Figure 1: a) SEM micrograph of a lateral spin-valve structure featuring an atomic scale point contact in the normal metal junction. b) Differential conductance spectra of a Co/Pd point contact excited with microwaves at different magnetic fields. A splitting of the zero-bias anomaly occurs and a spin-inversion is achieved, when the resonance condition ℏω=gμB is matched.

Recent, mainly theoretical, reports suggest that novel transport-related phenomena in magnetic nano-junctions occur under strong thermodynamic non-equilibrium conditions. One of the most intriguing effects is the demonstration of photoemission in magnetic point contacts driven by a spin-polarized current

In this project, the spin-flip photoemission in magnetic point contacts between a ferromagnet (F) and a normal metal (N) or a dilute ferromagnet (f) is studied experimentally. In these point contacts a non-equilibrium spin-population is generated between energy-split spin-subbands. The energy splitting is created by inducing a Zeeman-splitting in a normal metal (N) or by utilizing the exchange splitting in a dilute ferromagnet (f). Common to both, the Zeeman-type (F/N) and exchange-type (F/f) spin-flip radiation sources is to achieve a spin-population inversion by pumping hot, spin-polarized electrons from the ferromagnet (F) into the normal metal (N) or the dilute ferromagnet (f) respectively. This non-equilibrium situation then relaxes into the ground state via photoemission.

In lateral spin-valve structures composed of magnetic and non-magnetic metals (Figure 1a) under high voltage bias and high frequency excitation in the GHz and THz regime, we investigate the spin-flip photoemission experimentally.

A spin-population inversion is created via microwave absorption in the point contact and can be detected via transport spectroscopy (Figure 1b).

  1. Kadigrobov, A. M.; Shekhter, R. I.; Jonson, M. Low Temperature Physics 2005, 31, 352-357.
  2. Kadigrobov, A. M.; Ivanov, Z.; Claeson, T.; Shekhter, R. I.; Jonson, M. Europhysics Letters 2004, 67,948-954.

Publications

  1. Torsten Pietsch, Stefan Egle, Martin Keller, Hans Fridtjof Pernau, Florian Strigl and Elke Scheer
    Microwave-induced direct spin-flip transitions in mesoscopic Pd/Co heterojunctions
    New J. Phys. 18 (2016) 093045

Information

Contributors: Julian Braun, Mengqi Fu
Former contributors: Torsten Pietsch, Stefan Egle
External cooperations: Vladislav Korenivski (KTH, Stockholm), Anatoly Kadigrobov (Ruhr-Universität Bochum), Robert Shekhter (University of Gothenburg)
Fundings: German Science Foundation
Period: Jan 2014 - Dec 2017