17 research outputs found
Current correlations and quantum localization in 2D disordered systems with broken time-reversal invariance
We study long-range correlations of equilibrium current densities in a
two-dimensional mesoscopic system with the time reversal invariance broken by a
random or homogeneous magnetic field. Our result is universal, i.e. it does not
depend on the type (random potential or random magnetic field) or correlation
length of disorder. This contradicts recent sigma-model calculations of
Taras-Semchuk and Efetov (TS&E) for the current correlation function, as well
as for the renormalization of the conductivity. We show explicitly that the new
term in the sigma-model derived by TS&E and claimed to lead to delocalization
does not exist. The error in the derivation of TS&E is traced to an incorrect
ultraviolet regularization procedure violating current conservation and gauge
invariance.Comment: 8 pages, 3 figure
Effect of a gap opening on the conductance of graphene superlattices
The electronic transmission and conductance of a gapped graphene superlattice
were calculated by means of the transfer-matrix method. The system that we
study consists of a sequence of electron-doped graphene as wells and hole-doped
graphene as barriers. We show that the transmission probability approaches
unity at some critical value of the gap. We also find that there is a domain
around the critical gap value for which the conductance of the system attains
its maximum value.Comment: 14 pages, 5 figures. To appear in Solid State Communication