Figure 4: Nonreciprocal superconducting transport probed by second harmonic signals in AC magnetoresistance.

(a) Magnetic field dependence of the second harmonic components in the AC resistance (R^2ω) measured from sample 4. Scale bar, 0.5 Ω. Finite R^2ω signals reflecting the symmetry breaking in the chiral structure are observed during the superconducting transition. (b) Temperature dependence of upper critical magnetic field H_c2 and characteristic minimum positions in R^2ω. Each set of minimum positions gradually changes with temperature, showing similar behaviour as the critical magnetic field H_c2. (c–e) Comparative plots of R^ω and R^2ω in low-magnetic field region at T=6, 4 and 2 K. Periodic oscillations were observed for both signals in the superconducting state (2 and 4 K), which disappears rapidly in the normal state (6 K). R^2ω shows the stepwise behaviour at low temperature (2 K). (f) Temperature variation of the resistance and magnitude of the quantum oscillations in R^ω and R^2ω. For R^2ω oscillations, we estimate the magnitude of the jumps which are observed in low-field region. Both oscillating signals are enhanced around T_c.