Author(s): J. Fransson, D. Thonig, P. F. Bessarab, S. Bhattacharjee, J. Hellsvik, and L. Nordström
An ab initio framework for combined atomistic spin and lattice dynamics is introduced. The new approach comprises the descriptions of the damped driven oscillator for the ionic displacements as well as the spin dynamics according to Landau-Lifshitz-Gilbert theory. Both schemes are recovered in the limit of small spin-lattice coupling.
[Phys. Rev. Materials 1, 074404] Published Wed Dec 13, 2017
Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM), and subsequently perform electron spin resonance (ESR) on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system. Interactions between the atoms are mapped over a range of distances extending from highly anisotropic dipole coupling, to strong exchange coupling. The local magnetic field of the magnetic STM tip serves to precisely tune the superposition states of a pair of spins. The precise control of the spin-spin interactions and ability to probe the states of the coupled-spin network by addressing individual spins will enable exploration of quantum many-body systems based on networks of spin-1/2 atoms on surfaces.
We present the appearance of negative differential resistance (NDR) in spin-dependent electron transport through a few-atom spin-chain. A chain of three antiferromagnetically coupled Fe atoms(Fe trimer) was positioned on a Cu2N/Cu(100) surface and contacted with the spin-polarized tip of a scanning tunneling microscope, thus coupling the Fe trimer to one non-magnetic and one magnetic lead. Pronounced NDR appears at the low bias of 7 mV where inelastic electron tunneling dynamically locks the atomic spin in a long-lived excited state. This causes a rapid increase of the magnetoresistance between spin-polarized tip and Fe trimer and quenches elastic tunneling. By varying the coupling strength between tip and Fe trimer we find that in this transport regime the dynamic locking of the Fe trimer competes with magnetic exchange interaction, which statically forces the Fe trimer into the high-magnetoresistance state and removes the NDR.
Author(s): Fang Yang, Jasmin Jandke, Tim Storbeck, Timofey Balashov, Anuva Aishwarya, and Wulf Wulfhekel
Islands of Bi showing (110)- and (111)-orientated facets were grown on a Nb(110) single crystal and were studied with a scanning tunneling microscope at low temperatures. On the (111) facets, several states localized at step edges are identified from maps of the local differential conductance. We fi...
[Phys. Rev. B 96, 235413] Published Mon Dec 11, 2017
Author(s): M. Tanveer, J. Dorantes-Dávila, and G. M. Pastor
First-principles electronic calculations show how the adsorption morphology, orbital magnetism, and magnetic anisotropy energy (MAE) of small CoN and FeN clusters (N≤3) on graphene (G) can be reversibly controlled under the action of an external electric field (EF). A variety of cluster-specific and...
[Phys. Rev. B 96, 224413] Published Fri Dec 08, 2017
Author(s): Xiao-Gang Wen
The subject of this Colloquium is related to the topic of the 2016 Physics Nobel Prize that was awarded to David J. Thouless, F. Duncan M. Haldane, and J. Michael Kosterlitz “for theoretical discoveries of topological phase transitions and topological phases of matter.” The Colloquium provides a pedagogical introduction to topological phases of matter from comprehensive point of view of many-body entanglement which is important in quantum physics.
[Rev. Mod. Phys. 89, 041004] Published Mon Dec 04, 2017
Magnetic impurities have a dramatic effect on superconductivity by breaking the time-reversal symmetry and inducing so-called Yu-Shiba-Rusinov (YSR) low energy bound states within the superconducting gap. The spatial extent of YSR states is greatly enhanced in 2D systems, which should facilitate the formation of coupled states. Here, we observe YSR states on single cobalt phthalocyanine (CoPC) molecules on a 2D superconductor NbSe$_2$ using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). We use STM lateral manipulation to create controlled CoPc dimers and demonstrate the formation of coupled YSR states. The experimental results are corroborated by theoretical analysis of the coupled states in lattice and continuum models. Our work forms an important step towards the realization of exotic topological states in designer magnetic lattices.
Author(s): Kai Yang, Yujeong Bae, William Paul, Fabian D. Natterer, Philip Willke, Jose L. Lado, Alejandro Ferrón, Taeyoung Choi, Joaquín Fernández-Rossier, Andreas J. Heinrich, and Christopher P. Lutz
Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable, because they readily manifest coherent quantum fluctuations. Here we introduce a ...
