Sensitive temperature gradiometer for use at low temperatures.
A device capable of very sensitive temperature gradient measurements in the presence of relatively large ambient temperature fluctuations is described. The device uses a pair of ''matched'' superconducting thin films in a bridge arrangement, with a SQUID magnetometer probe as the null detector.
DYNAMICS OF VORTEX LINES IN SUPERFLUID 4HELIUM *
Solid-body rotation, characteristic of a uniformly rotating ordinary fluid, is therefore clearly forbidden. It does not follow, however, that for superfluid contained within a cylindrical container rotating about the cylinder axis, the velocity itself is necessarily zero. Above some critical angular velocity (much smaller than the angular velocities investigated in the experiments discussed in this paper), the free energy of the system is decreased with the introduction of a filamentary discontinuity threading the fluid from container wall to container wall along the rotational axis. In the presence of this discontinuity (termed a vortex line), the superfluid executes azimuthal motion about the line, with a velocity given by
Motion of the vortex lattice in a dirty type II superconductor
We reexamine here microscopically the transport properties of the vortex state in a dirty type II superconductor in the high-field region. We show that the previous theory by Caroli and Maki predicts the entropy carried by a single vortex line, which is consistent with recent experiments, provided the expression of the heat current is properly corrected. Furthermore, we show that a large heat delivered by vortex lines together with the normal thermoelectric effect, which persists even in the vortex state, results in a large Hall current in the vortex state. This may account for a large Hall effect observed by Niessenet al. in Nb-Ta alloys.