Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor
Abstract
The precessing magnetization of a magnetic islands coupled to a quantum spin Hall edge pumps charge along the edge. Conversely, a bias voltage applied to the edge makes the magnetization precess. We point out that this device realizes an adiabatic quantum motor and discuss the efficiency of its operation based on a scattering matrix approach akin to Landauer-Büttiker theory. Scattering theory provides a microscopic derivation of the Landau-Lifshitz-Gilbert equation for the magnetization dynamics of the device, including spin-transfer torque, Gilbert damping, and Langevin torque. We find that the device can be viewed as a Thouless motor, attaining unit efficiency when the chemical potential of the edge states falls into the magnetization-induced gap. For more general parameters, we characterize the device by means of a figure of merit analogous to the ZT value in thermoelectrics.
- Publication:
-
Physica E Low-Dimensional Systems and Nanostructures
- Pub Date:
- November 2015
- DOI:
- 10.1016/j.physe.2015.08.031
- arXiv:
- arXiv:1507.06505
- Bibcode:
- 2015PhyE...74..596A
- Keywords:
-
- Quantum spin Hall effect;
- Topological insulators;
- Magnetization dynamics;
- Condensed Matter - Mesoscale and Nanoscale Physics
- E-Print:
- 9 pages, 2 figures. Contribution to a special issue in Physica E on "Frontiers in quantum electronic transport" - in memory of Markus B"uttiker