Time-reversal symmetry broken by charge order in CsV3Sb5

The recently discovered vanadium-based kagome metals AV(3)Sb(5) (A = K, Rb, Cs) exhibit superconductivity at low temperatures and charge density wave (CDW) order at high temperatures. A prominent feature of the charge ordered state in this family is that it breaks time-reversal symmetry (TRSB), which is connected to the underlying topological nature of the band structure. In this work, a powerful combination of zero-field and high-field muonspin rotation/relaxation is used to study the signatures of TRSB of the charge order in CsV3Sb5, as well as its anisotropic character. By tracking the temperature evolution of the in-plane and out-of-plane components of the muon-spin polarization, an enhancement of the internal field width sensed by the muon-spin ensemble was observed below T-TRSB = T-CDW similar or equal to 95 K. Additional increase of the internal field width, accompanied by a change of the local field direction at the muon site from the ab plane to the c axis, was detected below T* similar or equal to 30 K. Remarkably, this two-step feature becomes well pronounced when a magnetic field of 8 T is applied along the crystallographic c axis, thus indicating a field-induced enhancement of the electronic response at the CDW transition. These results point to a TRSB in CsV3Sb5 by charge order with an onset of similar or equal to 95 K, followed by an enhanced electronic response below similar or equal to 30 K. The observed two-step transition is discussed within the framework of different charge-order instabilities, which, in accordance with density functional theory calculations, are nearly degenerate in energy.

Automated summary

The recently discovered vanadium-based kagome metals AV(3)Sb(5) exhibit superconductivity at low temperatures and charge density wave (CDW) order at high temperatures. In this study, the signatures of time-reversal symmetry breaking in the charge order of CsV3Sb5 were investigated using muon-spin rotation/relaxation techniques. The results showed enhanced electronic response below 30 K and a field-induced enhancement of the response at the CDW transition.