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Brief report of EPSRC grant
GR/H99202
Investigators: Dr M. Elliott, Dr W.G. Herrenden-Harker
(Cardiff University); Dr Alan Usher (University of Exeter).
This was a 2-year collaborative pilot programme to demonstrate the feasibility of performing torque magnetometry measurements in a dilution refrigerator. The motivation for doing this is to study the phase diagram of the exotic new states of matter which occur when a 2- dimensional electron system (2DES) is subjected to high magnetic fields and low temperatures.
Magnetometry has two distinct advantages for such studies: (1) the equilibrium magnetisation of a 2DES is a thermodynamic state variable and therefore provides direct information about the equilibrium Free Energy of the system; this information is very difficult to obtain using more conventional techniques. (2) non-equilibrium magnetisation, originating from induced eddy currents, can be used to study the integer and fractional quantum Hall effects, and the contactless geometry of such a measurement means that the results obtained are unequivocally associated with the 2DES rather than its contacts. The principal achievements of this programme have been:
References
[1] JP Watts, A Usher, AJ Matthews, M Elliott, WG Herrenden-Harker, MY
Simmons and
DA Ritchie, Phys Rev Lett (1998) 81, 4220
[2] CL Jones, A Usher, M Elliott, WG Herrenden-Harker, A Potts, RA
Shepherd, TS Cheng,
CT Foxon, Solid State Comm (1996) 97 763
[3] A Potts, RA Shepherd, M Elliott, WG Herrenden-Harker, CL Jones, A
Usher, GAC
Jones, DA Ritchie, EH Linfield, M Grimshaw, J Phys: Condensed Matter (1996)
8 5189
[4] CL Jones, A Usher, M Elliott, WG Herrenden-Harker, A Potts, RA
Shepherd, TS Cheng,
CT Foxon, Solid State Comm (1995) 95 409