laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

Seminar, 12 Fev 2018 (13h30 salle L 363-365)

Sergey Krishtopenko, Laboratoire Charles Coulomb, Montpellier, France
Topological phase transitions in HgTe/CdTe-based quantum wells

A time-reversal invariant topological insulator in two dimensions, also
known as a quantum spin Hall insulator (QSHI) is a new state of matter
characterized by an insulating bulk and spin-polarized gapless helical
states at the sample edges. So far, evidence for the helical edge mode
in QSHI, particularly quantized transport, has been limited to two
semiconductor systems – inverted HgTe/CdHgTe quantum wells (QWs) and
broken-gap InAs/GaSb QW bilayers. In my talk, I review recent
theoretical and experimental results on single and double HgTe QWs,
obtained in our group in Montpellier. In the first part, I will focus on
phase transitions in single HgTe QWs induced by temperature and present
the picture of the edge states in QSHI phase beyond the
Bernevig-Hughes-Zhang model. In the second part, I report theoretical
study of phase transitions in double HgTe QWs consisting of two HgTe
layers separated by tunneling CdHgTe barrier. Particularly, I show an
existence of specific “bilayer-graphene” metal and trivial insulator
phases, arising in the inverted double HgTe QWs. Finally, motivated by
recent observation of quantum spin Hall effect at temperatures up 100 K
in 1T′-WTe_2 monolayers with a band-gap of 45 meV (/Science/ *359*, 76
(2018)), I will briefly discuss a possibility of realization of
high-temperature QSHI in multi-layer InAs/GaSb QWs with temperature
stable band gap.