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The superconducting properties of mercury cuprates are extremely sensitive to compression. The highest transition temperatures obtained up to date have been measured on Hg-1223 at 25–30 Gpa ( T c ∼ 164 K at the onset) and imply an increase of about 20 K with respect to the ambient pressure T c 0 . We report here the largest total pressure effect (> 50 K over a span of 20 GPa) ever observed for several samples of bi-mercury layer Hg 2 Ba 2 (Y 1− x Ca x )Cu 2 O 8−δ compositions. Different Ca doping levels give different initial T c s but retain the same strong pressure dependence. The large T c increase with pressure for all the Hg-based compounds, independently of their doping level, is revealing the existence of a common structural parameter, which identification will be a guide for future synthesis efforts of record-high T c materials.

Attenuation of acoustical surface waves in the range 100–500 MHz has been measured in sublimed C 60 films. A large attenuation governed by a thermally activated relaxation mechanism having an activation energy of 0.07 eV is observed around 180 K. The ultrasonic results are compared with the NMR and low frequency elastic measurements.

We correlate s-shape resistivity in A-15, C-15 and charge density wave compounds with structural instabilities. We propose that the exponential term of the resistivity is caused by the scattering against thermally excited molecular states. We show that this interpretation is supported by a large number of experimental data and naturally explains the apparent violation of Mathiessen's rule in irradiation experiments. Connections with recent theoretical developments on strong electron-phonon coupling are discussed.