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Conductivity-scaling in highly-resistive two-dimensional electron gases

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The weak localization (WL) regime of low-disorder, two-dimensional electron gases (2DEGs) displays many outwardly metal-like characteristics [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] and the temperature (T)-dependence of electrical conductivity σ [3, 4], ultimately, the undeniably large σ achievable in ultra-high-mobility 2DEGs in the WL regime remains a constant source of uncertainty.

Here we demonstrate 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 mean-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 quantum 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 and hopping transport due to strong localization appears as small corrections in σ(T). Importantly, we establish the need to exercise caution while identifying σ/(e2/h) with kfl, which is routinely done despite contradicting the one-parameter scaling theory [5].

Our results provide fundamentally new insights into the WL regime and, moreover, provide a powerful diagnostic with which to understand the putative 2D metal-insulator transition.

[1] E. Abrahams, S. V. Kravchenko, and M. P. Sarachik, Rev. Mod. Phys. 73, 251 (2001). [2] M. Y. Simmons et al., Phys. Rev. Lett. 84, 2489 (2000). [3] A. R. Hamilton, M. Y. Simmons, M. Pepper, E. H. Linfield, and D. A. Ritchie, Phys. Rev. Lett. 87, 126802 (2001). [4] M. J. Uren, R. A. Davies, M. Kaveh, and M. Pepper, J. Phys. C 14 , 5737 (1981). [5] E. Abrahams, P. W. Anderson, D. C. Licciardello, and T. V. Ramakrishnan, Phys. Rev. Lett. 42, 673 (1979).

This talk is part of the Semiconductor Physics Group Seminars series.

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