Manuel Steinbrecher

Author(s): Andreas Heimes, Panagiotis Kotetes, and Gerd Schön

We propose a new mechanism for topological superconductivity based on an antiferromagnetically ordered chain of magnetic atoms on the surface of a conventional superconductor. In a weak Zeeman field, a supercurrent in the substrate generates a staggered spin current, which converts the preexisting t...

[Phys. Rev. B 90, 060507] Published Thu Aug 28, 2014

Based on first-principles calculations in the framework of van der Waals density functional theory, we find that giant, Rashba-like spin splittings can be induced in both the surface states and quantum well states of thin Bi 2 Se 3 films by application of an external electric field. The charge is redistributed so that the Dirac cones of the upper and lower surfaces become nondegenerate and completely gapless. Interestingly, a momentum-dependent spin texture is developed on the two surfaces of the films. Some of the quantum well states, which reside in the middle of the Bi 2 Se 3 film under zero field, are driven to the surface by the electric field. The Rashba splitting energy has a highly non-linear dependence on the momentum and the electric field due to the large contribution of the high-order Rashba terms, which suggests complex spin dynamics in the thin films of Bi 2 Se 3 under an electric field.

Author(s): Vikas Kashid, Timo Schena, Bernd Zimmermann, Yuriy Mokrousov, Stefan Blügel, Vaishali Shah, and H. G. Salunke

We investigate the chiral magnetic order in freestanding planar 3d-5d biatomic metallic chains (3d: Fe, Co; 5d: Ir, Pt, Au) using first-principles calculations based on density functional theory. We find that the antisymmetric exchange interaction, commonly known as the Dzyaloshinskii-Moriya interac...

[Phys. Rev. B 90, 054412] Published Mon Aug 18, 2014

Author(s): Prokop Hapala, Georgy Kichin, Christian Wagner, F. Stefan Tautz, Ruslan Temirov, and Pavel Jelínek

High-resolution atomic force microscopy (AFM) and scanning tunneling 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 pro...

[Phys. Rev. B 90, 085421] Published Tue Aug 19, 2014

Author(s): Mathieu Taillefumier, Julien Robert, Christopher L. Henley, Roderich Moessner, and Benjamin Canals

We investigate the dynamical properties of the classical antiferromagnetic Heisenberg model on the kagome lattice using a combination of Monte Carlo and molecular dynamics simulations. We find that frustration induces a distribution of time scales in the cooperative paramagnetic regime (i.e., far ab...

[Phys. Rev. B 90, 064419] Published Tue Aug 19, 2014

Author(s): N. Y. Yao, L. I. Glazman, E. A. Demler, M. D. Lukin, and J. D. Sau

Nonperturbative analysis of magnetic impurities embedded in a superconducting host demonstrates that the RKKY theory for simple metals - coupling between the magnetic moments and conduction elections - is insufficient to describe exchange interactions, and localized electronic bound states near the impurity must also be taken into account.

[Phys. Rev. Lett. 113, 087202] Published Mon Aug 18, 2014

Nature Nanotechnology 9, 574 (2014). doi:10.1038/nnano.2014.164

Authors: Sebastian Loth, Jacob A. J. Burgess & Shichao Yan

Ultrafast, coherent spin dynamics in semiconductor heterostructures can be measured with a scanning tunnelling microscope by using femtosecond pulses of circularly polarized light.

Nature Physics 10, 572 (2014). doi:10.1038/nphys3012

Authors: Ilija Zeljkovic, Yoshinori Okada, Cheng-Yi Huang, R. Sankar, Daniel Walkup, Wenwen Zhou, Maksym Serbyn, Fangcheng Chou, Wei-Feng Tsai, Hsin Lin, A. Bansil, Liang Fu, M. Zahid Hasan & Vidya Madhavan

The newly discovered topological crystalline insulators feature a complex band structure involving multiple Dirac cones, and are potentially highly tunable by external electric field, temperature or strain. Theoretically, it has been predicted that the various Dirac cones, which are offset in energy and momentum, might harbour vastly different orbital character. However, their orbital texture, which is of immense importance in determining a variety of a material’s properties remains elusive. Here, we unveil the orbital texture of Pb1−xSnxSe, a prototypical topological crystalline insulator. By using Fourier-transform scanning tunnelling spectroscopy we measure the interference patterns produced by the scattering of surface-state electrons. We discover that the intensity and energy dependences of the Fourier transforms show distinct characteristics, which can be directly attributed to orbital effects. Our experiments reveal a complex band topology involving two Lifshitz transitions and establish the orbital nature of the Dirac bands, which could provide an alternative pathway towards future quantum applications.

Nature Physics 10, 561 (2014). doi:10.1038/nphys3004

Authors: Luqiao Liu, Ching-Tzu Chen & J. Z. Sun

The spin Hall effect (SHE) and its inverse have been widely used to generate and detect spin currents. To date, most experiments focus only on characterizing electrons near the Fermi surface, whereas the SHE, which originates from the spin–orbit interaction, is expected to be energy dependent. Here, we report a tunnelling spectroscopy technique developed to measure the SHE under finite bias voltages. We studied the SHE for typical 5d transition metals. At zero d.c. bias, the obtained spin Hall angles confirm the results from spin-torque experiments. At high bias, the transverse spin Hall signals of these materials exhibit very different voltage dependences. The SHE tunnelling spectra have important implications in pinpointing the mechanisms of the SHE and provide guidelines for engineering high-SHE materials. Moreover, SHE tunnelling spectroscopy can be directly applied to two-dimensional surface states with strong spin–orbit coupling, such as Dirac electrons in topological insulators.

