Dr.jens.brede

Author(s): V. I. Litvinov

The effective Hamiltonian that describes magnetic exchange interaction in a topological insulator is calculated, projecting bulk contact s-d interaction onto surface electron states. This model consistently describes the indirect exchange between magnetic atoms mediated either by massless Dirac ferm…

[Phys. Rev. B 89, 235316] Published Mon Jun 23, 2014

Author(s): Fabian Schulz, Robert Drost, Sampsa K. Hämäläinen, Thomas Demonchaux, Ari P. Seitsonen, and Peter Liljeroth

Hexagonal boron nitride (h-BN) is a prominent member in the growing family of two-dimensional materials with potential applications ranging from being an atomically smooth support for other two-dimensional materials to templating growth of molecular layers. We have studied the structure of monolayer...

[Phys. Rev. B 89, 235429] Published Mon Jun 23, 2014

Article

Organic electronics with good electrical performance and high mechanical stability are of great potential because of their low cost and scalability. Here, Fukuda et al. report the large-area fabrication of fully printable organic thin-film transistors that are only 1 μm thick.

Nature Communications doi: 10.1038/ncomms5147

Authors: Kenjiro Fukuda, Yasunori Takeda, Yudai Yoshimura, Rei Shiwaku, Lam Truc Tran, Tomohito Sekine, Makoto Mizukami, Daisuke Kumaki, Shizuo Tokito

Nature Chemistry 6, 608 (2014). doi:10.1038/nchem.1955

Authors: Gaston R. Schaller, Filip Topić, Kari Rissanen, Yoshio Okamoto, Jun Shen & Rainer Herges

Most cyclic conjugated molecules, such as benzene, exhibit two sides. Möbius annulenes, however, with an odd number of 180° twists in their π system, are one-sided and violate the Hückel rule. Now, using a topological trick it is demonstrated that triply twisted systems are not particularly strained and probably easier to synthesize than singly twisted ones.

A microscope based on a single spin of a diamond defect is used to observe magnetism dynamics. Authors: J.-P. Tetienne, T. Hingant, J.-V. Kim, L. Herrera Diez, J.-P. Adam, K. Garcia, J.-F. Roch, S. Rohart, A. Thiaville, D. Ravelosona, V. Jacques

Article

Understanding and being able to predict alignment between the electrode Fermi energy and the transport states in the organic semiconductor is important. Here, the authors report an electrostatic model, capable of reproducing the full range of interfacial energy level alignment regimes.

Nature Communications doi: 10.1038/ncomms5174

Authors: Martin Oehzelt, Norbert Koch, Georg Heimel

Measurement of the magnetic interaction between two bound electrons of two separate ions

Nature 510, 7505 (2014). doi:10.1038/nature13403

Authors: Shlomi Kotler, Nitzan Akerman, Nir Navon, Yinnon Glickman & Roee Ozeri

Electrons have an intrinsic, indivisible, magnetic dipole aligned with their internal angular momentum (spin). The magnetic interaction between two electronic spins can therefore impose a change in their orientation. Similar dipolar magnetic interactions exist between other spin systems and have been studied experimentally. Examples include the interaction between an electron and its nucleus and the interaction between several multi-electron spin complexes. The challenge in observing such interactions for two electrons is twofold. First, at the atomic scale, where the coupling is relatively large, it is often dominated by the much larger Coulomb exchange counterpart. Second, on scales that are substantially larger than the atomic, the magnetic coupling is very weak and can be well below the ambient magnetic noise. Here we report the measurement of the magnetic interaction between the two ground-state spin-1/2 valence electrons of two 88Sr+ ions, co-trapped in an electric Paul trap. We varied the ion separation, d, between 2.18 and 2.76 micrometres and measured the electrons’ weak, millihertz-scale, magnetic interaction as a function of distance, in the presence of magnetic noise that was six orders of magnitude larger than the magnetic fields the electrons apply on each other. The cooperative spin dynamics was kept coherent for 15 seconds, during which spin entanglement was generated, as verified by a negative measured value of −0.16 for the swap entanglement witness. The sensitivity necessary for this measurement was provided by restricting the spin evolution to a decoherence-free subspace that is immune to collective magnetic field noise. Our measurements show a d−3.0(4) distance dependence for the coupling, consistent with the inverse-cube law.

