Confinement versus interface bound states in spin-orbit coupled nanowires
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Confinement versus interface bound states in spin-orbit coupled nanowires Lorenzo Rossi, Fabrizio Dolcinia
, Fausto Rossi
Dipartimento di scienza Applicata e Tecnologia, Politecnico di Torino, Torino, Italy Received: 14 May 2020 / Accepted: 15 July 2020 © The Author(s) 2020, corrected publication 2020
Abstract Semiconductor nanowires with strong Rashba spin-orbit coupling are currently on the spotlight of several research fields such as spintronics, topological materials and quantum computation. While most theoretical models assume an infinitely long nanowire, in actual experimental setups the nanowire has a finite length, is contacted to metallic electrodes and is partly covered by gates. By taking these effects into account through an inhomogeneous spin-orbit coupling profile, we show that in general two types of bound states arise in the nanowire, namely confinement bound states and interface bound states. The appearance of confinement bound states, related to the finite length of the nanowire, is favoured by a mismatch of the bulk band bottoms characterizing the lead and the nanowire, and occurs even in the absence of magnetic field. In contrast, an interface bound states may only appear if a magnetic field applied perpendicularly to the spin-orbit field direction overcomes a critical value, and is favoured by an alignment of the band bottoms of the two regions across the interface. We describe in details the emergence of these two types of bound states, pointing out their differences. Furthermore, we show that when a nanowire portion is covered by a gate the application of a magnetic field can change the nature of the electronic ground state from a confinement to an interface bound state, determining a redistribution of the electron charge.
1 Introduction Bound states play a relevant role in nanotechnological applications. For instance, it has been known for decades that a suitable engineering of semiconductor heterostructures yields nanometer scale confined bound states along the growth direction, forcing the electron dynamics to effectively take place in a two-dimensional plane, thereby creating a 2DEG. Also, since bound states are characterized by discrete energy separations that can even be greater than thermal energy, one can exploit them to realize optical devices, such as photodetectors or lasers. In the field of hetero-junctions, the existence of interface bound states at the separation between two materials can reduce or even mask the desired features of the current–voltage characteristics, so that suitable techniques such as lattice matching have to be adopted to prevent their formation.
a e-mail: [email protected] (corresponding author)
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However, bound states are also crucial in terms of fundamental Physics. In Condensed Matter Physics, for instance, it has been realized that bound states can be the hallmark of topological transitions: When a material enters a topological phase, a bound state emerges at
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