Spin transport and Spin Tunnelling Magneto-Resistance (STMR) of F|NCSC|F spin valve

Abstract

In this work, we study the spin transport at the Ferromagnet|Noncentrosymmetric Superconductor (F|NCSC) junction of a Ferromagnet|Noncentrosymmetric Superconductor|Ferromagnet (F|NCSC|F) spin valve. We investigate the Tunnelling Spin-Conductance (TSC), spin current and Spin Tunnelling Magneto-Resistance (STMR), and their dependence on various important parameters like Rashba Spin-Orbit Coupling (RSOC), strength and orientation of magnetization, an external in-plane magnetic field, barrier strength and a significant Fermi Wavevector Mismatch (FWM) at the ferromagnetic and superconducting regions. The study has been carried out for different singlet-triplet mixing of the NCSC gap parameter. We develop Bogoliubov-de Gennes (BdG) Hamiltonian and use the extended Blonder -Tinkham -Klapwijk (BTK) approach along with the scattering matrix formalism to calculate the scattering coefficients. Our results strongly suggest that the TSC is highly dependent on RSOC, magnetization strength and its orientation, and singlet-triplet mixing of the gap parameter. It is observed that NCSC with moderate RSOC shows maximum conductance for a partially opaque barrier in presence of low external magnetic field. For a strongly opaque barrier and a nearly transparent barrier a moderate value and a low value of field respectively are found to be suitable. Moreover, NCSC with large singlet component is appeared to be useful. In addition, for NCSC with large RSOC and low magnetization strength, a giant STMR (%) is observed. We have also seen that the spin current is strongly magnetization orientation dependent. With the increase in bias voltage spin current increases in transverse direction, but the component along the direction of flow is almost independent. PACS numbers: 67.30.hj, 74.90.+n

Signature of Anomalous Andreev bound states in magnetic Josephson junction of noncentrosymmetric superconductor on a topological insulator

“…The last term in the first square backet of Eq. ( 5) is the contribution due to the RSOC, with V R being the strength of the RSOC and it arises due to the asymmetry of the interface as well as due to NCSC [58][59][60][61][62].…”

“…Since both even and odd frequency correlations are present in NCSC at the same time, so the gap matrix ∆αβ appearing in Eq. ( 2) can be represented as a superposition of the singlet and triplet components [60][61][62], i.e.…”

“…where, k y is the momentum parallel to the interface and Ψ L NCSC (x), Ψ HM (x), Ψ R NCSC (x) are the quasi particle wave functions in the left NCSC, half metal and right NCSC respectively. The wave functions in different layers are obtained by diagonalizing the Hamiltonian (7) and can be written as [62]…”

“…The reasons for considering NCSC are: (i) Coexistence of spin-singlet and spin-triplet superconducting correlations and (ii) the existence of strong Antisymmetric Spin-Orbit Coupling (ASOC) due to the absence of inversion symmetry . Earlier studies indicate that due to the presence of the Rashba Spin-Orbit Coupling (RSOC) the pairing symmetry and hence the transport properties drastically get influenced in NCSC heterostructure [56][57][58][59][60][61][62]. Moreover, it is also reported that the RSOC and singlet-triplet mixing ratio of NCSC play very significant roles in the formation of ABS and supercurrent [72][73][74][75][76][77][78].…”

Spin Torque Oscillator and Magnetization Switching in Double Barrier Rashba Zeeman Magnetic Tunnel Junction

“…These materials have some unique characteristics and also have the ability to trigger insulator to conductor via an exchange field [24] and can also be used as spin filters [25][26][27]. In general, the Rashba SOC (RSOC) is an antisymmetric SOC responsible for splitting of energy sub-bands [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. The impact of RSOC on STOs is worth mentioning, which shows the utilization of RSOC in magnetization switching and also its contribution to self-oscillations in STOs.…”