SFB Colloquium

Topological phenomena are a relevant theme in modern condensed matter physics. Skyrmions, for instance, are robust ‘non-trivial’ spin textures, characterized by a winding number (‘topological invariant’), usually occurring in interacting electron systems, e.g., chiral magnets and fractional quantum Hall states. In this talk I will show how the mesoscopic spin-orbit interaction present in ordinary non-topological and non-interacting electrons in (GaAs) wells with two subbands [1] can give rise to topological phenomena. More specifically, I will discuss (i) all-electron topological insulators [2] and (ii) electronic Skyrmion lattice textures [3] in III-V double wells. I will also present the interesting possibility of devising stretchable ‘persistent spin helices’ [4], i.e., robust non-interacting spin-density-wave-like excitations with variable pitches, thus possibly providing a platform for the much-heralded long-distance spin communication ~ 8 – 20 micrometers between solid-state spin qubits. I should also briefly touch upon the recent experimental realization of the intrinsic spin Hall effect in two-subband quantum wells [5], its theoretical explanation [6], and extensions in the context of wurtzite systems [7]. Finally, I will flash a slide or two about recent unpublished results on the existence of geometrically-protected edge states in non-topological cylindrical quantum dots [8]. The research presented here has been carried out in collaboration with students, postdocs and colleagues both at my research group and abroad.

[1] E. S. Bernardes et al. Phys Rev. Lett. 99, 076603 (2007).

[2] S. Erlingsson and J. C. Egues, Phys. Rev. 91, 035312 (2015).

[3] J. Fu, P. H. Penteado, M. O. Hachya, D. Loss, and J. C. Egues, Phys. Rev. Lett. 117, 226401 (2016).

[4] F. Dettwiler, J. Fu, Pirmin J. Weigele, S. Mack, J. C. Egues, D. D. Awschalom, and D. Zumbühl, Phys. Rev. X 7, 031010 (2017);

[5] Hernandez et al., Phys. Rev. B 88, 161305(R) (2013).

[6] A. Khaetskii and J. C. Egues, Europhys. Lett. 118, 57006 (2017)

[7] J. Fu, P. H. Penteado, D. Paiva, D. R. Candido, G. J. Ferreira, E. S. Bernardes, and J. C. Egues, to be submitted.

[8] D. R. Candido, M. E. Flatté and J. C. Egues, to be submitted.