19 research outputs found
Role of the cooling rate in the stability of the superconducting phase of (TMTSF)_2ClO_4
The noncentrosymmetric ClO anions of the organic superconductor
(TMTSF)ClO order below 24K. The size of domains where the anions are
ordered is substantially dependent on the cooling rate which is a key parameter
for the stability of the low temperature electronic ground states. We study the
effect of the cooling rate on the SC phase within a self consistent approach in
the framework of the time dependent Ginzburg-Landau theory taking into account
the superconducting fluctuations. We derive the superconducting transition
temperature which is found to decrease with increasing cooling rate in
agreement with recent experimental data.Comment: 5 pages including one figure. Published online in Europhysics Letter
Disorder-induced superconductivity in ropes of carbon nanotubes
We study the interplay between disorder and superconductivity in a rope of
metallic carbon nanotubes. Based on the time dependent Ginzburg Landau theory,
we derive the superconducting transition temperature T taking into account
the critical superconducting fluctuations which are expected to be
substantially strong in such low dimensional systems. Our results indicate
that, contrary to what is expected, T increases by increasing the amount of
disorder. We argue that this behavior is due to the dynamics of the tubes which
reduces the drastic effect of the local disorder on superconductivity by
enhancing the intertube Josephson tunneling. We also found that T is
enhanced as the effective dimensionality of the rope increases by increasing
the number N of the tubes forming the rope. However, T tends to saturate
for large values of N, expressing the establishment of a bulk three dimensional
(3D) superconducting order.Comment: 9 pages, 4 figur
Renormalization of the hopping parameters in quasi-one-dimensional conductors in the presence of a magnetic field
Abstract. We consider the competition between the one dimensionalization effect due to a magnetic field and the hopping parameters in quasi-one-dimensional conductors. Our study is based on a perturbative renormalization group method with three cut-off parameters, the bandwidth E0, the 1D-2D crossover temperature T * 1 , which is related to the hopping process t1, and the magnetic energy ωc. We have found that the renormalized crossover temperatures T * 1 and T * 2 , at which the respectively hopping processes t1 and t2 become coherent, are reduced compared to the bare values as the field is increased. We discuss the consequences of these renormalization effects on the temperature-field phase diagram of the organic conductors. PAC
Antiferromagnetic Excitations and Van Hove Singularities in YBaCuO
We show that in quasi-two-dimensional -wave superconductors Van Hove
singularities close to the Fermi surface lead to novel magnetic quasi-particle
excitations. We calculate the temperature and doping dependence of dynamical
magnetic susceptibility for YBCO and show that the proposed excitations are in
agreement with inelastic neutron scattering experiments. In addition, the
values of the gap parameter and in-plane antiferromagnetic coupling are much
smaller than usually believed.Comment: REVTeX, 4 pages + 3 PostScript (compressed) figures; to appear in
Phys. Rev. B (Rap. Comm.
Field-induced confinement in (TMTSF)2ClO4 under accurately aligned magnetic fields
We present transport measurements along the least conducting c direction of
the organic superconductor (TMTSF)2ClO4, performed under an accurately aligned
magnetic field in the low temperature regime. The experimental results reveal a
two-dimensional confinement of the carriers in the (a,b) planes which is
governed by the magnetic field component along the b' direction. This 2-D
confinement is accompanied by a metal-insulator transition for the c axis
resistivity. These data are supported by a quantum mechanical calculation of
the transverse transport taking into account in self consistent treatment the
effect of the field on the interplane Green function and on the intraplane
scattering time
Competing phases in the high field phase diagram of (TMTSF)ClO
A model is presented for the high field phase diagram of (TMTSF)ClO,
taking into account the anion ordering, which splits the Fermi surface in two
bands. For strong enough field, the largest metal-SDW critical temperature
corresponds to the N=0 phase, which originates from two intraband nesting
processes. At lower temperature, the competition between these processes puts
at disadvantage the N=0 phase vs. the N=1 phase, which is due to interband
nesting. A first order transition takes then place from the N=0 to N=1 phase.
We ascribe to this effect the experimentally observed phase diagrams.Comment: 5 pages, 3 figures (to appear in Phys. Rev. Lett.
Inhomogeneous superconductivity in organic conductors: role of disorder and magnetic field
Several experimental studies have shown the presence of spatially
inhomogeneous phase coexistence of superconducting and non superconducting
domains in low dimensional organic superconductors. The superconducting
properties of these systems are found to be strongly dependent on the amount of
disorder introduced in the sample regardless of its origin. The suppression of
the superconducting transition temperature shows clear discrepancy with
the result expected from the Abrikosov-Gor'kov law giving the behavior of
with impurities. Based on the time dependent Ginzburg-Landau theory, we derive
a model to account for the striking feature of in organic superconductors
for different types of disorder by considering the segregated texture of the
system. We show that the calculated quantitatively agrees with
experiments. We also focus on the role of superconducting fluctuations on the
upper critical fields of layered superconductors showing slab
structure where superconducting domains are sandwiched by non-superconducting
regions. We found that may be strongly enhanced by such fluctuations.Comment: to appear in Journal of Physics: Condensed Matte
Neutron scattering and superconducting order parameter in YBa2Cu3O7
We discuss the origin of the neutron scattering peak at 41 meV observed in
YBaCuO below . The peak may occur due to spin-flip electron
excitations across the superconducting gap which are enhanced by the
antiferromagnetic interaction between Cu spins. In this picture, the experiment
is most naturally explained if the superconducting order parameter has -wave
symmetry and opposite signs in the bonding and antibonding electron bands
formed within a CuO bilayer.Comment: In this version, only few minor corrections and the update of
references were done in order to make perfect correspondence with the
published version. RevTeX, psfig, 5 pages, and 3 figure
Superconductivity, Spin Density Wave and Field Induced Spin Density Wave versus anion ordering in the (TMTSF) 2 ClO 4 salt
We study the effect of the ClO4 anion ordering on the superconducting (SC