Full counting statistics of incoherent Andreev transport

We study the full counting statistics of heterostructures consisting of normal metal parts connected to a superconducting terminal. Assuming that coherent superconducting correlations are suppressed in the normal metals we show, using Keldysh-Nambu Green's functions, that the system can be mapped onto a purely normal system with twice the number of elements. For a superconducting beam splitter with several normal terminals we obtain general results for the counting statistics.Comment: 7 pages, submitted to Europhys. Let

Spectral Features of the Proximity Effect

We calculate the local density of states (LDOS) of a superconductor-normal metal sandwich at arbitrary impurity concentration. The presence of the superconductor induces a gap in the normal metal spectrum that is proportional to the inverse of the elastic mean free path $l$ for rather clean systems. For a mean free path much shorter than the thickness of the normal metal, we find a gap size proportional to $l$ that approaches the behavior predicted by the Usadel equation (diffusive limit).Comment: LT22 proceeding

Local Density of States in a Dirty Normal Metal connected to a Superconductor

A superconductor in contact with a normal metal not only induces superconducting correlations, known as proximity effect, but also modifies the density of states at some distance from the interface. These modifications can be resolved experimentally in microstructured systems. We, therefore, study the local density of states $N(E,x)$ of a superconductor - normal metal heterostructure. We find a suppression of $N(E,x)$ at small energies, which persists to large distances. If the normal metal forms a thin layer of thickness $L_n$, a minigap in the density of states appears which is of the order of the Thouless energy $\sim \hbar D/L_n^2$. A magnetic field suppresses the features. We find good agreement with recent experiments of Gu\'eron {\it et al.}Comment: 5 pages, RevTeX, 7 Figures (included), Submitted to PRB. Revised version: One figure changed, missprints correcte

Charge transport through a SET with a mechanically oscillating island

We consider a single-electron transistor (SET) whose central island is a nanomechanical oscillator. The gate capacitance of the SET depends on the mechanical displacement, thus, the vibrations of the island vibrations may strongly influence the current-voltage characteristics, current noise, and higher cumulants of the current. Harmonic oscillations of the island and oscillations with random amplitude (e.g., due to the thermal activation) change the transport characteristics in a different way. The noise spectrum has a peak at the frequency of the island oscillations; when the island oscillates harmonically, the peak reduces to a $\delta$-peak. We show that knowledge of the SET transport properties helps to determine in what way the island oscillates, to estimate the amplitude, and the frequency of the oscillations

Quantum transport signatures of chiral edge states in Sr2_2RuO4_4

We investigate transport properties of a double quantum dot based Cooper pair splitter, where the superconducting lead consists of Sr$_2$RuO$_4$. The proposed device can be used to explore the symmetry of the superconducting order parameter in Sr$_2$RuO$_4$ by testing the presence of gapless chiral edge states, which are predicted to exist if the bulk superconductor is described by a chiral $p$--wave state. The odd orbital symmetry of the bulk order parameter ensures that we can realize a regime where the electrons tunneling into the double dot system come from the chiral edge states and thereby leave their signature in the conductance. The proposed Cooper pair splitter has the potential to probe order parameters in unconventional superconductors.Comment: 5 page

The connection between noise and quantum correlations in a double quantum dot

We investigate the current and noise characteristics of a double quantum dot system. The strong correlations induced by the Coulomb interaction create entangled two-electron states and lead to signatures in the transport properties. We show that the interaction parameter phi, which measures the admixture of the double-occupancy contribution to the singlet state and thus the degree of entanglement, can be directly accessed through the Fano factor of super-Poissonian shot noise.Comment: 5 pages, major revision, to be published in Phys. Rev.

Circuit theory for crossed Andreev reflection and nonlocal conductance

Nonlocal currents, in devices where two normal metal terminals are contacted to a superconductor, are determined using the circuit theory of mesoscopic superconductivity. We calculate the conductance associated with crossed Andreev reflection and electron transfer between the two normal metal terminals, in addition to the conductance from direct Andreev reflection and quasiparticle tunneling. Dephasing and proximity effect are taken into account.Comment: Included in special issue Spin Physics of Superconducting heterostructures of Applied Physics A: Materials Science & Processin