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Presented By: Department of Physics

CM-AMO Seminar | Unconventional Charge Order in Kagome Superconductors

Rafael Fernandes (University of Minnesota)

Materials with an underlying kagome lattice provide a unique window into the collective behavior of interacting electrons. In insulating kagome systems, the magnetic frustration introduced by the kagome lattice can promote exotic magnetic quantum states. In metallic kagome systems, the typical electronic dispersion displays features usually associated with strong correlations and topological phenomena, such as flat bands, Dirac points, and van Hove singularities. Recently, a new family of metallic kagome compounds with chemical formula AV3Sb5 (with A=Cs, K, Rb) has been found to display superconductivity, attracting significant attention from the condensed matter physics community. Interestingly, superconductivity is preceded by the onset of a charge-density wave (CDW), whose transition temperature can be suppressed by pressure, doping, and strain. Moreover, the CDW has been reported to display unusual features, some of which are suggestive of time-reversal symmetry-breaking, which would be consistent with the presence of loop currents. In this talk, I will introduce a phenomenological model, constructed from the low-energy states near the van Hove points, for the complex-valued CDW order parameter. This model features a rich interplay between the real component of the CDW – which describes bond distortions – and its imaginary component – which describes loop currents. As a result, a rich landscape of secondary orders emerges from the possible loop-current patterns, displaying threefold rotational symmetry breaking, ferromagnetism, octupolar magnetic moment, and toroidal magnetic order. I will discuss the experimental manifestations of these different types of CDW, as well as the impact of out-of-plane charge modulation and the interplay with superconductivity.

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