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Jian Liu, Wen-Jie Hou, Cai Cheng, Hui-Xia Fu, Jia-Tao Sun, Sheng Meng
Intrinsic valley polarization can be obtained in VSe2 monolayers with broken inversion symmetry and time reversal symmetry. First-principles investigations reveal that the magnitude of the valley splitting in magnetic VSe2 induced by spin-orbit coupling reaches as high as 78.2 meV and can be linearly tuned by biaxial strain. Besides conventional polarized light, hole doping or illumination with light of proper frequency can offer effective routes to realize valley polarization. Moreover, spin-orbit coupling in monolayer VSe2 breaks not only the valley degeneracy but also the three-fold rotational symmetry in band structure...
May 18, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Lihong Wang, Jingsong He, Hui Xu, Ji Wang, Kuppuswamy Porsezian
In this paper, we construct a special kind of breather solution of the nonlinear Schrödinger (NLS) equation, the so-called breather-positon (b-positon for short), which can be obtained by taking the limit λ_{j}→λ_{1} of the Lax pair eigenvalues in the order-n periodic solution, which is generated by the n-fold Darboux transformation from a special "seed" solution-plane wave. Further, an order-n b-positon gives an order-n rogue wave under a limit λ_{1}→λ_{0}. Here, λ_{0} is a special eigenvalue in a breather of the NLS equation such that its period goes to infinity...
April 2017: Physical Review. E
Rok Žitko, Michele Fabrizio
We study how the non-Fermi-liquid nature of the overscreened multi-channel Kondo impurity model affects the response to a BCS pairing term that, in the absence of the impurity, opens a gap Δ. We find that the low-energy spectrum in the limit Δ → 0 actually does not correspond to the spectrum strictly at Δ = 0. In particular, in the two-channel Kondo model the Δ → 0 ground state is an orbitally degenerate spin-singlet, while it is an orbital singlet with a residual spin degeneracy at Δ = 0. In addition, there are fractionalized spin-1/2 sub-gap excitations whose energy in units of Δ tends towards a finite and universal value when Δ → 0; as if the universality of the anomalous power-law exponents that characterise the overscreened Kondo effect turned into universal energy ratios when the scale invariance is broken by Δ ≠ 0...
February 16, 2017: Physical Review. B
Hsin-Hua Lai, Wen-Jun Hu, Emilian M Nica, Rong Yu, Qimiao Si
The magnetic and nematic properties of the iron chalcogenides have recently been the subject of intense interest. Motivated by the proposed antiferroquadrupolar and Ising-nematic orders for the bulk FeSe, we study the phase diagram of an S=1 generalized bilinear-biquadratic model with multineighbor interactions. We find a large parameter regime for a (π, 0) antiferroquadrupolar phase, showing how quantum fluctuations stabilize it by lifting an infinite degeneracy of certain semiclassical states. Evidence for this C_{4}-symmetry-breaking quadrupolar phase is also provided by an unbiased density matrix renormalization group analysis...
April 28, 2017: Physical Review Letters
Y Quan, Z P Yin, W E Pickett
The existence of closed loops of degeneracies in crystals has been intimately connected with associated crystal symmetries, raising the following question: What is the minimum symmetry required for topological character, and can one find an example? Triclinic CaAs_{3}, in the space group P1[over ¯] with only a center of inversion, has been found to display, without need for tuning, a nodal loop of accidental degeneracies with topological character, centered on one face of the Brillouin zone that is otherwise fully gapped...
April 28, 2017: Physical Review Letters
Cindy C Shu, Margaret M Smith, Susan M Smith, Andrew J Dart, Christopher B Little, James Melrose
The purpose of this study was to develop a quantitative histopathological scoring scheme to evaluate disc degeneration and regeneration using an ovine annular lesion model of experimental disc degeneration. Toluidine blue and Haematoxylin and Eosin (H&E) staining were used to evaluate cellular morphology: (i) disc structure/lesion morphology; (ii) proteoglycan depletion; (iii) cellular morphology; (iv) blood vessel in-growth; (v) cell influx into lesion; and (vi) cystic degeneration/chondroid metaplasia...
