Detection of spin bias in a four-terminal quantum-dot ring

In this work, via introducing local Rashba spin-orbit interaction in a four-terminal quantum-dot (QD) ring, we show that the spin bias in the transverse terminals induces apparent charge currents in the longitudinal terminals, accompanied by the similar magnitude and opposite directions of them. The reason is that the Rashba interaction destroys the space-reversal symmetry of this structure and causes the spin dependence of the quantum interference. Then the opposite-spin currents driven by the spin bias present different magnitudes, which gives rise to the emergence of finite charge currents in the longitudinal terminals. Via these results, we suggest that the spin bias can be measured by observing the longitudinal charge currents, which provides an electrical but practical scheme to detect the spin bias (or spin current).