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Physical Review Letters

Magnus O Borgh, Janne Ruostekoski
We calculate the energetic structure of defect cores and propose controlled methods to imprint a nontrivially entangled vortex pair that undergoes non-Abelian vortex reconnection in a biaxial nematic spin-2 condensate. For a singular vortex, we find three superfluid cores in addition to depletion of the condensate density. These exhibit order parameter symmetries that are different from the discrete symmetry of the biaxial nematic phase, forming an interface between the defect and the bulk superfluid. We provide a detailed analysis of phase mixing in the resulting vortex cores and find an instability dependent upon the orientation of the order parameter...
December 30, 2016: Physical Review Letters
F Nowacki, A Poves, E Caurier, B Bounthong
Large-scale shell-model calculations predict that the region of deformation which comprises the heaviest chromium and iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the neon and magnesium isotopes. We propose a valence space including the full pf shell for the protons and the full sdg shell for the neutrons, which represents a comeback of the the harmonic oscillator shells in the very neutron- rich regime. The onset of deformation is understood in the framework of the algebraic SU(3)-like structures linked to quadrupole dominance...
December 30, 2016: Physical Review Letters
E Wiens, A Yu Nevsky, S Schiller
In order to investigate the long-term dimensional stability of matter, we have operated an optical resonator fabricated from crystalline silicon at 1.5 K continuously for over one year and repeatedly compared its resonance frequency f_{res} with the frequency of a GPS-monitored hydrogen maser. After allowing for an initial settling time, over a 163-day interval we found a mean fractional drift magnitude |f_{res}^{-1}df_{res}/dt|<1.4×10^{-20}/s. The resonator frequency is determined by the physical length and the speed of light and we measure it with respect to the atomic unit of time...
December 30, 2016: Physical Review Letters
A Seiler, P Piekarz, S Ibrahimkutty, D G Merkel, O Waller, R Pradip, A I Chumakov, R Rüffer, T Baumbach, K Parlinski, M Fiederle, S Stankov
We report a systematic lattice dynamics study of EuSi_{2} films and nanoislands by in situ nuclear inelastic scattering on ^{151}Eu and ab initio theory. The Eu-partial phonon density of states of the nanoislands exhibits anomalous excess of phonon states at low and high energies, not present in the bulk and at the EuSi_{2}(001) surface. We demonstrate that atomic vibrations along the island-substrate interface give rise to phonon states both at low and high energies, while atomic vibrations across the island-island interface result in localized high-energy phonon modes...
December 30, 2016: Physical Review Letters
Gang Yang
Using color-kinematics duality, we construct for the first time the full integrand of the five-loop Sudakov form factor in N=4 super-Yang-Mills theory, including nonplanar contributions. This result also provides a first manifestation of the color-kinematics duality at five loops. The integrand is explicitly ultraviolet finite when D<26/5, coincident with the known finiteness bound for amplitudes. If the double-copy method could be applied to the form factor, this would indicate an interesting ultraviolet finiteness bound for N=8 supergravity at five loops...
December 30, 2016: Physical Review Letters
M C Hels, B Braunecker, K Grove-Rasmussen, J Nygård
We demonstrate experimentally that noncollinear intrinsic spin-orbit magnetic fields can be realized in a curved carbon nanotube two-segment device. Each segment, analyzed in the quantum dot regime, shows near fourfold degenerate shell structure allowing for identification of the spin-orbit coupling and the angle between the two segments. Furthermore, we determine the four unique spin directions of the quantum states for specific shells and magnetic fields. This class of quantum dot systems is particularly interesting when combined with induced superconducting correlations as it may facilitate unconventional superconductivity and detection of Cooper pair entanglement...
December 30, 2016: Physical Review Letters
N Leefer, A Gerhardus, D Budker, V V Flambaum, Y V Stadnik
We propose a new method to search for hypothetical scalar particles that have feeble interactions with standard-model particles. In the presence of massive bodies, these interactions produce a nonzero Yukawa-type scalar-field magnitude. Using radio-frequency spectroscopy data of atomic dysprosium, as well as atomic clock spectroscopy data, we constrain the Yukawa-type interactions of a scalar field with the photon, electron, and nucleons for a range of scalar-particle masses corresponding to length scales >10  cm...
