Tunable magnetic textures in spin valves: From spintronics to Majorana bound states

Abstract

Spin-valve structures in which a change of magnetic configuration is responsible for magnetoresistance led to impressive advances in spintronics, focusing on magnetically storing and sensing information. However, this mature technology also offers versatile control of magnetic textures with usually neglected underlying fringing fields to enable entirely different applications by realizing topologically-nontrivial states. Together with proximity-induced superconductivity in a two-dimensional electron gas with a large g-factor, these fringing fields realized in commercially-available spin valves provide Zeeman splitting, synthetic spin-orbit coupling, and confinement, needed for Majorana bound states (MBS). Detailed support for the existence and control of MBS is obtained by combining accurate micromagnetic simulation of fringing fields used as an input in Bogoliubov de Gennes equation to calculate low-energy spectrum, wavefunction localization, and local charge neutrality. A generalized condition for a quantum phase transition in these structures provides valuable guidance for the MBS evolution and implementing reconfigurable effective topological wires.

Electrical Control of Majorana Bound States Using Magnetic Stripes

“…Therefore, there has been an increasing interest in the use of magnetic textures for the generation of MBS [29][30][31][32][33][34][35][36][37][38][39][40][41]. In particular, the use of locally tunable magnetic fringing fields can enable the realization of both braiding and fusion operations [42][43][44]. The suitability of using synthetic SOC generated by magnetic fringing fields for the creation of MBS in a superconducting carbon nanotube has recently been experimentally demonstrated [45,46].…”

Phase Control of Majorana Bound States in a Topological X Junction

“…A push to seek alternative platforms for topological superconductivity led to the demonstration of robust proximityinduced superconductivity in a two-dimensional electron gas (2DEG) [18][19][20] which offers important opportunities to realize and control MBS [21][22][23][24][25][26][27]. Recent experiments in planar Josephson junctions (JJs) [28][29][30] reveal that topological superconductivity exists over a large parameter space without requiring fine tuning, while demonstrating the key role of superconducting phase to control the topological transition.…”

“…For example, state-of-the art fabrication of superconducting junctions with topological insulators [38] would support fabrication of similar X-shaped junctions. With the progress in tunable magnetic textures used to modify proximity-induced superconductivity [23,27,[39][40][41][42][43][44][45][46][47][48][49], X-shaped junctions could be considered with a reduced role of an applied magnetic field.…”

Topological superconductivity in skyrmion lattices

“…While the latter can change with increasing magnetic field 17 , the existence of topological phases in skyrmion MSH systems is robust against these changes. Our results present the extension to 2D topological superconductors of recent work [32][33][34] which demonstrated that the manipulation of non-collinear magnetic textures imposed on a 2D superconductor-either through the application of an external magnetic field 32 or current 33 , or through quantum engineering 34 -can give rise to a one-dimensional topological superconductor exhibiting localized Majorana zero modes at its ends. Moreover, skyrmion MSH systems provide a unique opportunity to employ JSTS to visualize a necessary requirement for the emergence of topological superconductivity, the existence of induced spin-triplet superconducting correlations.…”