553 research outputs found
Temperature-dependence of spin-polarized transport in ferromagnet / unconventional superconductor junctions
Tunneling conductance in ferromagnet / unconventional superconductor
junctions is studied theoretically as a function of temperatures and
spin-polarization in feromagnets. In d-wave superconductor junctions, the
existence of a zero-energy Andreev bound state drastically affects the
temperature-dependence of the zero-bias conductance (ZBC). In p-wave triplet
superconductor junctions, numerical results show a wide variety in
temperature-dependence of the ZBC depending on the direction of the magnetic
moment in ferromagnets and the pairing symmetry in superconductors such as
, and -wave pair potential. The last one is a
promising symmetry of SrRuO. From these characteristic features in the
conductance, we may obtain the information about the degree of
spin-polarization in ferromagnets and the direction of the -vector in
triplet superconductors
Zero-bias conductance peak splitting due to multiband effect in tunneling spectroscopy
We study how the multiplicity of the Fermi surface affects the zero-bias peak
in conductance spectra of tunneling spectroscopy. As case studies, we consider
models for organic superconductors -(BEDT-TTF)Cu(NCS) and
(TMTSF)ClO. We find that multiplicity of the Fermi surfaces can lead to
a splitting of the zero-bias conductance peak (ZBCP). We propose that the
presence/absence of the ZBCP splitting is used as a probe to distinguish the
pairing symmetry in -(BEDT-TTF)Cu(NCS).Comment: 7 pages, 7 figure
Odd-frequency pairing in normal metal/superconductor junctions
We study the induced odd-frequency pairing states in ballistic normal
metal/superconductor (N/S) junctions where a superconductor has even-frequency
symmetry in the bulk and a normal metal layer has an arbitrary length. Using
the quasiclassical Green's function formalism, we demonstrate that, quite
generally, the pair amplitude in the junction has an admixture of an
odd-frequency component due to the breakdown of translational invariance near
the N/S interface where the pair potential acquires spatial dependence. If a
superconductor has even-parity pair potential (spin-singlet s-wave state), the
odd-frequency pairing component with odd-parity is induced near the N/S
interface, while in the case of odd-parity pair potential (spin-triplet
-wave or spin-singlet -wave) the odd-frequency component with
even-parity is generated. We show that in conventional s-wave junctions, the
amplitude of the odd-frequency pairing state is enhanced at energies
corresponding to the peaks in the local density of states (LDOS). In - and
-wave junctions, the amplitude of the odd-frequency component on the S
side of the N/S interface is enhanced at zero energy where the midgap Andreev
resonant state (MARS) appears due to the sign change of the pair potential. The
odd-frequency component extends into the N region and exceeds the
even-frequency component at energies corresponding to the LDOS peak positions,
including the MARS.Comment: 27 pages, 12 figure
A phenomenological theory of zero-energy Andreev resonant states
A conceptual consideration is given to a zero-energy state (ZES) at the
surface of unconventional superconductors. The reflection coefficients in
normal-metal / superconductor (NS) junctions are calculated based on a
phenomenological description of the reflection processes of a quasiparticle.
The phenomenological theory reveals the importance of the sign change in the
pair potential for the formation of the ZES. The ZES is observed as the
zero-bias conductance peak (ZBCP) in the differential conductance of NS
junctions. The split of the ZBCP due to broken time-reversal symmetry states is
naturally understood in the present theory. We also discuss effects of external
magnetic fields on the ZBCP.Comment: 12 page
Influence of impurity scattering on tunneling conductance in normal metal- d -wave superconductor junctions
Tunneling conductance spectra between a normal metal / d-wave superconductor
junction under the presence of bulk impurities in the superconductor are
studied. The quasiclassical theory has been applied to calculate the spatial
variation of the pair potential and the effect of impurity scattering has been
introduced by t-matrix approximation. The magnitude of a subdominant s-wave
component at the interface is shown to robust against the impurity scattering
while that for a subdominant -wave component is largely suppressed with
the increase of the impurity scattering rate. The zero-bias conductance peak
due to the zero-energy Andreev bound states is significantly broadened for the
case of Born limit impurity compared with that of unitary limit impurity.Comment: 14 pages, 5 figure
Influence of impurity-scattering on tunneling conductance in d-wave superconductors with broken time reversal symmetry
Effects of impurity scattering on tunneling conductance in dirty
normal-metal/insulator/superconductor junctions are studied based on the Kubo
formula and the recursive Green function method. The zero-bias conductance peak
(ZBCP) is a consequence of the unconventional pairing symmetry in
superconductors. The impurity scattering in normal metals suppresses the
amplitude of the ZBCP. The degree of the suppression agrees well with results
of the quasiclassical Green function theory. When superconductors have
+is-wave pairing symmetry, the time-reversal symmetry is broken in
superconductors and the ZBCP splits into two peaks. The random impurity
scattering reduces the height of the two splitting peaks. The position of the
splitting peaks, however, almost remains unchanged even in the presence of the
strong impurity scattering. Thus the two splitting peaks never merge into a
single ZBCP.Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.st
Layer dependent band dispersion and correlations using tunable Soft X-ray ARPES
Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study
in-plane band dispersions of Nickel as a function of probing depth. Photon
energies between 190 and 780 eV were used to effectively probe up to 3-7
layers. The results show layer dependent band dispersion of the Delta_2
minority-spin band which crosses the Fermi level in 3 or more layers, in
contrast to known top 1-2 layers dispersion obtained using ultra-violet rays.
The layer dependence corresponds to an increased value of exchange splitting
and suggests reduced correlation effects in the bulk compared to the surface.Comment: 7 pages, 3 figures Revised text and figur
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