Optical Manipulation of the Spin and Valley degree of freedom in semiconductor nano-structures

The mesoscopic spin system formed by the 10E4–10E6 nuclear spins in a semiconductor quantum dot offers a unique setting for the study of many-body spin physics in the condensed matter. The dynamics of this system and its coupling to electron spins is fundamentally different from its bulk counterpart or the case of individual atoms due to increased fluctuations that result from reduced dimensions. In recent years, the interest in studying quantum-dot nuclear spin systems and their coupling to confined electron spins has been further fueled by its importance for possible quantum information processing applications. The fascinating nonlinear (quantum) dynamics of the coupled
electron-nuclear spin system is universal in quantum dot optics [1] and transport. In the first part of this talk, experimental work performed over the last decade in studying this mesoscopic, coupled electronuclear spin system is reviewed, with special focus on how optical addressing of electron spins can be exploited to manipulate and read out the quantum-dot nuclei.
The second part of the talk will be devoted to another degree of freedom: the valley index of electrons in atomically thin two-dimensional crystals. Monolayer MoS2 has emerged as a very promising material for optoelectronic and spin applications for mainly two reasons: First, the indirect bulk semiconductor MoS2 becomes direct when thinned to one monolayer, resulting in efficient optical absorption and emission. Second, the inherent inversion symmetry breaking (usually absent in graphene) together with the strong spin-orbit interaction leads to a coupling of carrier spin and k-space valley physics [2]. The resulting chiral optical selectivity allows exciting one of these non-equivalent K valleys. Both the magnetic field and the temperature dependence of this optical initialization of the valley index will be discussed [3] in the context of preparing valley-Hall coupled to spin-Hall measurements.
[1] B. Urbaszek et al, Reviews of Modern Physics 85, 79 (2013)
[2] D. Xiao et al, Phys. Rev. Lett. 108, 196802 (2012)
[3] G. Sallen et al, Phys. Rev. B 86, 081301(R) (2012)