16,111 research outputs found
Rashba spin-orbit interaction enhanced by graphene in-plane deformations
Graphene consists in a single-layer carbon crystal where 2 electrons
display a linear dispersion relation in the vicinity of the Fermi level,
conveniently described by a massless Dirac equation in spacetime.
Spin-orbit effects open a gap in the band structure and offer perspectives for
the manipulation of the conducting electrons spin. Ways to manipulate
spin-orbit couplings in graphene have been generally assessed by proximity
effects to metals that do not compromise the mobility of the unperturbed system
and are likely to induce strain in the graphene layer. In this work we explore
the gauge fields that result from the uniform
stretching of a graphene sheet under a perpendicular electric field.
Considering such deformations is particularly relevant due to the
counter-intuitive enhancement of the Rashba coupling between 30-50% for small
bond deformations well known from tight-binding and DFT calculations. We report
the accessible changes that can be operated in the band structure in the
vicinity of the K points as a function of the deformation strength and
direction.Comment: 10 pages, 7 figure
Orthogonality Relations and Supercharacter Formulas of U(m|n) Representations
In this paper we obtain the orthogonality relations for the supergroup
U(m|n), which are remarkably different from the ones for the U(N) case. We
extend our results for ordinary representations, obtained some time ago, to the
case of complex conjugated and mixed representations. Our results are expressed
in terms of the Young tableaux notation for irreducible representations. We use
the supersymmetric Harish-Chandra-Itzykson-Zuber integral and the character
expansion technique as mathematical tools for deriving these relations. As a
byproduct we also obtain closed expressions for the supercharacters and
dimensions of some particular irreducible U(m|n) representations. A new way of
labeling the U(m|n) irreducible representations in terms of m + n numbers is
proposed. Finally, as a corollary of our results, new identities among the
dimensions of the irreducible representations of the unitary group U(N) are
presented.Comment: 56 pages, LaTeX, changes only in the writing of the titl
Infinite charge mobility in muscovite at 300K
Evidence is presented for infinite charge mobility in natural crystals of
muscovite mica at room temperature. Muscovite has a basic layered structure
containing a flat monatomic sheet of potassium sandwiched between mirror
silicate layers. It is an excellent electrical insulator. Studies of defects in
muscovite crystals indicated that positive charge could propagate over great
distances along atomic chains in the potassium sheets in absence of an applied
electric potential. The charge moved in association with anharmonic lattice
excitations that moved at about sonic speed and created by nuclear recoil of
the radioactive isotope K40. This was verified by measuring currents passing
through crystals when irradiated with energetic alpha particles at room
temperature. The charge propagated more than 1000 times the range of the alpha
particles of average energy and 250 times the range of channelling particles of
maximum energy. The range is limited only by size of the crystal.Comment: 6 pages, 8 figure
Antiresonances as precursors of decoherence
We show that, in presence of a complex spectrum, antiresonances act as a
precursor for dephasing enabling the crossover to a fully decoherent transport
even within a unitary Hamiltonian description. This general scenario is
illustrated here by focusing on a quantum dot coupled to a chaotic cavity
containing a finite, but large, number of states using a Hamiltonian
formulation. For weak coupling to a chaotic cavity with a sufficiently dense
spectrum, the ensuing complex structure of resonances and antiresonances leads
to phase randomization under coarse graining in energy. Such phase
instabilities and coarse graining are the ingredients for a mechanism producing
decoherence and thus irreversibility. For the present simple model one finds a
conductance that coincides with the one obtained by adding a ficticious voltage
probe within the Landauer-Buettiker picture. This sheds new light on how the
microscopic mechanisms that produce phase fluctuations induce decoherence.Comment: 7 pages, 2 figures, to appear in Europhys. Let
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