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lattice degeneration

Kimberly H Hartstein, Carl K Brozek, Stijn O M Hinterding, Daniel R Gamelin
Copper-sulfide nanocrystals can accommodate considerable densities of delocalized valence-band holes, introducing localized surface plasmon resonances (LSPRs) attractive for infrared plasmonic applications. Chemical control over nanocrystal shape, composition, and charge-carrier densities further broadens their scope of potential properties and applications. Although a great deal of control over LSPRs in these materials has been demonstrated, structural complexities have inhibited detailed descriptions of the microscopic chemical processes that transform them from nearly intrinsic to degenerately doped semiconductors...
February 20, 2018: Journal of the American Chemical Society
Hatem Brahmi, Ram Neupane, Lixin Xie, Shivkant Singh, Milad Yarali, Giwan Katwal, Shuo Chen, Maggie Paulose, Oomman K Varghese, Anastassios Mavrokefalos
Manipulating the transport properties of titania nanotubes (NTs) is paramount in guaranteeing the material's successful implementation in various solid state applications. Here we present the unique semiconducting properties of individual titania NTs as revealed from thermoelectric and structural studies performed on the same individual NTs. The NTs were in the anatase phase fabricated by anodic oxidation and doped with intrinsic defects created by reducing the lattice thermally. Despite their polycrystalline nature and nanoscale walls, the doped NTs were found to be 4-5 orders of magnitude more electrically conducting than TiO2 nanowires and thin films, with values approaching the bulk single crystal conductivity...
February 8, 2018: Nanoscale
M Bakarezos, E Tzianaki, S Petrakis, G Tsibidis, P A Loukakos, V Dimitriou, C Kosmidis, M Tatarakis, N A Papadogiannis
Nanoacoustic strains are generated in Silicon by chirped femtosecond laser pulses using thin Titanium films as transducers. We investigate the effect that the generating laser pulse chirp has on the amplitude of the induced strains, manifested as Brillouin oscillations observed in degenerate femtosecond pump-probe transient reflectivity measurements. The strain amplitude is larger when negatively chirped pulses are used, which is attributed to the more efficient conversion of laser pulse light into acoustic strain in the Titanium transducer...
January 25, 2018: Ultrasonics
Daniella A Ferluccio, Ronald I Smith, Jim Buckman, Jan-Willem G Bos
The half-Heuslers NbCoSn and NbCoSb have promising thermoelectric properties. Here, an investigation of the NbCo1+ySn1-zSbz (y = 0, 0.05; 0 ≤ z ≤ 1) solid-solution is presented. In addition, the p-type doping of NbCoSn using Ti and Zr substitution is investigated. Rietveld analysis reveals the gradual creation of Nb vacancies to compensate for the n-type doping caused by the substitution of Sb in NbCoSn. This leads to a similar valence electron count (∼18.25) for the NbCo1+ySn1-zSbz samples (z > 0)...
January 19, 2018: Physical Chemistry Chemical Physics: PCCP
E Jurčišinová, M Jurčišin
We investigate in detail the process of adiabatic cooling in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model in the presence of the external magnetic field on an approximate lattice with pyrochlore structure. The behavior of the entropy of the model is studied and exact values of the residual entropies of all ground states are found. The temperature variation of the system under adiabatic (de)magnetization is investigated and the central role of the macroscopically degenerated ground states in cooling processes is explicitly demonstrated...
November 2017: Physical Review. E
Konrad Jerzy Kapcia, Jan Barański, Andrzej Ptok
The phenomenon associated with inhomogeneous distribution of electron density is known as a charge ordering. In this work, we study the zero-bandwidth limit of the extended Hubbard model, which can be considered as a simple effective model of charge ordered insulators. It consists of the on-site interaction U and the intersite density-density interactions W_{1} and W_{2} between nearest neighbors and next-nearest neighbors, respectively. We derived the exact ground state diagrams for different lattice dimensionalities and discuss effects of small finite temperatures in the limit of high dimensions...
