arXiv subjects

V. Kaladzhyan

Publications and source records attributed to V. Kaladzhyan.

4 recordsLinked to original sources

arXiv2019

RKKY interaction on the surface of three-dimensional Dirac semimetals

We study the RKKY interaction between two magnetic impurities located on the surface of a three-dimensional Dirac semimetal with two Dirac nodes in the band structure. By taking into account both bulk and surface contributions to the exchange interaction between the localized spins, we demonstrate that the surface contribution in general dominates the bulk one at distances larger than the inverse node separation due to a weaker power-law decay. We find a strong anisotropy of the surface term with respect to the spins being aligned along the node separation axis or perpendicular to it. In the many impurity dilute regime, this implies formation of quasi-one-dimensional magnetic stripes orthogonal to the node axis. We also discuss the effects of a surface spin-mixing term coupling electrons from spin-degenerate Fermi arcs.

cond-mat.mes-hall↗

arXiv2018

Obtaining Majorana and other boundary modes from the metamorphosis of impurity-induced states: exact solutions via T-matrix

We provide here a new and exact formalism to describe the formation of end, edge or surface states through the evolution of impurity-induced states. We propose a general algorithm that consists of finding the impurity states via the T-matrix formalism and showing that they evolve into boundary modes when the impurity potential goes to infinity. We apply this technique to obtain Majorana states in 1D and 2D systems described by the Kitaev model with point-like and respectively line-like impurities. We confirm our exact analytical results by a numerical tight-binding approach. We argue that our formalism can be applied to other topological models, as well as to any model exhibiting edge states.

cond-mat.mes-hall↗

arXiv2016

Dynamical Shiba states by precessing magnetic moments in an s-wave superconductor

We study theoretically the dynamics of a Shiba state forming around precessing classical spin in an s-wave superconductor. Utilizing a rotating wave description for the precessing magnetic impurity, we find the resulting Shiba bound state quasi-energy and the spatial extension of the Shiba wavefunction. We show that such a precession pertains to dc charge and spin currents flowing through a normal STM tip tunnel coupled to the superconductor in the vicinity of the impurity. We calculate these currents and find that they strongly depend on the magnetic impurity precession frequency, precession angle, and on the position of the Shiba energy level in the superconducting gap. The resulting charge current is found to be proportional to the difference between the electron and hole wavefunctions of the Shiba state, being a direct measure for such an asymmetry. By dynamically driving the impurity one can infer the spin dependence of the Shiba states in the absence of a spin-polarized STM tip

cond-mat.mes-hall↗

arXiv2016

Determining the spin-orbit coupling via spin-polarized spectroscopy of magnetic impurities

We study the spin-resolved spectral properties of the impurity states associated to the presence of magnetic impurities in two-dimensional, as well as one-dimensional systems with Rashba spin-orbit coupling. We focus on Shiba bound states in superconducting materials, as well as on impurity states in metallic systems. Using a combination of a numerical T-matrix approximation and a direct analytical calculation of the bound state wave function, we compute the local density of states (LDOS) together with its Fourier transform (FT). We find that the FT of the spin-polarized LDOS, a quantity accessible via spin-polarized STM, allows to accurately extract the strength of the spin-orbit coupling. Also we confirm that the presence of magnetic impurities is strictly necessary for such measurement, and that non-spin-polarized experiments cannot have access to the value of the spin-orbit coupling.

cond-mat.mes-hall↗