Unveiling Majorana quasiparticles by a quantum phase transition: Proposal of a current switch

Abstract

We propose a theoretical approach based on an interferometer composed by two quantum dots asymmetrically coupled to isolated Majorana quasiparticles (MQPs), lying on the edges of two topological Kitaev chains, respectively via couplings (t + ∆) and (∆ − t). This setup enables us to probe MQPs in a quite distinct way from the zero-bias peak feature. Most importantly, the system behaves as a current switch made by two distinct paths: (i) for the upper dot connected to both chains, the device perceives both MQPs as an ordinary fermion and the current crosses solely the lower dot, since current in the upper dot is prevented due to the presence of the superconducting gap; and (ii) by suppressing slightly the hybridization of the upper dot with one chain, the current is abruptly switched to flow through this dot, once a trapped electron as a bound state in the continuum (BIC) [Phys. Rev. B 93, 165116 (2016)] appears in the lower dot. Such a current switch between upper and lower dots characterizes the Quantum Phase Transition (QPT) proposed here, being the ratio t/∆ the control parameter of the transition. This QPT is associated with a change from an ordinary fermionic excitation regime to a MQP in the interferometer, which enables not only the fundamental revealing of MQPs, but also yields a current switch assisted by them.

Magnetic Grüneisen parameter for model systems

“…From Eq. 16 we can see that as B → 0, also M → 0, which means that there is no spontaneous magnetization at finite temperature for the 1DI model, as previously stated. Figures 8 and 9 show the behavior of the magnetization when T is held constant and B varies and when B is held constant and T varies, respectively.…”

Spin-dependent coupling between quantum dots and topological quantum wires

“…In this paper we study MBSs formed in a quantum wire with proximity-induced superconductivity near a quantum dot [28][29][30][31][32][33][34][35][36][37], which is also formed inside a quantum wire, all of which are subject to an applied magnetic field perpendicular to the SOI. First calculating the wave functions of the quantum dot and MBSs, which can be done analytically in the strong spin-orbit regime, we are able to find the spin dependence of the quantum dot-MBS coupling which has been largely neglected [21,22,28,29].…”

Majorana oscillations modulated by Fano interference and degree of nonlocality in a topological superconducting-nanowire–quantum-dot system

“…First, at eV = 0, G = e 2 /2h and is independent on the values of |λ 1 | and applied field B. Moreover, differential conductance as function of bias-voltage reveals fractional Fano-like resonances around eV = 0 with intriguing minimal and maximal values equal to e 2 /4h and 3e 2 /4h 31,38 . Similar fractional Fano interference process was already reported by Barański et al 32 in a T-shaped geometry with a QD between metallic and superconducting leads, side-coupled to a MBS.…”

“…is the density of states (DoS) of the leads, T b = 4x/(x + 1) 2 and R b = 1 − T b are the background transmittance and reflectance, respectively 9,38 .…”