Incorporation of Se to increase the tensile strain and so the bulk gap. ➢
Topological superconductivity : proximity up to. 800 nm. ➢ Development of
spintronic ...
Strained HgTe/CdTe topological insulators C. Thomas
1,2*
, P. Ballet
1,
X. Baudry
1,
C. Bouvier
2,
O. Crauste
2,
2
T. Meunier , L.P. Lévy
2
1: CEA – LETI, MINATEC Campus, 17 rue des Martyrs, F-38054 Grenoble , France 2: Institut Néel, C.N.R.S.- Université Joseph Fourier, BP 166, 38042 Grenoble, France
HgTe/CdTe 3D topological insulator
Growth by Molecular Beam Epitaxy
HgTe = strong SO coupling Qy*10000(rlu) Inverted band structure.
HgTe
CdTe
(a)
Tgrowth = 140°C, vgrowth = 1ML/s. Growth under Te-rich conditions and Hg pressure. In-situ annealing + cooling down under Hg flux : to preserve the 2D characteristic of the surface.
+HgTe
6000 5980
*
[email protected]
HgTe/CdTe = tensile strain Bulk gap. 5960
CdTe
5940
=
Surfaces conductor with Dirac electrons + Bulk insulator
MBE Riber 32P chamber in CEA-Leti.
5920
Material characterization 1660 1680 1700 1720 Qx*10000(rlu)
Cristalline quality and strain
(b)
Qy*10000(rlu)
High Resolution X-Ray Diffraction : crystal quality. CdTe and HgTe well-defined peaks + Pendelössung fringes.
Relaxation line 6000
Surfaces and interfaces AFM : annealing + cooling down under Hg flux roughness from 5/6 nm (a) to the monolayer (b).
decrease of the
HgTe a
c
b
5980
CdTe
Log Intensity (a.u.)
strained HgTe
5960
CdTe
13nm
5940 38nm
5920
(a) without and (b) with annealing and cooling down under Hg flux, (c) height profiles.
107nm
1640
1660
1680
1700
1720
Qx*10000(rlu) relax 2%
146nm
relax 18%
250nm
56,0
56,5
57,0
57,5
STEM : well-defined HgTe/CdHgTe/CdZnTe interfaces.
RSM following (511) of a 130 nm thick HgTe [1].
Reciprocal space mappings (RSM) : strain uniformity. Plastic limit ~150 nm.
58,0
2 - (°)
(a) Bright Field Mode and (b) EDX mapping [1].
Evolution of XRD diagram as a function of HgTe layer thickness [1].
Magneto-transport measurements ARPES
Conclusions Good quality HgTe/CdTe structures grown by MBE.
Set-up Band structure. Surface states. Dirac cone.
Improvement of surface roughness down to the monolayer.
Hall bar devices. 3He fridge : 400 mK. Variations of Vgate and B.
Experimental evidences of a topological insulator. HgTe/CdTe = 3D topological insulator
Band structure simulation.
ARPES measurement [2].
Existence of a 2DEG + Ambipolarity µ up to 430,000 cm²/V.s with ne =2.5 1011 cm-2
Results Non-trivial Berry phase : β = 1/2
Quantum Hall Effect : Plateaus at Rlong minimum Spin splitting ?
Perspectives Incorporation of Se to increase the tensile strain and so the bulk gap.
Topological superconductivity : proximity up to 800 nm.
β = 0.54 +/- 0.05
Development of spintronic devices without use of magnetic field and magnetic materials thanks to the strong spin-orbit coupling of HgTe.
Bouvier et al [3]
References
[1] Ballet et al, MBE growth of strained HgTe/CdTe topological insulator structures, Journ. of Elec. Materials, to be published [2] Crauste et al, Topological surface states of strained Mercury-Telluride probed by ARPES, arxiv 1307.2008 (2013) [3] Bouvier et al, Strained HgTe: a textbook 3D topological insulator, arxiv 1112.2092 (2011)
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