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, V R , 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 V R 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.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.

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We present an investigation of charge-compensated antiferromagnetic (Ca x La 1−x )(Ba 1.75−x La 0.25+x )Cu 3 O y single crystals using Raman scattering as well as muon spin rotation. In this system the parameter x controls the Cu-O-Cu superexchange interaction via bond distances and buckling angles. The oxygen content y controls the charge doping. In the absence of doping the two-magnon peak position is directly proportional to the superexchange strength J . We find that both x and y affect the peak position considerably. The Néel temperature determined from muon spin rotation on the same samples independently confirms the strong dependence of the magnetic interaction on x and y. We find a considerable increase in the maximum superconducting transition temperature T max c with J . This is strong evidence of the importance of orbital overlap to superconductivity in this family of cuprates.

We report the successful growth of a large (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy (CLBLCO) single crystal. In this material, x controls the maximum of Tc (T max c ), with minimal structural changes. Therefore, it allows a search for correlations between material properties and T max c . We demonstrate that the crystals are good enough for neutron scattering and cleave well enough for Raman scattering. These results open new possibilities for cuprate research.