9 research outputs found
Parallel and Perpendicular Susceptibility Above in LaSrCuO Single Crystals
We report direction-dependent susceptibility and resistivity measurements on
LaSrCuO single crystals. These crystals have rectangular
needle-like shapes with the crystallographic "c" direction parallel or
perpendicular to the needle axis,which, in turn, is in the applied field
direction. At optimal doping we find finite diamagnetic susceptibility above
, namely fluctuating superconductivity (FSC), only when the field is
perpendicular to the planes. In underdoped samples we could find FSC in both
field directions. We provide a phase diagram showing the FSC region, although
it is sample dependent in the underdoped cases. The variations in the
susceptibility data suggest a different origin for the FSC between underdoping
(below 10%) and optimal doping. Finally, our data indicates that the
spontaneous vortex diffusion constant above is anomalously high
Crack-Like Processes Governing the Onset of Frictional Slip
We perform real-time measurements of the net contact area between two blocks
of like material at the onset of frictional slip. We show that the process of
interface detachment, which immediately precedes the inception of frictional
sliding, is governed by three different types of detachment fronts. These
crack-like detachment fronts differ by both their propagation velocities and by
the amount of net contact surface reduction caused by their passage. The most
rapid fronts propagate at intersonic velocities but generate a negligible
reduction in contact area across the interface. Sub-Rayleigh fronts are
crack-like modes which propagate at velocities up to the Rayleigh wave speed,
VR, and give rise to an approximate 10% reduction in net contact area. The most
efficient contact area reduction (~20%) is precipitated by the passage of slow
detachment fronts. These fronts propagate at anomalously slow velocities, which
are over an order of magnitude lower than VR yet orders of magnitude higher
than other characteristic velocity scales such as either slip or loading
velocities. Slow fronts are generated, in conjunction with intersonic fronts,
by the sudden arrest of sub-Rayleigh fronts. No overall sliding of the
interface occurs until either of the slower two fronts traverses the entire
interface, and motion at the leading edge of the interface is initiated. Slip
at the trailing edge of the interface accompanies the motion of both the slow
and sub-Rayleigh fronts. We might expect these modes to be important in both
fault nucleation and earthquake dynamics.Comment: 19 page, 5 figures, to appear in International Journal of Fractur
The Fermi surface and band folding in La2−xSrxCuO4, probed by angle-resolved photoemission
A systematic angle-resolved photoemission study of the electronic structure of La2−xSrxCuO4 in a wide doping range is presented in this paper. In addition to the main energy band, we observed a weaker additional band, the (π, π) folded band, which shows unusual doping dependence. The appearance of the folded band suggests that a Fermi surface reconstruction is doping dependent and could already occur at zero magnetic field.ISSN:1367-263