Kolloquiumsvortrag Physik: Optical control of spin currents in lead halide perovskites

Apr 16
16. April 2018 16:00 Uhr bis 17:00 Uhr
Hörsaal E, Staudtstr. 5, 91058 Erlangen

Optical control of spin currents in lead halide perovskites

Lead halide perovskites (LHPs) form a class of semiconductors with an almost direct band gap, whose size can be tuned across the near-infrared, visible, and near-ultraviolet spectral range by varying their chemical composition. Despite the ionic character of the materials, the effective masses of both electrons and holes are small. Therefore, possible applications of LHPs in optoelectronics and especially in thin-film solar cells have attracted significant research interest.
The unusual band structure of LHPs is the result of strong spin-orbit coupling, which distinguishes the materials from semiconductors composed of lighter elements. The spin-orbit coupling does not only reduce carrier effective masses and affect the band ordering. In crystals without inversion symmetry, it also lifts the spin degeneracy of the electronic bands, an effect commonly referred to as the Rashba effect [1]. The occurrence of a Rashba effect in crystals with inversion symmetry, but a local site asymmetry was predicted in 2012 [2]. In LHPs, which have a cubic structure at sufficiently high temperature, the local symmetry can be broken by the incorporation of small dipolar molecules with rotational disorder into the lattice. For this situation, calculations predict a “dynamical” Rashba effect, even if the crystal maintains inversion-symmetry on average [3].
I will present electron [4] and optical spectroscopy [5] experiments which detect the fingerprints of the Rashba effect, and the optical excitation of spin currents in transport [6]. Implications for the photophysics in LHP solar cells will be discussed. The dynamical Rashba effect should general to a large class of materials with inversion symmetry containing heavy elements, opening new perspectives for (opto-)spintronics devices.

[1] E. I. Rashba, V. I. Sheka, Fiz. Tverd. Tela: Collected Papers 2, 162 (1959)
[2] X. Zhang et al.; Nat. Phys. 10, 387 (2014)
[3] B. Monserrat, D. Vanderbilt; arXiv:1711.06274 (2017)
[4] D. Niesner et al.; Phys. Rev. Lett. 117, 126401 (2016)
[5] D. Niesner et al.; Phys. Rev. B 95, 075207 (2017)
[6] D. Niesner et al.; arXiv:1703.08740 (2017)

Vortragender: Dr. Daniel Niesner

Kontakt: Prof. Dr. Thomas Fauster