May 12, 2017: International Journal of Molecular Sciences
Guoqing Chang, Su-Yang Xu, Shin-Ming Huang, Daniel S Sanchez, Chuang-Han Hsu, Guang Bian, Zhi-Ming Yu, Ilya Belopolski, Nasser Alidoust, Hao Zheng, Tay-Rong Chang, Horng-Tay Jeng, Shengyuan A Yang, Titus Neupert, Hsin Lin, M Zahid Hasan
Topological metals and semimetals (TMs) have recently drawn significant interest. These materials give rise to condensed matter realizations of many important concepts in high-energy physics, leading to wide-ranging protected properties in transport and spectroscopic experiments. It has been well-established that the known TMs can be classified by the dimensionality of the topologically protected band degeneracies. While Weyl and Dirac semimetals feature zero-dimensional points, the band crossing of nodal-line semimetals forms a one-dimensional closed loop...
May 10, 2017: Scientific Reports
Andrew Gaul, Qing Peng, David J Singh, Ganpati Ramanath, Theodorian Borca-Tasciuc
First-principles calculations revealing insulator-to-metal transitions in Bi2Te3 and Bi2Te2Se, at 9 GPa and 12.5 GPa, respectively, match with prior experiments. Our electronic band structure calculations and accompanying Boltzmann transport calculations of thermoelectric properties for Bi2-xSbxTe2-ySey alloys explain and predict large power factor changes induced by pressure. Complex band degeneracy changes preceding insulator-to-metal transitions significantly alter the density of states near the Fermi level, and foster the disentangling of the unfavorable coupling between Seebeck coefficient and electrical conductivity...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
Zhaojin Wang, Tianyu Wang, Chi Zhang, Mark G Humphrey
Fluorenyl-tethered o-carborane derivatives (Fl-Cb) as both mono- and di-aryl Cb assemblies were synthesized from the corresponding alkyne and B10H12(Et2S)2 in ca. 60% yields. Crystallographic studies of di-aryl examples show rigid head-to-tail or tail-to-tail packing, while for the mono-aryl examples, only loose packing was observed. In solution, the Fl-Cb compounds exhibit strong quenching of their emission, while aggregation in a mixed solvent results in an enhanced, but still weak, emission [0.11 quantum efficiency (Φ)]...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
Hiroki Isobe, Liang Fu
We study the pairing symmetry of the interlayer paired state of composite fermions in quantum Hall bilayers. Based on the Halperin-Lee-Read (HLR) theory, the effect of the long-range Coulomb interaction and the internal Chern-Simons gauge fluctuation is analyzed with the random-phase approximation beyond the leading order contribution in small momentum expansion, and we observe that the interlayer paired states with a relative angular momentum l=+1 are energetically favored for filling ν=1/2+1/2 and 1/4+1/4...
April 21, 2017: Physical Review Letters
D D Fan, H J Liu, L Cheng, J Zhang, P H Jiang, J Wei, J H Liang, J Shi
Using the first-principles pseudopotential method and Boltzmann transport theory, we give a comprehensive understanding of the electronic and phonon transport properties of the thermoelectric material BiCuSeO. By choosing an appropriate hybrid functional for the exchange-correlation energy, we find that the system is a semiconductor with a direct band gap of ∼0.8 eV, which is quite different from those obtained previously using standard functionals. Detailed analysis of a three-dimensional energy band structure indicates that there is a valley degeneracy of eight around the valence band maximum, which leads to a sharp density of states and is responsible for a large p-type Seebeck coefficient...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
Ivan V Sergeyev, Boris Itin, Rivkah Rogawski, Loren A Day, Ann E McDermott
An experimental strategy has been developed to increase the efficiency of dynamic nuclear polarization (DNP) in solid-state NMR studies. The method makes assignments simpler, faster, and more reliable via sequential correlations of both side-chain and Cα resonances. The approach is particularly suited to complex biomolecules and systems with significant chemical-shift degeneracy. It was designed to overcome the spectral congestion and line broadening that occur due to sample freezing at the cryogenic temperatures required for DNP...
May 1, 2017: Proceedings of the National Academy of Sciences of the United States of America
Chuan Zhao, Tenzin Norden, Peiyao Zhang, Puqin Zhao, Yingchun Cheng, Fan Sun, James P Parry, Payam Taheri, Jieqiong Wang, Yihang Yang, Thomas Scrace, Kaifei Kang, Sen Yang, Guo-Xing Miao, Renat Sabirianov, George Kioseoglou, Wei Huang, Athos Petrou, Hao Zeng
Exploiting the valley degree of freedom to store and manipulate information provides a novel paradigm for future electronics. A monolayer transition-metal dichalcogenide (TMDC) with a broken inversion symmetry possesses two degenerate yet inequivalent valleys, which offers unique opportunities for valley control through the helicity of light. Lifting the valley degeneracy by Zeeman splitting has been demonstrated recently, which may enable valley control by a magnetic field. However, the realized valley splitting is modest (∼0...
