1,349 research outputs found
Tunnelling between non-centrosymmetric superconductors with significant spin-orbit splitting studied theoretically within a two-band treatment
Tunnelling between non-centrosymmetric superconductors with significant
spin-orbit splitting is studied theoretically in a two-band treatment of the
problem. We find that the critical Josephson current may be modulated by
changing the relative angle between the vectors describing absence of inversion
symmetry on each side of the junction. The presence of two gaps also results in
multiple steps in the quasiparticle current-voltage characteristics. We argue
that both these effects may help to determine the pairing states in materials
like CePtSi, UIr and CdReO. We propose experimental tests of
these ideas, including scanning tunnelling microscopy.Comment: 5 pages, 1 figure. Minor changes. Some new references added.
Journal-ref. adde
Signature of superconducting states in cubic crystal without inversion symmetry
The effects of absence of inversion symmetry on superconducting states are
investigated theoretically. In particular we focus on the noncentrosymmetric
compounds which have the cubic symmetry like LiPtB. An appropriate
and isotropic spin-orbital interaction is added in the Hamiltonian and it acts
like a magnetic monopole in the momentum space. The consequent pairing
wavefunction has an additional triplet component in the pseudospin space, and a
Zeeman magnetic field can induce a collinear supercurrent
with a coefficient . The effects of anisotropy embedded in the cubic
symmetry and the nodal superconducting gap function on are also
considered. From the macroscopic perspectives, the pair of mutually induced
and magnetization can affect the distribution of magnetic
field in such noncentrosymmetric superconductors, which is studied through
solving the Maxwell equation in the Meissner geometry as well as the case of a
single vortex line. In both cases, magnetic fields perpendicular to the
external ones emerge as a signature of the broken symmetry.Comment: 16 pages in pre-print forma
On the spin susceptibility of noncentrosymmetric superconductors
We calculate the spin susceptibility of a superconductor without inversion
symmetry, both in the clean and disordered cases. The susceptibility has a
large residual value at zero temperature, which is further enhanced in the
presence of scalar impurities.Comment: 12 pages, 3 figure
Using Josephson junctions to determine the pairing state of superconductors without crystal inversion symmetry
Theoretical studies of a planar tunnel junction between two superconductors
with antisymmetric spin-orbit coupling are presented. The half-space Green's
function for such a superconductor is determined. This is then used to derive
expressions for the dissipative current and the Josephson current of the
junction. Numerical results are presented in the case of the Rashba spin-orbit
coupling, relevant to the much studied compound CePtSi. Current-voltage
diagrams, differential conductance and the critical Josephson current are
presented for different crystallographic orientations and different weights of
singlet and triplet components of the pairing state. The main conclusion is
that Josephson junctions with different crystallographic orientations may
provide a direct connection between unconventional pairing in superconductors
of this kind and the absence of inversion symmetry in the crystal.Comment: 16 pages, 10 figure
Andreev reflection from non-centrosymmetric superconductors and Majorana bound state generation in half-metallic ferromagnets
We study Andreev reflection at an interface between a half metal and a
superconductor with spin-orbit interaction. While the absence of minority
carriers in the half metal makes singlet Andreev reflection impossible, the
spin-orbit interaction gives rise to triplet Andreev reflection, i.e., the
reflection of a majority electron into a majority hole or vice versa. As an
application of our calculation, we consider a thin half metal film or wire
laterally attached to a superconducting contact. If the half metal is disorder
free, an excitation gap is opened that is proportional to the spin-orbit
interaction strength in the superconductor. For electrons with energy below
this gap a lateral half-metal--superconductor contact becomes a perfect triplet
Andreev reflector. We show that the system supports localized Majorana end
states in this limit.Comment: 14 pages, 3 figure
Magnetic properties of superconductors with strong spin-orbit coupling
We study the response of a superconductor with a strong spin-orbit coupling
on an external magnetic field. The Ginzburg-Landau free energy functional is
derived microscopically for a general crystal structure, both with and without
an inversion center, and for an arbitrary symmetry of the superconducting order
parameter. As a by-product, we obtain the general expressions for the intrinsic
magnetic moment of the Cooper pairs. It is shown that the Ginzburg-Landau
gradient energy in a superconductor lacking inversion symmetry has unusual
