Dr.jens.brede

Article

Spin-crossover complexes and single-chain magnets exhibit magnetic bistability and may be used in information storage applications. Here, the authors present a one-dimensional spin-crossover complex wherein the single-chain magnet behaviour is actuated by light-induced excited spin-state trapping.

Nature Communications doi: 10.1038/ncomms3826

Authors: Tao Liu, Hui Zheng, Soonchul Kang, Yoshihito Shiota, Shinya Hayami, Masaki Mito, Osamu Sato, Kazunari Yoshizawa, Shinji Kanegawa, Chunying Duan

Article

In superconductors with sign-preserving pairing symmetries, Cooper pairs break when they scatter off magnetic impurities but not non-magnetic impurities. An observation of pair breaking by copper impurities in Na(Fe 0.96 Co 0.03 Cu 0.01 )As demonstrates that its pairing symmetry is sign-reversed.

Nature Communications doi: 10.1038/ncomms3749

Authors: Huan Yang, Zhenyu Wang, Delong Fang, Qiang Deng, Qiang-Hua Wang, Yuan-Yuan Xiang, Yang Yang, Hai-Hu Wen

Author(s): R. C. Temple and C. H. Marrows

Building on spin-modified Coulomb blockade theory, we derive an approximate analytical solution which matches closely to the existing numerical models in the limit of a large difference in the resistance of the two tunnel junctions. Using this, we are able to explore the properties of an I(V) measur...

[Phys. Rev. B 88, 184415] Published Mon Nov 18, 2013

Author(s): M. Granovskij, A. Schrön, and F. Bechstedt

Magnetic exchange force microscopy (MExFM) is one of the most important methods to investigate the spin structure of magnetic surfaces. However, a deep understanding of the measured spin contrast and the spin-dependent forces is missing. For the prototypical antiferromagnetic MnO(001) and NiO(001) s...

[Phys. Rev. B 88, 184416] Published Mon Nov 18, 2013

Stabilizing the magnetic moment of single holmium atoms by symmetry

Nature 503, 7475 (2013). doi:10.1038/nature12759

Authors: Toshio Miyamachi, Tobias Schuh, Tobias Märkl, Christopher Bresch, Timofey Balashov, Alexander Stöhr, Christian Karlewski, Stephan André, Michael Marthaler, Martin Hoffmann, Matthias Geilhufe, Sergey Ostanin, Wolfram Hergert, Ingrid Mertig, Gerd Schön, Arthur Ernst & Wulf Wulfhekel

Single magnetic atoms, and assemblies of such atoms, on non-magnetic surfaces have recently attracted attention owing to their potential use in high-density magnetic data storage and as a platform for quantum computing. A fundamental problem resulting from their quantum mechanical nature is that the localized magnetic moments of these atoms are easily destabilized by interactions with electrons, nuclear spins and lattice vibrations of the substrate. Even when large magnetic fields are applied to stabilize the magnetic moment, the observed lifetimes remain rather short (less than a microsecond). Several routes for stabilizing the magnetic moment against fluctuations have been suggested, such as using thin insulating layers between the magnetic atom and the substrate to suppress the interactions with the substrate’s conduction electrons, or coupling several magnetic moments together to reduce their quantum mechanical fluctuations. Here we show that the magnetic moments of single holmium atoms on a highly conductive metallic substrate can reach lifetimes of the order of minutes. The necessary decoupling from the thermal bath of electrons, nuclear spins and lattice vibrations is achieved by a remarkable combination of several symmetries intrinsic to the system: time reversal symmetry, the internal symmetries of the total angular momentum and the point symmetry of the local environment of the magnetic atom.

Communication: Science is not about simple stories

Nature 503, 7475 (2013). doi:10.1038/503198f

Author: Jeroen Bergmann

Presenting science as a compelling story is becoming a popular way of communicating results — a technique that is guaranteed to capture the attention of the scientific community and the public. Although science needs great stories, stories are not science.Storytelling glosses over uncertainties; methodological

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows \textit{in situ} transfer from an ultra high vacuum (UHV) preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of $\text{Cu}_x\text{Bi}_2\text{Se}_3$. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 $\mu$eV.

Article

Chemical functionalization of graphene is a useful method for modulating its properties, although this is limited by a lack of control and resulting in poorly defined structures. Here the authors report the atomically precise chlorination of nanographenes and apply the methods to graphene nanoribbons.

