206 research outputs found
Erratum: Nodal Cooper-pair stabilized phase dynamics in granular d-wave superconductors
Recently, we discovered a mistake in our Letter on phase dynamics in granular
d-wave superconductors, which we corrected in an Erratum published last week.
This is an expanded version of the Erratum, containing details and supporting
numerical results.Comment: 3 pages, 3 figures, detailed version of the Erratu
The readout of the fullerene-based quantum computing by a scanning tunneling microscope
We consider to detect the electron spin of a doped atom, i.e., a nitrogen or
a phosphorus, caged in a fullerene by currently available technique of the
scanning tunneling microscope (STM), which actually corresponds to the readout
of a qubit in the fullerene-based quantum computing. Under the conditions of
polarized STM current and Coulomb blockade, we investigate the tunneling matrix
elements involving the exchange coupling between the tunneling polarized
electrons and the encapsulated polarized electron, and calculate the variation
of the tunneling current with respect to different orientations of the
encapsulated electron spin. The experimental feasibility of our scheme is
discussed under the consideration of some imperfect factors.Comment: RevTex file, 3 figures. To appear in New Journal of Physic
Spin and Current Variations in Josephson Junctions
We study the dynamics of a single spin embedded in the tunneling barrier
between two superconductors. As a consequence of pair correlations in the
superconducting state, the spin displays rich and unusual dynamics. To properly
describe the time evolution of the spin we derive the effective Keldysh action
for the spin. The superconducting correlations lead to an effective spin
action, which is non-local in time, leading to unconventional precession. We
further illustrate how the current is modulated by this novel spin dynamics
Absence of Wigner Crystallization in Graphene
Graphene, a single sheet of graphite, has attracted tremendous attention due
to recent experiments which demonstrate that carriers in it are described by
massless fermions with linear dispersion. In this note, we consider the
possibility of Wigner crystallization in graphene in the absence of external
magnetic field. We show that the ratio of potential and kinetic energy is
independent of the carrier density, the tuning parameter that usually drives
Wigner crystallization and find out that for given material parameters
(dielectric constant and Fermi velocity), Wigner crystallization is not
possible. We comment on the how these results change in the presence of a
strong external magnetic field.Comment: 3 pages, 1 figure,Submitted for PR
Dynamical magneto-electric coupling in helical magnets
Collective mode dynamics of the helical magnets coupled to electric
polarization via spin-orbit interaction is studied theoretically. The soft
modes associated with the ferroelectricity are not the transverse optical
phonons, as expected from the Lyddane-Sachs-Teller relation, but are the spin
waves hybridized with the electric polarization. This leads to the Drude-like
dielectric function in the limit of zero magnetic
anisotropy. There are two more low-lying modes; phason of the spiral and
rotation of helical plane along the polarization axis. The roles of these soft
modes in the neutron scattering and antiferromagnetic resonance are revealed,
and a novel experiment to detect the dynamical magneto-electric coupling is
proposed.Comment: 5 pages, 1 figur
Detection of the spin character of Fe(001) surface states by scanning tunneling microscopy: A theoretical proposal
We consider the magnetic structure on the Fe(001) surface and theoretically
study the scanning tunneling spectroscopy using a spin-polarized tip (SP-STM).
We show that minority-spin surface states induce a strong bias dependence of
the tunneling differential conductance which largely depends on the orientation
of the magnetization in the SP-STM tip relative to the easy magnetization axis
in the Fe(001) surface. We propose to use this effect in order to determine the
spin character of the Fe(001) surface states. This technique can be applied
also to other magnetic surfaces in which surface states are observed.Comment: 5 pages, 4 figure
Quantum Electronic Transport through a Precessing Spin
The conductance through a local nuclear spin precessing in a magnetic field
is studied by using the equations-of-motion approach. The characteristics of
the conductance is determined by the tunneling matrix and the position of
equilibrium chemical potential. We find that the spin flip coupling between the
electrons on the spin site and the leads produces the conductance oscillation.
When the spin is precessing in the magnetic field at Larmor frequency
(), the conductance develops the oscillation with the frequency of
both and 2 components, the relative spectrum weight of
which can be tuned by the chemical potential and the spin flip coupling.Comment: 5 pages, 3 figure
Minimal Model for Disorder-induced Missing Moment of Inertia in Solid He
The absence of a missing moment inertia in clean solid He suggests that
the minimal experimentally relevant model is one in which disorder induces
superfluidity in a bosonic lattice. To this end, we explore the relevance of
the disordered Bose-Hubbard model in this context. We posit that a clean array
He atoms is a self-generated Mott insulator, that is, the He atoms
constitute the lattice as well as the `charge carriers'. With this assumption,
we are able to interpret the textbook defect-driven supersolids as excitations
of either the lower or upper Hubbard bands. In the experiments at hand,
disorder induces a closing of the Mott gap through the generation of mid-gap
localized states at the chemical potential. Depending on the magnitude of the
disorder, we find that the destruction of the Mott state takes place for
either through a Bose glass phase (strong disorder) or through a direct
transition to a superfluid (weak disorder). For , disorder is always
relevant. The critical value of the disorder that separates these two regimes
is shown to be a function of the boson filling, interaction and the momentum
cut off. We apply our work to the experimentally observed enhancement He
impurities has on the onset temperature for the missing moment of inertia. We
find quantitative agreement with experimental trends.Comment: 9 pages, 5 figures: Extended version of previous paper in which the
pase diagram for the disordered Bose-Hubbard model is computed using
mean-field theory and one-loop RG. The criterion for the Bose glass is
derived explicitly. (a few typos are corrected
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