structure. The general formalism is illustrated using as an example CePtSi,
which is the first known heavy-fermion superconductor without an inversion
center.Comment: Published version, 14 pages, minor correction
Phase diagram of a surface superconductor in parallel magnetic field
Detailed theory of phase diagram of clean 2D surface superconductor in a
parallel magnetic field is presented. Regular spin-orbital interaction of the
Rashba type is known to produce inhomogeneous superconductive state similar to
the Larkin-Ovchinnikov-Fulde-Ferrel (LOFF) state with at high magnetic fields, with . We
consider the case of relatively strong Rashba interaction and show that at low
temperatures the LOFF-type state is separated from the usual
homogeneous state by the first-order phase transition line. At higher
temperatures new "helical" state with
intervene between uniform BCS state and LOFF-like state. One component of
superfluid density tensor vanishes on the second-order transition line
between BCS state and helical state. Nonmagnetic impurities suppresses both
inhomogeneous states, and eliminate them completely at .Comment: 5 pages, 1 figure; v2: as published, minor correction
Singularity resolution in gauged supergravity and conifold unification
We obtain a unified picture for the conifold singularity resolution. We propose that the gauged supergravity, through a novel prescription for the twisting, provides as appropriate framework to smooth out singularities in the context of gravity duals of supersymmetric gauge theories.Instituto de Física La Plat
Spin fluctuations and superconductivity in noncentrosymmetric heavy fermion systems CeRhSi and CeIrSi
We study the normal and the superconducting properties in noncentrosymmetric
heavy fermion superconductors CeRhSi and CeIrSi. For the normal state,
we show that experimentally observed linear temperature dependence of the
resistivity is understood through the antiferromagnetic spin fluctuations near
the quantum critical point (QCP) in three dimensions. For the superconducting
state, we derive a general formula to calculate the upper critical field
, with which we can treat the Pauli and the orbital depairing effect on
an equal footing. The strong coupling effect for general electronic structures
is also taken into account. We show that the experimentally observed features
in , the huge value up to 30(T), the downward
curvatures, and the strong pressure dependence, are naturally understood as an
interplay of the Rashba spin-orbit interaction due to the lack of inversion
symmetry and the spin fluctuations near the QCP. The large anisotropy between
and is explained in terms of
the spin-orbit interaction. Furthermore, a possible realization of the
Fulde-Ferrell- Larkin-Ovchinnikov state for is studied. We
also examine effects of spin-flip scattering processes in the pairing
interaction and those of the applied magnetic field on the spin fluctuations.
We find that the above mentioned results are robust against these effects. The
consistency of our results strongly supports the scenario that the
superconductivity in CeRhSi and CeIrSi is mediated by the spin
fluctuations near the QCP.Comment: 21pages, 13figures, to be published in Phys. Rev.
Quantum transport in noncentrosymmetric superconductors and thermodynamics of ferromagnetic superconductors
We consider a general Hamiltonian describing coexistence of itinerant
ferromagnetism, spin-orbit coupling and mixed spin-singlet/triplet
superconducting pairing in the context of mean-field theory. The Hamiltonian is
diagonalized and exact eigenvalues are obtained, thus allowing us to write down
the coupled gap equations for the different order parameters. Our results may
then be applied to any model describing coexistence of any combination of these
three phenomena. As a specific application of our results, we consider
tunneling between a normal metal and a noncentrosymmetric superconductor with
mixed singlet and triplet gaps. The conductance spectrum reveals information
about these gaps in addition to how the influence of spin-orbit coupling is
manifested. We also consider the coexistence of itinerant ferromagnetism and
triplet superconductivity as a model for recently discovered ferromagnetic
superconductors. The coupled gap equations are solved self-consistently, and we
study the conditions necessary to obtain the coexistent regime of
ferromagnetism and superconductivity. Analytical expressions are presented for
the order parameters, and we provide an analysis of the free energy to identify
the preferred system state. Moreover, we make specific predictions concerning
the heat capacity for a ferromagnetic superconductor. In particular, we report
a nonuniversal relative jump in the specific heat, depending on the
magnetization of the system, at the uppermost superconducting phase transition.
[Shortened abstract due to arXiv submission.]Comment: 19 pages, 15 figures (high quality figures available in published
version). Accepted for publication in Phys. Rev.
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