Transport through a Majorana Island in the Strong Tunneling Regime

In the presence of Rashba spin-orbit coupling, a magnetic field can drive a proximitized nanowire into a topological superconducting phase [R. M. Lutchyn, J. D. Sau, and S. Das Sarma, Phys. Rev. Lett. 105, 077001 (2010). and Y. Oreg, G. Refael, and F. von Oppen, Phys. Rev. Lett. 105, 177002 (2010).]. We study the transport properties of such nanowires in the Coulomb blockade regime. The associated with topological superconductivity Majorana modes significantly modify transport and lead to single-electron coherent transmission through the nanowire—a nonlocal signature of topological superconductivity. In this Letter, we focus on the case of strong hybridization of the Majorana modes with normal leads. The induced by hybridization broadening of the Majorana zero-energy states competes with the charging energy, leading to a considerable modification of the Coulomb blockade in a nanowire contacted by two normal leads. We evaluate the two-terminal conductance as a function of the gate voltage, junctions transmission coefficients, and the geometric capacitance of and the induced superconducting gap in the nanowire.

Figure 1

Panel (a): Schematic plot of the device. Panel (b): Conductance $G$ as a function of the dimensionless gate voltage ${\mathcal{N}}_g$. In a symmetric device $g_1=g_2\equiv g$, conductance reaches $G_0$. Solid (black) curve: Coulomb blockade peak at $g\ll 1$ is a Lorentzian [33] of width given by Eq. (23). Dashed and solid (red) curve: $G({\mathcal{N}}_g)$ at intermediate values of $g$ such that ${\mathrm{\Delta }}_P/E_C\ll 1-g\ll 1$; see Eq. (21) for the width of the maximum and Eq. (22) for the crossover to the weak-tunneling limit. Dot-dashed (blue) curve: $G({\mathcal{N}}_g)$ of a symmetric device in the strong tunneling limit, $E_C(1-g)\ll {\mathrm{\Delta }}_P$. Conductance approaches the unitary limit, exhibiting weak ${\mathcal{N}}_g$-dependent oscillations; see Eq. (20).