Kavli Affiliate: Leon Balents
| First 5 Authors: Yishuai Xu, Zhuoliang Ni, Yizhou Liu, Brenden R. Ortiz, Stephen D. Wilson
| Summary:
The kagome lattice provides a fascinating playground to study geometrical
frustration, topology and strong correlations. The newly discovered kagome
metals AV$_3$Sb$_5$ (A=K, Rb, Cs) exhibit various interesting phenomena
including topological band structure and superconductivity. Nevertheless, the
nature of the symmetry breaking in the CDW phase is not yet clear, despite the
fact that it is crucial to understand whether the superconductivity is
unconventional. In this work, we perform scanning birefringence microscopy and
find that six-fold rotation symmetry is broken at the onset of the CDW
transition temperature in all three compounds. Spatial imaging and angle
dependence of the birefringence show a universal three nematic domains that are
120$^circ$ to each other. We propose staggered CDW orders with a relative
$pi$ phase shift between layers as a possibility to explain the three-state
nematicity in AV$_3$Sb$_5$. We also perform magneto-optical Kerr effect and
circular dichroism measurements on all three compounds, and the onset of the
both signals is at the CDW transition temperature, indicating broken
time-reversal symmetry and the existence of the long-sought loop currents in
the CDW phase. Our work strongly constrains the nature of the CDWs and sheds
light on possible unconventional superconductivity in AV$_3$Sb$_5$.
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