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Peter Grünberg Institute

# Topological Insulators

Recently a new state of matter, the topological insulator (TI), has sparked enormous scientific activities – both on the theoretical and experimental side – due to its fascinating properties.

he TIs have insulating properties in bulk and surface states with a linear energy dispersion. Hence, carriers at the surface of TIs are regarded quasi-relativistic Dirac fermions with intriguing properties, such as dissipationless and spin-locked transport. Besides, TIs may also serve as a base for the discovery of groundbreaking new phenomena, such as the detection of Majorana fermions and magnetic monopoles [1].

Prominent examples of TIs are Bi2Te3, Bi2Se3, and Sb2Te3, as well as their (qua)ternary alloys and heterostructures. We have been carrying out molecular-beam epitaxy (MBE) of TI materials since 2010, as one of the first groups worldwide. Since then we have demonstrated that single-crystal ultrathin TI films can be grown by MBE [2], and the TI behavior of these films has been verified by photoemission spectroscopy [3] and THz photocurrent measurements [4]. Recently, we have been working on superconductor / TI junctions, which are predicted to host Majorana fermions, as well as trivial insulator / TI quantum wells in the context of studying the impact of the surrounding trivial insulators on the TI surface states.

The research activities are part of the Virtual Institute for Topological Insulators.

Molecular beam epitaxy system for topoligical insulators

### References

[1] D. Hsieh et al., Nature 452, 970 (2008).
[2] J. Krumrain et al., J. Crystal Growth 324, 115 (2011)
[3] M. Eschbach et al., Nature Communications 6, 8816 (2015)
[4] P. Olbrich et al., Phys. Rev. Lett. 113, 096601 (2014)

# Contact:

Growth:
Dr. Gregor Mussler

Transport:
Prof. Dr. Thomas Schäpers