Unidirectional spin transport of a spin-orbit-coupled atomic matter wave using a moving Dirac δ -potential well

Abstract

We study the transport of a spin-orbit-coupled atomic matter wave using a moving Dirac $\ensuremath{\delta}$-potential well. In a spin-orbit-coupled system, bound states can be formed in both ground and excited energy levels with a Dirac $\ensuremath{\delta}$ potential. Because Galilean invariance is broken in a spin-orbit-coupled system, moving of the potential will induce a velocity-dependent effective detuning. This induced detuning breaks the spin symmetry and makes the ground-state transporting channel be spin-$\ensuremath{\uparrow}$ ($\ensuremath{\downarrow}$) favored while makes the excited-state transporting channel be spin-$\ensuremath{\downarrow}$ ($\ensuremath{\uparrow}$) favored for a positive-direction (negative-direction) transporting. When the $\ensuremath{\delta}$-potential well moves at a small velocity, both the ground-state and the excited-state channels contribute to the transportation, and thus both the spin components can be efficiently transported. However, when the moving velocity of the $\ensuremath{\delta}$-potential well exceeds a critical value, the induced detuning is large enough to eliminate the excited bound state, and makes the ground bound state the only transporting channel, in which only the spin-$\ensuremath{\uparrow}$ ($\ensuremath{\downarrow}$) component can be efficiently transported in a positive (negative) direction. This work demonstrates a prototype of unidirectional spin transport.