21495965
Pressure-induced cubic to monoclinic phase transformation in erbium sesquioxide Er(2)O(3).
Cubic Er(2)O(3) was compressed in a symmetric diamond anvil cell at room temperature and studied in situ using energy-dispersive X-ray diffraction. A transition to a monoclinic phase began at 9.9 GPa and was complete at 16.3 GPa and was accompanied by a approximately 9% volume decrease. The monoclinic phase was stable up to at least 30 GPa and could be quenched to ambient conditions. The normalized lattice parameter compression data for both phases were fit to linear equations, and the volume compression data were fit to third-order Birch-Murnaghan equations of state. The zero-pressure isothermal bulk moduli (B(0)) and the first-pressure derivatives (B(0)') for the cubic and monoclinic phases were 200(6) GPa and 8.4 and also 202(2) GPa and 1.0, respectively. Ab initio density functional theory calculations were performed to determine optimized lattice parameters and atom positions for the cubic, monoclinic, and hexagonal phases of Er(2)O(3). The calculated X-ray spectra and predicted transition pressure are in good qualitative agreement with the experimental results.
10267449
Cubic to tetragonal phase transformation in cold-compressed Pd nanocubes.
Pd nanocubes with an average side length of approximately 10 nm were compressed up to 24.8 GPa in a diamond-anvil cell (DAC). In situ synchrotron X-ray diffraction was used to monitor structural changes, and a face-centered cubic (fcc) to face-centered tetragonal (fct) distortion was observed for the first time. This novel discovery not only provides new insights into the pressure-induced behavior of faceted nanocrystals of palladium and other noble metals but also gives guidance for finding new phases in close-packed metals.
119278662
Symmetry, Defects, and Gauging of Topological Phases
We examine the interplay of symmetry and topological order in $2+1$ dimensional topological phases of matter. We present a definition of the topological symmetry group, which characterizes the symmetry of the emergent topological quantum numbers of a topological phase $\mathcal{C}$, and we describe its relation with the microscopic symmetry of the underlying physical system. We derive a general framework to classify symmetry fractionalization in topological phases, including phases that are non-Abelian and symmetries that permute the quasiparticle types and/or are anti-unitary. We develop a theory of extrinsic defects (fluxes) associated with elements of the symmetry group, which provides a general classification of symmetry-enriched topological phases derived from a topological phase of matter $\mathcal{C}$ with symmetry group $G$. The algebraic theory of the defects, known as a $G$-crossed braided tensor category $\mathcal{C}_{G}^{\times}$, allows one to compute many properties, such as the number of topologically distinct types of defects associated with each group element, their fusion rules, quantum dimensions, zero modes, braiding exchange transformations, a generalized Verlinde formula for the defects, and modular transformations of the $G$-crossed extensions of topological phases. We also examine the promotion of the global symmetry to a local gauge invariance, wherein the extrinsic $G$-defects are turned into deconfined quasiparticle excitations, which results in a different topological phase $\mathcal{C}/G$. A number of instructive and/or physically relevant examples are studied in detail.
118614871
THE LIKELY ORBITAL PERIOD OF THE ULTRACOMPACT LOW-MASS X-RAY BINARY 2S 0918-549
We report the discovery of the likely orbital period of the ultracompact low-mass X-ray binary (LMXB) 2S 0918-549. Using time-resolved optical photometry carried out with the 8 m Gemini South Telescope, we obtained a 2.4 hr long, Sloan r' light curve of 2S 0918-549 and found a periodic, sinusoidal modulation at 17.4 +/- 0.1 minutes with a semiamplitude of 0.015 +/- 0.002 mag, which we identify as the binary period. In addition to 4U 0513-40 in the globular cluster NGC 1851 and the Galactic disk source 4U 1543-624, 2S 0918-549 is the third member of the ultracompact LMXBs that have orbital periods around 18 minutes. Our result verifies the suggestion that 2S 0918-549 is an ultracompact binary based on its X-ray and optical spectroscopic properties. Given that the donor in 2S 0918-549 has been suggested to be either a C-O or He white dwarf, its likely mass and radius are around 0.024-0.029 M-circle dot and 0.03-0.032 R-circle dot, respectively, for the former case and 0.034-0.039 M-circle dot and 0.033-0.035 R-circle dot for the latter case. If the optical modulation arises from X-ray heating of the mass donor, its sinusoidal shape suggests that the binary has a low inclination angle, probably around 10 degrees.
15557783
ELECTROMAGNETIC FORM-FACTOR OF THE π MESON WITH LIGHT-CONE QCD SUM RULES
In this paper, we calculate the electromagnetic form-factor of the π meson with the light-cone QCD sum rules. The numerical value is in excellent agreement with the experimental data (extrapolated to the limit of zero momentum transfer or the normalization condition Fπ(0) = 1). For large momentum transfers, the values from the two sum rules are all comparable with the experimental data and theoretical estimations.
119270278
Strongly correlated topological superconductors and topological phase transitions via Green's function
We propose several topological order parameters expressed in terms of Green's function at zero frequency for topological superconductors, which generalizes the previous work for interacting insulators. The coefficient in topological field theory is expressed in terms of zero frequency Green's function. We also study topological phase transition beyond noninteracting limit in this zero frequency Green's function approach.
120385604
Von Hove model of quantum field theory‐from the point of view of infinite dimensional stationary Markov process theory
There are two ways to quantize the classical von Hove model. One way is to quantize the classical von Hove field equation, and the other is to quantize the classical energy functional. In this paper, their relation to each other is pointed out. As an application the second‐order approximate quantization of (φ4)2‐kink field is studied.