14 research outputs found
Conductivity of underdoped YBa2Cu3O7-d : evidence for incoherent pair correlations in the pseudogap regime
Conductivity due to superconducting fluctuations studied in optimally doped
YBa2Cu3O7-d films displays a stronger decay law in temperature than explainable
by theory. A formula is proposed, which fits the data very well with two
superconductive parameters, Tc and the coherence length ksi_c0, and an energy
scale Delta*. This is also valid in underdoped materials and enables to
describe the conductivity up to 300 K with a single-particle excitations
channel in parallel with a channel whose contribution is controlled by ksi_c0,
Tc and Delta*.
This allows to address the nature of the pseudogap in favour of incoherent
pairing.Comment: 14 pages, 4 figures, 1 tabl
Disordered Josephson Junctions of d-Wave Superconductors
We study the Josephson effect between weakly coupled d-wave superconductors
within the quasiclassical theory, in particular, the influence of interface
roughness on the current-phase relation and the critical current of mirror
junctions and asymmetric junctions. For mirror junctions the
temperature dependence of the critical current is non-monotonic in the limit of
low roughness, but monotonic for very rough interfaces. For
asymmetric junctions with a linear dimension much larger than the
superconducting coherence length we find a -like current-phase
relation, whereas for contacts on the scale of the coherence length or smaller
the usual -like behavior is observed. Our results compare well with
recent experimental observations.Comment: 10 pages, 12 figures; accepted for publication in Phys. Rev.
Motor, somatosensory and auditory cortex localization by fMRI and MEG
FUNCTIONAL magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrast vs neuronal biomagnetic activity