Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L50: Quantum Criticality and Exotic Excitations in Strange MetalsInvited Live
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Sponsoring Units: DCMP Chair: Alexei Tsvelik, Brookhaven National Laboratory |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L50.00001: Singular charge fluctuations at a magnetic quantum critical point Invited Speaker: Lukas Prochaska The heavy fermion compound YbRh2Si2 is well known for its large fan of linear-in-temperature “strange metal” resistivity emerging from a quantum critical point at the border of antiferromagnetic order. Previous studies revealed properties [1] that are beyond the description of the Landau framework of order parameter fluctuations, and compatible with a Kondo destruction quantum critical point [2]. Here, we probed the charge dynamics of this system by performing terahertz time-domain transmission spectroscopy experiments on high-quality YbRh2Si2 thin films grown by molecular beam epitaxy. We observe frequency over temperature scaling of the optical conductivity, with a critical exponent close to 1 in agreement with the linear-in-temperature dc resistivity, over a wide temperature and frequency range [3]. This dynamical scaling proves that charge carriers are a central ingredient to the singular physics at the border of antiferromagnetic order, and therefore strongly underpins the Kondo destruction nature of the observed quantum criticality. |
Wednesday, March 17, 2021 8:36AM - 9:12AM Live |
L50.00002: Critical charge fluctuations at the Kondo breakdown of heavy-fermions Invited Speaker: Yashar Komijani Recent experiments on quantum critical materials CeRuIn5, YbRh2Si2 and YbAlB4 have observed a natural coincidence of critical charge and spin fluctuations, a phenomenon that goes beyond the Landau-Ginzburg paradigm. We study these effects in the framework of local quantum criticality and argue that soft charge fluctuations are natural consequences of an abrupt change in Fermi surface volume and the entanglement pattern that accompanies Kondo breakdown in heavy-fermion systems. |
Wednesday, March 17, 2021 9:12AM - 9:48AM Live |
L50.00003: From Dynamical Charge Scaling to Quantum Entanglement at a Kondo Destruction Quantum Critical Point Invited Speaker: Haoyu Hu A prevailing question on quantum criticality is whether and how it goes beyond the Landau framework of order-parameter fluctuations. In the studies of antiferromagnetic heavy fermion metals, the notion of Kondo destruction has been developed to address this issue [1]. Microscopically, the Kondo destruction captures how the inter-local-moment singlet formation dynamically competes with the Kondo-singlet formation at the quantum critical point (QCP). |
Wednesday, March 17, 2021 9:48AM - 10:24AM Live |
L50.00004: Freezing of charge degrees of freedom across a critical point in CeCoIn5 Invited Speaker: James Analytis The presence of a quantum critical point separating two distinct zero-temperature phases is thought to underlie the strange metal state of many high-temperature superconductors. The nature of this quantum critical point, as well as a description of the resulting strange metal, are central open problems in condensed matter physics. In large part, the controversy stems from the lack of a clear broken symmetry to characterize the critical phase transition, and this challenge is no clearer than in the example of the unconventional superconductor CeCoIn5. By direct Hall effect and Fermi surface measurements, in comparison to ab initio calculations, we observe a critical point that connects two Fermi surfaces with different volumes without a finite-temperature symmetry breaking phase transition. Rather, the transition involves an abrupt localization of one sector of the charge degrees of freedom. At low fields and temperatures, this transition causes a divergence in the Hall coefficient that is cut off on diluting either particles or holes. This remarkable behavior is unexpected in the conventional picture of metals but does appear to be a non-trivial prediction of the theory of the fractionalized Fermi liquid. In this framework, the separation of spin and charge leads to a critical point connecting Fermi surfaces with different volumes. |
Wednesday, March 17, 2021 10:24AM - 11:00AM Live |
L50.00005: Metallic Spin Chains: the Effects of Electronic Correlations Invited Speaker: Meigan Aronson Much of what is known about one-dimensional systems comes from theories and experiments that are carried out on insulating spin chain systems where strong correlations localize electron moments, or alternatively on one-dimensional metals where correlations are very weak, and the electron states are fully delocalized. There is considerable evidence in three-dimensional materials that varying the strength of electron correlations can lead to electronic localization, accompanied by T=0 quantum fluctuations between two Fermi surfaces with different sizes, one where electron states are included and one where they are not. We seek experimental evidence that there is an analog of this sort of electronic localization in one-dimensional systems. We focus our search on metallic systems, where the degree of hybridization between moment-bearing electrons and conduction electrons can have different strengths. The first system is Yb2Pt2Pb, where the 1-D chains of Yb moments are only weakly coupled to itinerant states. Fractionalized spinon excitations are observed in neutron scattering measurements, evidence for the one dimensionality of the magnetic subsystem. We present as well measurements on Ti4MnBi2, whose crystal structure features well separated chains of Mn ions. The Curie –Weiss susceptibility reveals that the Mn moments are effective spin S=1/2, while spin-polarized DFT calculations suggest that magnetic order is present, associated with the significantly delocalized dx2-y2 and dxy Mn orbitals. Specific heat and susceptibility measurements find a very broad transition to antiferromagnetism at 1.9 K, accompanied by significant fluctuations that may originate with electronic localization, or with frustration of the magnetic order by low dimensionality. |
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