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Calem Kenward, Kyungsoo Shin, Jan Rainey
The strategy of applying fluorine NMR to characterize ligand binding to a membrane protein prepared with mixtures of tryptophans substituted with F at different positions on the indole ring was tested. The ¹⁹F NMR behavior of 4-, 5-, 6-, and 7-fluorotryptophan were directly compared as a function of both micellar environment and fragment size for two overlapping apelin receptor (AR/APJ) segments - one with a single transmembrane (TM) helix and two tryptophan residues, the other with three TM helices and two additional tryptophan residues...
January 17, 2018: Chemistry: a European Journal
Christian Ahoba-Sam, Kamelia V K Boodhoo, Unni Olsbye, Klaus-Joachim Jens
Cu nanoparticles are known to be very active for methanol (MeOH) synthesis at relatively low temperatures, such that smaller particle sizes yield better MeOH productivity. We aimed to control Cu nanoparticle (NP) size and size distribution for catalysing MeOH synthesis, by using the spinning disk reactor. The spinning disk reactor (SDR), which operates based on shear effect and plug flow in thin films, can be used to rapidly micro-mix reactants in order to control nucleation and particle growth for uniform particle size distribution...
January 17, 2018: Materials
Michihiro Yamada, Yuichi Fujita, Shinya Yamada, Kentarou Sawano, Kohei Hamaya
We study the influence of the junction size in ferromagnet (FM)/semiconductor (SC) contacts on four-terminal nonlocal spin signals in SC-based lateral spin-valve (LSV) structures. When we use FM/Ge Schottky-tunnel junctions with relatively low resistance-area products, the magnitude of the nonlocal spin signal depends clearly on the junction size, indicating the presence of the spin absorption effect at the spin-injector contact. The temperature-dependent spin signal can also be affected by the spin absorption effect...
January 17, 2018: Materials
Licong Peng, Ying Zhang, Min He, Bei Ding, Wenhong Wang, Jianqi Li, Jianwang Cai, Shouguo Wang, Guangheng Wu, Baogen Shen
Magnetic skyrmions are topologically protected spin configurations and have recently received growingly attention in magnetic materials. The existence of biskyrmions within a broad temperature range has been identified in our newly-discovered MnNiGa material, promising for potential application in physics and technological study. Here, the biskyrmion microscopic origination from the spin configuration evolution of stripe ground state is experimentally identified. The biskyrmion manipulations based on the influences of the basic microstructures and external factors such as grain boundary confinement, sample thickness, electric current, magnetic field and temperature have been systematically studied by using real-space Lorentz transmission electron microscopy...
January 17, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Jian Zhou, Qiang Sun, Puru Jena
The valley-polarized quantum anomalous Hall effect (VP-QAHE), which combines valleytronics and topology in one material, is of significant fundamental and practical importance in condensed-matter physics and materials science. In previous model studies, VP-QAHE occurs under strong Rashba spin-orbit coupling (SOC), which is an extrinsic effect. Here, using a low energy k·p model, we propose a different mechanism of VP-QAHE by introducing an intrinsic staggered magnetic exchange field and develop a general picture of valley dependent band inversion in honeycomb lattice...
July 28, 2017: Physical Review Letters
Aleksandr Kazakov, George Simion, Yuli Lyanda-Geller, Valery Kolkovsky, Zbigniew Adamus, Grzegorz Karczewski, Tomasz Wojtowicz, Leonid P Rokhinson
In this work, we use electrostatic control of quantum Hall ferromagnetic transitions in CdMnTe quantum wells to study electron transport through individual domain walls (DWs) induced at a specific location. These DWs are formed due to the hybridization of two counterpropagating edge states with opposite spin polarization. Conduction through DWs is found to be symmetric under magnetic field direction reversal, consistent with the helical nature of these DWs. We observe that long domain walls are in the insulating regime with a localization length of 4-6  μm...
July 28, 2017: Physical Review Letters
M A Broome, T F Watson, D Keith, S K Gorman, M G House, J G Keizer, S J Hile, W Baker, M Y Simmons
In this work we perform direct single-shot readout of the singlet-triplet states in exchange coupled electrons confined to precision-placed donor atoms in silicon. Our method takes advantage of the large energy splitting given by the Pauli-spin blockaded (2,0) triplet states, from which we can achieve a single-shot readout fidelity of 98.4±0.2%. We measure the triplet-minus relaxation time to be of the order 3 s at 2.5 T and observe its predicted decrease as a function of magnetic field, reaching 0.5 s at 1 T...