[Phys. Rev. Lett. 119, 227206] Published Wed Nov 29, 2017
Author(s): Seokhwan Choi, Hyoung Joon Choi, Jong Mok Ok, Yeonghoon Lee, Won-Jun Jang, Alex Taekyung Lee, Young Kuk, SungBin Lee, Andreas J. Heinrich, Sang-Wook Cheong, Yunkyu Bang, Steven Johnston, Jun Sung Kim, and Jhinhwan Lee
A current of electrons with aligned spins can be used to modify magnetic order and superconductivity in an iron-based superconductor.
[Phys. Rev. Lett. 119, 227001] Published Mon Nov 27, 2017
Author(s): A. Chiesa, T. Guidi, S. Carretta, S. Ansbro, G. A. Timco, I. Vitorica-Yrezabal, E. Garlatti, G. Amoretti, R. E. P. Winpenny, and P. Santini
Researchers characterize the spin couplings in the prototypical single-molecule magnet Mn12 using an advanced neutron scattering technique.
[Phys. Rev. Lett. 119, 217202] Published Wed Nov 22, 2017
Author(s): E. Frantzeskakis, S. V. Ramankutty, N. de Jong, Y. K. Huang, Y. Pan, A. Tytarenko, M. Radovic, N. C. Plumb, M. Shi, A. Varykhalov, A. de Visser, E. van Heumen, and M. S. Golden
Electron spectroscopy and electron transport experiments are key techniques to probing the electronic structure of topological insulators, but results from these two methods disagree. A new analysis shows that the problem is inherent to ultraviolet light used in electron spectroscopy, and offers a solution.
[Phys. Rev. X 7, 041041] Published Mon Nov 20, 2017
Author(s): Peizhe Tang, Quan Zhou, and Shou-Cheng Zhang
Exotic massless fermionic excitations with nonzero Berry flux, other than the Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with threefold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions. Herein, by ...
[Phys. Rev. Lett. 119, 206402] Published Fri Nov 17, 2017
The single-particle spectral function measures the density of electronic states in a material as a function of both momentum and energy, providing central insights into strongly correlated electron phenomena. Here we demonstrate a high-resolution method for measuring the full momentum- and energy-resolved electronic spectral function of a two-dimensional (2D) electronic system embedded in a semiconductor. The technique remains operational in the presence of large externally applied magnetic fields and functions even for electronic systems with zero electrical conductivity or with zero electron density. Using the technique on a prototypical 2D system, a GaAs quantum well, we uncover signatures of many-body effects involving electron-phonon interactions, plasmons, polarons, and a phonon analog of the vacuum Rabi splitting in atomic systems.
Author(s): L. Cornils, A. Kamlapure, L. Zhou, S. Pradhan, A. A. Khajetoorians, J. Fransson, J. Wiebe, and R. Wiesendanger
Experimental evidence is presented for the spin polarization of Yu-Shiba-Rusinov states induced by the presence of a single magnetic atom on a superconductor.
[Phys. Rev. Lett. 119, 197002] Published Thu Nov 09, 2017
One-dimensional topological superconductors host Majorana zero modes (MZMs), the nonlocal property of which could be exploited for quantum computing applications. We use spin-polarized scanning tunneling microscopy to show that MZMs realized in self-assembled Fe chains on the surface of Pb have a spin polarization that exceeds that stemming from the magnetism of these chains. This feature, captured by our model calculations, is a direct consequence of the nonlocality of the Hilbert space of MZMs emerging from a topological band structure. Our study establishes spin-polarization measurements as a diagnostic tool to distinguish topological MZMs from trivial in-gap states of a superconductor.
Graphene nanoribbons (GNRs) make up an extremely interesting class of materials. On the one hand GNRs share many of the superlative properties of graphene, while on the other hand they display an exceptional degree of tunability of their optoelectronic properties. The presence or absence of correlated low-dimensional magnetism, or of a widely tunable band gap, is determined by the boundary conditions imposed by the width, crystallographic symmetry and edge structure of the nanoribbons. In combination with additional controllable parame-ters like the presence of heteroatoms, tailored strain, or the formation of hetero-structures, the possibilities to shape the electronic properties of GNRs according to our needs are fantastic. However, to really benefit from that tunability and harness the opportunities offered by GNRs, atomic precision is strictly required in their synthesis. This can be achieved through an on-surface synthesis approach, in which one lets appropriately designed precursor molecules to react in a selective way that ends up forming GNRs. In this chapter we review the structure-property relations inherent to GNRs, the synthesis approach and the ways in which the var-ied properties of the resulting ribbons have been probed, finalizing with selected examples of demonstrated GNR applications.
