Dr.jens.brede

Nature Physics. doi:10.1038/nphys3742

Authors: D. B. Szombati, S. Nadj-Perge, D. Car, S. R. Plissard, E. P. A. M. Bakkers & L. P. Kouwenhoven

The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.

Author(s): E. M. Reinisch, P. Puschnig, T. Ules, M. G. Ramsey, and G. Koller

The buried interface between a molecular thin film and the metal substrate is generally not accessible to the photoemission experiment. With the example of a sexiphenyl (6P) bilayer on Cu we show that photoemission tomography can be used to study the electronic level alignment and geometric structur…

[Phys. Rev. B 93, 155438] Published Fri Apr 29, 2016

Article

The Einstein-de Haas effect is a manifestation of the conservation of angular momentum, causing a magnetic object to rotate as its magnetization state is changed. Here, the authors demonstrate this effect at the single spin level for a molecular magnet suspended on a nanomechanical resonator.

Nature Communications doi: 10.1038/ncomms11443

Authors: Marc Ganzhorn, Svetlana Klyatskaya, Mario Ruben, Wolfgang Wernsdorfer

Abstract

Author(s): Xiang-Bing Li, Wen-Kai Huang, Yang-Yang Lv, Kai-Wen Zhang, Chao-Long Yang, Bin-Bin Zhang, Y. B. Chen, Shu-Hua Yao, Jian Zhou, Ming-Hui Lu, Li Sheng, Shao-Chun Li, Jin-Feng Jia, Qi-Kun Xue, Yan-Feng Chen, and Ding-Yu Xing

We report an atomic-scale characterization of ZrTe5 by using scanning tunneling microscopy. We observe a bulk band gap of ∼80  meV with topological edge states at the step edge and, thus, demonstrate that ZrTe5 is a two-dimensional topological insulator. We also find that an applied magnetic field i…

[Phys. Rev. Lett. 116, 176803] Published Thu Apr 28, 2016

Author(s): Ashis Kumar Nandy, Nikolai S. Kiselev, and Stefan Blügel

We report on a general principle using interlayer exchange coupling to extend the regime of chiral magnetic films in which stable or metastable magnetic Skyrmions can appear at a zero magnetic field. We verify this concept on the basis of a first-principles model for a Mn monolayer on a W(001) subst…

[Phys. Rev. Lett. 116, 177202] Published Thu Apr 28, 2016

Author(s): Mallika T. Randeria, Benjamin E. Feldman, Ilya K. Drozdov, and Ali Yazdani

Unconventional superconductors, with order parameters that are predicted to have short range spatial modulations, have held long standing interest in the field. The Josephson effect, which directly probes the strength of the pairing potential is an ideal technique to study these materials, in contrast to a majority of probes which rely on deductions made from quasiparticle measurements. The authors combine the Josephson effect with the high spatial resolution afforded by scanning tunneling microscopy to study atomic scale variations of the order parameter in a model system consisting of magnetic adatoms on a BCS superconductor. The atomic resolution achieved establishes scanning Josephson spectroscopy as a promising tool for the study of novel superconducting materials.

[Phys. Rev. B 93, 161115(R)] Published Thu Apr 28, 2016

Europe plans giant billion-euro quantum technologies project

Nature 532, 7600 (2016). http://www.nature.com/doifinder/10.1038/nature.2016.19796

Author: Elizabeth Gibney

Third European Union flagship will be similar in size and ambition to graphene and human brain initiatives.

Nature Physics. doi:10.1038/nphys3737

Authors: Taner Esat, Benedikt Lechtenberg, Thorsten Deilmann, Christian Wagner, Peter Krüger, Ruslan Temirov, Michael Rohlfing, Frithjof B. Anders & F. Stefan Tautz

The Rashba effect as an electrically tunable spin-orbit interaction is the base for a multitude of possible applications such as spin filters, spin transistors, and quantum computing using Majorana states in nanowires. Moreover, this interaction can determine the spin dephasing and antilocalization phenomena in two dimensions. However, the real space pattern of the Rashba parameter has never been probed, albeit it critically influences, e.g., the more robust spin transistors using the spin helix state and the otherwise forbidden electron backscattering in topologically protected channels. Here, we map this pattern down to nanometer length scales by measuring the spin splitting of the lowest Landau level using scanning tunnelling spectroscopy. We reveal strong fluctuations correlated with the local electrostatic potential for an InSb inversion layer with a large Rashba coefficient (~1 eV{\AA}). The novel type of Rashba field mapping enables a more comprehensive understanding of the critical fluctuations, which might be decisive towards robust semiconductor-based spintronic devices.

Article

The physical implementation of quantum information processing requires individual qubits and entangling gates. Here, the authors demonstrate a modular implementation through chemistry, assembling molecular {Cr 7 Ni} rings acting as qubits, with supramolecular structures realizing gates by choice of the linker.

Nature Communications doi: 10.1038/ncomms11377

Authors: Jesús Ferrando-Soria, Eufemio Moreno Pineda, Alessandro Chiesa, Antonio Fernandez, Samantha A. Magee, Stefano Carretta, Paolo Santini, Iñigo J. Vitorica-Yrezabal, Floriana Tuna, Grigore A. Timco, Eric J.L. McInnes, Richard E.P. Winpenny

The pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism with local magnetic moments ~ 1.5 per vacancy1-6. Theoretically, both the electrons and electrons of graphene contribute to the magnetic moment of the defects, and the pi magnetism is characterizing of two spin-split DOS (density-of-states) peaks close to the Dirac point1,6. Since its prediction, many experiments attempt to study this pi magnetism in graphene, whereas, only a notable resonance peak has been observed around the atomic defects6-9, leaving the pi magnetism experimentally so elusive. Here, we report direct experimental evidence of the pi magnetism by using scanning tunnelling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens meV and the two spin-polarized states degenerate into a profound peak at positions with distance of ~ 1 nm away from the monovacancy. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. The effective g-factors geff around the atomic defect is measured to be about 40. Such a giant enhancement of the g-factor is attributed to the strong spin polarization of electron density and large electron-electron interactions near the atomic vacancy.

