang Fu We study the effect of electron interaction in an electronic system with a high-order Van Hove singularity, where the density of states shows a power-law divergence. Owing to scale invariance, we perform a renormalization group (RG) analysis to find a nontrivial metallic behavior where various divergent susceptibilities coexist but no long-range order appears. We term such a metallic state as a supermetal. Our RG analysis reveals noninteracting and interacting fixed points, which draws an analogy to the φ4 theory. We further present a finite anomalous dimension at the interacting fixed point by a controlled RG analysis, thus establishing an interacting supermetal as a non-Fermi liquid. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G56.00013: A symmetry-breaking analysis for non-Fermi liquids induced by order fluctuations in correlated electron systems Zhen-Su She, Rong Li Correlated electron systems display multi-order fluctuations, which are thought of the origin for non-Fermi liquids. Here, we present a symmetry-breaking analysis for establishing this relationship. Specifically, we establish a sequence of symmetry-breakings under increasing temperature with varying orders such as density wave, nematicity and loop current in cuprates. In particular, we propose that the underlying order for strange metal (SM) is vortex fluctuation, as a fluctuating loop current excited by thermal fluctuations and field. Furthermore, a theory for scattering rate by multi-order fluctuations is constructed based on a symmetry analysis of multi-dimensional Hamiltonian with elements determined by length order function (i.e. orders' periodicity). It then yields a formula for resistivity, i.e., ρ=ρa+(ρb2+α2T2+β2B2)1/2, capturing the scaling transition from T2 in pseudogap phase to T in SM phase, as well as anomalous magnetoresistance near quantum critical point. We report the validation evidence of dozens of cuprate samples. The most remarkable outcome is the revelation of the role of a length order function in linking macroscopic resistivity to microscopic fluctuating orders, which is essential for understanding anomalous transport in correlated electron systems. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G56.00014: The role of electron-electron collisions for charge and heat transport at intermediate temperatures Woo-Ram Lee, Alexander Finkelstein, Karen Michaeli, Georg Schwiete We study electric, thermal and thermoelectric transport in correlated electron systems in the intermediate temperature regime, in which elastic and inelastic scattering are both important. To this end, we study the Boltzmann equation in the presence of an electric field and a temperature gradient for two cases: First, when electron-electron collisions are treated within the relaxation-time approximation while the full momentum dependence of electron-impurity scattering is included and, second, when the electron-impurity scattering is momentum-independent, but the electron-electron collisions give rise to a momentum-dependent inelastic scattering rate of the Fermi-liquid type. We find that the inelastic relaxation rate enters the electric conductivity and the Seebeck coefficient only when the momentum dependence of the electron-impurity collisions is included. Specifically, we show that inelastic processes only mildly affect the electric conductivity, but can generate a non-monotonic dependence of the Seebeck coefficient on temperature and even a change of sign. Thermal conductivity always depends on the inelastic scattering rate even for a constant elastic relaxation rate. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G56.00015: Charge Transport in the Non-ergodic Extended phase of Quasi-periodic systems Soumi Ghosh, Jyotsna Gidugu, Subroto Mukerjee We study the transport properties and the spectral statistics of a one-dimensional closed quantum system of spinless fermions in a quasi-periodic potential which produces a single particle mobility edge. For such systems, it has been shown that many body eigenstates can be of three different kinds: extended and ETH (energy thermalization hypothesis) obeying (thermal), localized and ETH violating (many body localized) and extended and ETH violating (non-ergodic extended). Here we investigate the non-ergodic extended phase from the point of view of level spacing statistics and charge transport. We calculate the DC conductivity and the low frequency conductivity σ(ω) and show that both are consistent with sub-diffusive transport. This is contrasted with diffusive transport in the thermal phase and blocked transport in the MBL phase. |
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