Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

Abstract

Topological insulators (TIs) hold great promise for topological quantum computation in solidstate systems. Recently, several groups reported experimental data suggesting that signatures of Majorana modes have been observed in topological insulator Josephson junctions (TIJJs). A prerequisite for the exploration of Majorana physics is to obtain a good understanding of the properties of low-energy Andreev bound states (ABS) in a material with topologically non-trivial band structure. Here, we present experimental data and a theoretical analysis demonstrating that the band structure inversion close to the surface of a TI has observable consequences for supercurrent transport in TIJJs prepared on surface-doped Bi 2 Se 3 thin films. Electrostatic carrier depletion of the film surface leads to an abrupt drop in the critical current of such devices. The effect can be understood as a relocation of low-energy ABS from a region deeper in the bulk of the material to the more strongly disordered surface which is driven by the topology of the effective band structure in the presence of surface dopants.

Andreev reflection without Fermi surface alignment in high-Tcvan der Waals heterostructures

“…Due to the large » H 90 T c2 , we do not expect significant shifts in D 0 for the fields applied here (7.5 T) [68]. However, ifnABS emergedue to the small mesas seen in AFM, then their energywill be periodic in the magnetic field as the phase winds through 2π [33][34][35][36]. Using the cross-sectional area of our Bi 2 Sr 2 CaCu 2 O d + 8…”

“…In metals with no attractive potential, one expects [31]and observes [32] a pair amplitude that can result in a minigap, whose size depends on the device geometry and superconducting phase of the contacts. In confined devices, with two superconductors separated by a normal material, Andreev reflection can produce an Andreev bound state(nABS) inside the normal region [32][33][34][35][36]. The nABS can ultimately lead to a supercurrent inside such devices.…”

Topological supercurrents interaction and fluctuations in the multiterminal Josephson effect

“…In recent years the interest in Josephson physics has shifted towards junctions whose elements include topological materials [16][17][18][19][20][21][22][23][24] or where topological properties are enabled by a specific design of the hybrid junction with otherwise conventional materials [25][26][27][28][29]. These possibilities and advances motivate our work to investigate how universal mesoscopic effects manifest in topological Josephson junctions that, in particular, host Majorana states (see the review in [30] and references therein).…”

Sputtering-induced reemergence of the topological surface state inBi2Se3

“…The surface of Bi 2 Se 3 and other Bi-based topological insulators adsorbs H 2 O, H 2 , or CO molecules upon exposure to air or vacuum rest gas [32][33][34][35]. This introduces a large number of impurity scatterers.…”