1,241 research outputs found
Anomalous charge transport in mesoscopic triplet superconductor junctions
Charge transport properties of a diffusive normal metal /triplet
superconductor (DN/TS) junction are studied based on the Keldysh-Nambu
quasiclassical Green's function formalism. % Contrary to the unconventional
singlet superconductor junction case, the mid gap Andreev resonant state (MARS)
at the interface of the TS is shown to enhance the proximity effect in the DN.
% The total resistance of the DN/TS junction is drastically reduced and is
completely independent of the resistance of the DN in the extreme case. % Such
anomalous transport accompanies a giant zero-bias peak in the conductance
spectra and a zero-energy peak of the local density of states in the DN region.
% These striking features manifest the presence of novel proximity effect
peculiar to triplet superconductor junctions.Comment: 4 pages 3 figure
Axial Current driven by Magnetization Dynamics in Weyl Semimetals
We theoretically study the axial current (defined as the
difference between the charge current with opposite chirality) in doped Weyl
semimetal using a Green's function technique. We show that the axial current is
controlled by the magnetization dynamics in a magnetic insulator attached to a
Weyl semimetal. We find that the induced axial current can be detected by using
ferromagnetic resonance or the inverse spin Hall effect and can be converted
into charge current with no accompanying energy loss. These properties make
Weyl semimetal advantageous for application to low-consumption electronics with
new functionality.Comment: 5 pages, 3 figure
Influences of broken time-reversal symmetry on the d.c. Josephson effects in d-wave superconductors
In order to examine the influences of the spatial dependence of the pair
potential, the d.c. Josephson current in d-wave superconductors is calculated
using self-consistently determined pair potentials. The results show that the
suppression of the d-wave pair potential near the insulator does not have
serious effect on the properties of the Josephson current. On the other hand,
drastic changes are obtained due to the inducement of a subdominant s-wave
component, which spontaneously breaks time reversal symmetry. Especially, a
rapid enhancement of the Josephson current at low temperature predicted in
previous formulas is strongly suppressed.Comment: Latex 11 pages, 3 eps figure
Theory of Tunneling Effect in 1D AIII-class Topological Insulator (Nanowire) Proximity Coupled with a Superconductor
We study the tunneling effect in an AIII-class insulator proximity coupled
with a spin-singlet -wave superconductor, in which three phases are
characterized by the integer topological invariant . By solving
the Bogoliubov-de Gennes equation explicitly, we analytically obtain a normal
reflection coefficient and an Andreev reflection
coefficient , and derive a charge conductance formula,where
is the spin index of a reflected (injected) wave. The
resulting conductance indicates a wide variety of line shapes: (i)gap structure
without coherence peaks for , (ii)quantized zero-bias
conductance peak (ZBCP) with height for , and
(iii)ZBCP spitting for . At zero bias voltage ,
is satisfied and the spin direction of an injected electron
is rotated at approximately for the state.
Meanwhile, is satisfied for the state,
and the spin rotation angle can become
Spin-Dependent Conductance in a Junction with Dresselhaus Spin-Orbit Coupling
We studied spin-dependent conductance in a normal metal (NM)/NM junction with
Dresselhaus spin-orbit coupling (DSOC) and magnetization. As a reference, we
also studied the spin-dependent conductance in such a junction with Rashba
spin-orbit coupling (RSOC). Using a standard scattering method, we calculated
the gate-voltage dependence of the spin-dependent conductances in DSOC and
RSOC. In addition, we calculated the gate-voltage dependence of the
conductances in a ferromagnetic metal (FM)/NM junction with spin-orbit coupling
and magnetization, which we call ferromagnetic spin-orbit metal (FSOM). From
these results, we discuss the relation between these conductance in the
presence of DSOC and that in the presence of RSOC. We found that conductance in
DSOC is the same as that in RSOC for the NM/FSOM junction. In addition, we
found that in the FM/FSOM junction, the conductance in DSOC is the same as that
in RSOC only when the FM magnetization is along the out-of-plane direction.Comment: 6 pages, 8 figuers (4/1/2018
Tunneling conductance in two-dimensional junctions between a normal metal and a ferromagnetic Rashba metal
We have studied charge transport in ferromagnetic Rashba metal (FRM), where
both Rashba type spin-orbit coupling (RSOC) and exchange coupling coexist. It
has nontrivial metallic states, i.e., normal Rashba metal (NRM), anomalous
Rashba metal (ARM), and Rashba ring metal (RRM), and they are manipulated by
tuning the Fermi level with an applied gate voltage. We theoretically studied
tunneling conductance (G) in a normal metal / FRM junction by changing the
Fermi level via an applied gate voltage (Vg) on the FRM. We found a wide
variation in the Vg dependence of G, which depends on the metallic states. In
NRM, the Vg dependence of G is the same as that in a conventional
two-dimensional system. However, in ARM, the Vg dependence of G is similar to
that in a conventional one (two)-dimensional system for a large (small) RSOC.
