TY - JOUR A1 - Scharf, Benedikt A1 - Braggio, Alessandro A1 - Stambini, Elia A1 - Giazotto, Francesco A1 - Hankiewicz, Ewelina M. T1 - Topological Josephson heat engine JF - Communications Physics N2 - Topological superconductors represent a fruitful playing ground for fundamental research as well as for potential applications in fault-tolerant quantum computing. Especially Josephson junctions based on topological superconductors remain intensely studied, both theoretically and experimentally. The characteristic property of these junctions is their 4-periodic ground-state fermion parity in the superconducting phase difference. Using such topological Josephson junctions, we introduce the concept of a topological Josephson heat engine. We discuss how this engine can be implemented as a Josephson-Stirling cycle in topological superconductors, thereby illustrating the potential of the intriguing and fruitful marriage between topology and coherent thermodynamics. It is shown that the Josephson-Stirling cycle constitutes a highly versatile thermodynamic machine with different modes of operation controlled by the cycle temperatures. Finally, the thermodynamic cycle reflects the hallmark 4 pi -periodicity of topological Josephson junctions and could therefore be envisioned as a complementary approach to test topological superconductivity. Topological superconductors are expected to be a key component of quantum computing systems but reliably detecting their exotic properties is a challenge. Here, the authors propose a topological Josephson heat engine which uses thermodynamic effects to probe the 4 pi -periodic ground state of a topological superconductor. KW - superconductivity Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230603 VL - 3 ER - TY - JOUR A1 - Oostinga, Jeroen B. A1 - Maier, Luis A1 - Schüffelgen, Peter A1 - Knott, Daniel A1 - Ames, Christopher A1 - Brüne, Christoph A1 - Tkachov, Grigory A1 - Buhmann, Hartmut A1 - Molenkamp, Laurens W. T1 - Josephson Supercurrent through the Topological Surface States of Strained Bulk HgTe JF - Physical Review X N2 - 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. KW - topological insulators KW - mesoscopics KW - superconductivity Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129834 VL - 3 IS - 021007 ER - TY - JOUR A1 - Okada, Michio A1 - Rotenberg, Eli A1 - Kevan, S. D. A1 - Schäfer, J. A1 - Ujfalussy, Balazs A1 - Stocks, G. Malcolm A1 - Genatempo, B. A1 - Bruno, E. A1 - Plummer, E. W. T1 - Evolution of the electronic structure in \(Mo_{1-x}Re_x\) alloys JF - New Journal of Physics N2 - We report a detailed experimental and theoretical study of the electronic structure of \(Mo_{1-x}Re_x\) random alloys. We have measured electronic band dispersions for clean and hydrogen-covered \(Mo_{1-x}Re_x\) ( 110) with x = 0-0.25 using angle-resolved photoemission spectroscopy. Our results suggest that the bulk and most surface electronic bands shift relative to the Fermi level systematically and approximately rigidly with Re concentration. We distinguish and quantify two contributions to these shifts: a raise of the Fermi energy and an increase of the overall bandwidth. Alloy bands calculated using the first-principles Korringa-Kohn-Rostoker coherent-potential-approximation method accurately predict both of these effects. As derived from the rigid band model, the Fermi energy shift is inversely related to the bulk density of states in this energy region. Using our results, we also characterize an electronic topological transition of the bulk Fermi surface and relate this to bulk transport properties. Finally, we distinguish effects beyond the rigid band approximation: a highly surface-localized state and a composition-dependent impact of the spin-orbit interaction. KW - topological transitions KW - surface state KW - metals KW - total energy KW - W(110) KW - hydrogen KW - mo KW - superconductivity KW - spectra KW - coherent potential approximation Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-122993 SN - 1367-2630 VL - 15 IS - 093010 ER - TY - JOUR A1 - Bareille, C. A1 - Fortuna, F. A1 - Rödel, T. C. A1 - Bertran, F. A1 - Gabay, M. A1 - Hijano Cubelos, O. A1 - Taleb-Ibrahimi, A. A1 - Le Fèvre, P. A1 - Bibes, M. A1 - Barthelemy, A. A1 - Maroutian, T. A1 - Lecoeur, P. A1 - Rozenberg, M. J. A1 - Santander-Syro, A. F. T1 - Two-dimensional electron gas with six-fold symmetry at the (111) surface of KTaO3 JF - Scientific Reports N2 - Two-dimensional electron gases (2DEGs) at transition-metal oxide (TMO) interfaces, and boundary states in topological insulators, are being intensively investigated. The former system harbors superconductivity, large magneto-resistance, and ferromagnetism. In the latter, honeycomb-lattice geometry plus bulk spin-orbit interactions lead to topologically protected spin-polarized bands. 2DEGs in TMOs with a honeycomb-like structure could yield new states of matter, but they had not been experimentally realized, yet. We successfully created a 2DEG at the (111) surface of KTaO3, a strong insulator with large spin-orbit coupling. Its confined states form a network of weakly-dispersing electronic gutters with 6-fold symmetry, a topology novel to all known oxide-based 2DEGs. If those pertain to just one Ta-(111) bilayer, model calculations predict that it can be a topological metal. Our findings demonstrate that completely new electronic states, with symmetries not realized in the bulk, can be tailored in oxide surfaces, promising for TMO-based devices. KW - LAALO3/SRTIO3 interfaces KW - topological insulators KW - superconductivity KW - oxides KW - SRTIO3 Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117703 SN - 2045-2322 VL - 4 ER - TY - JOUR A1 - Hansmann, P. A1 - Parragh, N. A1 - Toschi, A. A1 - Sangiovanni, G. A1 - Held, K. T1 - Importance of d-p Coulomb interaction for high T-C cuprates and other oxides JF - New Journal of Physics N2 - Current theoretical studies of electronic correlations in transition metal oxides typically only account for the local repulsion between d-electrons even if oxygen ligand p-states are an explicit part of the effective Hamiltonian. Interatomic interactions such as U-pd between d- and (ligand) p-electrons, as well as the local interaction between p-electrons, are neglected. Often, the relative d-p orbital splitting has to be adjusted 'ad hoc' on the basis of the experimental evidence. By applying the merger of local density approximation and dynamical mean field theory to the prototypical case of the three-band Emery dp model for the cuprates, we demonstrate that, without any 'ad hoc' adjustment of the orbital splitting, the charge transfer insulating state is stabilized by the interatomic interaction U-pd. Our study hence shows how to improve realistic material calculations that explicitly include the p-orbitals. KW - correlated electrons KW - dynamical mean field theory KW - transition metal oxides KW - fermions KW - superconductivity KW - energy bands KW - transition metals KW - correlated systems KW - mean-field theory KW - electronic-structure calculations KW - inplane spectral weight KW - Hubbard model KW - infinite dimensions Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117165 SN - 1367-2630 VL - 16 IS - 33009 ER -