Visualizing spin-orbit driven effects at surfaces by scanning probe spectroscopies

by Paolo Sessi (University of Würzburg)

Friday 9 Oct 2015, 11:00 → 12:00 Europe/Stockholm

112:028 (Nordita South)

In a non-relativistic theory of solids, the spin degree of freedom appears just as an additional quantum number introduced to account for the Pauli exclusion principle. However, once the relativistic spin-orbit interaction is considered, spin moment and orbital motion become intimately coupled. In recent years, condensed matter systems characterized by strong spin-orbit coupling have gain a lot of attention. This is due to the large variety of unconventional physical effects they host which, beyond their fundamental interest, represent a promising playground to develop new applications, being spintronics and magneto-electrics the most prominent examples. Since the key consequences of strong-spin orbit coupling usually manifest at boundaries, i.e. edges in 2D and surfaces in 3D, scanning probe techniques are ideal tools to visualize them with both high spatial and energy resolution. In my talk, I will present recent results obtained in our group onto two prototypical systems: (i) Rashba surfaces: where the strong spin-orbit interaction causes a spinsplitting of a spin-degenerate electron gas in the presence of a structure inversion asymmetric potential [1] and (ii) topological insulators, where spin-orbit coupling acts as a kind of ’built-in magnetic field’ of a non-magnetic solid, that plays a role similar to the external magnetic field in the quantum Hall effect [2,3]. In both cases I will describe experiments that through quantum interference allow not only to visualize the presence of unconventional edge states, but also to demonstrate their unusual properties. Finally, I will discuss more recent efforts focused to their controlled manipulation, which can be achieved by directly coupling them to well defined charge and magnetic external perturbations [3,4,5]. [1] L. El-Kareh et al. Phys. Rev. Lett. 110, 176803 (2013); [2] P. Sessi et al. Phys. Rev. B 88,161407(R) (2013); [3] P. Sessi et al. Nature Communications 5,5349 (2014); [4] P. Sessi et al. Nano Letters 14, 5092 (2014); [5] T. Bathon et al. Nano Letters 15, 2442 (2015).