Reappearance of first Shapiro step in narrow topological Josephson junctions

In Josephson junctions, a supercurrent across a nonsuperconducting weak link is carried by electron-hole bound states. Because of the helical spin texture of nondegenerate topological surface states, gapless bound states are established in junctions with topological weak link. These have a characteristic 4π-periodic current phase relation (CΦR) that leads to twice the conventional Shapiro step separation voltage in radio frequency–dependent measurements. In this context, we identify an attenuated first Shapiro step in (Bi0.06Sb0.94)2Te3 (BST) Josephson junctions with AlOx capping layer. We further investigate junctions on narrow, selectively deposited BST nanoribbons, where surface charges are confined to the perimeter of the nanoribbon. Within these junctions, previously identified signatures of gapless bound states are absent. Because of confinement, transverse momentum sub-bands are quantized and a topological gap opening is observed. Surface states within these quantized sub-bands are spin degenerate, which evokes bound states of conventional 2π-periodic CΦR within the BST nanoribbon weak link.

Induced Topological Superconductivity in a BiSbTeSe2-Based Josephson Junction

A 4 π -periodic supercurrent through a Josephson junction can be a consequence of the presence of Majorana bound states. A systematic study of the radio frequency response for several temperatures and frequencies yields a concrete protocol for examining the 4 π -periodic contribution to the supercurrent. This work also reports the observation of a 4 π -periodic contribution to the supercurrent in BiSbTeSe 2 -based Josephson junctions. As a response to irradiation by radio frequency waves, the junctions showed an absence of the first Shapiro step. At high irradiation power, a qualitative correspondence to a model including a 4 π -periodic component to the supercurrent is found.

Shift of Shapiro Step in High Critical Temperature Superconductors

The influence of the charge imbalance effect on a system of intrinsic Josephson junctions of high temperature superconductors under external electromagnetic radiation is investigated. We find that the charge imbalance is responsible for the slope of the Shapiro step in the IV-characteristic. The nonperiodic boundary conditions shift the Shapiro step from the canonical position which is determined by the frequency of the external radiation. We also find how the system parameters influence the shift of the Shapiro step.