July 28, 2017: Physical Review Letters
Se Kwon Kim, Yaroslav Tserkovnyak
A domain wall in a magnet with easy-axis anisotropy is shown to harbor spin superfluid associated with its spontaneous breaking of the U(1) spin-rotational symmetry. The spin superfluid is shown to have several topological properties, which are absent in conventional superfluids. First, the associated phase slips create and destroy Skyrmions to obey the conservation of the total Skyrmion charge, which allows us to use a domain wall as a generator and detector of Skyrmions. Second, the domain wall engenders the emergent magnetic flux for magnons along its length, which are proportional to the spin supercurrent flowing through it, and thereby provides a way to manipulate magnons...
July 28, 2017: Physical Review Letters
M Padmanath, Nilmani Mathur
We present the ground and excited state spectra of Ω_{c}^{0} baryons with spin up to 7/2 from lattice quantum chromodynamics with dynamical quark fields. Based on our lattice results, we predict the quantum numbers of five Ω_{c}^{0} baryons, which have recently been observed by the LHCb Collaboration. Our results strongly indicate that the observed states Ω_{c}(3000)^{0} and Ω_{c}(3050)^{0} have spin-parity J^{P}=1/2^{-}, the states Ω_{c}(3066)^{0} and Ω_{c}(3090)^{0} have J^{P}=3/2^{-}, whereas Ω_{c}(3119)^{0} is possibly a 5/2^{-} state...
July 28, 2017: Physical Review Letters
G Gitgeatpong, Y Zhao, P Piyawongwatthana, Y Qiu, L W Harriger, N P Butch, T J Sato, K Matan
Inelastic neutron scattering measurements were performed to study spin dynamics in the noncentrosymmetric antiferromagnet α-Cu_{2}V_{2}O_{7}. For the first time, nonreciprocal magnons were experimentally measured in an antiferromagnet. These nonreciprocal magnons are caused by the incompatibility between anisotropic exchange and antisymmetric Dzyaloshinskii-Moriya interactions, which arise from broken symmetry, resulting in a collinear ordered state but helical spin dynamics. The nonreciprocity introduces the difference in the phase velocity of the counterrotating modes, causing the opposite spontaneous magnonic Faraday rotation of the left- and right-propagating spin waves...
July 28, 2017: Physical Review Letters
Josef Grenz, Arne Köhler, Alexander Schwarz, Roland Wiesendanger
We demonstrate that the magnetic nano-Skyrmion lattice on the Fe monolayer on Ir(111) and the positions of the Fe atoms can be resolved simultaneously using magnetic exchange force microscopy. Thus, the relation between magnetic and atomic structure can be determined straightforwardly by evaluating the Fourier transformation of the real space image data. We further show that the magnetic contrast can be mapped on a Heisenberg-like magnetic interaction between tip and sample spins. Since our imaging technique is based on measuring forces, our observation paves the way to study Skyrmions or other complex spin textures on insulating sample systems with atomic resolution...
July 28, 2017: Physical Review Letters
Romain Couvreur, Jesper Lykke Jacobsen, Hubert Saleur
Entanglement entropy has proven invaluable to our understanding of quantum criticality. It is natural to try to extend the concept to "nonunitary quantum mechanics," which has seen growing interest from areas as diverse as open quantum systems, noninteracting electronic disordered systems, or nonunitary conformal field theory (CFT). We propose and investigate such an extension here, by focusing on the case of one-dimensional quantum group symmetric or supergroup symmetric spin chains. We show that the consideration of left and right eigenstates combined with appropriate definitions of the trace leads to a natural definition of Rényi entropies in a large variety of models...
July 28, 2017: Physical Review Letters
G Wang, C Robert, M M Glazov, F Cadiz, E Courtade, T Amand, D Lagarde, T Taniguchi, K Watanabe, B Urbaszek, X Marie
The optical selection rules for interband transitions in WSe_{2}, WS_{2}, and MoSe_{2} transition metal dichalcogenide monolayers are investigated by polarization-resolved photoluminescence experiments with a signal collection from the sample edge. These measurements reveal a strong polarization dependence of the emission lines. We see clear signatures of the emitted light with the electric field oriented perpendicular to the monolayer plane, corresponding to an interband optical transition forbidden at normal incidence used in standard optical spectroscopy measurements...