Nature Communications doi: 10.1038/ncomms3646

Authors: Yuan-Zhi Tan, Bo Yang, Khaled Parvez, Akimitsu Narita, Silvio Osella, David Beljonne, Xinliang Feng, Klaus Müllen

Article

The intercalation of graphene can result in many attractive functional properties. Here, the authors study the mechanism of caesium intercalation of graphene, finding that it nucleates at wrinkles on the graphene surface and is influenced by van der Waals interactions.

Nature Communications doi: 10.1038/ncomms3772

Authors: M. Petrović, I. Šrut Rakić, S. Runte, C. Busse, J. T. Sadowski, P. Lazić, I. Pletikosić, Z.-H. Pan, M. Milun, P. Pervan, N. Atodiresei, R. Brako, D. Šokčević, T. Valla, T. Michely, M. Kralj

Nature Physics. doi:10.1038/nphys2794

Authors: B. W. Heinrich, L. Braun, J. I. Pascual & K. J. Franke

The latest concepts for quantum computing and data storage rely on the addressing and manipulation of single spins. A limitation for single atoms or molecules in contact with a metal surface is the short lifetime of excited spin states, typically picoseconds, due to the exchange of energy and angular momentum with the itinerant electrons of the substrate. Here we show that paramagnetic molecules on a superconducting substrate exhibit excited spin states with a lifetime of τ≈10 ns. We ascribe this increase in lifetime by orders of magnitude to the depletion of electronic states around the Fermi level in the superconductor. This prohibits pathways of energy relaxation into the substrate and allows the magnetic molecule to be electrically pumped into higher spin states, making superconducting substrates prime candidates for spin manipulation. We further show that the proximity of the scanning tunnelling microscope tip modifies the magnetic anisotropy.

Nature Nanotechnology 8, 853 (2013). doi:10.1038/nnano.2013.188

Authors: Kh. Zakeri, T.-H. Chuang, A. Ernst, L. M. Sandratskii, P. Buczek, H. J. Qin, Y. Zhang & J. Kirschner

Nature Nanotechnology 8, 845 (2013). doi:10.1038/nnano.2013.207

Authors: A. Giugni, B. Torre, A. Toma, M. Francardi, M. Malerba, A. Alabastri, R. Proietti Zaccaria, M. I. Stockman & E. Di Fabrizio

Nature Nanotechnology 8, 839 (2013). doi:10.1038/nnano.2013.233

Authors: J. Sampaio, V. Cros, S. Rohart, A. Thiaville & A. Fert

Nature Nanotechnology 8, 839 (2013). doi:10.1038/nnano.2013.233

Authors: J. Sampaio, V. Cros, S. Rohart, A. Thiaville & A. Fert

We report here on the molecular self-assembly of 7, 7′, 8, 8′ tetracyanoquinodimethane (TCNQ) (schematic representation of the molecule on figure 1(b)) on a single-crystal Cu(111) surface, followed by deposition of Fe and Mn, and on the formation of an ordered metal–organic coordination network of Fe (or Mn)–TCNQ units, which contains magnetic ions separated by 0.9 nm.

We study how FeO wüstite films on Ru(0001) grow by oxygen-assisted molecular beam epitaxy at elevated temperatures (800–900 K). The nucleation and growth of FeO islands are observed in real time by low-energy electron microscopy (LEEM). When the growth is performed in an oxygen pressure of 10 −6 Torr, the islands are of bilayer thickness (Fe–O–Fe–O). In contrast, under a pressure of 10 −8  Torr, the islands are a single FeO layer thick. We propose that the film thickness is controlled by the concentration of oxygen adsorbed on the Ru. More specifically, when monolayer growth increases the adsorbed oxygen concentration above a limiting value, its growth is suppressed. Increasing the temperature at a fixed oxygen pressure decreases the density of FeO islands. However, the nucleation density is not a monotonic function of oxygen pressure.

The utilization of spin waves as eigenmodes of the magnetization dynamics for information processing and communication has been widely explored recently due to its high operational speed with low power consumption and possible applications for quantum computations. Previous proposals of spin wave Mach-Zehnder devices were based on the spin wave phase, a delicate entity which can be easily disrupted. Here, we propose a complete logic system based on the spin wave amplitude utilizing the nonreciprocal spin wave behavior excited by microstrip antennas. The experimental data reveal that the nonreciprocity of magnetostatic surface spin wave can be tuned by the bias magnetic field. Furthermore, engineering of the device structure could result in a high nonreciprocity factor for spin wave logic applications.

