Manuel Steinbrecher

Publication date: May 2015
Source:Surface Science, Volume 635
Author(s): Sam K. Jo
Step edges and kinks, abundant on multi-faceted nanoparticles, are catalytically active sites. Weakly-bound atomic H, at either topmost surface or subsurface sites, would be important for low-temperature hydrogenation in platinum-based catalysts. Here we report experimental results for such H atoms on Pt(111). Saturation-adsorbed atomic H from molecular H2 on the defect-free Pt(111) surface indeed gave only a single-peaked H2 desorption (β2) at 285K. Instead, defected Pt(111) surfaces rendered triple peaks (β1 to β3) including a prominent feature (β1) at as low as 205K in addition to another desorption (β3) at 360K. This β1–H state was inhibited and created by pre- and post-adsorbed CO, respectively. We attribute the β1–H2 desorption to H atoms trapped at interstitial sites beneath surface defects on the basis of: (1) its desorption at a very low temperature in addition to two other peaks from terrace- and defect-adsorbed H; (2) its and total H uptakes by far larger than the surface defect density; (3) its desorption amount up to ~3.6 times that of the β3 desorption from defects; (4) its complete inhibition by a small pre-coverage of CO; and (5) the complete β3-to-β1 H conversion, while the β1–H state remaining intact, by postdosed CO. Our proposed mechanism is that the derelaxation (upward lifting) of the H- or CO-bound Pt lattice atoms at (step) defects, as a result of strong H–H and even stronger H–CO lateral repulsions under (near) saturation surface coverages, opens a low-barrier path for H diffusion into the subsurface.

Graphical abstract

Author(s): W. Steurer, J. Repp, L. Gross, I. Scivetti, M. Persson, and G. Meyer

We show charge-state manipulation of single Au adatoms on 2–11 monolayer (ML) thick NaCl films on Cu surfaces by attaching or detaching single electrons via the tip of an atomic force microscope (AFM). Tristate charge control (neutral, negatively charged, and positively charged) is achieved. On Cu(1...

[Phys. Rev. Lett. 114, 036801] Published Thu Jan 22, 2015

Author(s): Y. Kono, T. Sakakibara, C. P. Aoyama, C. Hotta, M. M. Turnbull, C. P. Landee, and Y. Takano

High-precision dc magnetization measurements have been made on Cu(C₄H₄N₂)(NO₃)₂ in magnetic fields up to 14.7 T, slightly above the saturation field H_s=13.97  T, in the temperature range from 0.08 to 15 K. The magnetization curve and differential susceptibility at the lowest temperature show excelle...

[Phys. Rev. Lett. 114, 037202] Published Thu Jan 22, 2015

Author(s): Yin-Chen He and Yan Chen

By using the density matrix renormalization group approach, we study spin-liquid phases of spin-1/2 XXZ kagome antiferromagnets. We find that the emergence of the spin-liquid phase is independent of the anisotropy of the XXZ interaction. In particular, the two extreme limits—the Ising (a strong S^z i...

[Phys. Rev. Lett. 114, 037201] Published Thu Jan 22, 2015

Author(s): Ioannis Rousochatzakis, Johannes Richter, Ronald Zinke, and Alexander A. Tsirlin

We investigate the antiferromagnetic canting instability of the spin-1/2 kagome ferromagnet, as realized in the layered cuprates Cu₃Bi(SeO₃)₂O₂X (X = Br, Cl). While the local canting can be explained in terms of competing exchange interactions, the direction of the ferrimagnetic order parameter fluc...

[Phys. Rev. B 91, 024416] Published Fri Jan 16, 2015

What would happen if grant reviews were made public?

Nature 517, 7534 (2015). doi:10.1038/517247f

Author: Chris Woolston

Researchers on social media discuss the potential impact of making peer review more transparent.

Author(s): S. C. Martin, S. Samaddar, B. Sacépé, A. Kimouche, J. Coraux, F. Fuchs, B. Grévin, H. Courtois, and C. B. Winkelmann

We report the coexistence of charge puddles and topographic ripples in graphene decoupled from the Ir(111) substrate it was grown on. We show the topographic and the charge disorder to be locally correlated as a result of the intercalation of molecular species. From the analysis of quasiparticle sca...

[Phys. Rev. B 91, 041406] Published Tue Jan 13, 2015

Author(s): Camille Aron and Gabriel Kotliar

We study the emergence of quasiparticles in Hund's metals with an SU(M)×SU(N)-symmetric Kondo impurity model carrying both spin and orbital degrees of freedom. We show that the coupling of the impurity spin to the conduction electrons can be ferromagnetic, notably for hole-doped iron pnictides. We d...

