M B Ketchen | PubMed Health

PubMed2001

Diamagnetic persistent current in diffusive normal-metal rings.

We have measured a diamagnetic persistent current with flux periodicities of both h/e and h/2e in an array of thirty diffusive mesoscopic gold rings. At the lowest temperatures, the magnitudes of the currents per ring corresponding to the h/e- and h/2e-periodic responses are both comparable to the Thouless energy E(c) identical with Planck's over 2pi/tau(D), where tau(D) is the diffusion time. Taken in conjunction with earlier experiments, our results strongly challenge the conventional theories of persistent current. We consider a new approach associated with the saturation of the phase coherence time tau(phi).

Journal Article↗

PubMed1991

Multichannel hybrid system for neuromagnetic measurements.

This paper describes progress toward the development of a 28-multichannel system for neuromagnetic measurements. A novel 'hybrid' design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimises the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the centre of the array and features a localisation power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnetic measurements over a circular scalp region of 16 cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at the IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low cost electronic system has been designed and fabricated for the DC SQUID sensors.

Equipment Design↗