@article{PeixotoBentmannRuessmannetal.2020,
  author    = {Peixoto, Thiago R. F. and Bentmann, Hendrik and R{\"u}ßmann, Philipp and Tcakaev, Abdul-Vakhab and Winnerlein, Martin and Schreyeck, Steffen and Schatz, Sonja and Vidal, Raphael Crespo and Stier, Fabian and Zabolotnyy, Volodymyr and Green, Robert J. and Min, Chul Hee and Fornari, Celso I. and Maaß, Henriette and Vasili, Hari Babu and Gargiani, Pierluigi and Valvidares, Manuel and Barla, Alessandro and Buck, Jens and Hoesch, Moritz and Diekmann, Florian and Rohlf, Sebastian and Kall{\"a}ne, Matthias and Rossnagel, Kai and Gould, Charles and Brunner, Karl and Bl{\"u}gel, Stefan and Hinkov, Vladimir and Molenkamp, Laurens W. and Friedrich, Reinert},
  title     = {Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators},
  series = {NPJ Quantum Materials},
  volume    = {5},
  journal   = {NPJ Quantum Materials},
  doi       = {10.1038/s41535-020-00288-0},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230686},
  year      = {2020},
  abstract  = {Since the discovery of the quantum anomalous Hall (QAH) effect in the magnetically doped topological insulators (MTI) Cr:(Bi,Sb)\(_2\)Te\(_3\) and V:(Bi,Sb)\(_2\)Te\(_3\), the search for the magnetic coupling mechanisms underlying the onset of ferromagnetism has been a central issue, and a variety of different scenarios have been put forward. By combining resonant photoemission, X-ray magnetic circular dichroism and density functional theory, we determine the local electronic and magnetic configurations of V and Cr impurities in (Bi,Sb)\(_2\)Te\(_3\). State-of-the-art first-principles calculations find pronounced differences in their 3d densities of states, and show how these impurity states mediate characteristic short-range pd exchange interactions, whose strength sensitively varies with the position of the 3d states relative to the Fermi level. Measurements on films with varying host stoichiometry support this trend. Our results explain, in an unified picture, the origins of the observed magnetic properties, and establish the essential role of impurity-state-mediated exchange interactions in the magnetism of MTI.},
  language  = {en}
}
@article{SanchezThierschmannMolenkamp2017,
  author    = {S{\´a}nchez, Rafael and Thierschmann, Holger and Molenkamp, Laurens W.},
  title     = {Single-electron thermal devices coupled to a mesoscopic gate},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa8b94},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172982},
  year      = {2017},
  abstract  = {We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron-electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.},
  language  = {en}
}
@article{MaCalvoWangetal.2015,
  author    = {Ma, Eric Yue and Calvo, M. Reyes and Wang, Jing and Lian, Biao and M{\"u}hlbauer, Mathias and Br{\"u}ne, Christoph and Cui, Yong-Tao and Lai, Keji and Kundhikanjana, Worasom and Yang, Yongliang and Baenninger, Matthias and K{\"o}nig, Markus and Ames, Christopher and Buhmann, Hartmut and Leubner, Philipp and Molenkamp, Laurens W. and Zhang, Shou-Cheng and Goldhaber-Gordon, David and Kelly, Michael A. and Shen, Zhi-Xun},
  title     = {Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry},
  series = {Nature Communications},
  volume    = {6},
  journal   = {Nature Communications},
  number    = {7252},
  doi       = {10.1038/ncomms8252},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-143185},
  year      = {2015},
  abstract  = {The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a noninverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.},
  language  = {en}
}
@article{BrueneThienelStuiberetal.2014,
  author    = {Br{\"u}ne, Christoph and Thienel, Cornelius and Stuiber, Michael and B{\"o}ttcher, Jan and Buhmann, Hartmut and Novik, Elena G. and Liu, Chao-Xing and Hankiewicz, Ewelina M. and Molenkamp, Laurens W.},
  title     = {Dirac-Screening Stabilized Surface-State Transport in a Topological Insulator},
  series = {Physical Review X},
  volume    = {4},
  journal   = {Physical Review X},
  number    = {4},
  issn      = {2160-3308},
  doi       = {10.1103/PhysRevX.4.041045},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-118091},
  pages     = {041045},
  year      = {2014},
  abstract  = {We report magnetotransport studies on a gated strained HgTe device. This material is a three-dimensional topological insulator and exclusively shows surface-state transport. Remarkably, the Landau-level dispersion and the accuracy of the Hall quantization remain unchanged over a wide density range (3×1011  cm-2<n<2×1012  cm-2). These observations imply that even at large carrier densities, the transport is surface-state dominated, where bulk transport would have been expected to coexist already. Moreover, the density dependence of the Dirac-type quantum Hall effect allows us to identify the contributions from the individual surfaces. A k⋅p model can describe the experiments but only when assuming a steep band bending across the regions where the topological surface states are contained. This steep potential originates from the specific screening properties of Dirac systems and causes the gate voltage to influence the position of the Dirac points rather than that of the Fermi level.},
  language  = {en}
}
@article{KoenigBaenningerGarciaetal.2013,
  author    = {K{\"o}nig, Markus and Baenninger, Matthias and Garcia, Andrei G. F. and Harjee, Nahid and Pruitt, Beth L. and Ames, C. and Leubner, Philipp and Br{\"u}ne, Christoph and Buhmann, Hartmut and Molenkamp, Laurens W. and Goldhaber-Gordon, David},
  title     = {Spatially Resolved Study of Backscattering in the Quantum Spin Hall State},
  series = {Physical Review X},
  volume    = {3},
  journal   = {Physical Review X},
  number    = {2},
  issn      = {2160-3308},
  doi       = {10.1103/PhysRevX.3.021003},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-127225},
  pages     = {21003},
  year      = {2013},
  abstract  = {The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations.},
  language  = {en}
}
@article{OostingaMaierSchueffelgenetal.2013,
  author    = {Oostinga, Jeroen B. and Maier, Luis and Sch{\"u}ffelgen, Peter and Knott, Daniel and Ames, Christopher and Br{\"u}ne, Christoph and Tkachov, Grigory and Buhmann, Hartmut and Molenkamp, Laurens W.},
  title     = {Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe},
  series = {Physical Review X},
  volume    = {3},
  journal   = {Physical Review X},
  number    = {021007},
  doi       = {10.1103/PhysRevX.3.021007},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-129834},
  year      = {2013},
  abstract  = {Strained bulk HgTe is a three-dimensional topological insulator, whose surface electrons have a high mobility (~ 30 000 cm\(^2\)=Vs), while its bulk is effectively free of mobile charge carriers. These properties enable a study of transport through its unconventional surface states without being hindered by a parallel bulk conductance. Here, we show transport experiments on HgTe-based Josephson junctions to investigate the appearance of the predicted Majorana states at the interface between a topological insulator and a superconductor. Interestingly, we observe a dissipationless supercurrent flow through the topological surface states of HgTe. The current-voltage characteristics are hysteretic at temperatures below 1 K, with critical supercurrents of several microamperes. Moreover, we observe a magnetic-field-induced Fraunhofer pattern of the critical supercurrent, indicating a dominant \(2\pi\)-periodic Josephson effect in the unconventional surface states. Our results show that strained bulk HgTe is a promising material system to get a better understanding of the Josephson effect in topological surface states, and to search for the manifestation of zero-energy Majorana states in transport experiments.},
  language  = {en}
}