Abstract. Details of the Fermi-surface topology of deuterated κ-(BEDT-TTF) 2 Cu(NCS) 2 have been measured as a function of pressure, and compared with equivalent measurements of the undeuterated salt. We find that the superconducting transition temperature is much more dramatically suppressed by increasing pressure in the deuterated salt. It is suggested that this is linked to pressure-induced changes in the Fermi-surface topology, which occur more rapidly in the deuterated salt than in the undeuterated salt as the pressure is raised. Our data suggest that the negative isotope effect observed on deuteration is due to small differences in Fermi-surface topology caused by the isotopic substitution.
We present a systematic study of the effect of the disorder in copper point
contacts. We show that peaks in the conductance histogram of copper point
contacts shift upon addition of nickel impurities. The shift increases
initially linerarly with the nickel concentration, thus confirming that it is
due to disorder in the nanowire, in accordance with predictions. In general,
this shift is modelled as a resistance R_s which is placed in series with the
contact resistance R_c. However, we obtain different R_s values for the two
peaks in the histogram, R_s being larger for the peak at higher conductance.Comment: 6 pages, 4 figure
We have measured conductance histograms of atomic point contacts made from the noble-transition-metal alloys CuNi, AgPd, and AuPt for a concentration ratio of 1:1. For all alloys these histograms at low-bias voltage ͑below 300 mV͒ resemble those of the noble metals, whereas at high bias ͑above 300 mV͒ they resemble those of the transition metals. We interpret this effect as a change in the composition of the point contact with bias voltage. We discuss possible explanations in terms of electromigration and differential diffusion induced by current heating.
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