Fig. 1. Schematic illustration of nonreciprocal transport in noncentrosymmetric bulk crystals.

(A) I-V curve in the normal state of a noncentrosymmetric crystal, whose nonreciprocal current is usually small. (The dashed line is the linear I-V relation.) Inset: Electron motion in the asymmetric potential, which represents the lack of inversion symmetry. (B) I-V curve in the resistive superconducting state, whose nonreciprocal current is much larger than that of the normal state below the critical current (I_c), whereas it remains unchanged at larger I. Inset: Enhanced nonreciprocity due to the coherence of Cooper pairs.