Shot-Noise in a Quantum Dot as a Spin-current Diode

Shot-noise is an unavoidable non-equilibrium current fluctuation that arises from the granularity of the electron charge. In the present work, we investigate shot-noise for the recently proposed spin diode system (1,2). This consists of a quantum dot coupled to two metallic leads, one nonmagnetic (NM) and another ferromagnetic (FM). In the Coulomb blockade regime this system displays a spin-diode effect (1,2), which has recently been probed in a carbon nanotube based quantum dot (2). Our calculation shows that the shot-noise provides a robust signature for this spin-polarization rectification effect. In the bias range for which the current polarization is zero the shot-noise is super-Poissonian. In contrast, for voltages such that the current is spin polarized, the shot-noise becomes sub-Poissonian. Hence shot noise can provide an interesting additional tool to probe spin-polarized transport in these systems. We shall also discuss recent experimental progress in this direction (3). (1) F. M. Souza, J. C. Egues, and A. P. Jauho, Phys. Rev. B 75, 165303 (2007). (2) C. A. Merchant and N. Markovic, Phys. Rev. Lett. 100, 156601 (2008). (3) C. A. Merchant and N. Markovic, J. Appl. Phys. 105, 07C711 (2009).