Article

The goal of quantum simulation is to probe many-body phenomena in controlled systems, but Fermi-Hubbard phenomena are typically hard to simulate in cold atomic. Here, the authors simulate them with subsurface dopants in silicon, achieving a low effective temperature and reading out spin states with STM.

Nature Communications doi: 10.1038/ncomms11342

Authors: J. Salfi, J. A. Mol, R. Rahman, G. Klimeck, M. Y. Simmons, L. C. L. Hollenberg, S. Rogge

Nature Materials. doi:10.1038/nmat4623

Authors: Z. Wang, S. McKeown Walker, A. Tamai, Y. Wang, Z. Ristic, F. Y. Bruno, A. de la Torre, S. Riccò, N. C. Plumb, M. Shi, P. Hlawenka, J. Sánchez-Barriga, A. Varykhalov, T. K. Kim, M. Hoesch, P. D. C. King, W. Meevasana, U. Diebold, J. Mesot, B. Moritz, T. P. Devereaux, M. Radovic & F. Baumberger

Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

Nature Physics. doi:10.1038/nphys3722

Authors: R. Toskovic, R. van den Berg, A. Spinelli, I. S. Eliens, B. van den Toorn, B. Bryant, J.-S. Caux & A. F. Otte

The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be used as fundamental building blocks for the realization of textbook many-body quantum models, illustrating key concepts such as quantum phase transitions, topological order or frustration as a function of system size. Here, we use low-temperature scanning tunnelling microscopy to construct arrays of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg chains in a transverse field, for which a quantum phase transition from an antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic limit. Site-resolved measurements on these finite-size realizations reveal a number of sudden ground state changes when the field approaches the critical value, each corresponding to a new domain wall entering the chains. We observe that these state crossings become closer for longer chains, suggesting the onset of critical behaviour. Our results present opportunities for further studies on quantum behaviour of many-body systems, as a function of their size and structural complexity.

Author(s): Albert Bruix, Jill A. Miwa, Nadine Hauptmann, Daniel Wegner, Søren Ulstrup, Signe S. Grønborg, Charlotte E. Sanders, Maciej Dendzik, Antonija Grubišić Čabo, Marco Bianchi, Jeppe V. Lauritsen, Alexander A. Khajetoorians, Bjørk Hammer, and Philip Hofmann

The electronic structure of epitaxial single-layer MoS2 on Au(111) is investigated by angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy, and first-principles calculations. While the band dispersion of the supported single layer is close to a free-standing layer in the vicini…

[Phys. Rev. B 93, 165422] Published Mon Apr 18, 2016

Author(s): Can-Li Song, Hui-Min Zhang, Yong Zhong, Xiao-Peng Hu, Shuai-Hua Ji, Lili Wang, Ke He, Xu-Cun Ma, and Qi-Kun Xue

Iron selenide films peppered with potassium atoms exhibit a high-temperature superconducting phase that emerges separately from a low-temperature superconducting phase.

[Phys. Rev. Lett. 116, 157001] Published Mon Apr 11, 2016

Author(s): Davide Iaia, André Kubetzka, Kirsten von Bergmann, and Roland Wiesendanger

The structural and magnetic properties of one atomic layer thin nanostructures of Ni deposited on fcc Fe monolayer stripes on Ir(111) have been studied by (spin-resolved) scanning tunneling microscopy measurements. Ni grows dominantly in fcc stacking on Ir(111), whereas it forms a dense reconstructi…

[Phys. Rev. B 93, 134409] Published Mon Apr 11, 2016

Author(s): Jörg Meyer, Robin Ohmann, Anja Nickel, Cormac Toher, Roland Gresser, Karl Leo, Dmitry A. Ryndyk, Francesca Moresco, and Gianaurelio Cuniberti

The Kondo resonance of an organic molecule containing a Co atom is investigated by scanning tunneling spectroscopy and ab initio calculations on a Ag(100) surface. High resolution mapping of the line shape shows evidence of local nonradially symmetric variations of the Fano factor and the Kondo ampl…

[Phys. Rev. B 93, 155118] Published Tue Apr 12, 2016

Article

The zero-determinant (ZD) strategies discovered by Press and Dyson overturned several decades of consensus about the iterated prisoner's dilemma. Here, the authors provide the first empirical evidence in support of Press and Dyson’s theory, by showing that knowledge of the opponent and the length of the interaction can facilitate the Generous and Extortionate ZD strategies as predicted.

Nature Communications doi: 10.1038/ncomms11125

Authors: Zhijian Wang, Yanran Zhou, Jaimie W. Lien, Jie Zheng, Bin Xu

Abstract

Abstract

Article

Thin FeSe film on SrTiO 3 substrate becomes a superconductor with a transition temperature over 100 K, yet the origin remains controversial. Here, Seo et al . show superconductivity below 20 K on the electron-doped surface of an FeSe crystal, suggesting a decisive role of interfacial effects in the enhancement of superconductivity.

Nature Communications doi: 10.1038/ncomms11116

Authors: J. J. Seo, B. Y. Kim, B. S. Kim, J. K. Jeong, J. M. Ok, Jun Sung Kim, J. D. Denlinger, S. -K. Mo, C. Kim, Y. K. Kim