Anomalous spin textures in a 2D topological superconductor induced by point impurities

Topological superconductors are foreseen as good candidates for the search of Majorana zero modes, where they appear as edge states and can be used for quantum computation. In this context, it becomes necessary to study the robustness and behavior of electron states in topological superconductors when a magnetic or non-magnetic impurity is present. We focus on scattering resonances in the bands and on spin texture to know what the spin behavior of the electrons in the system will be. We find that the scattering resonances appear outside the superconducting gap, thus providing evidence of topological robustness. We also find non-trivial and anisotropic spin textures related to the Dzyaloshinskii-Moriya interaction. The spin textures show a Ruderman-Kittel-Kasuya-Yosida interaction governed by Friedel oscillations. We believe that our results are useful for further studies which consider many-point-impurity scattering or a more structured impurity potential with a finite range

Majorana bound states in a driven quantum dot

We study a periodically driven quantum dot in two different configurations. In the first setup, a quantum dot coupled to a topological superconductor and a normal metal lead. In the second setup, a T-shape quantum dot connected to two topological superconductors and side coupled to a normal metal lead. By a combination of non-equilibrium Green's function techniques and Floquet's formalism, we obtain the quasienergy spectra as a function of the amplitude, frequency, and superconducting phase difference. We show that the states develop unique electronic responses, such as the broken particle-hole symmetry that appears when considering the non-locality of Majorana bound states. Finally, we compute the time-average current and the differential conductance to reveal these spectra signatures through physically measurable magnitudes in the two proposed configurations

Hard diffractive electroproduction, transverse momentum distribution and QCD vacuum structure

We study the impact of the "intrinsic" hadron transverse momentum on the pre-asymptotic behavior of the diffractive electroproduction of longitudinally polarized $\rho$-meson. Surprisingly, we find the onset of the asymptotic regime in this problem to be rather low, Q^2 ~ 10 GeV^2 where power corrections due to the transverse momentum do not exceed 20 % in the amplitude. This drastically contrasts with exclusive amplitudes where the asymptotics starts at much higher Q^2 = 50 - 100 GeV^2. The sources of such unexpected behavior are traced back to some general (the quark-hadron duality) as well as more silent (properties of higher dimensional vacuum condensates) features of QCD.Comment: 27 pages (LaTex), 1 figure (epsfig

Resonant spin-flavour precession of neutrinos and pulsar velocities

Young pulsars are known to exhibit large space velocities, up to $10^3$ km/s. We propose a new mechanism for the generation of these large velocities based on an asymmetric emission of neutrinos during the supernova explosion. The mechanism involves the resonant spin-flavour precession of neutrinos with a transition magnetic moment in the magnetic field of the supernova. The asymmetric emission of neutrinos is due to the distortion of the resonance surface by matter polarisation effects in the supernova magnetic field. The requisite values of the field strengths and neutrino parameters are estimated for various neutrino conversions caused by their Dirac or Majorana-type transition magnetic moments.Comment: 16 pages, LaTex. Corrected calculation of the geometrical factor and temperature derivatives of densities. Final results slightly changed. Replaced to match the published versio

Manipulation of Majorana bound states in proximity to a quantum ring with Rashba coupling

The quest for Majorana zero modes in the laboratory is an active field of research in condensed matter physics. In this regard, there have been many theoretical proposals; however, their experimental detection remains elusive. In this article, we present a realistic setting by considering a quantum ring with Rashba spin-orbit coupling and threaded by a magnetic flux, in contact with a topological superconducting nanowire. We focus on spin-polarized persistent currents to assess the existence of Majorana zero modes. We find that the Rashba spin-orbit coupling allows for tuning the position of the zero energy crossings in the flux parameter space and has sizable effects on spin-polarized persistent currents. We believe that our results will contribute towards probing the existence of Majorana zero modes