Author(s): J. Flipse, F. K. Dejene, D. Wagenaar, G. E. W. Bauer, J. Ben Youssef, and B. J. van Wees

Researchers demonstrate for the first time the spin Peltier effect, in which a spin current in a metal causes heat flow in an adjoining magnet.

[Phys. Rev. Lett. 113, 027601] Published Mon Jul 07, 2014

Publication date: December 2014
Source:Surface Science, Volume 630
Author(s): Sandeep Nigam , Chiranjib Majumder
The understanding of atomic adsorption on a solid surface is essential to understand the fundamental issue of chemical interaction at the hetero-junctions, formed by two metals. With an aim to compare the adsorption behavior between finite size cluster and extended surface, M atom (M=Ni, Pd, Pt) interaction with Ag n /Au n (n =3, 6) clusters and periodic slab of Ag(111)/Au(111) surfaces is investigated theoretically. All calculations are performed using plane-wave pseudo-potential approach under the spin-polarized density functional theory including the spin–orbit coupling term. The results show that the interaction of M atom with small clusters is primarily governed by the relative strength of MAg/Au vs. AgAg/AuAu bonds. The stronger interaction follows rearrangement of the host cluster. For the periodic slab, M atom prefers to adsorb on the fcc site with small local distortion. Due to variation in the strength of interaction and amount of distortion, the cluster and periodic slab differs in absolute adsorption energy values. Further a comparative analysis of chemical bonding through electronic density of state (EDOS) and orbital decomposed charge distribution infers that interaction of Ni/Pd/Pt with gold substrate is stronger than silver substrate.

Graphical abstract

Author(s): E. Orignac and S. Burdin

We consider a magnetic impurity deposited on the surface of a strong topological insulator and interacting with the surface modes by a Kondo exchange interaction. Taking into account the warping of the Fermi line of the surface modes, we derive a mapping to an effective one-dimensional model and sho...

[Phys. Rev. B 88, 035411] Published Mon Jul 08, 2013

Author(s): Manuel Steinbrecher, Hasmik Harutyunyan, Christian R. Ast, and Daniel Wegner

We have studied the BiCu₂/Cu(111) surface alloy using low-temperature scanning tunneling microscopy and spectroscopy. We observed standing waves caused by scattering off defects and step edges. Different from previous studies on similar Rashba-type surfaces, we identified multiple scattering vectors...

[Phys. Rev. B 87, 245436] Published Fri Jun 28, 2013

The accuracy of finite difference methods is related to the mesh choice and cell size. Concerning the micromagnetism of nano-objects, we show here that discretization issues can drastically affect the symmetry of the problem and therefore the resulting computed properties of lattices of interacting curved nanomagnets. In this paper, we detail these effects for the multi-axis kagome lattice. Using the OOMMF finite difference method, we propose an alternative way of discretizing the nanomagnet shape via a variable moment per cell scheme. This method is shown to be efficient in reducing discretization effects.

Assemblies of interacting quantum particles often surprise us with properties that are difficult to predict. One of the simplest quantum many-body systems is the spin 1/2 Heisenberg antiferromagnetic chain, a linear array of interacting magnetic moments. Its exact ground state is a macroscopic singlet entangling all spins in the chain. Its elementary excitations, called spinons, are fractional spin 1/2 quasiparticles; they are created and detected in pairs by neutron scattering. Theoretical predictions show that two-spinon states exhaust only 71% of the spectral weight while higher-order spinon states, yet to be experimentally located, are predicted to participate in the remaining. Here, by accurate absolute normalization of our inelastic neutron scattering data on a compound realizing the model, we account for the full spectral weight to within 99(8)%. Our data thus establish and quantify the existence of higher-order spinon states. The observation that within error bars, the entire weight is confined within the boundaries of the two-spinon continuum, and that the lineshape resembles a rescaled two-spinon one, allow us to develop a simple physical picture for understanding multi-spinon excitations.

Experiments have reported the entanglement of two spatially separated macroscopic atomic ensembles at room temperature (Krauter et al 2011 Phys. Rev. Lett. 107 080503; Julsgaard et al 2001 Nature 413 400). We show how an Einstein–Podolsky–Rosen (EPR) paradox is realizable with this experiment. Our proposed test involves violation of an inferred Heisenberg uncertainty principle, which is a sufficient condition for an EPR paradox. This is a stronger test of nonlocality than entanglement. Our proposal would enable the first definitive confirmation of quantum EPR paradox correlations between two macroscopic objects at room temperature. This is a necessary intermediate step towards a nonlocal experiment with causal measurement separations. As well as having fundamental significance, the realization of an atomic EPR paradox could provide a resource for novel applications in quantum technology.

Author(s): Jinhong Park, S.-S. B. Lee, Yuval Oreg, and H.-S. Sim

We propose a method to directly measure, by electrical means, the Kondo screening cloud formed by an Anderson impurity coupled to semi-infinite quantum wires, on which an electrostatic gate voltage is applied at distance L from the impurity. We show that the Kondo cloud, and hence the Kondo temperat...

[Phys. Rev. Lett. 110, 246603] Published Fri Jun 14, 2013