Seminar presentation

At the group meeting of the

Centre of Low Temperature Physics

Zoltán Tajkov

2022.09.29

Manipulating the topological properties of thin heterostructures

TOPICS

Graphene

Competition of trivial and topological phases in graphene based hybrid systems

ZrTe5

Revealing the topological phase diagram of ZrTe using the complex strain fields of microbubbles

Competing gapped and gapless ground state in the flat surface band of multilayer rhombohedral graphite

Graphite

BiTeX/graphene heterostructures

BiTeI sandwich: Kou et al. ACS Nano, 8 10448 (2014)

BiTeX/graphene heterostructures

Z. Tajkov et al. Nanoscale 11, 12704 (2019)

DFT (SIESTA) results

topological

trivial

Sandwich:

~40 meV topological gap

One sided:

~1 meV trivial gap

BiTeX/graphene heterostructures

Z. Tajkov et al. Nanoscale 11, 12704 (2019)

topological

trivial

BiTeX/graphene heterostructures

Z. Tajkov et al. Nanoscale 11, 12704 (2019)

The most important parameters

Kekulé

Kane-Mele

Strain promotes SOC $ \rightarrow $ TI

topological

trivial

BiTeX/graphene heterostructures

\begin{array}{c} \hat{H}=-v\left( {\boldsymbol{k}}\cdot\boldsymbol{\sigma}\otimes\tau_{0} +\boldsymbol{A}\cdot\boldsymbol{\sigma}\otimes\tau_{z} \right)\\ +\Delta\sigma_z\otimes\tau_x -m\sigma_z\otimes\tau_0 \end{array}

\boldsymbol{A}=\underbrace{\frac{\beta}{2a_{0}}\varepsilon\left(1+\rho\right)}\left(\begin{array}{r} \cos2\vartheta\\ -\sin2\vartheta \end{array}\right)

|\xi|=\sqrt{\Delta^2-m^2}

\xi/v

Strain can close the gap at $\boldsymbol{k}=\boldsymbol{0}$ if

Gamayun et al. New J. Phys. 20, 023016 (2018)

Z. Tajkov et. al. Physical Review B 101 (23), 235146 (2020)

\Psi_\boldsymbol{k}=\left(-\left| A, \boldsymbol{k}+ \boldsymbol{G} \right. \rangle \left|B,\boldsymbol{k}-G\right.\rangle \left|B,\boldsymbol{k}+G\right.\rangle \left|A,\boldsymbol{k}+G\right.\rangle \right)