[Seminar] Prof. Hiroshi Kontani "Exotic QLC states in Fe-based superconductors, kagome metals, and twisted bilayer graphene"

Speaker

Prof. Hiroshi Kontani - Nagoya University

2004 - present： Associate Professor - Professor, Nagoya University
2000 - 2004： Associate Professor, Saitama University
1999 - 2000： Researcher, Augsburg University
1995 - 2000： Assistant Professor, ISSP, The University of Tokyo
1991 - 1995： Graduate Student, Kyoto University

Title

Exotic QLC states in Fe-based superconductors, kagome metals, and twisted bilayer graphene

Abstract

Various strongly correlated metals exhibit rich quantum liquid crystal (QLC) states, such as the nematic orbital order, the d-wave bond-order and the current order. These QLCs originates from the strong electron correlations. To understand the origin of the QLCs, we focus on the “quantum interference mechanism among spin/valley fluctuations”. This mechanism is important in low-dimensional or geometrically-frustrated strongly correlated metals. Here, we present the recent studies on the following strongly correlated metals with QCL states.

(1) Nematic quantum-critical behaviors in FeSe [1]: We find that the nematic-fluctuation-mediated interaction causes the T-linear resistivity and the strong-coupling superconductivity near the nematic QCP.
(2) Geometrically frustrated kagome metal AV3Sb5 (A=Cs, Rb, K) [2]: We find that the star-of-David CDW originates from the quantum interference between short-range paramagnons thanks to the geometrical frustration. The derived CDW fluctuations mediate anisotropic s-wave SC state, consistently with recent experiments.
(3) XY-type nematicity due to SU(4) fluctuations in Magic-angle-twisted-bilayer graphene (MATBG) [3]: We find that novel XY-type nematic order, in which the director of nematicity is nearly isotropic, is induced by the quantum interference between high-symmetry valley+spin SU(4) fluctuations. 

[1] Y. Yamakawa et al., unpublished; S. Matsubara et al., unpublished.
[2] R. Tazai, Y. Yamakawa, S. Onari, and H. Kontani, Sci. Adv. (2022) (arXiv:2107.05372).
[3] S. Onari and H. Kontani, Phys. Rev. Lett. (2022) (arXiv:2011.01158) 

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