404 research outputs found
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 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 .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 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 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
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