Dr.jens.brede

Author(s): Benjamin Stadtmüller, Johannes Seidel, Norman Haag, Lisa Grad, Christian Tusche, Gerben van Straaten, Markus Franke, Jürgen Kirschner, Christian Kumpf, Mirko Cinchetti, and Martin Aeschlimann

Hybridization-related modifications of the first metal layer of a metal-organic interface are difficult to access experimentally and have been largely neglected so far. Here, we study the influence of specific chemical bonds (as formed by the organic molecules CuPc and PTCDA) on a Pb-Ag surface allo…

[Phys. Rev. Lett. 117, 096805] Published Fri Aug 26, 2016

Abstract

Nature Chemistry 8, 825 (2016). doi:10.1038/nchem.2553

Authors: Michael S. Inkpen, Stefan Scheerer, Michael Linseis, Andrew J. P. White, Rainer F. Winter, Tim Albrecht & Nicholas J. Long

Cyclic molecules often exhibit unusual properties; consider for example the resonance stabilization energy of benzene or the strong cation binding of crown ethers. Now, a family of rings comprising varying numbers of directly linked ferrocenes has been prepared. These compounds are highly symmetric in solution and undergo rapid ‘oxidation-state isomerism’ when charged.

Negative differential resistance remains an attractive but elusive functionality, so far only finding niche applications. Atom scale entities have shown promising properties, but viability of device fabrication requires fuller understanding of electron dynamics than has been possible to date. Using an all-electronic time-resolved scanning tunneling microscopy technique and a Green's function transport model, we study an isolated dangling bond on a hydrogen terminated silicon surface. A robust negative differential resistance feature is identified as a many body phenomenon related to occupation dependent electron capture by a single atomic level. We measure all the time constants involved in this process and present atomically resolved, nanosecond timescale images to simultaneously capture the spatial and temporal variation of the observed feature.

Author(s): P. Sessi, P. Rüßmann, T. Bathon, A. Barla, K. A. Kokh, O. E. Tereshchenko, K. Fauth, S. K. Mahatha, M. A. Valbuena, S. Godey, F. Glott, A. Mugarza, P. Gargiani, M. Valvidares, N. H. Long, C. Carbone, P. Mavropoulos, S. Blügel, and M. Bode

Recently it has been shown that surface magnetic doping of topological insulators induces backscattering of Dirac states which are usually protected by time-reversal symmetry [Sessi et al., Nat. Commun. 5, 5349 (2014)]. Here we report on quasiparticle interference measurements where, by improved Fe…

[Phys. Rev. B 94, 075137] Published Wed Aug 17, 2016

Author(s): E. C. T. O’Farrell, J. Y. Tan, Y. Yeo, G. K. W. Koon, B. Özyilmaz, K. Watanabe, and T. Taniguchi

We intercalate a van der Waals heterostructure of graphene and hexagonal boron nitride with Au, by encapsulation, and show that the Au at the interface is two dimensional. Charge transfer upon current annealing indicates the redistribution of the Au and induces splitting of the graphene band structu…

[Phys. Rev. Lett. 117, 076603] Published Fri Aug 12, 2016

Author(s): Masahiko G. Yamada, Tomohiro Soejima, Naoto Tsuji, Daisuke Hirai, Mircea Dincă, and Hideo Aoki

We design from first principles a type of two-dimensional metal-organic framework (MOF) using phenalenyl-based ligands to exhibit a half-filled flat band of the kagome lattice, which is one of a family of lattices that show Lieb-Mielke-Tasaki's flat-band ferromagnetism. Among various MOFs, we find t…

[Phys. Rev. B 94, 081102(R)] Published Mon Aug 08, 2016

Author(s): Hao Ding, Yan-Feng Lv, Kun Zhao, Wen-Lin Wang, Lili Wang, Can-Li Song, Xi Chen, Xu-Cun Ma, and Qi-Kun Xue

We report on the observation of high-temperature (Tc) superconductivity and magnetic vortices in single-unit-cell FeSe films on anatase TiO2(001) substrate by using scanning tunneling microscopy. A systematic study and engineering of interfacial properties has clarified the essential roles of substr…

[Phys. Rev. Lett. 117, 067001] Published Fri Aug 05, 2016

Recent advances in large-scale synthesis of graphene and other 2D materials have underscored the importance of local defects such as dislocations and grain boundaries (GBs), and especially their tendency to alter the electronic properties of the material. Understanding how the polycrystalline morphology affects the electronic properties is crucial for the development of applications such as flexible electronics, energy harvesting devices or sensors. We here report on atomic scale characterization of several GBs and on the structural-dependence of the localized electronic states in their vicinity. Using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS), together with tight binding and ab initio numerical simulations we explore GBs on the surface of graphite and elucidate the interconnection between the local density of states (LDOS) and their atomic structure. We show that the electronic fingerprints of these GBs consist of pronounced resonances which, depending on the relative orientation of the adjacent crystallites, appear either on the electron side of the spectrum or as an electron-hole symmetric doublet close to the charge neutrality point. These two types of spectral features will impact very differently the transport properties allowing, in the asymmetric case to introduce transport anisotropy which could be utilized to design novel growth and fabrication strategies to control device performance.

Article

Chiral p-wave superconductors may form the basis for topological quantum computers however one has yet to be identified. Here, the authors propose that such a state may be created by a two-dimensional array of magnetic adatoms on the surface of a superconductor with strong spin-orbit coupling.

