Simultaneous formation of two-fold rotation symmetry with charge order in the kagome superconductor CsV3Sb5 by optical polarization rotation measurement

Anomalous enhancement of charge density wave in kagome superconductor CsV3Sb5 approaching the 2D limit

“…This can be intimately related to the observed giant anomalous Hall effect 45 , 46 . Moreover, a nematic ordering emerging from this CDW was suggested in STM 33 , magneto-resistance 34 , and optical investigations 42 , 43 . All the evidences tend to suggest a possible loop current ordering 29 , 43 , 44 with an electronic origin.…”

“…Scanning tunneling microscopy (STM) measurements proposed a 2 × 2 in-plane 26 , 37 , 38 and a 2 × 2 × 2 three-dimensional (3D) 28 , 39 reconstruction and chiral nature of the CDW ordering 26 . In addition, recent zero-field muon spin relaxation (μSR) measurements revealed an enhanced relaxation rate 40 , 41 and the optical signatures including the polarization rotation and the magneto-optical Kerr effect were observed 42 – 44 , implying an intrinsic time-reversal symmetry breaking. This can be intimately related to the observed giant anomalous Hall effect 45 , 46 .…”

Theory of nematic charge orders in kagome metals

“…Other measurements have confirmed that the CO observed in kagome metals breaks time-reversal symmetry (TRS), suggesting the three order parameters ∆ j to be complex. The breaking of TRS is confirmed by µSR experiments [26,38,39], by the detection of a giant anomalous Hall effect [40,41], and by magneto-optical Kerr measurements [28,31,42], even if more recent analyses question these observations [43][44][45]. The absence of magnetic ordering together with broken TRS suggested an orbital current state as a possible candidate for this phase, akin to the ones described by the Haldane model on the honeycomb lattice or by the Varma model on the Lieb lattice [46,47].…”

“…nuclear magnetic resonance (NMR) [25], muon-spin relaxation/rotation (µSR) [26], polarization resolved Raman spectroscopy [27] and optical polarization rotation [28] have confirmed that CO in AV 3 Sb 5 (A =K, Rb, Cs) has only twofold (C 2 ) symmetry, which is believed to be connected to electronic nematicity. This is also related to the chiral nature of the state, i.e., the broken in-plane mirror symmetry, which has been observed by measuring the electronic magnetochiral anisotropy [29].…”

“…This way of lowering the rotational symmetry can be regarded as "weak" nematicity, as opposed to the "strong" one which is found at much lower temperatures than the CO, T nem ∼ 30K [25,34], where the system explicitly breaks the sixfold rotational symmetry of each kagome layer. Thus, for a twodimensional kagome lattice, the "weak" nematic regime would be characterized by A different perspective on this topic is provided by a recent optical polarization rotation measurement performed on CsV 3 Sb 5 , which shows the nematic CO to already be stable at the transition temperature for the translational symmetry breaking [28], questioning the interpretation above. This observation would imply the presence of a nematic metal above T C (at the transition point, the ordered state must inherit the point group symmetries of the high-temperature phase [35]), which might be related to anisotropic fluctuations of the order parameters [36,37].…”