Professor Shaun Fisher
Professor
Room: A47 Physics Building
Tel: +44 (0)1524 594480
Fax: +44 (0)1524 844037
Email: s.fisher@lancaster.ac.uk
Research
Since graduating from St Edmund Hall, Oxford in 1988, I have been researching various aspects of quantum fluids and solids with the Lancaster Ultra-Low Temperature Group. Over the past years, with colleagues Ian Bradley, Tony Guénault, Richard Haley and George Pickett, we have advanced microKelvin cooling techniques and have made many novel experiments on superfluid 3He and related systems. Our group is well known internationally for our novel 'Lancaster-Style Nuclear cooling cells' which allow us to cool electrons in copper to just a few microKelvin and, more routinely, superfluid 3He to temperatures as low as 80 microKelvin. We also built the world's coldest dilution refrigerator as part of our advanced microKelvin cooling machine.
Our research interests are focussed primarily on the exotic properties of superfluid 3He at ultra-low temperatures. Our record-breaking cooling techniques give us the (almost) unique possibility to instigate experiments on the B-phase superfluid in the ballistic quasiparticle regime where the excitation mean free path is effectively infinite (~ km). We have developed ballistic quasiparticle beam techniques on macroscopic (cm) length scales. We have applied such techniques to study a wide variety of phenomena. For example, we have made direct measurements of Andreev Scattering, we have made the first studies of both the thermodynamic and dynamic properties of the A-B phase boundary at low temperatures and we have made the first measurements of quantum turbulence in superfluid 3He at low temperatures.
We have also developed techniques for using black-body radiators for particle detection allowing nuclear recoil energies on the scale of 1keV to be measured, and during my stay in Grenoble, we applied radiator techniques to infer that quantum vortices are generated following the rapid phase transition back into the superfluid state after local heating produced by nuclear reactions with neutrons. This experiment gave a quantitative test of the Kibble mechanism, originally proposed as a mechanism for cosmic string creation shortly after the big bang.
Our group have discovered exotic NMR phenomena in the B-phase. We find extremely long-lived modes of spin precession, named ‘persistent precessing domains’ (PPD) at the lowest achievable temperatures. These are regions of coherent spin–precession which may have free-decays exceeding half an hour even in quite inhomogeneous magnetic fields. Recent theoretical work within our group suggests that we may be observing, for the first time, the effects of orbital superfluidity.
Recently, we have performed novel experiments on dirty superfluid 3Heusing silica aerogels. The aerogels provide a skeletal network of nanometer sized silica strands which give us an ideal system for studying the effects of impurity scattering in unconventional condensates. We have performed the first measurements of the A-B phase diagram in aerogel at low temperatures and have discovered gapless superfluidity in aerogel.
We have performed various experiments on superfluid 4He, including studies of turbulence at milliKelvin temperatures. On dilute 3He- 4He solutions our research includes mesoscopic experimentsin the nanometer sized pores of vycor glass, high spin polarisation experiments, and thermal Kapitza boundary resistance measurements.
Teaching
I have taught various undergraduate courses including matter at low temperatures, statistical physics, low temperature mini-projects, physical systems and various experimental projects. I have been director of studies for part II students, director of experimental skills, and from 2005/6, I will be the director of undergraduate physics teaching.