Transport in magnetically doped one-dimensional wires: can the helical protection emerge without the global helicity?

Abstract

We study the phase diagram and transport properties of arbitrarily doped quantum wires functionalized by magnetic adatoms. The appropriate theoretical model for these systems is a dense one-dimensional Kondo lattice (KL) which consists of itinerant electrons interacting with localized quantum magnetic moments. We discover the novel phase of the locally helical metal where transport is protected from a destructive influence of material imperfections. Paradoxically, such a protection emerges without a need of the global helicity, which is inherent in all previously studied helical systems and requires breaking the spin-rotation symmetry. We explain the physics of this protection of the new type, find conditions, under which it emerges, and discuss possible experimental tests. Our results pave the way to the straightforward realization of the protected ballistic transport in quantum wires made of various materials. © 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft New J. Phys. 22 (2020) 053013 A M Tsvelik and O M Yevtushenkohelix spin configuration which gaps out one helical sector of the electrons. The second helical sector remains gapless. In the resulting helical metal (HM), the disorder induced localization is parametrically suppressed and, therefore, the ballistic transport acquires a partial protection [66,67].All previous studies, including the TIs and the interacting helical systems, revealed protection of transport governed by the global helicity, i.e., helicity of the gapless electrons and/or the spiral spin configuration were uniquely defined in the entire sample. The global helicity always requires breaking the spin-rotation symmetry, either internally (e.g., due to the spin-orbit interaction, or the magnetic anisotropy) or spontaneously (e.g. in relatively short samples with a strong electrostatic interaction of the electrons). This certainly diminishes experimental capabilities to fabricate the helical states, especially those governed by the interactions: one always needs either specially selected materials or a nontrivial fine-tuning of physical parameters. For instance, the prediction of references [66,67] remains practically useless for the experiments because one can hardly control the magnetic anisotropy.Thus, further progress in obtaining the helical quantum wires, in particular by means of the magnetic doping, has been hampered by two open questions: (i) is the global helicity accompanied by breaking the spin-rotation symmetry really necessary to obtain HM? (ii) If the global helicity is not really needed, which parameters must be tuned for detecting HM in the KLs (theoretically) and in the magnetically doped quantum wires (experimentally)? We note that numerical studies have never provided a reliable signature of the helical phase in the KLs [53,61,65].In this paper, we answer both questions: protection of the ballistic transport can be provided by the local helicity which, paradoxically, requires neither the glo...

Distribution of RKKY coupling value in 1D crystal with disorder. Specific heat in XY model

“…The progress in 1D systems fabrication [1] makes it possible to study in practice many phenomena predicted theoretically or not previously discussed at all [2][3][4][5][6]. Recently, for example, the possibility of observing new phase states of a magnetic chain in 1D was demonstrated theoretically [7][8][9][10]. However, to observe such fine effects, one needs to control the value of the exchange interaction of magnetic moments in the experiment.…”