December 30, 2016: Physical Review Letters
D Iablonskyi, K Nagaya, H Fukuzawa, K Motomura, Y Kumagai, S Mondal, T Tachibana, T Takanashi, T Nishiyama, K Matsunami, P Johnsson, P Piseri, G Sansone, A Dubrouil, M Reduzzi, P Carpeggiani, C Vozzi, M Devetta, M Negro, F Calegari, A Trabattoni, M C Castrovilli, D Faccialà, Y Ovcharenko, T Möller, M Mudrich, F Stienkemeier, M Coreno, M Alagia, B Schütte, N Berrah, A I Kuleff, G Jabbari, C Callegari, O Plekan, P Finetti, C Spezzani, E Ferrari, E Allaria, G Penco, C Serpico, G De Ninno, I Nikolov, B Diviacco, S Di Mitri, L Giannessi, K C Prince, K Ueda
Ne clusters (∼5000  atoms) were resonantly excited (2p→3s) by intense free electron laser (FEL) radiation at FERMI. Such multiply excited clusters can decay nonradiatively via energy exchange between at least two neighboring excited atoms. Benefiting from the precise tunability and narrow bandwidth of seeded FEL radiation, specific sites of the Ne clusters were probed. We found that the relaxation of cluster surface atoms proceeds via a sequence of interatomic or intermolecular Coulombic decay (ICD) processes while ICD of bulk atoms is additionally affected by the surrounding excited medium via inelastic electron scattering...
December 30, 2016: Physical Review Letters
Daixiang Mou, Tai Kong, William R Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S L Bud'ko, Ilya Eremin, D D Johnson, P C Canfield, Adam Kaminski
We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe_{4}As_{4}. In contrast to the related CaFe_{2}As_{2} compounds, CaKFe_{4}As_{4} has a high T_{c} of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters...
December 30, 2016: Physical Review Letters
Lukas Janssen, Eric C Andrade, Matthias Vojta
The Heisenberg-Kitaev model is a paradigmatic model to describe the magnetism in honeycomb-lattice Mott insulators with strong spin-orbit coupling, such as A_{2}IrO_{3} (A=Na, Li) and α-RuCl_{3}. Here, we study in detail the physics of the Heisenberg-Kitaev model in an external magnetic field. Using a combination of Monte Carlo simulations and spin-wave theory, we map out the classical phase diagram for different directions of the magnetic field. Broken SU(2) spin symmetry renders the magnetization process rather complex, with sequences of phases and metamagnetic transitions...
December 30, 2016: Physical Review Letters
Michael Renzler, Martin Kuhn, Andreas Mauracher, Albrecht Lindinger, Paul Scheier, Andrew M Ellis
We report the first experimental observation of negatively charged hydrogen and deuterium cluster ions, H_{n}^{-} and D_{n}^{-}, where n≥5. These anions are formed by an electron addition to liquid helium nanodroplets doped with molecular hydrogen or deuterium. The ions are stable for at least the lifetime of the experiment, which is several tens of microseconds. Only anions with odd values of n are detected, and some specific ions show anomalously high abundances. The sizes of these "magic number" ions suggest an icosahedral framework of H_{2} (D_{2}) molecules in solvent shells around a central H^{-} (D^{-}) ion...
December 30, 2016: Physical Review Letters
Mohammad Rashidi, Marco Taucer, Isil Ozfidan, Erika Lloyd, Mohammad Koleini, Hatem Labidi, Jason L Pitters, Joseph Maciejko, Robert A Wolkow
Negative differential resistance remains an attractive but elusive functionality, so far only finding niche applications. Atom scale entities have shown promising properties, but the viability of device fabrication requires a 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...
December 30, 2016: Physical Review Letters
M Gedalin, W Dröge, Y Y Kartavykh
Diffusive shock acceleration (DSA) of ions occurs due to pitch-angle diffusion in the upstream and downstream regions of the shock and multiple crossing of the shock by these ions. The classical DSA theory implies continuity of the distribution at the shock transition and predicts a universal spectrum of accelerated particles, depending only on the ratio of the upstream and downstream fluid speeds. However, the ion dynamics at the shock front occurs within a collision-free region and is gyrophase dependent...
