Shapiro steps in ballistic Josephson junction based on a single Bi2Te2.3Se0.7 nanocrystal

Josephson junctions based on topological insulators are expected to host Majorana-type bound states that promote a 4π-periodic current-phase relationship. One experimental consequence of this periodicity is the absence of odd Shapiro steps in the current-voltage characteristics under microwave radiation. Here, we experimentally study the frequency-dependent amplitude of Shapiro steps in a ballistic Josephson junction involving a 23 nm-thick single nanocrystal of topological insulator Bi2Te2.3Se0.7 connected to two planar Nb-electrodes. We observe a progressive suppression of the first step while decreasing the frequency below 2 GHz. Using the two-channel thermal resistively shunted junction (tRSJ) model, we show that despite a ballistic regime, the overheating phenomena are enough to account for the observed effect. Our results highlight the complex physics of Josephson junctions and underscore that the missing first Shapiro step alone is not a definitive signature of topological superconductivity. Josephson junctions based on topological insulators are expected to host Majorana bound states which are accompanied by the experimental absence of odd Shapiro steps in current-voltage characteristics. Here, the authors investigate Shapiro steps in a ballistic junction with Bi2Te2.3Se0.7, finding that overheating effects, rather than topological superconductivity, are sufficient to explain the suppression of the first step, challenging conventional interpretations.