7,848 research outputs found
Counting Majorana bound states using complex momenta
Recently, the connection between Majorana fermions bound to defects in
arbitrary dimensions, and complex momentum roots of the vanishing determinant
of the corresponding bulk Bogoliubov-de Gennes (BdG) Hamiltonian, has been
established (EPL, 2015, , 67005). Based on this understanding, a
formula has been proposed to count the number () of the zero energy Majorana
bound states, which is related to the topological phase of the system. In this
paper, we provide a proof of the counting formula and we apply this formula to
a variety of 1d and 2d models belonging to the classes BDI, DIII and D. We show
that we can successfully chart out the topological phase diagrams. Studying
these examples also enables us to explicitly observe the correspondence between
these complex momentum solutions in the Fourier space, and the localized
Majorana fermion wavefunctions in the position space. Finally, we corroborate
the fact that for systems with a chiral symmetry, these solutions are the
so-called "exceptional points", where two or more eigenvalues of the
complexified Hamiltonian coalesce.Comment: 21 pages, 10 figure
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
Parity Nonconservation in Odd-isotopes of Single Trapped Atomic Ions
We have estimated the size of the light-shifts due to parity nonconservation
(PNC) interactions in different isotopes of Ba+ and Ra+ ions based on the work
of Fortson [Phys. Rev. Lett. 70, 2383 (1993)]. We have used the nuclear spin
independent (NSI) amplitudes calculated earlier by us [Phys. Rev. Lett. 96,
163003 (2006); Phys. Rev. A 78, 050501(R) (2008)] and we have employed the
third order many-body perturbation theory (MBPT(3)) in this work to estimate
the nuclear spin dependent (NSD) amplitudes in these ions. Ra+ is found to be
more favourable than Ba+ for measuring both the NSI and NSD PNC observables.Comment: 5 pages, 1 tabl
Relating Gribov-Zwanziger theory to effective Yang-Mills theory
We consider the Gribov-Zwanziger (GZ) theory with appropriate horizon term
which exhibits the nilpotent BRST invariance. This infinitesimal BRST
transformation has been generalized by allowing the parameter to be finite and
field dependent (FFBRST). By constructing appropriate finite field dependent
parameter we show that the generating functional of GZ theory with horizon term
is related to that of Yang-Mills (YM) theory through FFBRST transformation.Comment: 14 pages, No figure, to appear in Europhysics Lette
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
Neutrality of a magnetized two-flavor quark superconductor
We investigate the effect of electric and color charge neutrality on the
two-flavor color superconducting (2SC) phase of cold and dense quark matter in
presence of constant external magnetic fields and at moderate baryon densities.
Within the framework of the Nambu-Jona-Lasinio (NJL) model, we study the
inter-dependent evolution of the quark's BCS gap and constituent mass with
increasing density and magnetic field. While confirming previous results
derived for the highly magnetized 2SC phase with color neutrality alone, we
obtain new results as a consequence of imposing charge neutrality. In the
charge neutral gapless 2SC phase (g2SC), a large magnetic field drives the
color superconducting phase transition to a crossover, while the chiral phase
transition is first order. At larger diquark-to-scalar coupling ratio
, where the 2SC phase is preferred, we see hints of the
Clogston-Chandrasekhar limit at a very large value of the magnetic field
(G), but this limit is strongly affected by Shubnikov de
Haas-van Alphen oscillations of the gap, indicating the transition to a
domain-like state.Comment: 19 pages, 7 figures, Matches with the published versio
Emergence of topological Mott insulators in proximity of quadratic band touching points
Recently, the field of strongly correlated electrons has begun an intense
search for a correlation induced topological insulating phase. An example is
the quadratic band touching point which arises in a checkerboard lattice at
half-filling, and in the presence of interactions gives rise to topological
Mott insulators. In this work, we perform a mean-field theory computation to
show that such a system shows instability to topological insulating phases even
away from half-filling (chemical potential ). The interaction
parameters consist of on-site repulsion (), nearest-neighbour repulsion (), and a next-nearest-neighbour correlated hopping (). The
interaction originates from strong Coulomb repulsion. By tuning
the values of these parameters, we obtain a desired topological phase that
spans the area around , extending to regions with
and . This extends the realm of current experimental
efforts to find these topological phases.Comment: 10 pages, 5 figure
Current-driven orbital order-disorder transition in LaMnO3
We report significant influence of electric current on the orbital
order-disorder transition in LaMnO3. The transition temperature T_OO, thermal
hysteresis in the resistivity (rho) versus temperature (T) plot around T_OO,
and latent heat L associated with the transition decrease with the increase in
current density. Eventually, at a critical current density, L reaches zero. The
transition zone, on the other hand, broadens with the increase in current
density. The states at ordered, disordered, and transition zone are all found
to be stable within the time window from ~10^-3 to ~10^4 seconds.Comment: 7 pages including 5 figures; resolution of Fig.1 is better here than
the published versio
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
Scaling of NonOhmic Conduction in Strongly Correlated Systems
A new scaling formalism is used to analyze nonlinear I-V data in the vicinity
of metal-insulator transitions (MIT) in five manganite systems. An exponent,
called the nonlinearity exponent, and an onset field for nonlinearity, both
characteristic of the system under study, are obtained from the analysis. The
onset field is found to have an anomalously low value corroborating the
theoretically predicted electronically soft phases. The scaling functions above
and below the MIT of a polycrystalline sample are found to be the same but with
different exponents which are attributed to the distribution of the MIT
temperatures. The applicability of the scaling in manganites underlines the
universal response of the disordered systems to electric field
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