December 30, 2016: Physical Review Letters
Javier Del Pino, Francisco J Garcia-Vidal, Johannes Feist
When the collective coupling of the rovibrational states in organic molecules and confined electromagnetic modes is sufficiently strong, the system enters into vibrational strong coupling, leading to the formation of hybrid light-matter quasiparticles. In this Letter, we demonstrate theoretically how this hybridization in combination with stimulated Raman scattering can be utilized to widen the capabilities of Raman laser devices. We explore the conditions under which the lasing threshold can be diminished and the system can be transformed into an optical parametric oscillator...
December 30, 2016: Physical Review Letters
Geoffroy Prévot, Conor Hogan, Thomas Leoni, Romain Bernard, Eric Moyen, Laurence Masson
We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT...
December 30, 2016: Physical Review Letters
V Zaburdaev, I Fouxon, S Denisov, E Barkai
It is recognized now that a variety of real-life phenomena ranging from diffusion of cold atoms to the motion of humans exhibit dispersal faster than normal diffusion. Lévy walks is a model that excelled in describing such superdiffusive behaviors albeit in one dimension. Here we show that, in contrast to standard random walks, the microscopic geometry of planar superdiffusive Lévy walks is imprinted in the asymptotic distribution of the walkers. The geometry of the underlying walk can be inferred from trajectories of the walkers by calculating the analogue of the Pearson coefficient...
December 30, 2016: Physical Review Letters
Cesar I N Sampaio Filho, André A Moreira, Nuno A M Araújo, José S Andrade, Hans J Herrmann
We report on a novel dynamic phase in electrical networks, in which current channels perpetually change in time. This occurs when the elementary units of the network are fuse-antifuse devices, namely, become insulators within a certain finite interval of local applied voltages. As a consequence, the macroscopic current exhibits temporal fluctuations which increase with system size. We determine the conditions under which this exotic situation appears by establishing a phase diagram as a function of the applied field and the size of the insulating window...
December 30, 2016: Physical Review Letters
G Labeyrie, R Kaiser
When applying two counterpropagating laser beams to a cold cloud of rubidium atoms, we observe the spontaneous formation of intensity patterns associated with a spatial structuration of the atomic spins. We study the average number of defects in these patterns as a function of the sweep time employed to cross the instability threshold. We observe a power-law decrease of the number of defects with increasing sweep time, typical of the Kibble-Zurek mechanism. The measured exponent is consistent with the prediction for a supercritical bifurcation...
December 30, 2016: Physical Review Letters
M K Chan, Y Tang, C J Dorow, J Jeong, L Mangin-Thro, M J Veit, Y Ge, D L Abernathy, Y Sidis, P Bourges, M Greven
We use neutron scattering to study magnetic excitations near the antiferromagnetic wave vector in the underdoped single-layer cuprate HgBa_{2}CuO_{4+δ} (superconducting transition temperature T_{c}≈88  K, pseudogap temperature T^{*}≈220  K). The response is distinctly enhanced below T^{*} and exhibits a Y-shaped dispersion in the pseudogap state, whereas the superconducting state features an X-shaped (hourglass) dispersion and a further resonancelike enhancement. A large spin gap of about 40 meV is observed in both states...
December 30, 2016: Physical Review Letters
Moshe Goldstein, Yuval Gefen
Mach-Zehnder interferometry has been proposed as a probe for detecting the statistics of anyonic quasiparticles in fractional quantum Hall (FQH) states. Here, we focus on interferometers made of multimode edge states with upstream modes. We find that the interference visibility is suppressed due to downstream-upstream mode entanglement; the latter serves as a "which path" detector to the downstream interfering trajectories. Our analysis tackles a concrete realization of a filling factor of ν=2/3, but its applicability goes beyond that specific case, and encompasses the recent observation of the ubiquitous emergence of upstream neutral modes in FQH states...
December 30, 2016: Physical Review Letters
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