1,025 research outputs found
Random Spin-orbit Coupling in Spin Triplet Superconductors: Stacking Faults in Sr_2RuO_4 and CePt_3Si
The random spin-orbit coupling in multicomponent superconductors is
investigated focusing on the non-centrosymmetric superconductor CePt_3Si and
the spin triplet superconductor Sr_2RuO_4. We find novel manifestations of the
random spin-orbit coupling in the multicomponent superconductors with
directional disorders, such as stacking faults. The presence of stacking faults
is indicated for the disordered phase of CePt_3Si and Sr_2RuO_4. It is shown
that the d-vector of spin triplet superconductivity is locked to be d = k_y x -
k_x y with the anisotropy \Delta T_c/T_c0 \sim \bar{\alpha}^2/T_c0 W_z, where
\bar{\alpha}, T_c0, and W_z are the mean square root of random spin-orbit
coupling, the transition temperature in the clean limit, and the kinetic energy
along the c-axis, respectively. This anisotropy is much larger (smaller) than
that in the clean bulk Sr_2RuO_4 (CePt_3Si). These results indicate that the
helical pairing state d = k_y x - k_x y in the eutectic crystal
Sr_2RuO_4-Sr_3Ru_2O_7 is stabilized in contrast to the chiral state d = (k_x
\pm i k_y) z in the bulk Sr_2RuO_4. The unusual variation of T_c in CePt_3Si is
resolved by taking into account the weak pair-breaking effect arising from the
uniform and random spin-orbit couplings. These superconductors provide a basis
for discussing recent topics on Majorana fermions and non-Abelian statistics.Comment: J. Phys. Soc. Jpn. 79 (2010) 08470
Revisiting Theoretical Analysis of Electric Dipole Moment of Xe
Linear response approach to the relativistic coupled-cluster (RCC) theory has
been extended to estimate contributions from the parity and time-reversal
violating pseudoscalar-scalar (Ps-S) and scalar-pseudoscalar (S-Ps)
electron-nucleus interactions along with electric dipole moments (EDMs) of
electrons () interacting with internal electric and magnetic fields.
Random phase approximation (RPA) is also employed to produce results to compare
with the earlier reported values and demonstrate importance of the non-RPA
contributions arising through the RCC method. It shows that contributions from
the S-Ps interactions and arising through the hyperfine-induced effects
are very sensitive to the contributions from the high-lying virtual orbitals.
Combining atomic results with the nuclear shell-model calculations, we impose
constraints on the pion-nucleon coupling coefficients, and EDMs of proton and
neutron. These results are further used to constrain EDMs and chromo-EDMs of
up- and down-quarks by analyzing particle physics models.Comment: 15 pages including appendix, 8 tables and 1 figur
Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNiBC
We have studied the field-orientational dependence of zero-energy density of
states (FODOS) for a series of systems with different Fermi surface and
superconducting gap structures. Instead of phenomenological Doppler-shift
method, we use an approximate analytical solution of Eilenberger equation
together with self-consistent determination of order parameter and a
variational treatment of vortex lattice. First, we compare zero-energy density
of states (ZEDOS) when a magnetic field is applied in the nodal direction
() and in the antinodal direction (), by taking
account of the field-angle dependence of order parameter. As a result, we found
that there exists a crossover magnetic field so that for for , consistent with our previous analyses. Next, we showed that and the
shape of FODOS are determined by contribution from the small part of Fermi
surface where Fermi velocity is parallel to field-rotational plane. In
particular, we found that is lowered and FODOS has broader minima, when a
superconducting gap has point nodes, in contrast to the result of the
Doppler-shift method. We also studied the effects of in-plane anisotropy of
Fermi surface. We found that in-plane anisotropy of quasi-two dimensional Fermi
surface sometimes becomes larger than the effects of Doppler-shift and can
destroy the Doppler-shift predominant region. In particular, this tendency is
strong in a multi-band system where superconducting coherence lengths are
isotropic. Finally, we addressed the problem of cusp-like singularity in
YNiBC and present a possible explanation of this phenomenon.Comment: 13pages, 23figure
Magnetic Field Effects in the Pseudogap Phase: A Precursor Superconductivity Scenario
We demonstrate that the observed dependences of and on small
magnetic fields can be readily understood in a precursor superconductivity
approach to the pseudogap phase. In this approach, the presence of a pseudogap
at (but not at ) and the associated suppression of the density of
states lead to very different sensitivities to pair-breaking perturbations for
the two temperatures. Our semi-quantitative results address the puzzling
experimental observation that the coherence length is weakly dependent on
hole concentration throughout most of the phase diagram. We present our
results in a form which can be compared with the recent experiments of
Shibauchi et al, and argue that orbital effects contribute in an important way
to the dependence of .Comment: 6 pages, 1 figure, elsart.cls included. Submitted to the proceeding
of SNS 2001, Chicag
Fourth Order Perturbation Theory for Normal Selfenergy in Repulsive Hubbard Model
We investigate the normal selfenergy and the mass enhancement factor in the
Hubbard model on the two-dimensional square lattice. Our purpose in this paper
