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- Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond doi link

Auteur(s): Krishtopenko S., Knap W., Teppe F.

(Article) Publié: Scientific Reports, vol. 6 p.30755 (2016)
Texte intégral en Openaccess : openaccess


Ref HAL: hal-01469295_v1
DOI: 10.1038/srep30755
WoS: WOS:000381043900001
Exporter : BibTex | endNote
20 Citations
Résumé:

HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electricallytunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives thesystem into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.