Majorana modes with side features in magnet-superconductor hybrid systems

Abstract

Magnet-superconductor hybrid (MSH) systems represent promising platforms to host Majorana zero modes (MZMs), the elemental building blocks for fault-tolerant quantum computers. Theoretical description of such MSH structures is mostly based on simplified models, not accounting for the complexity of real materials. Here, based on density functional theory, we derive a superconducting 80-band model to study an MSH system consisting of a magnetic manganese chain on the s wave superconductor niobium. For a wide range of values of the superconducting order parameter, the system is a topological superconductor, with MZMs exhibiting non-universal spatial patterns and a drastic accumulation of spectral weight on both sides along the magnetic chain. These side feature states can be explained by an effective model which is guided by the ab initio results. Performing scanning tunneling spectroscopy experiments on the same system, we observe a spatial structure in the low-energy local density of states that is consistent with the theoretical findings. Our results open a first-principle approach to the discovery of topological superconductors.

Topological superconductivity from first principles. I. Shiba band structure and topological edge states of artificial spin chains

“…The problem of insufficient modeling of the semiinfinite host appears in most tight-binding approximations. These calculations resulted in an unrealistic gap to match the localization of MZMs [76,77], since the proximity-induced superconducting pairing was introduced into the chain as a parameter and not via an interaction with a superconducting host. The localization length is one of the most important quantities that decides whether the MZMs are separated enough to be feasible for topological quantum computation.…”

Coulomb-assisted nonlocal electron transport between two pairs of Majorana bound states in a superconducting island

“…[2][3][4][5] Experimental efforts to implement the nanowire proposal have uncovered evidence for a zero bias peak in tunneling spectroscopy studies of hybrid superconductor-semiconductor devices. [6][7][8][9][10][11][12][13][14] Despite suggestive observations, however, unambiguous experimental verification remains elusive because zero-bias peaks can also result from non-Majorana sources. [15][16][17][18][19][20][21][22][23][24][25] The signal of current noise cross correlation (CC) could provide a confirmative proof to check existence of MBSs.…”