Majorana states in inhomogeneous spin ladders

We propose an inhomogeneous open spin ladder, related to the Kitaev honeycomb model, which can be tuned between topological and nontopological phases. In extension of Lieb's theorem, we show numerically that the ground state of the spin ladder is either vortex free or vortex full. We study the robustness of Majorana end states (MES) which emerge at the boundary between sections in different topological phases and show that while the MES in the homogeneous ladder are destroyed by single-body perturbations, in the presence of inhomogeneities at least two-body perturbations are required to destabilize MES. Furthermore, we prove that x, y, or z inhomogeneous magnetic fields are not able to destroy the topological degeneracy. Finally, we present a trijunction setup where MES can be braided. A network of such spin ladders provides thus a promising platform for realization and manipulation of MES

Effect of topological length on Bound states signatures in a Topological nanowire

Majorana bound states (MBS) at the end of nanowires have been proposed as one of the most important candidate for the topological qubits. However, similar tunneling conductance features for both the MBS and Andreev bound states (ABS) have turned out to be a major obstacle in the verification of the presence of MBS in semiconductor-superconductor heterostructures. In this article, we use a protocol to probe properties specific to the MBS and use it to distinguish the topological zero-bias peak (ZBP) from a trivial one. For a scenario involving quantized ZBP in the nanowire, we propose a scheme wherein the length of the topological region in the wire is altered. The tunneling conductance signatures can then be utilized to gauge the impact on the energy of the low-energy states. We show that the topological and trivial ZBP behave differently under our protocol, in particular, the topological ZBP remains robust at zero bias throughout the protocol, while the trivial ZBP splits into two peaks at finite bias. This protocol probes the protection of near zero energy states due to their separable nature, allowing us to distinguish between topological and trivial ZBP.Comment: 35 figure

Spin-orbit mediated anisotropic spin interaction in interacting electron systems

We investigate interactions between spins of strongly correlated electrons subject to the spin-orbit interaction. Our main finding is that of a novel, spin-orbit mediated anisotropic spin-spin coupling of the van der Waals type. Unlike the standard exchange, this interaction does not require the wave functions to overlap. We argue that this ferromagnetic interaction is important in the Wigner crystal state where the exchange processes are severely suppressed. We also comment on the anisotropy of the exchange between spins mediated by the spin-orbital coupling.Comment: 4.1 pages, 1 figure; (v2) minor changes, published versio