Scientific Reports 3 doi: 10.1038/srep03160

Scientific articles are retracted at increasing rates, with the highest rates among top journals. Here we show that a single retraction triggers citation losses through an author's prior body of work. Compared to closely-matched control papers, citations fall by an average of 6.9% per year for each prior publication. These chain reactions are sustained on authors' papers (a) published up to a decade earlier and (b) connected within the authors' own citation network by up to 4 degrees of separation from the retracted publication. Importantly, however, citation losses among prior work disappear when authors self-report the error. Our analyses and results span the range of scientific disciplines.

Scientific Reports 3 doi: 10.1038/srep03146

A methodology of atomically resolved Land\'{e} g factor mapping of a single molecule is reported. Mn(II)-phthalocyanine (MnPc) molecules on Au(111) surface can be dehydrogenated via atomic manipulation with manifestation of tailored extended Kondo effect, which can allow atomically resolved imaging of the Land\'{e} g factor inside a molecule for the first time. By employing dehydrogenated MnPc molecules with removal of six H atoms (-6H-MnPc) as an example, Land\'{e} g factor of atomic constituents of the molecule can be obtained, therefore offering a unique g factor mapping of single molecule. Our results open up a new avenue to access local spin texture of a single molecule.

In an article written five years ago [arXiv:0809.0522], we described a method for predicting which scientific papers will be highly cited in the future, even if they are currently not highly cited. Applying the method to real citation data we made predictions about papers we believed would end up being well cited. Here we revisit those predictions, five years on, to see how well we did. Among the over 2000 papers in our original data set, we examine the fifty that, by the measures of our previous study, were predicted to do best and we find that they have indeed received substantially more citations in the intervening years than other papers, even after controlling for the number of prior citations. On average these top fifty papers have received 23 times as many citations in the last five years as the average paper in the data set as a whole, and 15 times as many as the average paper in a randomly drawn control group that started out with the same number of citations. Applying our prediction technique to current data, we also make new predictions of papers that we believe will be well cited in the next few years.

Author(s): Adam Jacobsson, Biplab Sanyal, Marjana Ležaić, and Stefan Blügel

We present a method of extracting the exchange parameters of the classical Heisenberg model from first-principles calculations of spin-spiral total energies based on density functional theory. The exchange parameters of the transition-metal monoxides MnO and NiO are calculated and used to estimate m...

[Phys. Rev. B 88, 134427] Published Mon Oct 28, 2013

We present an approach to control the magnetic structure of adatoms adsorbed on a substrate having a high magnetic susceptibility. Using finite Ni-Pt and Fe-Pt nanowires and nanostructures on Pt(111) surfaces, our ab initio results show that it is possible to tune the exchange interaction and magnetic configuration of magnetic adatoms (Fe or Ni) by introducing different numbers of Pt atoms to link them, or by including edge effects. The exchange interaction between Ni (or Fe) adatoms on Pt(111) can be considerably increased by introducing Pt chains to link them. The magnetic ordering can be regulated allowing for ferromagnetic or antiferromagnetic configurations. Noncollinear magnetic alignments can also be stabilized by changing the number of Pt-mediated atoms. An Fe-Pt triangularly-shaped nanostructure adsorbed on Pt(111) shows the most complex magnetic structure of the systems considered here: a spin-spiral type of magnetic order that changes its propagation direction at the triangle vertices.

Scientific Reports 3 doi: 10.1038/srep03054

Nature advance online publication 27 October 2013. doi:10.1038/nature12597

Authors: Marc Warner, Salahud Din, Igor S. Tupitsyn, Gavin W. Morley, A. Marshall Stoneham, Jules A. Gardener, Zhenlin Wu, Andrew J. Fisher, Sandrine Heutz, Christopher W. M. Kay & Gabriel Aeppli

Organic semiconductors are studied intensively for applications in electronics and optics, and even spin-based information technology, or spintronics. Fundamental quantities in spintronics are the population relaxation time (T1) and the phase memory time (T2): T1 measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and T2 measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine, in easily processed thin-film form of the type used for device fabrication. At 5 K, a temperature reachable using inexpensive closed-cycle refrigerators, T1 and T2 are respectively 59 ms and 2.6 μs, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 μs and 1 μs, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range. T2 is more than two orders of magnitude greater than the duration of the spin manipulation pulses, which suggests that copper phthalocyanine holds promise for quantum information processing, and the long T1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.

Article

Short-lived precursors typically occur before molecules chemisorb on surfaces. Liu et al . predict that for benzene derivatives on metal surfaces, the precursors can be long-lived and the transition to chemisorption states can be reversible, which may be useful in molecular switch applications.

Nature Communications doi: 10.1038/ncomms3569

Authors: Wei Liu, Sergey N. Filimonov, Javier Carrasco, Alexandre Tkatchenko