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SUMMARY:Interactions and the dHvA Effect - P.C.E. Stamp \, University of B
 ritish Columbia\; Pacific Institute of Theoretical Physics
DTSTART:20081029T111500Z
DTEND:20081029T121500Z
UID:TALK14543@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:Since 1930 it has been known that any system of charged mobile
  fermions will show ‘quantum oscillation effects’ in all of its thermo
 dynamic and transport properties\, as a function of applied field B (and o
 scillatory in 1/B). These effects (known as dHvA oscillations in the case 
 of the thermodynamic effect) arise from Landau level quantization – as t
 hese levels pass through the Fermi energy with increasing field\, they dum
 p the fermions to the levels below. Starting with experiments by Shoenberg
 \, and theory by Landau\, in 1938\, the idea that dHvA effects could be us
 ed as ‘calipers’ to measure the Fermi surface began to take hold. By t
 he 1960’s this was a major tool in solid-state physics.\n     However it
  was never obvious how strong correlations between fermions would affect t
 his. Fundamental work by Luttinger\, Bychkov\, and Gorkov indicated that i
 n a 3d metal\, interactions would not change the fundamental dHvA behaviou
 r\, which would now be looking at Fermi surface ‘quasiparticles’ . How
 ever in 2D we now know that a fundamental change occurs at very high field
 s\, when the Landau level filling fraction in of order one or less – we 
 than get Fractional Hall fluids\, which involve a fundamental reorganizati
 on of the wave functions. As I will discuss\, the breakdown of the usual 
 ‘quasiparticle’ picture actually persists right down to low fields in 
 2d – Landau level quantization immediately destroys standard Fermi liqui
 d behaviour in the presence of interactions\, and one cannot assume the us
 ual dHvA behaviour\, which is radically changed. This requires a reassessm
 ent of the recent dHvA results in high-Tc materials as well as that in oth
 er quasi-2d systems. In particular\, these results do not yet demonstrate 
 Fermi liquid behaviour in these systems.  \n\n
LOCATION:Small Lecture Theatre\, Cavendish Laboratory\, Department of Phys
 ics
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