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

Abstract

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 2π-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 4π 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.

Josephson Diode Effect in Parallel-Coupled Double Quantum Dots Connected to Majorana Nanowires

“…Since the MBSs often emerge with the help of spin-orbit interaction, strong magnetic field or magnetic materials, they also play an important role in the research field of spintronics [31]. In recent years, some works have been devoted to the study of Josephson current through a QD connected to two semiconductor nanowires hosting MBSs (MNWs) [32][33][34][35][36], which are stimulated by the interesting results found in various system composed of QDs connected to superconductors with normal phase [37][38][39][40][41][42][43][44][45][46]. It was shown that the Josephson current driven by the topological phase difference is quite stronger than that by normal phase difference, and the bent angle formed by the two MNWs as well as the magnetic fields in the QD will significantly suppress the Josephson current [32,33].…”

“…Until now, there are two limitations in previous work on Josephson current through MNWs-QD-MNWs systems: one is that only the current's magnitude and period were studied, whereas less attention has been paid on the control of its direction [32][33][34][35][36]; the other is that only single QD was proposed to be inserted between two MNWs, and the interesting quantum interference effect was left untouched [14,16,20,21,38,[40][41][42][43]46,47]. In view of these, we propose a structure composed of parallel double QDs (DQDs) sandwiched between the left and right MNWs to achieve the JDE based on quantum interference effect arising from the two transport paths through the DQDs, as well as the magnetic flux penetrating through the loop, which is shown in Figure 1.…”