| When taking into account the nuclear spins, a quantum wire is a finite size Kondo lattice system. In such a system, the RKKY interaction can result in an ordered state at low temperatures, in which the Kondo lattice spins form one or several helices. These helices in turn induce a partial ordering of the electrons, and open up gaps in their spectrum. The helical order is a relatively stable phenomenon that persists even for multiple electronic subbands. The electrons in this state form a quasi-helical (or "spiral") Luttinger liquid, equivalent to a Rashba nanowire in a magnetic field. (Quasi-) helical Luttinger liquids have applications as spin filters or Cooper pair splitters, and are a crucial ingredient for topological wires with Majorana end states. |
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