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We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high Tc record (166 K +/- 1 K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic $a$-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the $a$ axes is one of the keys that controls the Tc of high temperature superconductors., 4 pages, 4 figures, submitted to Phys. Rev. B

We measure the pressure dependence of the electrical resistivity and the crystal structure of iron superconductor Sr2VO3FeAs. Below ~10 GPa the structure compresses but remains undeformed, with regular FeAs4 tetrahedrons, and a constant Tc. Beyond 10 GPa, the tetrahedron strongly distorts, while Tc goes gradually to zero. Band structure calculations of the undistorted structure show multiple-nesting features that hinder the development of an antiferromagnetic (AF) ground state, allowing the appearance of superconductivity. The deformation of the tetrahedra that breaks band degeneracy degrades multiple nesting, thus favouring one particular AF state at the expense of Tc.

Presents a method of measuring the thermal conductivity of very tiny and fragile samples, based on the differential thermal conductivity technique. To illustrate the possibilities of this method the authors have measured the thermal conductivity of filaments of NbSe3 (10 mu m in diameter and 3 mm in length) in the temperature range 2 to 150K with good resolution.

The resistance of single crystals of NbSe3 under pressure, between 1.2 and 70K has been measured in magnetic fields up to 180 kG. The CDW which appears at ambient pressures at 59K, is totally suppressed for pressures greater than 5.5 kbar. At this pressure NbSe3 is fully superconducting as shown by a total Meissner effect. Fermi surface studies by Shubnikov-de Haas oscillations show that the Fermi surface is strongly affected by the CDW formation. At ambient pressure, when H is parallel to the plane (b, c) one frequency (0.3 MG) is detected, but when the pressure has suppressed the CDW, at least eight frequencies (up to 7 MG) were detected. The experiments are consistent with the model of different types of chains in NbSe3 on which the two CDW form.