Ullmann Coupling Reactions on Ag(111) and Ag(110); Substrate Influence on the Formation of Covalently Coupled Products and Intermediate Metal-Organic Structures
Ullmann Coupling Reactions on Ag(111) and Ag(110); Substrate Influence on the Formation of Covalently Coupled Products and Intermediate Metal-Organic Structures, Published online: 06 November 2017; doi:10.1038/s41598-017-13315-1
Plasmonics provides a possible route to overcome both the speed limitations of electronics and the critical dimensions of photonics. We present an all-plasmonic 116–gigabits per second electro-optical modulator in which all the elements—the vertical grating couplers, splitters, polarization rotators, and active section with phase shifters—are included in a single metal layer. The device can be realized on any smooth substrate surface and operates with low energy consumption. Our results show that plasmonics is indeed a viable path to an ultracompact, highest-speed, and low-cost technology that might find many applications in a wide range of fields of sensing and communications because it is compatible with and can be placed on a wide variety of materials.
Author(s): C. Godfrin, A. Ferhat, R. Ballou, S. Klyatskaya, M. Ruben, W. Wernsdorfer, and F. Balestro
Grover’s algorithm, which finds an element in an unsorted list, has been implemented using a nuclear spin in a single-molecule magnet.
[Phys. Rev. Lett. 119, 187702] Published Thu Nov 02, 2017
Quantum algorithms use the principles of quantum mechanics, as for example quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimisation, simulation and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3/2-spin carried by a Single Molecular Magnet (SMM) transistor. The coherent manipulation of this multi-level qudit is achieved by means of electric fields only. Grover's search algorithm was implemented by constructing a quantum database via a multi-level Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multi-level quantum system with non-equal spaced energy levels, opening the way to novel quantum search algorithms.
Author(s): Naoya Kawakami, Chun-Liang Lin, Kazuaki Kawahara, Maki Kawai, Ryuichi Arafune, and Noriaki Takagi
We present the structural evolution of Bi on Au(111) from monolayer to multilayer regimes explored mainly by scanning tunneling microscopy. At the monolayer regime, Bi clusters distribute homogeneously to make an array with 5×5 periodicity. Further increase of the coverage converts these clusters to...
[Phys. Rev. B 96, 205402] Published Wed Nov 01, 2017
Author(s): Karen Michaeli, L. Aviad Landau, Eran Sela, and Liang Fu
Majorana zero modes are localized zero-energy degrees of freedom in topological superconductors that can store quantum information in a protected manner. Finding a direct proof of the Majorana identity of zero-energy states has been a challenge. The authors show that, in a Coulomb blockaded superconductor island coupled to normal metal leads, Majorana zero modes on the island bind with electrons in the leads to form a charge-e boson, thereby converting the quantum statistics of charge carriers. This statistical transmutation leads to unusual temperature and voltage dependence of the tunneling current as a unique signature of the Majorana zero modes.
[Phys. Rev. B 96, 205403] Published Wed Nov 01, 2017
In an academic landscape where female physicists are still strongly underrepresented, underlying causes like unconscious gender bias deserve specific attention. Members of academia are often not aware of their intrinsic, hence unconscious, biases; this can have negative effects on students and staff at all career levels. At the Queen's University Belfast, I have developed and conducted a workshop on unconscious gender bias awareness at the School of Mathematics and Physics. The first installment of the workshop was attended by 63 members of the School, among them 26 academic staff (lecturer level and above). Participants attended an informational talk followed by a discussion session, and then took part in the Harvard Implicit Association Test for association of gender with science. The participants self-reported their results and their previous expectations, followed by a group discussion. Here I present the observed magnitude of unconscious gender bias and summarise the discussion points of the participants. The outcomes that bias can have on the success of physics students as well as the careers of physicists in an academic context will be highlighted. Putting the results into context, I discuss steps forward to make physics a level playing field for all genders.
