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Mohamed S Seghilani, Mikhael Myara, Mohamed Sellahi, Luc Legratiet, Isabelle Sagnes, Grégoire Beaudoin, Philippe Lalanne, Arnaud Garnache
The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here "orbital birefringence", based on a dielectric metasurface...
December 5, 2016: Scientific Reports
Wil Biddle, Margaret A Schmitt, John D Fisk
Breaking the degeneracy of the genetic code via sense codon reassignment has emerged as a way to incorporate multiple copies of multiple non-canonical amino acids into a protein of interest. Here, we report the modification of a normally orthogonal tRNA by a host enzyme and show that this adventitious modification has a direct impact on the activity of the orthogonal tRNA in translation. We observed nearly equal decoding of both histidine codons, CAU and CAC, by an engineered orthogonal M. jannaschii tRNA with an AUG anticodon: tRNA(Opt) We suspected a modification of the tRNA(Opt)AUG anticodon was responsible for the anomalous lack of codon discrimination and demonstrate that adenosine 34 of tRNA(Opt)AUG is converted to inosine...
December 1, 2016: Nucleic Acids Research
Jian Kang, Rafael M Fernandes
The origin of the high-temperature superconducting state observed in FeSe thin films, whose phase diagram displays no sign of magnetic order, remains a hotly debated topic. Here we investigate whether fluctuations arising due to the proximity to a nematic phase, which is observed in the phase diagram of this material, can promote superconductivity. We find that nematic fluctuations alone promote a highly degenerate pairing state, in which both s-wave and d-wave symmetries are equally favored, and T_{c} is consequently suppressed...
November 18, 2016: Physical Review Letters
R P M J W Notermans, R J Rengelink, W Vassen
We observe a dramatic difference in optical line shapes of a ^{4}He Bose-Einstein condensate and a ^{3}He degenerate Fermi gas by measuring the 1557-nm 2 ^{3}S-2 ^{1}S magnetic dipole transition (8 Hz natural linewidth) in an optical dipole trap. The 15 kHz FWHM condensate line shape is only broadened by mean field interactions, whereas the degenerate Fermi gas line shape is broadened to 75 kHz FWHM due to the effect of Pauli exclusion on the spatial and momentum distributions. The asymmetric optical line shapes are observed in excellent agreement with line shape models for the quantum degenerate gases...
November 18, 2016: Physical Review Letters
Po-Jen Hsu, Kun-Lin Ho, Sheng-Hsien Lin, Jer-Lai Kuo
The potential energy surface (PES), structures and thermal properties of methanol clusters (MeOH)n with n = 8-15 were explored by replica-exchange molecular dynamics (REMD) simulations with an empirical model and refined using density functional theory (DFT) methods. For a given size, local minima structures were sampled from REMD trajectories and archived by a newly developed molecular database via a two-stage clustering algorithm (TSCA). Our TSCA utilizes both the topology of O-HO hydrogen bonding networks and the similarity of the shapes to filter out duplicates...
December 2, 2016: Physical Chemistry Chemical Physics: PCCP
Youngwook Kim, Jaesung Park, Intek Song, Jong Mok Ok, Younjung Jo, Kenji Watanabe, Takashi Taniquchi, Hee Cheul Choi, Dong Su Lee, Suyong Jung, Jun Sung Kim
Twisted bilayer graphene offers a unique bilayer two-dimensional-electron system where the layer separation is only in sub-nanometer scale. Unlike Bernal-stacked bilayer, the layer degree of freedom is disentangled from spin and valley, providing eight-fold degeneracy in the low energy states. We have investigated broken-symmetry quantum Hall (QH) states and their transitions due to the interplay of the relative strength of valley, spin and layer polarizations in twisted bilayer graphene. The energy gaps of the broken-symmetry QH states show an electron-hole asymmetric behaviour, and their dependence on the induced displacement field are opposite between even and odd filling factor states...
December 1, 2016: Scientific Reports
David K Cole, Hugo A van den Berg, Angharad Lloyd, Michael D Crowther, Konrad Beck, Julia Ekeruche-Makinde, John J Miles, Anna M Bulek, Garry Dolton, Andrea J Schauenburg, Aaron Wall, Anna Fuller, Mathew Clement, Bruno Laugel, Pierre J Rizkallah, Linda Wooldridge, Andrew K Sewell
T-cell cross-reactivity is essential for effective immune surveillance, but has also been implicated as a pathway to autoimmunity. Previous studies have demonstrated that T-cell receptors (TCRs) that focus on a minimal motif within the peptide are able to facilitate a high level of T-cell cross-reactivity. However, the structural database shows that most TCRs exhibit less focussed antigen binding involving contact with more peptide residues. To further explore the structural features that allow the clonally expressed TCR to functionally engage with multiple peptide-major histocompatibility complexes (pMHCs), we examined the ILA1 CD8+ T-cell clone that responds to a peptide sequence derived from human telomerase reverse transcriptase (hTERT)...
