ABSTRACT
We consider mesoscopic fluctuations of the Coulomb drag coefficient rho(D) in the system of two separated two-dimensional electron gases. It is shown that at low temperatures sample-to-sample fluctuations of rho(D) exceed its ensemble average. It means that in such a regime the sign of rho(D) is random and the temperature dependence almost saturates, rho(D) approximately 1/sqrt[T].
ABSTRACT
We show that in ultrasmall superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states, and find analytically the exponential tail at low energies. Thus, the tunneling density of states exhibits the "soft gap" behavior. As the energy approaches zero, it vanishes linearly with excitation energy.