is to evaluate the mass enhancement factor more quantitatively than the
conventional third order perturbation theory. We calculate it by expanding
perturbatively up to the fourth order with respect to the on-site repulsion
. We consider the cases that the system is near the half-filling, which are
similar situations to high- cuprates. As results of the calculations, we
obtain the large mass enhancement on the Fermi surface by introducing the
fourth order terms. This is mainly originated from the fourth order
particle-hole and particle-particle diagrams. Although the other fourth order
terms have effect of reducing the effective mass, this effect does not cancel
out the former mass enhancement completely and there remains still a large mass
enhancement effect. In addition, we find that the mass enhancement factor
becomes large with increasing the on-site repulsion and the density of
state (DOS) at the Fermi energy . According to many current reseaches,
such large and enhance the effective interaction between
quasiparticles, therefore the superconducting transition temperature
increases. On the other hand, the large mass enhancement leads the reduction of
the energy scale of quasiparticles, as a result, is reduced. When we
discuss , we have to estimate these two competitive effects.Comment: 6pages,8figure
Analysis of Superconductivity in d-p Model on Basis of Perturbation Theory
We investigate the mass enhancement factor and the superconducting transition
temperature in the d-p model for the high-\Tc cuprates. We solve the
\'Eliashberg equation using the third-order perturbation theory with respect to
the on-site Coulomb repulsion . We find that when the energy difference
between d-level and p-level is large, the mass enhancement factor becomes large
and \Tc tends to be suppressed owing to the difference of the density of
state for d-electron at the Fermi level. From another view point, when the
energy difference is large, the d-hole number approaches to unity and the
electron correlation becomes strong and enhances the effective mass. This
behavior for the electron number is the same as that of the f-electron number
in the heavy fermion systems. The mass enhancement factor plays an essential
role in understanding the difference of \Tc between the LSCO and YBCO
systems.Comment: 4pages, 9figures, to be published in J. Phys. Soc. Jp
In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O
We report the Co NMR studies of the in-plane anisotropy of bilayer
hydrated Na using a oriented
powder sample by a magnetic field in Fluorinert FC70. We found for the first
time the -plane anisotropy of the Co NMR Knight shift , the
nuclear spin-lattice relaxation rate 1/ and the nuclear spin-spin
relaxation rate 1/ at a magnetic field 7.5 T up to 200K. Below
75 K, the anisotropy of is large compared with that at high temperatures.
The hyperfine coupling constants seem to change around the temperature 150 K,
in which the bulk susceptibility shows broad minimum, suggesting a
change of the electronic state of CoO plane. 1/ also shows a
significant anisotropy, which cannot be explained only by the anisotropy of the
hyperfine coupling constants nor the anisotropic uniform spin susceptibility.
The difference in the in-plane anisotropy of from that of indicates
that the magnetic fluctuation at a finite wave vector is also
anisotropic and the anisotropy is different from that at .Comment: 4 pages, 5 figure
Antiferromagnetic Order and \pi-triplet Pairing in the Fulde-Ferrell-Larkin-Ovchinnikov State
The antiferromagnetic Fulde-Ferrell-Larkin-Ovchinnikov (AFM-FFLO) state of
coexisting d-wave FFLO superconductivity and incommensurate AFM order is
studied on the basis of Bogoliubov-de Gennes (BdG) equations. We show that the
incommensurate AFM order is stabilized in the FFLO state by the appearance of
the Andreev bound state localized around the zeros of the FFLO order parameter.
The AFM-FFLO state is further enhanced by the induced \pi-triplet
superconductivity (pair density wave). The AFM order occurs in the FFLO state
even when it is neither stable in the normal state nor in the BCS state. The
order parameters of the AFM order, d-wave superconductivity, and \pi-triplet
pairing are investigated by focusing on their spatial structures. Roles of the
spin fluctuations beyond the BdG equations are discussed. Their relevance to
the high-field superconducting phase of CeCoIn_5 is discussed.Comment: Typos are fixed. Published versio
Ginzburg-Landau Analysis for the Antiferromagnetic Order in the Fulde-Ferrell-Larkin-Ovchinnikov Superconductor
Incommensurate antiferromangetic (AFM) order in the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor is investigated on the
basis of the Ginzburg-Landau theory. We formulate the two component
Ginzburg-Landau model to discuss two degenerate incommensurate AFM states in
the tetragonal crystal structure. Owing to the broken translation symmetry in
the FFLO state, a multiple phase diagram of single-q phase and double-q phase
is obtained under the magnetic field along [100] or [010] direction. Magnetic
properties in each phase are investigated and compared with the neutron
scattering and NMR measurements for a heavy fermion superconductor CeCoIn_5. An
ultrasonic measurement is proposed for a future experimental study to identify
the AFM-FFLO state. The field orientation dependence of the AFM order in
CeCoIn_5 is discussed.Comment: 8 page
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