July 28, 2017: Physical Review Letters
Alberto Camjayi, Liliana Arrachea, Armando Aligia, Felix von Oppen
Time-reversal-invariant topological superconducting (TRITOPS) wires are known to host a fractional spin ℏ/4 at their ends. We investigate how this fractional spin affects the Josephson current in a TRITOPS-quantum dot-TRITOPS Josephson junction, describing the wire in a model that can be tuned between a topological and a nontopological phase. We compute the equilibrium Josephson current of the full model by continuous-time Monte Carlo simulations and interpret the results within an effective low-energy theory...
July 28, 2017: Physical Review Letters
William E East, Frans Pretorius
We study the growth and saturation of the superradiant instability of a complex, massive vector (Proca) field as it extracts energy and angular momentum from a spinning black hole, using numerical solutions of the full Einstein-Proca equations. We concentrate on a rapidly spinning black hole (a=0.99) and the dominant m=1 azimuthal mode of the Proca field, with real and imaginary components of the field chosen to yield an axisymmetric stress-energy tensor and, hence, spacetime. We find that in excess of 9% of the black hole's mass can be transferred into the field...
July 28, 2017: Physical Review Letters
F Arnold, A Isidori, E Kampert, B Yager, M Eschrig, J Saunders
Graphite is a model system for the study of three-dimensional electrons and holes in the magnetic quantum limit, in which the charges are confined to the lowest Landau levels. We report magneto-transport measurements in pulsed magnetic fields up to 60 T, which resolve the collapse of two charge density wave states in two, electron and hole, Landau levels at 52.3 and 54.2 T, respectively. We report evidence for a commensurate charge density wave at 47.1 T in the electron Landau level, and discuss the likely nature of the density wave instabilities over the full field range...
September 29, 2017: Physical Review Letters
G Éthier-Majcher, D Gangloff, R Stockill, E Clarke, M Hugues, C Le Gall, M Atatüre
A controlled quantum system can alter its environment by feedback, leading to reduced-entropy states of the environment and to improved system coherence. Here, using a quantum-dot electron spin as a control and probe, we prepare the quantum-dot nuclei under the feedback of coherent population trapping and observe their evolution from a thermal to a reduced-entropy state, with the immediate consequence of extended qubit coherence. Via Ramsey interferometry on the electron spin, we directly access the nuclear distribution following its preparation and measure the emergence and decay of correlations within the nuclear ensemble...
September 29, 2017: Physical Review Letters
Jan Müller, Jayaraman Rajeswari, Ping Huang, Yoshie Murooka, Henrik M Rønnow, Fabrizio Carbone, Achim Rosch
Skyrmions are nanometric spin whirls that can be stabilized in magnets lacking inversion symmetry. The properties of isolated Skyrmions embedded in a ferromagnetic background have been intensively studied. We show that single Skyrmions and clusters of Skyrmions can also form in the helical phase and investigate theoretically their energetics and dynamics. The helical background provides natural one-dimensional channels along which a Skyrmion can move rapidly. In contrast to Skyrmions in ferromagnets, the Skyrmion-Skyrmion interaction has a strong attractive component and thus Skyrmions tend to form clusters with characteristic shapes...
