Tunable Josephson Current through a Semiconductor Quantum Dot Hybridized to Majorana Trijunction

We investigate theoretically the Josephson current through one semiconductor quantum dot (QD) coupled to triple nanowires (junctions) with Majorana bound states (MBSs) prepared at their ends. We find that not only the strength but also the period of the Josephson current flowing between the left and right Josephson junctions via the dot can be fully controlled in terms of the third junction side-coupled to the QD. When the phase factor is zero in the third junction, which acts as a current regulator, the Josephson current is a 2 pi-period function of the difference in phases of the left and right junctions. Now, the magnitude of the current is suppressed by hybridization between the QD and the regulator junction. The period of the current becomes 4 pi under the condition of nonzero phase factor in the regular junction, and thus either the magnitude or the sign (flow direction) of the current can be controlled in this trijunction device. This is difficult to realize in the usual tow-terminal structure. It is also found that the direct overlap between the MBSs in the regulator junction generally enhances the current's amplitude, but those in the left and right Majorana junctions suppress the current. The above results are explained with the help of the device's energy diagram and the current carrying density of states (CCDOS) and might be applied for adjusting the current density in the superconducting coated conductors technologies.

Automated summary

This study theoretically investigates the Josephson current through a single semiconductor quantum dot with Majorana bound states. The strength and period of the Josephson current can be controlled by adjusting the coupling between the quantum dot and a third junction. The results suggest potential applications in adjusting current density in superconducting coated conductors technologies.