Abstract
In spintronics the active control and manipulation of spin currents is studied in solid-state systems. Opposed to charge currents, spin currents are strongly damped due to collisions between different spin carriers in addition to relaxation due to impurities and lattice vibrations. The phenomenon of relaxation of spin currents is called spin drag. Here we study spin drag in ultra-cold bosonic atoms deep in the hydrodynamic regime and show that spin drag is the dominant damping mechanism for spin currents in this system. By increasing the phase space density we find that spin drag is enhanced in the quantum regime by more than a factor of two due to Bose stimulation, which is in agreement with recent theoretical predictions and, surprisingly, already occurs considerably above the phase transition.
Highlights
The field of spintronics [1,2,3,4,5], where the spin of the electron is manipulated rather than its charge, has recently led to interest in spin currents
By increasing the phase space density we find that spin drag is enhanced in the quantum regime by more than a factor of two due to Bose stimulation, which is in agreement with recent theoretical predictions and, surprisingly, already occurs considerably above the phase transition
These spin currents can be subject to strong relaxation due to collisions between different spin species, a phenomenon known as spin drag [6]
Summary
The field of spintronics [1,2,3,4,5], where the spin of the electron is manipulated rather than its charge, has recently led to interest in spin currents. These spin currents can be subject to strong relaxation due to collisions between different spin species, a phenomenon known as spin drag [6] This effect has been observed for electrons in semi-conductors [7] and for cold fermionic atoms [8,9,10], where in both cases it is reduced at low temperatures due to the fermionic nature of the particles. We here show that for bosons the opposite behavior occurs and the spin drag is quantum enhanced This enhancement is due to Bose statistics and gives rise to an extra factor (1 + ni) for scattering of bosonic particles into states already containing ni particles. For fermions one would have Pauli blocking and an extra factor (1 − ni) that implements the Pauli exclusion principle and in that case forbids scattering into a state that is already occupied
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