Flux-flow properties of a dirty two-band superconductor in the mixed state near H/sub c2/
The transport equations describing the flux-flow states of a dirty two- band superconductor near H/sub c2/ are obtained by adding the normal-state thermoelectric, thermomagnetic. and galvanomagnetic effects to the electric and heat currents arising from the motion of the two energy gaps. In the limit of high-impurity concentrations, these two gaps merge into a single gap whose behavior is determined by a single set of Landau-- Ginzburg equations. The flux- flow properties of the dirty two-band superconductor are obtained by imposing a set of boundary conditions on the transport equations. It is seen that the dirty two-band expression for the Hall angle has a form nearly identical to the usual expression for the Hall angle in a dirty superconductor in the mixed state. It is concluded that the two-band expressions for the flux-flow properties in the dirty transition-metal superconductors predict the same qualititative behavior as the usual oneband expressions. (auth) An experimental investigation was carried out on the physical properties of PrCu/sub 6/ relevant to its use, when adiabatically demagnetized, as a coolant for attaining ultralow temperatures. The crystal strncture of PrCu/sub 6/ results in a singlet ground state for the Pr electron system and an externally applied magnetic field polarizes the two 4f Fr electrons to give an effective enhancement, via the hyperfine interaction, to the magnetic field seen by the Pr nuclear magnetic moment. As determined from magnetic susceptibility measurements, this enhancement factor was found to be 15.0 plus or minus 1.0 in a 0.55-kG applied magnetic field. Starting conditions of 20 kG and approximately 22 mK yielded 3.0 mK for a final field of 0.55 kG. The specific heat of PrCu/sub 6/ was found to obey an a/T/sup 2/ law over the approximate range 6 to 30 mK with a = 4 x 10/sup -5/ Jdeg/mole in a 0.55- kG field. At higher and lower temperatures an excess specific heat appears; around 4.5 mK there appears to be a large, very sharp specific heat anomaly. The nuclear magnetic sugceptibility shows Curie law behavior down to 10 mK, where the susceptibility begins increasing more rapidly until apparently resuming its higher-temperature behavior below 4 mK. The bulk electronic thermal relaxation time of PrCu/sub 6/ would seem to go through a peak value of approximately one hour just above 3 mK and decrease to much less than a minute by 8 mK. The above results point to a possible nuclear ordering in the Pr nuclear spin system at approximately 4.5 mK. (19 figures, 52 references) (auth)
- Research Organization:
- American Univ., Beirut, Lebanon
- NSA Number:
- NSA-29-011338
- OSTI ID:
- 4395628
- Journal Information:
- Phys. Rev., B, v. 8, no. 3, pp. 1276-1278, Other Information: Orig. Receipt Date: 30-JUN-74
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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