[Phys. Rev. B 91, 041110] Published Mon Jan 12, 2015

Author(s): J. K. Schoelz, P. Xu, V. Meunier, P. Kumar, M. Neek-Amal, P. M. Thibado, and F. M. Peeters

Ripples in pristine freestanding graphene naturally orient themselves in an array that is alternately curved-up and curved-down; maintaining an average height of zero. Using scanning tunneling microscopy (STM) to apply a local force, the graphene sheet will reversibly rise and fall in height until t...

[Phys. Rev. B 91, 045413] Published Mon Jan 12, 2015

Author(s): Ilia Zintchenko, Matthew B. Hastings, and Matthias Troyer

We consider whether it is possible to find ground states of frustrated spin systems by solving them locally. Using spin glass physics and Imry-Ma arguments in addition to numerical benchmarks we quantify the power of such local solution methods and show that for the average low-dimensional spin glas...

[Phys. Rev. B 91, 024201] Published Mon Jan 05, 2015

Author(s): Yasir Iqbal, Didier Poilblanc, and Federico Becca

We report variational Monte Carlo calculations for the spin-1/2 Heisenberg model on the kagome lattice in the presence of both nearest-neighbor J₁ and next-nearest-neighbor J₂ antiferromagnetic superexchange couplings. Our approach is based upon Gutzwiller projected fermionic states that represent a...

[Phys. Rev. B 91, 020402] Published Fri Jan 09, 2015

Schachcomputer sind unbesiegbar - nun gilt das auch für Pokersoftware. Gegen das von Forschern entwickelte Programm haben Menschen keine Chance, sofern ausreichend viele Partien nacheinander gespielt werden.

The smallest common poker game, two-player limit Texas Hold'em, is essentially solved [Also see Research Article by Bowling et al.] Author: Tuomas Sandholm

Author(s): Andreas Burtzlaff, Alexander Weismann, Mads Brandbyge, and Richard Berndt

Measurements of the shot noise through a gold STM tip contacted to a gold adatom reveal the open spin-polarized transport channels between the tip and the surface underneath.

[Phys. Rev. Lett. 114, 016602] Published Tue Jan 06, 2015

Author(s): Stefan Schumacher, Felix Huttmann, Marin Petrović, Christian Witt, Daniel F. Förster, Chi Vo-Van, Johann Coraux, Antonio J. Martínez-Galera, Violetta Sessi, Ignacio Vergara, Reinhard Rückamp, Markus Grüninger, Nicolas Schleheck, Frank Meyer zu Heringdorf, Philippe Ohresser, Marko Kralj, Tim O. Wehling, and Thomas Michely

The intercalation of Eu underneath Gr on Ir(111) is comprehensively investigated by microscopic, magnetic, and spectroscopic measurements, as well as by density functional theory. Depending on the coverage, the intercalated Eu atoms form either a (2×2) or a (√3×√3)R30^∘ superstructure with respect to...

[Phys. Rev. B 90, 235437] Published Mon Dec 29, 2014

Nature Physics 10, 956 (2014). doi:10.1038/nphys3140

Authors: Yang Xu, Ireneusz Miotkowski, Chang Liu, Jifa Tian, Hyoungdo Nam, Nasser Alidoust, Jiuning Hu, Chih-Kang Shih, M. Zahid Hasan & Yong P. Chen

Author(s): F. Donati, L. Gragnaniello, A. Cavallin, F. D. Natterer, Q. Dubout, M. Pivetta, F. Patthey, J. Dreiser, C. Piamonteze, S. Rusponi, and H. Brune

We determine the magnetic properties of individual Co atoms adsorbed on graphene (G) with x-ray absorption spectroscopy and magnetic circular dichroism. The magnetic ground state of Co adatoms strongly depends on the choice of the metal substrate on which graphene is grown. Cobalt atoms on G/Ru(0001...

[Phys. Rev. Lett. 113, 177201] Published Mon Oct 20, 2014

Author(s): Hirofumi Oka, Oleg O. Brovko, Marco Corbetta, Valeri S. Stepanyuk, Dirk Sander, and Jürgen Kirschner

Experimental investigations of spin-polarized electron confinement in nanostructures by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are reviewed. To appreciate the experimental results on the electronic level, the physical basis of STM is elucidated with special emp…

[Rev. Mod. Phys. 86, 1127] Published Fri Oct 03, 2014

Author(s): E. Simon, K. Palotás, L. Rózsa, L. Udvardi, and L. Szunyogh

We perform an extensive study of the spin-configurations in a PdFe bilayer on Ir(111) in terms of ab initio and spin-model calculations. We use the spin-cluster expansion technique to obtain spin model parameters, and solve the Landau-Lifshitz-Gilbert equations at zero temperature. In particular, we...

