Dephasing-enabled triplet Andreev conductance

We study the conductance of normal-superconducting quantum dots with strong spin-orbit scattering, coupled to a source reservoir using a single-mode spin-filtering quantum point contact. The choice of the system is guided by the aim to study triplet Andreev reflection without relying on half metallic materials with specific interface properties. Focusing on the zero temperature, zero-bias regime, we show how dephasing due to the presence of a voltage probe enables the conductance, which vanishes in the quantum limit, to take nonzero values. Concentrating on chaotic quantum dots, we obtain the full distribution of the conductance as a function of the dephasing rate. As dephasing gradually lifts the conductance from zero, the dependence of the conductance fluctuations on the dephasing rate is nonmonotonic. This is in contrast to chaotic quantum dots in usual transport situations, where dephasing monotonically suppresses the conductance fluctuations.Comment: 6 pages, 3 figure

A basic optimization problem in linear systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48017/1/224_2005_Article_BF01691464.pd

Relative asymptotics for orthogonal matrix polynomials with respect to a perturbed matrix measure on the unit circle

19 pages, no figures.-- MSC2000 codes: 42C05, 47A56.MR#: MR1970413 (2004b:42058)Zbl#: Zbl 1047.42021Given a positive definite matrix measure Ω supported on the unit circle T, then main purpose of this paper is to study the asymptotic behavior of L_n(\tilde{\Omega}) L_n(\Omega) -1} and \Phi_n(z, \tilde{\Omega}) \Phi_n(z, \tilde{\Omega}) -1} where $\tilde{\Omega}(z) = \Omega(z) + M \delta ( z - w)$, $1$, M is a positive definite matrix and δ is the Dirac matrix measure. Here, Ln(·) means the leading coefficient of the orthonormal matrix polynomials Φn(z; •).Finally, we deduce the asymptotic behavior of $\Phi_n(omega, \tilde{\Omega}) \Phi_n(omega, \Omega)$ in the case when M=I.The work of the second author was supported by Dirección General de Enseñanza Superior (DGES) of Spain under grant PB96-0120-C03-01 and INTAS Project INTAS93-0219 Ext.Publicad