October 2017: Physical Review. E
R M Liu, W Z Zhuo, J Chen, M H Qin, M Zeng, X B Lu, X S Gao, J-M Liu
We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses...
July 2017: Physical Review. E
Bogdan Galilo, Derek K K Lee, Ryan Barnett
In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states...
November 17, 2017: Physical Review Letters
Dorothee Braun, Martin Schmidbauer, Michael Hanke, Jutta Schwarzkopf
The formation process of a ferroelectric multi-rank domain pattern in the thickness range of 7-52 nm is investigated for monoclinic K0.9Na0.1NbO3 strained epitaxial films on (110) NdScO3 substrates. Although the elastic strain energy density is degenerated for two pseudocubic orientations, a distinctive hierarchy of domain evolution is observed with exclusive in-plane a1a2 domains for very thin films and the retarded onset of a ferroelectric MC phase at larger film thickness. This is accompanied by a thickness dependent transformation from stripe domains to a herringbone pattern and, eventually, for the thickest film, to a checkerboard-like structure...
November 29, 2017: Nanotechnology
Shan-Shan Wang, Ying Liu, Zhi-Ming Yu, Xian-Lei Sheng, Shengyuan A Yang
Nonsymmorphic symmetries, which involve fractional lattice translations, can generate exotic types of fermionic excitations in crystalline materials. Here we propose a topological phase arising from nonsymmorphic symmetries-the hourglass Dirac chain metal, and predict its realization in the rhenium dioxide. We show that ReO2 features hourglass-type dispersion in the bulk electronic structure dictated by its nonsymmorphic space group. Due to time reversal and inversion symmetries, each band has an additional two-fold degeneracy, making the neck crossing-point of the hourglass four-fold degenerate...
November 29, 2017: Nature Communications
Sarra Gattoussi, Quraish Ghadiali, Rosa Dolz-Marco, K Bailey Freund
PURPOSE: We describe with multimodal imaging the presentation and follow-up for a patient with idiopathic multifocal choroiditis and a transient peripapillary white ring. METHODS: Case report. RESULTS: A 39-year-old Asian woman was initially seen for an evaluation of lattice degeneration in 2015. Her medical history included Graves disease and psoriasis. Best-corrected visual acuity was 20/25 in her right eye and 20/25 in her left eye. Ultra-widefield fundus autofluorescence imaging showed a curvilinear hyperautofluorescent line in her right eye...
November 22, 2017: Retinal Cases & Brief Reports
Yong Hu, Xiaodan Chi, Xuesi Li, Yan Liu, An Du
In triangular-lattice magnets, the coexistence of third-neighbor antiferromagnetic and nearest-neighbor ferromagnetic exchange interactions can induce rich magnetic phases including noncoplanar skyrmion crystals. Based on Monte Carlo simulation, we studied the dependence of magnetic phase transition on exchange interaction strength. Under the consideration of uniaxial anisotropy and magnetic field both perpendicular to the film plane, a large antiferromagnetic exchange interaction induces a high frustration...
November 22, 2017: Scientific Reports
Emre Bukusoglu, Jose A Martinez-Gonzalez, Xiaoguang Wang, Ye Zhou, Juan J de Pablo, Nicholas L Abbott
We report on the influence of surface confinement on the phase behavior and strain-induced alignment of thin films of blue phase liquid crystals (BPs). Confining surfaces comprised of bare glass, dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP)-functionalized glass, or polyvinyl alcohol (PVA)-coated glass were used with or without mechanically rubbing to influence the azimuthal anchoring of the BPs. These experiments reveal that confinement can change the phase behavior of the BP films...
November 22, 2017: Soft Matter
Yanqing Feng, Hong Xi Sun, Junhui Sun, Zhibin Lu, Yong You
We study the conventional electron--phonon mediated superconducting properties of hole-doped Black Phosphorus by density functional calculations and get a quite large electron--phonon coupling (EPC) constant λ ~ 1.0 with transition temperature TC ~ 10 K, which is comparable to MgB2 when holes are doped into degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency B3g1 optical mode and its phonon displacement which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC...
