Magnetic tilting and emergent Majorana spin connection in topological superconductors

Due to the charge neutral and localized nature of surface Majorana modes, detection schemes usually rely on local spectroscopy or interference through the Josephson effect. Here, we theoretically study the magnetic response of a two-dimensional cone of Majorana fermions localized at the surface of class DIII Topological Superconductors. For a field parallel to the surface the Zeeman term vanishes and the orbital term induces a Doppler shift of the Andreev levels resulting in a tilting of the surface Majorana cone. For fields larger than a critical threshold field $H^*$ the system undergoes a transition from type I to type II Dirac-Majorana cone. In a spherical geometry the surface curvature leads to the emergence of the Majorana spin connection in the tilting term via an interplay between orbital and Zeeman, that generates a finite non-trivial coupling between negative and positive energy states. Majorana modes are thus expected to show a finite response to the applied field, that acquires a universal character in finite geometries and opens the way to detection of Majorana modes via time-dependent magnetic fields.Comment: 5 pages Main text, 5 pages Appendix, 3 figures. arXiv admin note: substantial text overlap with arXiv:1802.0920

Electronic dephasing in wires due to metallic gates

The dephasing effect of metallic gates on electrons moving in one quasi--one--dimensional diffusive wires is analyzed. The incomplete screening in this geometry implies that the effect of the gate can be described, at high energies or temperatures, as an electric field fluctuating in time. The resulting system can be considered a realization of the Caldeira-Leggett model of an environment coupled to many particles. Within the range of temperatures where this approximation is valid, a simple estimation of the inverse dephasing time gives $\tau_{\rm G}^{-1} \propto T^{1/2}$.Comment: 6 page

Electron heating and mechanical properties of graphene

The heating of electrons in graphene by laser irradiation, and its effects on the lattice structure, are studied. Values for the temperature of the electron system in realistic situations are obtained. For sufficiently high electron temperatures, the occupancy of the states in the $\sigma$ band of graphene is modified. The strength of the carbon-carbon bonds changes, leading to the emergence of strains, and to buckling in suspended samples. While most applications of `strain engineering' in two dimensional materials focus on the effects of strains on electronic properties, the effect studied here leads to alterations of the structure induced by light. This novel optomechanical coupling can induce deflections in the order of $\sim 50$ nm in micron size samples

Generation and morphing of plasmons in graphene superlattices

Recent experimental studies on graphene on hexagonal Boron Nitride (hBN) have demonstrated that hBN is not only a passive substrate that ensures superb electronic properties of graphene's carriers, but that it actively modifies their massless Dirac fermion character through a periodic moir\'e potential. In this work we present a theory of the plasmon excitation spectrum of massless Dirac fermions in a moir\'e superlattice. We demonstrate that graphene-hBN stacks offer a rich platform for plasmonics in which control of plasmon modes can occur not only via electrostatic gating but also by adjusting e.g. the relative crystallographicComment: 10 pages, 12 figures, 3 appendice