[Phys. Rev. B 90, 094410] Published Tue Sep 16, 2014

Author(s): M. B. Stone, Y. Chen, D. H. Reich, C. Broholm, G. Xu, J. R. D. Copley, and J. C. Cook

We examine the magnetic field dependent excitations of the dimerized spin-1/2 chain, copper nitrate, with antiferromagnetic intradimer exchange J1=0.44(1)meV and exchange alternation α=J2/J1=0.26(2). Magnetic excitations in three distinct regimes of magnetization are probed through inelastic neutron...

[Phys. Rev. B 90, 094419] Published Mon Sep 29, 2014

Author(s): Keola Wierschem and Pinaki Sengupta

We study the behavior of the recently proposed “strange correlator” [Y.-Z. You, Z. Bi, A. Rasmussen, K. Slagle, and C. Xu, Phys. Rev. Lett. 112, 247202 (2014)PRLTAO10.1103/PhysRevLett.112.247202] in spin-1 Heisenberg antiferromagnetic chains with uniaxial single-ion anisotropy. Using projective quan...

[Phys. Rev. B 90, 115157] Published Tue Sep 30, 2014

Author(s): Mohammed Moaied, J. V. Alvarez, and J. J. Palacios

We calculate the electronic structure and magnetic properties of hydrogenated graphite surfaces using van der Waals density functional theory (DFT) and model Hamiltonians. We find, as previously reported, that the interaction between hydrogen atoms on graphene favors adsorption on different sublatti...

[Phys. Rev. B 90, 115441] Published Tue Sep 30, 2014

Author(s): M. D. LeBlanc, B. W. Southern, M. L. Plumer, and J. P. Whitehead

Classical spin-wave calculations demonstrate that the macroscopic continuous degeneracy associated with the two-dimensional kagome Heisenberg spin lattice persists in the case of the stacked fcc structure, giving rise to zero-energy modes in three dimensions. The addition of an effective local cubic...

[Phys. Rev. B 90, 144403] Published Thu Oct 02, 2014

The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

Author(s): Praveen Deorani, Jaesung Son, Karan Banerjee, Nikesh Koirala, Matthew Brahlek, Seongshik Oh, and Hyunsoo Yang

Bismuth Selenide (Bi2Se3) is a topological insulator exhibiting helical spin polarization and strong spin-orbit coupling. The spin-orbit coupling links the charge current to spin current via the spin Hall effect (SHE). We demonstrate a Bi2Se3 spin detector by injecting the pure spin current from a m...

[Phys. Rev. B 90, 094403] Published Wed Sep 03, 2014

Author(s): P. D. Gorman, J. M. Duffy, S. R. Power, and M. S. Ferreira

Of fundamental interest in the field of spintronics is the mechanism of indirect exchange coupling between magnetic impurities embedded in metallic hosts. A range of physical features, such as magnetotransport and overall magnetic moment formation, are predicated upon this magnetic coupling, often r...

[Phys. Rev. B 90, 125411] Published Mon Sep 08, 2014

Author(s): Hiroki Isobe and Naoto Nagaosa

Hund's rule is one of the fundamentals of the correlation physics at the atomic level, determining the ground state multiplet of the electrons. It consists of three laws: (i) maximum S (total spin), (ii) maximum L (total orbital angular momentum) under the constraint of (i), and (iii) the total angu...

[Phys. Rev. B 90, 115122] Published Thu Sep 11, 2014

The effect of stoichiometry on magnetocrystalline anisotropy energy (MAE) of Fe 1+ x Pt 1− x and Co 1+ x Pt 1− x(−0.5 

Nature Physics 10, 670 (2014). doi:10.1038/nphys3037

Authors: Ian Gilbert, Gia-Wei Chern, Sheng Zhang, Liam O’Brien, Bryce Fore, Cristiano Nisoli & Peter Schiffer

Nature Physics 10, 664 (2014). doi:10.1038/nphys3048

Authors: Ilya K. Drozdov, A. Alexandradinata, Sangjun Jeon, Stevan Nadj-Perge, Huiwen Ji, R. J. Cava, B. Andrei Bernevig & Ali Yazdani