Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K44: Quantum Criticality and Strange Metal PhysicsInvited Live Streamed
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Sponsoring Units: DCMP DMP GMAG Chair: Piers Coleman, Rutgers University Room: McCormick Place W-375C |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K44.00001: Extreme strange metal behavior and unconventional superconductivity in YbRh2Si2 Invited Speaker: Mathieu Taupin The heavy fermion compound YbRh2Si2 continues to surprise. It is a key example for beyond-order parameter quantum criticality [1], as evidenced most notably by a jump in the Fermi surface volume at its quantum critical point [2] and dynamical energy-over-temperature scaling in the THz conductivity [3]. We have recently succeeded to expand the temperature range of electrical resistivity measurements down to ultralow temperatures – into the micro-Kelvin regime – and discovered that the strange metal state in YbRh2Si2 is even more extreme than previously known: Linear resistivity extends over 3.5 orders of magnitude in temperature [4]. At even lower temperatures, superconductivity condenses directly out of this strange metal state. We propose that the Cooper pairing is mediated by the same fluctuations that are responsible for the unconventional quantum criticality and discuss possible implications for other strange metal superconductors [4]. |
Tuesday, March 15, 2022 3:36PM - 4:12PM |
K44.00002: Ni3In: a flat band-induced correlated kagome metal Invited Speaker: Linda Ye The notion of an electronic flat band refers to a collectively degenerate set of quantum mechanical eigenstates in periodic solids. The vanishing kinetic energy of flat bands relative to the electron-electron interaction is expected to result in a variety of many-body quantum phases of matter. Despite intense theoretical interest, systematic design and experimental realization of such flat band-driven correlated states in natural crystals have remained a challenge. Here we report the realization of a partially filled flat band in a new single crystalline kagome metal Ni3In. This flat band is found to arise from the Ni-orbital wave functions localized at triangular motifs within the kagome lattice plane, where an underlying destructive interference among hopping paths flattens the dispersion. We observe unusual metallic and thermodynamic responses suggestive of the presence of local fluctuating magnetic moments originating from the flat band states, which together with non-Fermi liquid behavior indicate proximity to quantum criticality. These results demonstrate a lattice and orbital engineering approach to designing flat band-based many-body phenomena that may be applied to integrate correlation with topology and as a novel means to construct quantum criticality. |
Tuesday, March 15, 2022 4:12PM - 4:48PM |
K44.00003: Local quantum criticality in an SU(4) spin-orbital coupled Kondo system Invited Speaker: Chia-Chuan Liu In this talk, I will discuss a theory of quantum criticality in a spin-orbital coupled Kondo system [1]. Electronic localization-delocalization has played a prominent role in realizing beyond-Landau metallic quantum critical points [2-4]. It typically involves local spins induced by strong correlations, with a “small” to “large” jump of the Fermi surface being one of its characteristic features. The involvement of multipolar degrees of freedom opens up a new window into --and novel platforms for the exploration of—unconventional metallic quantum criticality [5]. |
Tuesday, March 15, 2022 4:48PM - 5:24PM |
K44.00004: Quantum criticality and dynamical scaling in a Mn-based kagome metal Invited Speaker: Dalmau Reig-i-Plessis
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Tuesday, March 15, 2022 5:24PM - 6:00PM |
K44.00005: Strange metal behavior of the Hall angle in twisted bilayer graphene Invited Speaker: Marc Bockrath Twisted bilayer graphene (tBLG) with interlayer twist angles near the magic angle ~1.08º hosts flat bands and exhibits correlated states including Mott-like insulators, superconductivity and magnetism. We will discuss our recent measurements on a tBLG device with a twist angle of 0.93º, below the magic angle. We find in addition to Mott-like insulator and superconducting states near half filling, evidence for a novel correlated state at five electrons/moire´ unit cell. Our results reveal that the magic range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG. Out latest measurements of the superconducting phase in tBLG will be discussed. Moreover, we will discuss combined temperature-dependent transport measurements of the longitudinal and Hall resistivities in close to magic-angle tBLG. While the observed longitudinal resistivity follows linear temperature T dependence consistent with previous reports, the Hall resistance shows an anomalous T dependence with the cotangent of the Hall angle ~ T2. Boltzmann theory for quasiparticle transport predicts that both the resistivity and the Hall angle cotangent should have the same T dependence, contradicting the observed behavior. This failure of quasiparticle-based theories is reminiscent of other correlated strange metals such as cuprates. |
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