May 1, 2017: Nature Nanotechnology
Yuxin Sun, Katharine Best, Mattia Cinelli, James M Heather, Shlomit Reich-Zeliger, Eric Shifrut, Nir Friedman, John Shawe-Taylor, Benny Chain
T cells recognize antigen using a large and diverse set of antigen-specific receptors created by a complex process of imprecise somatic cell gene rearrangements. In response to antigen-/receptor-binding-specific T cells then divide to form memory and effector populations. We apply high-throughput sequencing to investigate the global changes in T cell receptor sequences following immunization with ovalbumin (OVA) and adjuvant, to understand how adaptive immunity achieves specificity. Each immunized mouse contained a predominantly private but related set of expanded CDR3β sequences...
2017: Frontiers in Immunology
T Petersen, J D Zuegel, J Bromage
A high-energy, extended-cavity femtosecond BiBO optical parametric oscillator synchronously pumped by a 1.0-ps, 1030-nm Yb:YAG, thin-disk pump laser is presented. The oscillator operated near degeneracy in a noncollinear interaction geometry, producing signal wavelength tunability from 1.99 to 2.20 μm. The signal pulses have an average power exceeding 2 W, producing 455-fs pulses at 7.08 MHz with energies up to 350 nJ, showing increased potential for tunable sources of scalable ultrafast pulses in the infrared...
April 17, 2017: Optics Express
Ioannis Rousochatzakis, Natalia B Perkins
We show that the off-diagonal exchange anisotropy drives Mott insulators with strong spin-orbit coupling to a classical spin liquid regime, characterized by an infinite number of ground states and Ising variables living on closed or open strings. Depending on the sign of the anisotropy, quantum fluctuations either fail to lift the degeneracy down to very low temperatures, or select noncoplanar magnetic states with unconventional spin correlations. The results apply to all 2D and 3D tricoordinated materials with bond-directional anisotropy and provide a consistent interpretation of the suppression of the x-ray magnetic circular dichroism signal reported recently for β-Li_{2}IrO_{3} under pressure...
April 7, 2017: Physical Review Letters
L Pinto da Silva, C M Magalhães, D M A Crista, J C G Esteves da Silva
Coelenterazine, a member of the imidazopyrazinone class of chemiluminescent substrates, presents significant potential as a dynamic probe of reactive oxygen species in a biological environment, such as a superoxide anion, in which these species are important in cellular biology and pathology. The objective of the current study was to understand in what way the efficiency of singlet and triplet chemiexcitation could be modulated, towards a more efficient use of imidazopyrazinone-based compounds as dynamic chemiluminescent probes...
April 21, 2017: Photochemical & Photobiological Sciences
Carlos G Avendaño, Arturo Reyes
We theoretically study the dispersion relation for axially propagating electromagnetic waves throughout a one-dimensional helical structure whose pitch and dielectric and magnetic properties are spatial random functions with specific statistical characteristics. In the system of coordinates rotating with the helix, by using a matrix formalism, we write the set of differential equations that governs the expected value of the electromagnetic field amplitudes and we obtain the corresponding dispersion relation...
March 2017: Physical Review. E
Luiz H Santos, Taylor L Hughes
We explore a scenario where local interactions form one-dimensional gapped interfaces between a pair of distinct chiral two-dimensional topological states-referred to as phases 1 and 2-such that each gapped region terminates at a domain wall separating the chiral gapless edge states of these phases. We show that this type of T junction supports pointlike fractionalized excitations obeying parafermion statistics, thus implying that the one-dimensional gapped interface forms an effective topological parafermionic wire possessing a nontrivial ground state degeneracy...
March 31, 2017: Physical Review Letters
J Ren, H Hodaei, G Harari, A U Hassan, W Chow, M Soltani, D Christodoulides, M Khajavikhan
We propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non-Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed (Ω), thus enhancing the sensitivity to low angular rotations by orders of magnitudes. In addition, at its maximum sensitivity limit, the measurable spectral splitting is independent of the radius of the rings involved. This Letter paves the way toward a new class of ultrasensitive miniature ring laser gyroscopes on chip...
April 15, 2017: Optics Letters
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