Furthermore, in RRM, which is generated by a large RSOC, the Vg dependence of
the is similar to that in the one-dimensional system. In addition, these
anomalous properties stem from the spin-momentum locking of RSOC rather than
the density of states in ARM and RRM because of the large RSOC and exchange
coupling.Comment: 10 pages, 8 figures Replace(2018/01/12) changing the title
(2017/11/30
Theory of the d.c. Josephson effect in Pb / Sr2RuO4 / Pb
To clarify the origin of anomalous behaviors in Pb/Sr2RuO4/Pb junctions in
terms of the pairing symmetry, a theory of the d.c. Josephson current in s-wave
superconductor / p-wave superconductor / s-wave superconductor junctions is
developed. Calculated results on the temperature dependence of the critical
Josephson current exhibit non-monotonous behaviors when the thickness of the
p-wave superconductor is comparable to the coherence length. The consistency
between present results with recent experimental measurement supports the
possibility of a unitary p-wave pairing state in Sr2RuO4.Comment: 6 pages, 4 eps figure
Odd-frequency pairing and proximity effect in Kitaev chain systems including topological critical point
In this paper, we investigate the relation between odd-frequency pairing and
proximity effect in non-uniform Kitaev chain systems with a particular interest
in the topological critical point. First, we correlate the odd-frequency
pairing and Majorana fermion in a semi-infinite Kitaev chain, where we find
that the spatial dependence of the odd-frequency pair amplitude coincides with
that of the local density of states at low frequencies. Second, we demonstrate
that, contrary to the standard view, the odd-frequency pair amplitude spreads
into the bulk of a semi-infinite Kitaev chain at the topological critical
point. Finally, we show that odd-frequency Cooper pairs cause the proximity
effect in a normal metal/diffusive normal metal/ Kitaev chain junction even at
the topological critical point. Our results hold relevance to the investigation
of odd-frequency pairing and topological superconductivity in more complicated
systems that involve Rashba nanowire with magnetic fields.Comment: 15 pages, 10 figure
Odd-Frequency Pairs in Chiral Symmetric Systems: Spectral Bulk-Boundary Correspondence and Topological Criticality
Odd-frequency Cooper pairs with chiral symmetry emerging at the edges of
topological superconductors are a useful physical quantity for characterizing
the topological properties of these materials. In this work, we show that the
odd-frequency Cooper pair amplitudes can be expressed by a winding number
extended to a nonzero frequency, which is called a `spectral bulk-boundary
correspondence,' and can be evaluated from the spectral features of the bulk.
The odd-frequency Cooper pair amplitudes are classified into two categories:
the amplitudes in the first category have the singular functional form (where is a complex frequency) that reflects the presence of a
topological surface Andreev bound state, whereas the amplitudes in the second
category have the regular form and are regarded as non-topological. We
discuss the topological phase transition by using the coefficient in the latter
category, which undergoes a power-law divergence at the topological phase
transition point and is used to indicate the distance to the critical point.
These concepts are established based on several concrete models, including a
Rashba nanowire system that is promising for realizing Majorana fermions.Comment: 14 pages, 11 figure
Two-dimensional p-wave superconducting states with magnetic moments on a conventional s-wave superconductor
Unconventional superconductivity induced by the magnetic moments in a
conventional spin-singlet s-wave superconductor is theoretically studied. By
choosing the spin directions of these moments, one can design spinless pairing
states appearing within the s-wave superconducting energy gap. It is found that
the helix spins produce px + py-wave state while the skyrmion crystal
configuration px + ipy-wave like state. Nodes in the energy gap and the zero
energy flat band of Majorana edge states exist in the former one, while the
chiral Majorana channels along edges of the sample and the zero energy Majorana
bound state at the core of the vortex appear in the latter case.Comment: 9 pages including Supplemental Material, 9 figure
- β¦