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SUMMARY:Emergence of a novel correlated-electron metal in a 2D electron ga
 s - Dr. Vijay Narayan\, Semiconductor Physics Group\, Cavendish Laboratory
DTSTART:20140612T100000Z
DTEND:20140612T103000Z
UID:TALK52957@talks.cam.ac.uk
CONTACT:Leona Hope-Coles
DESCRIPTION:This seminar is being given as part of the recruitment process
  for the Early Career Lectureships. Members of the Department are encourag
 ed to attend as the selection panel would welcome any feedback by email to
  hod@phy.cam.ac.uk\n\n*ABSTRACT*: Two-dimensional electron gases (2DEGs) a
 re a rich playground for inter-electron interactions and host to several f
 ascinating phenomena such as the quantum Hall effect\, the fractional quan
 tum Hall effect and the 2D ‘metal-to-insulator transition’. They are i
 deal test beds to observe the delicate interplay of the many-body Coulomb 
 potential and disorder which theoretically has been predicted to give rise
  to very rich electronic phase behaviour.\n\nIn this talk I will present s
 ome of my recent experimental studies on the thermopower (_S_) of GaAs-bas
 ed mesoscopic 2DEGs where I am looking for novel electron phase behaviour.
  I will start with an introduction to many-electron physics in 2DEGs\, and
  then briefly discuss why  _S_ is a powerful probe of such many-body effec
 ts\, before going into the experimental results. Remarkably\, the data sug
 gest a density-driven transition between two distinct electron phases both
  of which show metal-like transport. Interestingly\, neither _S_ nor the e
 lectrical resistivity _ρ_ show any indication of the more conventional 2D
  metal-insulator transition even when _ρ_ is two orders of magnitude grea
 ter than the resistance quantum h/e^2^. Instead\, as _n_ is lowered\, the 
 2DEG shows an abrupt departure from simple\, non-interacting\, _Drude meta
 l_-like behaviour to strongly-interacting\, correlated-electron behaviour.
  The latter include (i) A metallic character as evidenced by the linear _T
 _-dependence of _S_ and  _T_-independent nature of _ρ_ even when _ρ_ >> 
 h/e^2^\; (ii) strong oscillations and even _sign changes_ in _S_ while _ρ
 _ is absolutely monotonic\; and (iii) exceedingly large _S_-values of ~100
  mV/K at 1.5 K. Furthermore\, in the _T_-dependence of _S_\, there is an e
 arlier onset of phonon drag as compared to the non-interacting phase signi
 fying a sharp reduction in the number of charge carriers. This reduction c
 annot be simply explained by the gating action used to tune _n_ and is a s
 trong indicator of correlated electron behaviour. I will conclude with an 
 explanation of these results based on a picture of the 2DEG tending toward
 s a spatially ordered state as _n_ is reduced and in which collective elec
 tron excitations mediate both thermal and electrical transport.
LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory\, Department of Ph
 ysics
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