Cooling a nanoscale device by a spin-polarized nonequilibrium current
Final Report Abstract
The active cooling of nanoscale devices which carry an electron current is an important ingredient in the technological use of quantum electronics. In order to operate nanoscale devices in the quantum regime, low temperatures have to be realized. In this research project, we have transfered the thermodynamic concept of demagnetization cooling to the realm of nanophysics. Instead of using global magnetic fields and mechanically moving coolants as done on the macroscale, we have formulated the proof-of-principle of a magnetic molecular nanojunction which is placed in between two ferromagnetic electrical contacts. A charge current of spin-polarized electrons polarizes the magnetic moment of the nanojunction in a lower energy state. A magneto-mechanical interaction between the magnetic and the vibrational degree of freedom of the nanodevice allows it to transfer energy from the thermal vibration into the magnetic degree of freedom. Overall, a net cooling of the vibrational degree of freedom results. Most importantly, we have shown that the unavoidable Ohmic heating due to the flowing electron charges can be outrun by the magnetomechanical cooling. We have shown that cooling is possible in almost the entire range of parameters which were chosen in agreement with existing experiments. When the bias voltage is reversed, also heating is possible in the same set-up. As a further unexpected result, we have found that an effective exchange magnetic field at the position of the molecular bridge can be generated for a nonmagnetic bridge by an intricate interplay of the spin polarization of the ferromagnetic leads and the vibrational degree of freedom. A ’vibrational spin valve’ can thus be realized. These results were published in three publications in high-ranking scientific journals, among which a publication in Physical Review Letters came out. This work received considerable attention in a broader media coverage. Two popular journals (Physics, Popular Mechanics) have recognized the conceptual importance of our results for a possible technological basis of future nanocooling schemes in quantum electronic devices.
Publications
- Cooling a magnetic nanoisland by spin-polarized currents. Phys. Rev. Lett. 113, 076602 (2014)
J. Brüggemann, S. Weiss, P. Nalbach, and M. Thorwart
(See online at https://doi.org/10.1103/PhysRevLett.113.076602) - Spin-vibronics in interacting nonmagnetic molecular nanojunctions. Phys. Rev. B 92, 045431 (2015)
S. Weiss, J. Brüggemann, and M. Thorwart
(See online at https://doi.org/10.1103/PhysRevB.92.045431) - Exploiting the magnetomechanical interaction for cooling magnetic molecular junctions by spin-polarized currents. New J. Phys. 18, 023026 (2016)
J. Brüggemann, S. Weiss, P. Nalbach, and M. Thorwart
(See online at https://doi.org/10.1088/1367-2630/18/2/023026)
