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SUMMARY:Conductivity-scaling in highly-resistive two-dimensional electron 
 gases - Dr Dirk Backes\, University of Cambridge\, Semiconductor Physics G
 roup
DTSTART:20150325T141500Z
DTEND:20150325T151500Z
UID:TALK57822@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:The weak localization (WL) regime of low-disorder\, two-dimens
 ional electron gases (2DEGs) displays many outwardly metal-like characteri
 stics [1\, 2\, 3] which have led to the long-standing debate of whether or
  not 2D systems can harbour truly metallic ground-states. While signatures
  of insulating behaviour can be found in the 2DEG magnetoresistance [2] an
 d the temperature (T)-dependence of electrical conductivity σ [3\, 4]\, u
 ltimately\, the undeniably large σ achievable in ultra-high-mobility 2DEG
 s in the WL regime remains a constant source of uncertainty.\n\nHere we de
 monstrate dramatic imprints of WL in mesoscopic-sized 2DEGs in which σ is
  two orders of magnitude smaller than e2/h even in the low disorder limit\
 , 1 < kfl < 7\, where kf is the Fermi wavevector and l is the electronic m
 ean-free path. By systematically varying the size of the 2DEGs under study
 \, we are able to show that the suppression in σ arises solely due to qua
 ntum interference effects [5] rather than disorder. Remarkably\, the 2DEGs
  are in a regime where\, despite σ << e2/h\, at low T the WL is obvious a
 nd hopping transport due to strong localization appears as small correctio
 ns in σ(T). Importantly\, we establish the need to exercise caution while
  identifying σ/(e2/h) with kfl\, which is routinely done despite contradi
 cting the one-parameter scaling theory [5]. \n\nOur results provide fundam
 entally new insights into the WL regime and\, moreover\, provide a powerfu
 l diagnostic with which to understand the putative 2D metal-insulator tran
 sition.\n\n[1] E. Abrahams\, S. V. Kravchenko\, and M. P. Sarachik\, Rev. 
 Mod. Phys. 73\, 251 (2001).\n[2] M. Y. Simmons et al.\, Phys. Rev. Lett. 8
 4\, 2489 (2000).\n[3] A. R. Hamilton\, M. Y. Simmons\, M. Pepper\, E. H. L
 infield\, and D. A. Ritchie\, Phys. Rev. Lett. 87\, 126802 (2001).\n[4] M.
  J. Uren\, R. A. Davies\, M. Kaveh\, and M. Pepper\, J. Phys. C 14\, 5737 
 (1981).\n[5] E. Abrahams\, P. W. Anderson\, D. C. Licciardello\, and T. V.
  Ramakrishnan\, Phys. Rev. Lett. 42\, 673 (1979).\n
LOCATION:Mott Seminar Room (Mott Building Room 531)\, Cavendish Laboratory
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