8,014 research outputs found
Self heating and nonlinear current-voltage characteristics in bilayer graphene
We demonstrate by experiments and numerical simulations that the
low-temperature current-voltage characteristics in diffusive bilayer graphene
(BLG) exhibit a strong superlinearity at finite bias voltages. The
superlinearity is weakly dependent on doping and on the length of the graphene
sample. This effect can be understood as a result of Joule heating. It is
stronger in BLG than in monolayer graphene (MLG), since the conductivity of BLG
is more sensitive to temperature due to the higher density of electronic states
at the Dirac point.Comment: 9 pages, 7 figures, REVTeX 4.
Effect of spin orbit scattering on the magnetic and superconducting properties of nearly ferromagnetic metals: application to granular Pt
We calculate the effect of scattering on the static, exchange enhanced, spin
susceptibility and show that in particular spin orbit scattering leads to a
reduction of the giant moments and spin glass freezing temperature due to
dilute magnetic impurities. The harmful spin fluctuation contribution to the
intra-grain pairing interaction is strongly reduced opening the way for BCS
superconductivity. We are thus able to explain the superconducting and magnetic
properties recently observed in granular Pt as due to scattering effects in
single small grains.Comment: 9 pages 3 figures, accepted for publication in Phys. Rev. Letter
Energy relaxation in graphene and its measurement with supercurrent
We study inelastic energy relaxation in graphene for low energies to find out
how electrons scatter with acoustic phonons and other electrons. By coupling
the graphene to superconductors, we create a strong dependence of the measured
signal, i.e.,\ critical Josephson current, on the electron population on
different energy states. Since the relative population of high- and low-energy
states is determined by the inelastic scattering processes, the critical
current becomes an effective probe for their strength. We argue that the
electron-electron interaction is the dominant relaxation method and, in our
model of two-dimensional electron-electron scattering, we find a scattering
time ps at T=500 mK, 1-2 orders of magnitude smaller than
predicted by theory.Comment: 10 pages, 13 figures submitted to Physical Review
Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
We have studied electronic conductivity and shot noise of bilayer graphene
(BLG) sheets at high bias voltages and low bath temperature K. As a
function of bias, we find initially an increase of the differential
conductivity, which we attribute to self-heating. At higher bias, the
conductivity saturates and even decreases due to backscattering from optical
phonons. The electron-phonon interactions are also responsible for the decay of
the Fano factor at bias voltages V. The high bias electronic
temperature has been calculated from shot noise measurements, and it goes up to
K at V. Using the theoretical temperature dependence of BLG
conductivity, we extract an effective electron-optical phonon scattering time
. In a 230 nm long BLG sample of mobility
cmVs, we find that decreases with increasing
voltage and is close to the charged impurity scattering time fs
at V.Comment: 7 pages, 7 figures. Extended version of the high bias part of version
1. The low bias part is discussed in arXiv:1102.065
Noether Symmetry of the Hyperextended Scalar Tensor theory for the FLRW models
We study in which conditions the Hyperextended Scalar Tensor theory in an
FLRW background admits a Noether symmetry and derive the vectors field
generating it.Comment: 11 page
A note on the Gauss decomposition of the elliptic Cauchy matrix
Explicit formulas for the Gauss decomposition of elliptic Cauchy type
matrices are derived in a very simple way. The elliptic Cauchy identity is an
immediate corollary.Comment: 5 page
Superconductivity and spin-glass like behavior in system with Pd sheet sandwiched between graphene sheets
Pd-metal graphite (Pd-MG) has a layered structure, where each Pd sheet is
sandwiched between adjacent graphene sheets. DC magnetization and AC magnetic
susceptibility of Pd-MG have been measured using a SQUID magnetometer. Pd-MG
undergoes a superconducting transition at ( K). The
superconductivity occurs in Pd sheets. The relaxation of (aging),
which is common to spin glass systems, is also observed below . The
relaxation rate shows a peak at a characteristic time , which is
longer than a wait time . The irreversibility between and
occurs well above . The susceptibility obeys a
Curie-Weiss behavior with a negative Curie-Weiss temperature ( K). The growth of antiferromagnetic order is limited by the
disordered nature of nanographites, forming spin glass-like behavior at low
temperatures in graphene sheets.Comment: 21 pages, 15 figures; submitted to J. Phys.: Condensed Matte
Dynamical study of the empty Bianchi type I model in generalised scalar-tensor theory
A dynamical study of the generalised scalar-tensor theory in the empty
Bianchi type I model is made. We use a method from which we derive the sign of
the first and second derivatives of the metric functions and examine three
different theories that can all tend towards relativistic behaviours at late
time. We determine conditions so that the dynamic be in expansion and
decelerated at late time.Comment: 18 pages, 3 figures, to appear in General Relativity and Gravitatio
Superconductivity in ferromagnetic metals and in compounds without inversion centre
The symmetry properties and the general overview of the superconductivity
theory in the itinerant ferromagnets and in materials without space parity are
presented. The basic notions of unconventional superconductivity are introduced
in broad context of multiband superconductivity which is inherent property of
ferromagnetic metals or metals without centre of inversion.Comment: 38 pages, no figure
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