@article{WiedenmannBocquillonDeaconetal.2016, author = {Wiedenmann, J. and Bocquillon, E. and Deacon, R.S. and Hartinger, S. and Herrmann, O. and Klapwijk, T.M. and Maier, L. and Ames, C. and Br{\"u}ne, C. and Gould, C. and Oiwa, A. and Ishibashi, K. and Tarucha, S. and Buhmann, H. and Molenkamp, L.W.}, title = {4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions}, series = {Nature Communications}, volume = {7}, journal = {Nature Communications}, doi = {10.1038/ncomms10303}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-175353}, year = {2016}, abstract = {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.}, language = {en} } @article{HerrmannHappMoellmannetal.1993, author = {Herrmann, K. H. and Happ, M. and M{\"o}llmann, K.-P. and Tomm, J. W. and Becker, Charles R. and Kraus, M. M. and Yuan, S. and Landwehr, G.}, title = {A new model for the absorption coefficient of narrow gap (Hg,Cd)Te that simultaneously considers band tails and band filling}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-37894}, year = {1993}, abstract = {A semiempirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model. This model correctly fits both the absorption and luminescence spectra of narrow-gap (Hg,Cd)Te samples that have been grown by the traveling heater method as well as by molecular-beam epitaxy. The accuracy of the band-gap determination is enhanced by this model.}, language = {en} } @article{GramAlbertovaSchirmeretal.2022, author = {Gram, Maximilian and Albertova, P. and Schirmer, V. and Blaimer, M. and Gamer, M. and Herrmann, M. J. and Nordbeck, P. and Jakob, P. M.}, title = {Towards robust in vivo quantification of oscillating biomagnetic fields using Rotary Excitation based MRI}, series = {Scientific Reports}, volume = {12}, journal = {Scientific Reports}, number = {1}, doi = {10.1038/s41598-022-19275-5}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300862}, year = {2022}, abstract = {Spin-lock based functional magnetic resonance imaging (fMRI) has the potential for direct spatially-resolved detection of neuronal activity and thus may represent an important step for basic research in neuroscience. In this work, the corresponding fundamental effect of Rotary EXcitation (REX) is investigated both in simulations as well as in phantom and in vivo experiments. An empirical law for predicting optimal spin-lock pulse durations for maximum magnetic field sensitivity was found. Experimental conditions were established that allow robust detection of ultra-weak magnetic field oscillations with simultaneous compensation of static field inhomogeneities. Furthermore, this work presents a novel concept for the emulation of brain activity utilizing the built-in MRI gradient system, which allows REX sequences to be validated in vivo under controlled and reproducible conditions. Via transmission of Rotary EXcitation (tREX), we successfully detected magnetic field oscillations in the lower nano-Tesla range in brain tissue. Moreover, tREX paves the way for the quantification of biomagnetic fields.}, language = {en} }