High resolution Atomic Force Microscopy (AFM) and Scanning Tunnelling Microscopy (STM) imaging with functionalized tips is well established, but a detailed understanding of the imaging mechanism is still missing. We present a numerical STM/AFM model, which takes into account the relaxation of the probe due to the tip-sample interaction. We demonstrate that the model is able to reproduce very well not only the experimental intra- and intermolecular contrasts, but also their evolution upon tip approach. At close distances, the simulations unveil a significant probe particle relaxation towards local minima of the interaction potential. This effect is responsible for the sharp sub-molecular resolution observed in AFM/STM experiments. In addition, we demonstrate that sharp apparent intermolecular bonds should not be interpreted as true hydrogen bonds, in the sense of representing areas of increased electron density. Instead they represent the ridge between two minima of the potential energy landscape due to neighbouring atoms.

The hyperfine interaction in a terbium bisphthalocyanine complex is modulated using electric fields to manipulate nuclear spin. Authors: Stefan Thiele, Franck Balestro, Rafik Ballou, Svetlana Klyatskaya, Mario Ruben, Wolfgang Wernsdorfer

We study the equilibrium phase diagram of ultrathin chiral magnets with easy-plane anisotropy $A$. The vast triangular skyrmion lattice phase that is stabilized by an external magnetic field evolves continuously as a function of increasing $A$ into a regime in which nearest-neighbor skyrmions start overlapping with each other. This overlap leads to a continuous reduction of the skyrmion number from its quantized value $Q=1$ and to the emergence of antivortices at the center of the triangles formed by nearest-neighbor skyrmions. The antivortices also carry a small "skyrmion number" $Q_A \ll 1$ that grows as a function of increasing $A$. The system undergoes a first order phase transition into a square vortex-antivortex lattice at a critical value of $A$. Finally, a canted ferromagnetic state becomes stable through another first order transition for a large enough anisotropy $A$. Interestingly enough, this first order transition is accompanied by {\it metastable} meron solutions.

Abstract

Article

Skyrmions—magnetic vortices that can behave like particles—have recently been observed in ultra-thin transition metal films. Dupé et al . show how the structure and composition of the interface influence the size and stability of the skyrmions.

Nature Communications doi: 10.1038/ncomms5030

Authors: Bertrand Dupé, Markus Hoffmann, Charles Paillard, Stefan Heinze

Author(s): Jin-Peng Xu, Canhua Liu, Mei-Xiao Wang, Jianfeng Ge, Zhi-Long Liu, Xiaojun Yang, Yan Chen, Ying Liu, Zhu-An Xu, Chun-Lei Gao, Dong Qian, Fu-Chun Zhang, and Jin-Feng Jia

Topological superconductors (TSCs), featuring fully gapped bulk and gapless surface states as well as Majorana fermions, have potential applications in fault-tolerant topological quantum computing. Because TSCs are very rare in nature, an alternative way to study the TSC is to artificially introduce...

[Phys. Rev. Lett. 112, 217001] Published Fri May 30, 2014

Article

Combining superconducting and magnetic layers offers a route to high-density and ultra-low power memory. Here, the authors extended this idea to more complicated structures by combining superconducting Josephson junctions and magnetic spin valves.

