Sequential tunneling and shot noise in ferromagnet/normal-metal/ferromagnet double tunnel junctions

TL;DR

This paper investigates how spin and charge interactions affect tunneling, TMR, and noise in ferromagnet/normal-metal/ferromagnet junctions, revealing oscillations and noise enhancements influenced by device asymmetry and temperature.

Contribution

It introduces a detailed analysis of spin-charge interplay in double tunnel junctions using the master equation, highlighting effects on TMR and noise oscillations.

Findings

Charge correlation causes oscillations in chemical potential and TMR.

Spin correlation can enhance finite-frequency noise.

Temperature smears the oscillatory effects.

Abstract

The tunneling through a ferromagnet/normal metal/ferromagnet double junction in the Coulomb blockade regime is studied, assuming that the spin relaxation time of electron in the central metallic island is sufficiently large. Using the master equation, the current, the tunnel magnetoresistance (TMR), and the current noise spectrum have been calculated for devices of different parameters. It was shown that the interplay between spin and charge correlations strongly depends on the asymmetry of measured device. The charge correlation makes both the chemical potential shift, which describes the spin accumulation in the central island, and the TMR oscillated with the same period as the Coulomb staircase in current-voltage characteristics. This effect is smeared by the temperature. The spin correlation may cause an enhancement of noise at finite frequencies, while the zero frequency noise is still always sub-poissonian. The gate voltage causes an oscillation of not only conductance, but also TMR and noise.