Alladi Ramakrishnan Hall

Quantum Transport in topological superconductor hybrid systems

Bhaskaran Muralidharan

Indian Institute of Technology Bombay

Semiconductor nanowire-superconductor hybrid systems provide a promising platform for
hosting unpaired Majorana fermions and thus realizing fault-tolerant topological qubits. In this talk, starting from
the basic tenets of quantum transport theory, we demonstrate how to adapt the Non-Equilibrium Green’s Function
(NEGF) formalism to model quantum transport in normal (N)-superconductor (S) junctions. We analyze Josephson
junctions based on semiconductor nanowires and derive the Andreev bound state spectrum and current-phase
relations. Recently, [1], and [2] have reported oscillations in the critical supercurrent with an axial magnetic field.
Our simulations indicate that this phenomenon arises from the interference of orbital angular momentum modes
[3,4] of the cylindrical nanowire. We also add disorder and study its effect on the critical current oscillations, with
an aim to gain a thoroughgoing understanding of the experiments. Finally, we also comment on the Majorana modes
in a finite topological superconductor [5], and most importantly the transport signatures that detect them.
[1] K. Gharavi et.al., ArXiv:1405.7455v2, (2014).
[2] Zuo, et. al. Phys. Rev. Lett. 119, 187704 (2017)
[3] P. Sriram et. al., Phys. Rev B, 100, 155431, (2019).
[4] A. Lahiri et.al., Phys Rev B, 98, 125417, (2018).
[5] N. Leumer et.al., ArXiv:1909.10971, (2019).