Nature Communications doi: 10.1038/ncomms12297

Authors: Jian Li, Titus Neupert, Zhijun Wang, A. H. MacDonald, A. Yazdani, B. Andrei Bernevig

Abstract

Quantum spin tunneling (QST) and Kondo effect are two very different quantum phenomena that produce the same effect on quantized spins, namely, the quenching of their magnetization. However, the nature of this quenching is very different so that QST and Kondo effects compete with each other. Importantly, both QST and Kondo produce very characteristic features in the spectral function that can be measured by means of single spin scanning tunneling spectroscopy that makes it possible to probe the crossover from one regime to the other. We model this crossover, and the resulting changes in transport, using a non-perturbative treatment of a generalized Anderson model including magnetic anisotropy that leads to quantum spin tunneling. We predict that, at zero magnetic field, integer spins can feature a split-Kondo peak driven by quantum spin tunneling.

We intercalate a van der Waals heterostructure of graphene and hexagonal Boron Nitride with Au, by encapsulation, and show that Au at the interface is two dimensional. A charge transfer upon current annealing indicates redistribution of Au and induces splitting of the graphene bandstructure. The effect of in plane magnetic field confirms that splitting is due to spin-splitting and that spin polarization is in the plane, characteristic of a Rashba interaction with magnitude approximately 25 meV. Consistent with the presence of intrinsic interfacial electric field we show that the splitting can be enhanced by an applied displacement field in dual gated samples. Giant negative magnetoresistance, up to 75%, and a field induced anomalous Hall effect at magnetic fields < 1 T are observed. These demonstrate that hybridized Au has a magnetic moment and suggests the proximity to formation of a collective magnetic phase. These effects persist close to room temperature.

Abstract

Author(s): Maria Stamenova, Jacopo Simoni, and Stefano Sanvito

The ultrafast demagnetization of small iron clusters initiated by an intense optical excitation is studied from the time-dependent spin density functional theory (TDSDFT). In particular we investigate the effect of the spin-orbit interaction on the onset of the demagnetization process. It is found t…

[Phys. Rev. B 94, 014423] Published Tue Jul 19, 2016

Article

The relationship between electronic ordering and superconductivity, crucial to understand high- T c superconductors, remains elusive. Here, Sun et al . report the pressure-induced dome shape of a magnetic phase superceding the nematic order in FeSe, suggesting competing nature between magnetism and superconductivity.

Nature Communications doi: 10.1038/ncomms12146

Authors: J. P. Sun, K. Matsuura, G. Z. Ye, Y. Mizukami, M. Shimozawa, K. Matsubayashi, M. Yamashita, T. Watashige, S. Kasahara, Y. Matsuda, J. -Q. Yan, B. C. Sales, Y. Uwatoko, J. -G. Cheng, T. Shibauchi

Article

Different ground states of high-temperature superconductors reveal complex nature of magnetism. Here, Wang et al . report stripe and Néel spin fluctuations coexisting with non-magnetic nematic phase in FeSe, providing a viewpoint towards understanding the magnetism of cuprate and iron-based superconductors.

Nature Communications doi: 10.1038/ncomms12182

Authors: Qisi Wang, Yao Shen, Bingying Pan, Xiaowen Zhang, K. Ikeuchi, K. Iida, A. D. Christianson, H. C. Walker, D. T. Adroja, M. Abdel-Hafiez, Xiaojia Chen, D. A. Chareev, A. N. Vasiliev, Jun Zhao

Article

Spin crossover molecules may find applications in ultimately small magnetic devices, given the sensitivity of their spin-states to external stimuli. Here, the authors show a light-induced transition between two ordered dynamic phases in two-dimensional spin crossover layers on a metallic surface.

Nature Communications doi: 10.1038/ncomms12212

Authors: Kaushik Bairagi, Olga Iasco, Amandine Bellec, Alexey Kartsev, Dongzhe Li, Jérôme Lagoute, Cyril Chacon, Yann Girard, Sylvie Rousset, Frédéric Miserque, Yannick J Dappe, Alexander Smogunov, Cyrille Barreteau, Marie-Laure Boillot, Talal Mallah, Vincent Repain

The inversion layer of p-InSb(110) obtained by Cs adsorption of 1.8 % of a monolayer is used to probe the Landau level wave functions within smooth potential valleys by scanning tunnelling spectroscopy at 14 T. The nodal structure becomes apparent as a double peak structure of each spin polarized first Landau level, while the zeroth Landau level exhibits a single peak per spin level only. The real space data show single rings of the valley-confined drift states for the zeroth Landau level and double rings for the first Landau level. The result is reproduced by a recursive Green's function algorithm using the potential landscape obtained experimentally. We show that the result is generic by comparing the local density of states from the Green's function algorithm with results from a well controlled analytic model based on the guiding center approach.

The highest-density magnetic storage media will code data in single-atom bits. To date, the smallest individually addressable bistable magnetic bits on surfaces consist of 5-12 atoms. Long magnetic relaxation times were demonstrated in molecular magnets containing one lanthanide atom, and recently in ensembles of single holmium (Ho) atoms supported on magnesium oxide (MgO). Those experiments indicated the possibility for data storage at the fundamental limit, but it remained unclear how to access the individual magnetic centers. Here we demonstrate the reading and writing of individual Ho atoms on MgO, and show that they independently retain their magnetic information over many hours. We read the Ho states by tunnel magnetoresistance and write with current pulses using a scanning tunneling microscope. The magnetic origin of the long-lived states is confirmed by single-atom electron paramagnetic resonance (EPR) on a nearby Fe sensor atom, which shows that Ho has a large out-of-plane moment of $(10.1 \pm 0.1)$ $\mu_{\rm B}$ on this surface. In order to demonstrate independent reading and writing, we built an atomic scale structure with two Ho bits to which we write the four possible states and which we read out remotely by EPR. The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is possible.