November 30, 2016: Journal of Biological Chemistry
Yawei Lv, Sheng Chang, Qijun Huang, Hao Wang, Jin He
In this paper, phosphorene nanoribbons (PNRs) are theoretically studied using a multiscale simulation flow from the ab initio level to the tight binding (TB) level. The scaling effects of both armchair PNRs (aPNRs) and zigzag PNRs (zPNRs) from material properties to device properties are explored. The much larger effective mass of holes compared to that of electrons in zPNR is responsible for its asymmetric transport. However, in aPNR, not only the effective mass difference but also the non-equal density of state (DOS) distributions near valence band maximum (VBM) and conduction band minimum (CBM) lead to the asymmetric transport...
November 29, 2016: Scientific Reports
Yann Perrin, Benjamin Canals, Nicolas Rougemaille
Artificial spin-ice systems are lithographically patterned arrangements of interacting magnetic nanostructures that were introduced as way of investigating the effects of geometric frustration in a controlled manner. This approach has enabled unconventional states of matter to be visualized directly in real space, and has triggered research at the frontier between nanomagnetism, statistical thermodynamics and condensed matter physics. Despite efforts to create an artificial realization of the square-ice model-a two-dimensional geometrically frustrated spin-ice system defined on a square lattice-no simple geometry based on arrays of nanomagnets has successfully captured the macroscopically degenerate ground-state manifold of the model...
November 28, 2016: Nature
Perttu J J Luukko, Byron Drury, Anna Klales, Lev Kaplan, Eric J Heller, Esa Räsänen
We discover and characterise strong quantum scars, or quantum eigenstates resembling classical periodic orbits, in two-dimensional quantum wells perturbed by local impurities. These scars are not explained by ordinary scar theory, which would require the existence of short, moderately unstable periodic orbits in the perturbed system. Instead, they are supported by classical resonances in the unperturbed system and the resulting quantum near-degeneracy. Even in the case of a large number of randomly scattered impurities, the scars prefer distinct orientations that extremise the overlap with the impurities...
November 28, 2016: Scientific Reports
Jian-Jun Shu
Degeneracy is a salient feature of genetic codes, because there are more codons than amino acids. The conventional table for genetic codes suffers from an inability of illustrating a symmetrical nature among genetic base codes. In fact, because the conventional wisdom avoids the question, there is little agreement as to whether the symmetrical nature actually even exists. A better understanding of symmetry and an appreciation for its essential role in the genetic code formation can improve our understanding of nature's coding processes...
November 23, 2016: Bio Systems
A Hofmann, V F Maisi, C Gold, T Krähenmann, C Rössler, J Basset, P Märki, C Reichl, W Wegscheider, K Ensslin, T Ihn
We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance and the ability to perform precise and efficient measurements of energy-dependent tunneling-in and -out rates from a reservoir. The method is realized using a GaAs/AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunneling with a precision enhanced by a feedback control. It is thoroughly tested by tuning orbital and spin degeneracies with electric and magnetic fields...
November 11, 2016: Physical Review Letters
E Estrecho, T Gao, S Brodbeck, M Kamp, C Schneider, S Höfling, A G Truscott, E A Ostrovskaya
Diabolical points (spectral degeneracies) can naturally occur in spectra of two-dimensional quantum systems and classical wave resonators due to simple symmetries. Geometric Berry phase is associated with these spectral degeneracies. Here, we demonstrate a diabolical point and the corresponding Berry phase in the spectrum of hybrid light-matter quasiparticles-exciton-polaritons in semiconductor microcavities. It is well known that sufficiently strong optical pumping can drive exciton-polaritons to quantum degeneracy, whereby they form a macroscopically populated quantum coherent state similar to a Bose-Einstein condensate...
November 25, 2016: Scientific Reports
I S S de Oliveira, W L Scopel, R H Miwa
We use first-principles simulations to investigate the topological properties of Bi2Se3 thin films deposited on amorphous SiO2, Bi2Se3/a-SiO2, which is a promising substrate for topological insulator (TI) based device applications. The Bi2Se3 films are bonded to a-SiO2 mediated by van der Waals interactions. Upon interaction with the substrate, the Bi2Se3 topological surface and interface states remain present, however the degeneracy between the Dirac-like cones is broken. The energy separation between the two Dirac-like cones increases with the number of Bi2Se3 quintuple layers (QLs) deposited on the substrate...
