Modern Physics Letters B

This paper gives a systematic review on studies of dimensional effects in pure- and quasi-two-dimensional (2D) Bose gases, focusing on the role of dimensionality in the fundamental relation among the universal behavior of breathing mode, scale invariance and dynamic symmetry. First, we illustrate the emergence of universal breathing mode in the case of pure 2D Bose gases, and elaborate on its connection with the scale invariance of the Hamiltonian and the hidden SO(2, 1) symmetry. Next, we proceed to quasi-2D Bose gases, where excitations are frozen in one direction and the scattering behavior exhibits a 3D to 2D crossover. We show that the original SO(2, 1) symmetry is broken by arbitrarily small 2D effects in scattering, which consequently shifts the breathing mode from the universal frequency. The predicted shift rises significantly from the order of 0.5% to more than 5% in transiting from the 3D-scattering to the 2D-scattering regime. Observing this dimensional effect directly would present an important step in revealing the interplay between dimensionality and quantum fluctuations in quasi-2D.

In this paper, we investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant nonlinear Schrödinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex–antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex–antivortex pair into multiple vortex rings and ultimately into sound waves.

In this paper, we studied the electromagnetic wave scattered by a time reversal symmetry broken topological insulator circular cylinder. According to the constitutive relations of topological insulator and Maxwell's equation, we derived the scattered electromagnetic fields and scattered coefficients. Numerical results show that the scattered width of the time reversal symmetry topological insulator circular cylinder is extraordinarily different from the width produced by the time reversal symmetry broken topological insulator.

The energy transfer from Tb³⁺ to Eu³⁺ co-doped TiO₂(TiO₂:Tb, Eu) inverse opal photonic crystals was investigated by photoluminescence. The results showed that the photonic band gap enhanced energy transfer from the donor Tb³⁺ to the acceptor Eu³⁺. When the fluorescence emission wavelength of Tb³⁺ overlaps with the photonic band gap, the fluorescence intensity of Tb³⁺ is suppressed, while the fluorescence intensity of Eu³⁺ is enhanced. Energy transfer efficiencies were attributed to the tuning effects of energy transfer in the photoluminescence process by photonic crystal structure.

The electronic structure, lattice dynamics, and electron–phonon (e–ph) coupling constant λ for the superconducting Ca_0.88Pr_0.12Fe₂As₂ are obtained by first principles calculations using norm-conserving pseudopotentials within virtual-crystal approximation treatment. The obtained λ for Ca_0.88Pr_0.12Fe₂As₂ is 0.45. Combined with the e–ph coupling constants λ for the superconducting CaFe₂As_1.925P_0.075 and vicinity of collapsed tetragonal phase of CaFe₂As₂, we show that although the obtained λ for them cannot account for the high superconducting transition temperatures T_C, they are a factor of two larger than that estimated in early calculations using the ultrasoft pseudopotentials for that of vicinity of collapsed tetragonal phase of CaFe₂As₂. We confirm that superconductivity in CaFe₂As₂ is not primarily phonon mediated. Nevertheless, the e–ph interactions are strong enough to be not negligible to investigate the superconductivity.

A simple plasmonic filter with symmetrical tooth-shaped waveguides is proposed and investigated by using finite element method. It is found that the structure with a single symmetrical tooth-shaped waveguide couple can realize a tunable band-stop filter. Attributed to cascaded symmetrical tooth-shaped waveguide couples, the structure can achieve a flat band-stop response with no intensity variation over the transmission spectrum. And the central wavelength of the stopband linearly increases with the simultaneous increasing of depths of waveguides. Moreover, reduced structure size can be achieved by controlling the dielectric constant of the medium.

We study the competition between a Pomeranchuk instability in the spin channel with angular momentum ℓ = 1 and an attractive interaction, favoring Cooper-pair formation. We found that the superconducting gap strongly suppresses the phase space for the Pomeranchuk instability. We computed a mean-field phase diagram displaying a first order transition between two superconductor phases with different symmetries: p-wave (with spontaneously generated spin-orbit interaction) and s-wave for greater values of the coupling constant. Moreover, we have looked for a possible modulated superconducting phase. We have found that this phase appears only as a metastable state in the strong coupling regime.

NiCr/NiSi thin film thermocouples (TFTCs) with a multi-layer structure were fabricated on Ni-based superalloy substrates (95 mm × 35 mm × 2 mm) by magnetron sputtering and electron beam evaporation. The five-layer structure is composed of NiCrAlY buffer layer (2 μm), thermally grown Al₂O₃ bond layer (200 nm), Al₂O₃ insulating layer (10 μm), NiCr/NiSi TFTCs (1 μm), and Al₂O₃ protective layer (500 nm). Influences of thermocouple layer thickness on thermoelectric properties were investigated. Seebeck coefficient of the samples with the increase in thermocouple layer thickness from 0.5 μm to 1 μm increased from 27.8 μV/°C to 33.8 μV/°C, but exhibited almost no change with further increase in thermocouple layer thickness from 1 μm to 2 μm. Dependence on temperature of the thermal electromotive force of the samples almost followed standard thermocouple characteristic curves when the thickness of the thermocouple layer was 1 μm and 2 μm. Sensitive coefficient K of the samples increased greatly with the increase in thickness of the thermocouple layer from 0.5 μm to 1 μm, but decreased insignificantly with the increase in thermocouple layer thickness from 1 μm to 2 μm, and continuously decreased with the increase in temperature. The sensitive coefficient and the stability of NiCr/NiSi TFTCs were both improved after annealing at 600°C.

In this paper, we investigate the transport properties of HgTe/CdTe-based topological insulator quantum dots (TIQDs) under magnetic field. Both disk and square shaped TIQDs are considered and the magneto-conductance are calculated numerically for various magnetic field strength. The magnetic field lifts the spin degeneracy, leading to spin polarized current at given Fermi energy. Meanwhile, the magneto-conductance demonstrates the Aharonov–Bohm (AB) oscillation with a period of one flux quantum . Numerical results for AB oscillation features indicate the mismatch between electron (e) and hole (h) doping conditions, which can be attributed to the e–h asymmetry in the full band Hamiltonian. Further, interference effect emerges around bulk and edge energy degenerate points, subsequently suppressing the magneto-conductance in both shaped systems. All these physical characteristics are qualitatively consistent for disk and square shaped TIQDs due to the topological nature of edge modes.

We study the Bose–Einstein condensate trapped in a three-dimensional spherically symmetrical potential. Exact solutions to the stationary Gross–Pitaevskii equation are obtained for properly modulated radial nonlinearity. The solutions contain vortices with different winding numbers and exhibit the shell-soliton feature in the radial distributions.

In this paper, we report an efficient preparation of silver telluride by rapid solid-state microwave heating. Single phase products have been obtained within as little as 30 min of irradiation time. The rate of the synthesis is significantly increased as compared to the solid state reaction method in a conventional furnace. The quality of the as-prepared samples are attested by structural, compositional and magnetoresistance characterizations.