In a class of type II superconductor films, the critical current is determined by the Bean-Livingston barrier posed by the film surfaces to vortex penetration into the sample. A bulk property thus depends sensitively on the surface or interface to an
adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-orbit coupling at their interfaces with adjacent materials. Considering an interface with a magnetic insulator, we find the spontaneous supercurrent resulting from the Zeeman field and interfacial spin-orbit coupling to substantially modify the vortex surface barrier. Thus, we show that the critical currents in superconductor-magnet heterostructures can be controlled, and even enhanced, via the interfacial spin-orbit coupling. Since the latter can be controlled via a gate voltage, our analysis predicts a class of heterostructures amenable to gate-voltage modulation of superconducting critical currents. It also sheds light on the recently observed gate-voltage enhancement of critical current in NbN superconducting films.
In a topological insulator (TI)/magnetic insulator (MI) hetero-structure, large spin-orbit coupling of the TI and inversion symmetry breaking at the interface could foster non-planar spin textures such as skyrmions at the interface. This is observed
as topological Hall effect in a conventional Hall set-up. While this effect has been observed at the interface of TI/MI, where MI beholds perpendicular magnetic anisotropy, non-trivial spin-textures that develop in interfacial MI with in-plane magnetic anisotropy is under-reported. In this work, we study Bi$_2$Te$_3$/EuS hetero-structure using planar Hall effect (PHE). We observe planar topological Hall and spontaneous planar Hall features that are characteristic of non-trivial in-plane spin textures at the interface. We find that the latter is minimum when the current and magnetic field directions are aligned parallel, and maximum when they are aligned perpendicularly within the sample plane, which maybe attributed to the underlying planar anisotropy of the spin-texture. These results demonstrate the importance of PHE for sensitive detection and characterization of non-trivial magnetic phase that has evaded exploration in the TI/MI interface.
The gate-voltage-induced suppression of critical currents in metallic superconductors observed recently [De Simoni et al., Nat. Nanotechnol. 13, 802 (2018)] has raised crucial questions regarding the nature and mechanism of the electric field effect
in these systems. Here, we demonstrate an enhancement of up to 30 % in critical current in the type II superconductor NbN, micro- and nano superconducting bridges, tunable via a back-gate voltage. Our suggested plausible mechanism of this enhancement in critical current based on surface nucleation and pinning of Abrikosov vortices is consistent with expectations and observations for type-II superconductor films with thicknesses comparable to their coherence length. Furthermore we demonstrate infinite electroresistance and a hysteretic resistance dependence on the applied electric field which could lead to logic and memory applications in a superconductors-based low-dissipation digital computing paradigm. Our work thus provides the first demonstration of an electric field enhancement in the superconducting property in metallic superconductors, constituting a crucial step towards understanding of electric field-effects on the fundamental properties of a superconductor and its exploitation for future technologies.
The Weyl semi-metal candidate MoTe$_{2}$ is expected to exhibit a range of exotic electronic transport properties. It exhibits a structural phase transition near room temperature that is evident in the thermal hysteresis in resistivity and thermopowe
r (Seebeck coefficient) as well as large spin-orbit interaction. Here, we also document a resistivity anomaly of up to 13% in the temperature window between 25 and 50 K, which is found to be strongly anisotropic. Based on the experimental data in conjunction with density functional theory calculations, we conjecture that the anomaly can be related to the presence of defects in the system. These findings open opportunities for further investigations and understanding of the transport behavior in these newly discovered semi-metallic layered systems.
Magnetic tunnel junctions comprising of an insulator sandwiched between two ferromagnetic films are the simplest spintronic devices. Theoretically, these can be modeled by a metallic Hamiltonian in both the lattice and the continuum with an addition
of Zeeman field. We calculate conductance at arbitrary orientations of the easy axes of the two ferromagnets. When mapped, the lattice and the continuum models show a discrepancy in conductance in the limit of a large Zeeman field. We resolve the discrepancy by modeling the continuum theory in an appropriate way.
