Nonreciprocal superconducting critical currents with normal state field trainability in kagome superconductor CsV₃Sb₅.

Abstract

Determining time-reversal symmetry (TRS) and chirality in the superconducting state and its relation to normal-state symmetry and topology are important issues in condensed matter physics. Here, we report nonreciprocal superconducting critical currents (I_c) at zero magnetic field in kagome superconductor CsV₃Sb₅ nanodevices: I_c differs for opposite directions, indicating spontaneous TRS and inversion symmetry breakings. The polarity of I_c asymmetry changes randomly in repeated thermal cycling to 300 K, consistent with spontaneous TRS breaking. Crucially, on applying a perpendicular magnetic field above the charge density wave (CDW) transition temperature and then removing it to zero above the superconducting onset temperature (T_c), the polarity of I_c asymmetry follows the field direction, ascertaining that the CDW state has a macroscopic and trainable TRS-breaking directionality. The symmetry breaking continues into the superconducting state and generates the nonreciprocal critical currents. These results provide evidence for the loop-current CDW normal state with TRS breaking in CsV₃Sb₅.