November 14, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Dorothee Braun, Martin Schmidbauer, Michael Hanke, Jutta Schwarzkopf
The formation process of a ferroelectric multi-rank domain pattern in the thickness range of 7 to 52 nm is investigated for monoclinic K<sub>0.9</sub>Na<sub>0.1</sub>NbO<sub>3</sub> strained epitaxial films on (110) NdScO<sub>3</sub> substrates. Although the elastic strain energy density is degenerated for two pseudocubic orientations, a distinctive hierarchy of domain evolution is observed with exclusive in-plane a<sub>1</sub>a<sub>2</sub> domains for very thin films and the retarded onset of a ferroelectric M<sub>C</sub> phase at larger film thickness...
November 7, 2017: Nanotechnology
Arun D Singh, Hansell Soto, Claudine Bellerive, Charles V Biscotti
PURPOSE: To report 3 cases providing insight into clinical progression of reactive retinal astrocytic tumor. METHODS: The clinical, imaging, and when available, the cytologic features of 3 cases of reactive retinal astrocytic tumor (focal nodular gliosis) were reviewed. RESULTS: A 6-year-old female, a 49-year-old man, and a 39-year-old man each developed a white retinal mass associated with laser photocoagulation, lattice degeneration, and treatment of a presumed vascular tumor, respectively...
September 2017: Ocular Oncology and Pathology
C Alexandrou, M Constantinou, K Hadjiyiannakou, K Jansen, C Kallidonis, G Koutsou, A Vaquero Avilés-Casco, C Wiese
We determine within lattice QCD the nucleon spin carried by valence and sea quarks and gluons. The calculation is performed using an ensemble of gauge configurations with two degenerate light quarks with mass fixed to approximately reproduce the physical pion mass. We find that the total angular momentum carried by the quarks in the nucleon is J_{u+d+s}=0.408(61)_{stat}(48)_{syst} and the gluon contribution is J_{g}=0.133(11)_{stat}(14)_{syst}, giving a total of J_{N}=0.54(6)_{stat}(5)_{syst} that is consistent with the spin sum...
October 6, 2017: Physical Review Letters
Matthieu David, Damien Connétable
While diffusion mechanisms of interstitial elements in fcc systems are generally well-known, especially in the case of H atoms, we show in this work that even in the case of a simple metallic system (aluminum), the diffusion of interstitials exhibits a wide variety of paths and mechanisms that depend on the specie. We used an approach based on first-principles calculations associated with kinetic Monte-Carlo simulations and a multi-state diffusion formalism to compute the diffusion coefficients of five interstitial elements: hydrogen, boron, carbon, nitrogen and oxygen...
October 19, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ruchi, Sushanta Kumar Pal, P Senthilkumaran
V-points normally do not occur in generic light fields as compared to C-points and L-lines. In structured optical fields, simultaneous existence of C-points, V-points and L-lines can be engineered in lattice forms. But lattices consisting only of V-points have not been realized so far. In this paper we demonstrate creation of lattices of V-point polarization singularities with translational periodicity. These lattice structures are obtained by the interference of four (six) linearly polarized plane waves arranged in symmetric umbrella geometry...
August 7, 2017: Optics Express
Jing Lu, Guiying Mai, Ruyuan Liu, Yan Luo, Lin Lu
A 63-year-old male presented with a round-shaped floater and visual obscuration in the right eye. Clinical evaluation showed a nonpigmented vitreous cyst connected to a lattice degeneration by a stalk. Immunostaining of the vitreous cyst obtained from vitrectomy showed its origin of retinal neuroepithelium. The cyst was formed by continuous vitreous traction, which might tear up the disrupted retina at the area of lattice degeneration. This report added the lattice degeneration to the list of causes for the acquired vitreous cyst...
October 1, 2017: Ophthalmic Surgery, Lasers & Imaging Retina
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