TY  - JOUR
A1  - Dziom, V.
A1  - Shuvaev, A.
A1  - Pimenov, A.
A1  - Astakhov, G.V.
A1  - Ames, C.
A1  - Bendias, K.
A1  - Böttcher, J.
A1  - Tkachov, G.
A1  - Hankiewicz, E.M.
A1  - Brüne, C.
A1  - Buhmann, H.
A1  - Molenkamp, L.W.
T1  - Observation of the universal magnetoelectric effect in a 3D topological insulator
JF  - Nature Communications
N2  - The electrodynamics of topological insulators (TIs) is described by modified Maxwell’s equations, which contain additional terms that couple an electric field to a magnetization and a magnetic field to a polarization of the medium, such that the coupling coefficient is quantized in odd multiples of α/4π per surface. Here we report on the observation of this so-called topological magnetoelectric effect. We use monochromatic terahertz (THz) spectroscopy of TI structures equipped with a semitransparent gate to selectively address surface states. In high external magnetic fields, we observe a universal Faraday rotation angle equal to the fine structure constant α=e\(^{2}\)/2E\(_{0}\)hc (in SI units) when a linearly polarized THz radiation of a certain frequency passes through the two surfaces of a strained HgTe 3D TI. These experiments give insight into axion electrodynamics of TIs and may potentially be used for a metrological definition of the three basic physical constants.
KW  - topological matter
KW  - infrared spectroscopy
KW  - topological insulators
KW  - topological magnetoelectric effect
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170875
VL  - 8
IS  - 15197
ER  - 
TY  - JOUR
A1  - Wiedenmann, J.
A1  - Bocquillon, E.
A1  - Deacon, R.S.
A1  - Hartinger, S.
A1  - Herrmann, O.
A1  - Klapwijk, T.M.
A1  - Maier, L.
A1  - Ames, C.
A1  - Brüne, C.
A1  - Gould, C.
A1  - Oiwa, A.
A1  - Ishibashi, K.
A1  - Tarucha, S.
A1  - Buhmann, H.
A1  - Molenkamp, L.W.
T1  - 4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
JF  - Nature Communications
N2  - The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature deeply influences the properties of the supercurrent. In recent years, considerable efforts have focused on the coupling of superconductors to the surface states of a three-dimensional topological insulator. In such a material, an unconventional induced p-wave superconductivity should occur, with a doublet of topologically protected gapless Andreev bound states, whose energies vary 4π-periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction made of a HgTe weak link. The response is understood as due to a 4π-periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet. Our work opens the way to more elaborate experiments to investigate the induced superconductivity in a three-dimensional insulator.
KW  - Josephson effect
KW  - supercurrent
KW  - superconductors
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-175353
VL  - 7
ER  -