September 29, 2017: Physical Review Letters
J P Lees, V Poireau, V Tisserand, E Grauges, A Palano, G Eigen, D N Brown, M Derdzinski, A Giuffrida, Yu G Kolomensky, M Fritsch, H Koch, T Schroeder, C Hearty, T S Mattison, J A McKenna, R Y So, V E Blinov, A R Buzykaev, V P Druzhinin, V B Golubev, E A Kravchenko, A P Onuchin, S I Serednyakov, Yu I Skovpen, E P Solodov, K Yu Todyshev, A J Lankford, J W Gary, O Long, A M Eisner, W S Lockman, W Panduro Vazquez, D S Chao, C H Cheng, B Echenard, K T Flood, D G Hitlin, J Kim, T S Miyashita, P Ongmongkolkul, F C Porter, M Röhrken, Z Huard, B T Meadows, B G Pushpawela, M D Sokoloff, L Sun, J G Smith, S R Wagner, D Bernard, M Verderi, D Bettoni, C Bozzi, R Calabrese, G Cibinetto, E Fioravanti, I Garzia, E Luppi, V Santoro, A Calcaterra, R de Sangro, G Finocchiaro, S Martellotti, P Patteri, I M Peruzzi, M Piccolo, M Rotondo, A Zallo, S Passaggio, C Patrignani, H M Lacker, B Bhuyan, U Mallik, C Chen, J Cochran, S Prell, H Ahmed, A V Gritsan, N Arnaud, M Davier, F Le Diberder, A M Lutz, G Wormser, D J Lange, D M Wright, J P Coleman, E Gabathuler, D E Hutchcroft, D J Payne, C Touramanis, A J Bevan, F Di Lodovico, R Sacco, G Cowan, Sw Banerjee, D N Brown, C L Davis, A G Denig, W Gradl, K Griessinger, A Hafner, K R Schubert, R J Barlow, G D Lafferty, R Cenci, A Jawahery, D A Roberts, R Cowan, S H Robertson, B Dey, N Neri, F Palombo, R Cheaib, L Cremaldi, R Godang, D J Summers, P Taras, G De Nardo, C Sciacca, G Raven, C P Jessop, J M LoSecco, K Honscheid, R Kass, A Gaz, M Margoni, M Posocco, G Simi, F Simonetto, R Stroili, S Akar, E Ben-Haim, M Bomben, G R Bonneaud, G Calderini, J Chauveau, G Marchiori, J Ocariz, M Biasini, E Manoni, A Rossi, G Batignani, S Bettarini, M Carpinelli, G Casarosa, M Chrzaszcz, F Forti, M A Giorgi, A Lusiani, B Oberhof, E Paoloni, M Rama, G Rizzo, J J Walsh, A J S Smith, F Anulli, R Faccini, F Ferrarotto, F Ferroni, A Pilloni, G Piredda, C Bünger, S Dittrich, O Grünberg, M Heß, T Leddig, C Voß, R Waldi, T Adye, F F Wilson, S Emery, G Vasseur, D Aston, C Cartaro, M R Convery, J Dorfan, W Dunwoodie, M Ebert, R C Field, B G Fulsom, M T Graham, C Hast, W R Innes, P Kim, D W G S Leith, S Luitz, D B MacFarlane, D R Muller, H Neal, B N Ratcliff, A Roodman, M K Sullivan, J Va'vra, W J Wisniewski, M V Purohit, J R Wilson, A Randle-Conde, S J Sekula, M Bellis, P R Burchat, E M T Puccio, M S Alam, J A Ernst, R Gorodeisky, N Guttman, D R Peimer, A Soffer, S M Spanier, J L Ritchie, R F Schwitters, J M Izen, X C Lou, F Bianchi, F De Mori, A Filippi, D Gamba, L Lanceri, L Vitale, F Martinez-Vidal, A Oyanguren, J Albert, A Beaulieu, F U Bernlochner, G J King, R Kowalewski, T Lueck, I M Nugent, J M Roney, R J Sobie, N Tasneem, T J Gershon, P F Harrison, T E Latham, R Prepost, S L Wu
We search for single-photon events in 53  fb^{-1} of e^{+}e^{-} collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A^{'} through the process e^{+}e^{-}→γA^{'}; A^{'}→invisible. Such particles, referred to as "dark photons," are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A^{'} to e^{+}e^{-} in the mass range m_{A^{'}}≤8  GeV...
September 29, 2017: Physical Review Letters
Toshiya Inami
The existence of novel magnetic circular dichroism in core-level x-ray emission is reported. By means of circular polarization analysis, the dichroic effect of the Fe Kα_{1} emission spectrum is measured on an Fe single crystal. The observed dichroic effect (12%) is remarkably large, if one takes into account the small dichroic effect (about 0.5%) in the conventional K-edge absorption spectroscopy of 3d transition metal elements. The mechanism is ascribed to exchange splitting of the 2p level possessing large spin-orbit coupling...
September 29, 2017: Physical Review Letters
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