Superconducting diode effect in a van der Waals trigonal superconductor

Noncentrosymmetric superconductors can exhibit a range of intriguing physical phenomena and functionalities. One example is the superconducting diode effect (SDE), which is a complete rectification effect between the superconducting and normal currents depending on the current direction. Symmetry must play important roles in the emergence of SDE but the effect of crystal symmetry, particularly in the context of SDE without time-reversal symmetry breaking, is still elusive. In this work, we report the rectification effect in a van der Waals layered superconductor PbTaSe₂ with a noncentrosymmetric trigonal structure. Firstly, we investigated the second harmonic nonlinear voltage without magnetic field, in the unstrained PbTaSe₂. By carefully examining the current directional dependence, we found that the signals are consistent with the crystal symmetry. Secondly, we investigated the SDE in the PbTaSe₂. The SDE is demonstrated exclusively in a strained PbTaSe₂ device while it is absent in an unstrained one, implying the critical role of broken threefold rotational symmetry induced by the strain. Furthermore, the zero-field or magnetic field-even (magnetic field-odd) SDE is demonstrated when the device is strained and current flows in the armchair (zigzag) direction. This current directional and magnetic field dependence is consistent with the crystal symmetry, providing firm evidence that the observed SDE is intrinsic to the material. Our findings offer a fundamental approach to probing symmetry-related effects in superconductors and open a promising pathway toward realizing field-free superconducting diodes.