RAPID THERMOELECTRIC-POWER DROP TO ZERO AT 250K IN SUPERCONDUCTING HG-COMPOUNDS

Abstract

We report for the first time that the thermoelectric power (TEP), S(T), drops to zero very rapidly around T-c,T-uso=250K in the superconducting He-compounds lie sign of TEP is negative and the room temperature value is small, S(RT)= -2 mu V/K. The temperature dependence of resistance of the same sample measured with the applied current I = 10 mu A, shows a step-like drop at T-c,T-uso=250K becoming zero resistance around T=120K. At T=230K which is the temperature below the step-like resistance drop, we measured the I-V characteristics of the sample. For the applied current lower than 1.8 mu A the measured resistance is zero initially and it gradually becomes finite in time. It takes approximately 30 seconds before it saturates to a stable value. For I > 1.8 mu A, the resistance becomes finite immediately after we turn on the current source, i.e., there is no time lagging response in voltage probe. The I-V characteristic is Ohmic for 1.8 mu A<I<10 mu A. Since the TEP is a zero current transport coefficient, the observed rapid drop of TEP around 250K together with the initial zero resistance behavior for T<250K at I<1.8 mu A, may indicate an intrinsic superconducting transition at T-c,T-uso=250K of the multi-phase Hg-compounds.