11,056 research outputs found
Manifestation of helical edge states as zero-bias magneto-tunneling-conductance peaks in non-centrosymmetric superconductors
Helical edge states exist in the mixed spin-singlet and -triplet phase of a
noncentrosymmetric superconductor (NCSS) when the pair amplitude (PA) in the
negative helicity band, , is smaller than the PA in the positive
helicity band, , i.e., when the PA in the triplet component is more
than the same in the singlet component. We numerically determine energies of
these edge states as a function of . The presence
of these edge states is reflected in the tunneling process from a normal metal
to an NCSS across a bias energy : (i) Angle resolved spin conductance (SC)
obeying the symmetry shows peaks when the bias energy
equals the available quasiparticle edge state energy provided . (ii) The total SC, , is zero but modulates with for finite
magnetic field . (iii) The zero bias peaks of and total charge
conductance, , at finite split into two at finite for moderate
. (iv) At zero bias, and increase with and show peaks at
where is a characteristic field.Comment: minor changes; one figure is adde
RVB gauge theory and the Topological degeneracy in the Honeycomb Kitaev model
We relate the Z gauge theory formalism of the Kitaev model to the SU(2)
gauge theory of the resonating valence bond (RVB) physics. Further, we
reformulate a known Jordan-Wigner transformation of Kitaev model on a torus in
a general way that shows that it can be thought of as a Z gauge fixing
procedure. The conserved quantities simplify in terms of the gauge invariant
Jordan-Wigner fermions, enabling us to construct exact eigen states and
calculate physical quantities. We calculate the fermionic spectrum for flux
free sector for different gauge field configurations and show that the ground
state is four-fold degenerate on a torus in thermodynamic limit. Further on a
torus we construct four mutually anti-commuting operators which enable us to
prove that all eigenstates of this model are four fold degenerate in
thermodynamic limit.Comment: 12 pages, 3 figures. Added affiliation and a new section,
'Acknowledgements'.Typos correcte
Frequency- and transverse wave-vector-dependent spin Hall conductivity in two-dimensional electron gas with disorder
We determine wave number and frequency dependent spin Hall
conductivity for a disordered two dimensional
electron system with Rashba spin orbit interaction when \q is {\it
transverse} to the electric field. Both the conventional definition of spin
current and its new definition which takes care of the conservation of spins,
have been considered. The spin Hall conductivitivities for both of these
definitions are qualitatively similar. is zero at
and is maximum at and at small but finite whose
value depends on different parameters of the system. Interestingly for , resonates when which are the
wavelength of the electric field's spatial variation and
the length for one cycle of spin precession respectively. The sign of the
out-of-plane component of the electrons' spin flips when the sign of electric
field changes due to its spatial variation along transverse direction. It
changes the mode of spin precession from clockwise to anti-clockwise or {\it
vice versa} and consequently a finite spin Hall current flows in the bulk of
the system.Comment: 6 pages; 6 figures; major changes including the titl
Rolling tachyon solution of two-dimensional string theory
We consider a classical (string) field theory of matrix model which was
developed earlier in hep-th/9207011 and subsequent papers. This is a
noncommutative field theory where the noncommutativity parameter is the string
coupling . We construct a classical solution of this field theory and show
that it describes the complete time history of the recently found rolling
tachyon on an unstable D0 brane.Comment: 19 pages, 2 figures, minor changes in text and additional references,
correction of decay time (version to appear in JHEP.
Phases of a two dimensional large N gauge theory on a torus
We consider two-dimensional large N gauge theory with D adjoint scalars on a
torus, which is obtained from a D+2 dimensional pure Yang-Mills theory on
T^{D+2} with D small radii. The two dimensional model has various phases
characterized by the holonomy of the gauge field around non-contractible cycles
of the 2-torus. We determine the phase boundaries and derive the order of the
phase transitions using a method, developed in an earlier work
(arxiv:0910.4526), which is nonperturbative in the 'tHooft coupling and uses a
1/D expansion. We embed our phase diagram in the more extensive phase structure
of the D+2 dimensional Yang-Mills theory and match with the picture of a
cascade of phase transitions found earlier in lattice calculations
(arxiv:0710.0098). We also propose a dual gravity system based on a
Scherk-Schwarz compactification of a D2 brane wrapped on a 3-torus and find a
phase structure which is similar to the phase diagram found in the gauge theory
calculation.Comment: 28 pages (+ 17 pages of appendix + 6 pages of ref.); 8 figures; (v2)
LaTeX Showkeys command deleted; (v3) refs and minor clarifications added;
emphasized the new proposal for applying holography to nonsupersymmetric
gauge theory; (v4) modified the arguments about holography; (v5) minor
corrections, version appeared in PR
Spin analog of the controlled Josephson charge current
We propose a controlled Josephson spin current across the junction of two
non-centrosymmetric superconductors like CePt_3Si. The Josephson spin current
arises due to direction dependent tunneling matrix element and different
momentum dependent phases of the triplet components of the gap function. Its
modulation with the angle \xi between the noncentrosymmetric axes of two
superconductors is proportional to \sin \xi. This particular dependence on \xi
may find application of the proposed set-up in making a Josephson spin switch.Comment: 4 pages, 1 figure; title is changed; article is rewritte
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