November 24, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Marçal Capdevila-Cortada, Núria López
Surface structure controls the physical and chemical response of materials. Surface polar terminations are appealing because of their unusual properties but they are intrinsically unstable. Several mechanisms, namely metallization, adsorption, and ordered reconstructions, can remove thermodynamic penalties rendering polar surfaces partially stable. Here, for CeO2(100), we report a complementary stabilization mechanism based on surface disorder that has been unravelled through theoretical simulations that: account for surface energies and configurational entropies; show the importance of the ion distribution degeneracy; and identify low diffusion barriers between conformations that ensure equilibration...
November 21, 2016: Nature Materials
Guoyan Dong, Ji Zhou, Xiulun Yang, Xiangfeng Meng
The phenomena of the minimum transmittance spectrum or the maximum reflection spectrum located around the Dirac frequency have been observed to demonstrate the 1/L scaling law near the Dirac-like point through the finite ribbon structure. However, so far there is no effective way to identify the Dirac-like point accurately. In this work we provide an effective measurement method to identify the Dirac-like point accurately through a finite photonic crystal square matrix. Based on the Dirac-like dispersion achieved by the accidental degeneracy at the centre of the Brillouin zone of dielectric photonic crystal, both the simulated and experimental results demonstrate that the transmittance spectra through a finite photonic crystal square matrix not only provide the clear evidence for the existence of Dirac-like point but also can be used to identify the precise location of Dirac-like point by the characteristics of sharp cusps embedded in the extremum spectra surrounding the conical singularity...
November 18, 2016: Scientific Reports
Benjamin E Feldman, Mallika T Randeria, András Gyenis, Fengcheng Wu, Huiwen Ji, R J Cava, Allan H MacDonald, Ali Yazdani
Nematic quantum fluids with wave functions that break the underlying crystalline symmetry can form in interacting electronic systems. We examined the quantum Hall states that arise in high magnetic fields from anisotropic hole pockets on the Bi(111) surface. Spectroscopy performed with a scanning tunneling microscope showed that a combination of single-particle effects and many-body Coulomb interactions lift the six-fold Landau level (LL) degeneracy to form three valley-polarized quantum Hall states. We imaged the resulting anisotropic LL wave functions and found that they have a different orientation for each broken-symmetry state...
October 21, 2016: Science
W Jiang, P Gartland, D Davidović
Superparamagnetism is an unwanted property of small magnetic particles where the magnetization of the particle flips randomly in time, due to thermal noise. There has been an increased attention in the properties of superparamagnetic particles recently, because of their potential applications in high density storage and medicine. In electron transport through single nanometer scale magnetic particles, the current can also cause the magnetization to flip randomly in time, even at low temperature. Here we show experimental evidence that when the current is then reduced towards zero in the applied magnetic field, the magnetization can reliably freeze about a higher anisotropy-energy minimum, where it tends to be inverted with respect to the magnetic field direction...
November 8, 2016: Scientific Reports
David Mendive-Tapia, Luuk Kortekaas, Jorn D Steen, Aurélie Perrier, Benjamin Lasorne, Wesley R Browne, Denis Jacquemin
Photochromism of the spiropyran radical cation to the corresponding merocyanine form is investigated by a combination of electrochemical oxidation, UV/vis absorption spectroscopy, spectroelectrochemistry and first-principles calculations (TD-DFT, CAS-SCF and CAS-PT2). First, we demonstrate that the ring-opening of mono-spiropyrans occurs upon one-electron oxidation and that it can be driven photochemically as well as thermally, with trapping of the merocyanine by protonation. Second, in order to explain this experimentally observed spectroelectrochemical behaviour we suggest a theoretical mechanism based on the reactivity of the two lowest electronic excited-states, which promotes effective electron transfer from the indoline (nitrogen-ring) to the pyran (oxygen-ring) moieties (and vice versa) through a conical intersection seam of degeneracy...
November 16, 2016: Physical Chemistry Chemical Physics: PCCP
Craig O Mackenzie, Jianfu Zhou, Gevorg Grigoryan
Here, we systematically decompose the known protein structural universe into its basic elements, which we dub tertiary structural motifs (TERMs). A TERM is a compact backbone fragment that captures the secondary, tertiary, and quaternary environments around a given residue, comprising one or more disjoint segments (three on average). We seek the set of universal TERMs that capture all structure in the Protein Data Bank (PDB), finding remarkable degeneracy. Only ∼600 TERMs are sufficient to describe 50% of the PDB at sub-Angstrom resolution...
November 22, 2016: Proceedings of the National Academy of Sciences of the United States of America
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