Nature Communications doi: 10.1038/ncomms4888

Authors: Burm Baek, William H. Rippard, Samuel P. Benz, Stephen E. Russek, Paul D. Dresselhaus

A cobalt atom bound to a single oxygen site on magnesia has the maximum magnetic anisotropy allowed for a transition metal [Also see Perspective by Khajetoorians and Wiebe] Authors: Ileana G. Rau, Susanne Baumann, Stefano Rusponi, Fabio Donati, Sebastian Stepanow, Luca Gragnaniello, Jan Dreiser, Cinthia Piamonteze, Frithjof Nolting, Shruba Gangopadhyay, Oliver R. Albertini, Roger M. Macfarlane, Christopher P. Lutz, Barbara A. Jones, Pietro Gambardella, Andreas J. Heinrich, Harald Brune

Article

Non-local spin valves that inject spin currents into non-magnetic metals hold great promise for spintronics, but a decrease in spin signal on cooling has perplexed researchers. O’Brien et al . now show this results from local magnetic moments forming in the nominally non-magnetic metals.

Nature Communications doi: 10.1038/ncomms4927

Authors: L. O'Brien, M. J. Erickson, D. Spivak, H. Ambaye, R. J. Goyette, V. Lauter, P. A. Crowell, C. Leighton

Article

Theory predicts that extortioners, individuals that obtain advantages through forces and threats, can outperform any generous co-player. Here, Hilbe et al. show experimentally that humans punish extortion by refusing to cooperate, which reduces the extortioner’s gains, and suggest that generosity is more profitable in the long run.

Nature Communications doi: 10.1038/ncomms4976

Authors: Christian Hilbe, Torsten Röhl, Manfred Milinski

In this review we summarize our experience gained from several recent ab initio studies aimed to investigate how the competition between short-ranged chemical and long-ranged dispersion interactions determines the bonding mechanism of a specific set of chemically functionalized π -conjugated organic molecules on non-magnetic and magnetic metal surfaces. A key point of this review is to provide a detailed analysis on the issue of how to tune the strength of the organic molecule-surface interaction, such that the nature of the molecular bonding exhibits the specific electronic features of the physisorption or chemisorption bonding mechanisms. In particular, we discuss in detail how the precise control of these bonding mechanisms can be used to design specific electronic and magnetic properties of hybrid organic-metallic interfaces. Furthermore, our first-principles simulations provide not only the basic insights needed to interpret surface-science experiments, but are ...

Vibrational excitation of a carbon monoxide molecule on a scanning tunneling microscope tip reveals bonding within adsorbed molecules Authors: Chi-lun Chiang, Chen Xu, Zhumin Han, W. Ho

To date, solid-state nanopores have been fabricated primarily through a focused-electronic beam via TEM. For mass production, however, a TEM beam is not suitable and an alternative fabrication method is required. Recently, a simple method for fabricating solid-state nanopores was reported by Kwok, H. et al. and used to fabricate a nanopore (down to 2 nm in size) in a membrane via dielectric breakdown. In the present study, to fabricate smaller nanopores stably—specifically with a diameter of 1 to 2 nm (which is an essential size for identifying each nucleotide)—via dielectric breakdown, a technique called “multilevel pulse-voltage injection” (MPVI) is proposed and evaluated. MPVI can generate nanopores with diameters of sub-1 nm in a 10-nm-thick Si3N4 membrane with a probability of 90%. The generated nanopores can be widened to the desired size (as high as 3 nm in diameter) with sub-nanometre precision, and the mean effective thickness of the fabricated nanopores was 3.7 nm.

Scientific Reports 4 doi: 10.1038/srep05000

Author(s): K. Wang, J. G. M. Sanderink, T. Bolhuis, W. G. van der Wiel, and M. P. de Jong

C₆₀ fullerenes are interesting molecular semiconductors for spintronics since they exhibit weak spin-orbit and hyperfine interactions, which is a prerequisite for long spin lifetimes. We report spin-polarized transport in spin-valve-like structures containing ultrathin (10 nm) C₆₀ layers, ferromagne...

[Phys. Rev. B 89, 174419] Published Fri May 16, 2014