Yan-Bin Chen

Acoustic topological insulator and robust one-way sound transport

The acoustic analogue of a topological insulator is shown: a metamaterial exhibiting one-way sound transport along its edge. The system — a graphene-like array of stainless-steel rods — is a promising new platform for exploring topological phenomena.

Tunable photonic crystals with superconductor constituents

Abstract In this paper, we propose a two-dimensional square superconductor photonic crystal (PC) with its band gap tunable. By means of plane-wave-expansion (PWE), we calculated the photonic band structure of E mode under different parameters. The results show that a photonic band gap, which is temperature-dependent, appears at temperatures lower than 0.86Tc (Tc is the phase transform temperature of the superconductor) due to the lowest photonic energy band being flattened. Such a photonic crystal can be used as temperature-controlled optical shutter. Moreover, the feasibility of realizing this kind of photonic crystal is also discussed.

Tunable negative refractions in two-dimensional photonic crystals with superconductor constituents

In this paper, a two-dimensional square photonic crystal (PC) with superconductor cylinders is proposed to realize tunable negative refraction. Based on the dependence of the superconductors’ permittivity on temperatures, photonic band structures thus negative refraction could be tuned by temperatures, whereby the refractive angle could be scanned from positive to negative. The feasibility of the PC operating in infrared and visible regions was discussed. The tunability resulted from the lattice, superconductors, operating frequency, and incident angle may lead the PC to great promise in photoelectronics and superconductor electronic applications.

Crucial effects of coupling coefficients on quasi-phase-matched harmonic generation in an optical superlattice.

Coupling of optical parametric processes in an optical superlattice through quadratic nonlinearity was analyzed theoretically. Solving the coupled equations, we found that efficient quasi-phase-matched third-harmonic (TH) generation depends not only on the magnitude of the coupling coefficients but also on their ratio. Theoretically, all the fundamental energy can be transferred to the TH at a particular ratio. In other cases, there exists an optimum condition that corresponds to a maximum TH conversion efficiency. The result is of practical importance for the design of TH devices.

Dirac line nodes and effect of spin-orbit coupling in the nonsymmorphic critical semimetals MSiS (M = Hf, Zr)

Topological Dirac semimetals (TDSs) represent a new state of quantum matter recently discovered that offers a platform for realizing many exotic physical phenomena. A TDS is characterized by the linear touching of bulk (conduction and valance) bands at discrete points in the momentum space [i.e., three-dimensional (3D) Dirac points], such as in Na3Bi and Cd3As2. More recently, new types of Dirac semimetals with robust Dirac line nodes (with nontrivial topology or near the critical point between topological phase transitions) have been proposed that extend the bulk linear touching from discrete points to one-dimensional (1D) lines. In this paper, using angle-resolved photoemission spectroscopy (ARPES), we explored the electronic structure of the nonsymmorphic crystals MSiS (M = Hf, Zr). Remarkably, by mapping out the band structure in the full 3D Brillouin zone (BZ), we observed two sets of Dirac line-nodes in parallel with the k(z) axis and their dispersions. Interestingly, along directions other than the line nodes in the 3D BZ, the bulk degeneracy is lifted by spin-orbit coupling (SOC) in both compounds with larger magnitude in HfSiS. Our paper not only experimentally confirms a new Dirac line-node semimetal family protected by nonsymmorphic symmetry but also helps understanding and further exploring the exotic properties, as well as practical applications of the MSiS family of compounds.

Second-harmonic and third-harmonic generation in a three-component fibonacci optical superlattice

Harmonic generation in a three-component Fibonacci optical superlattice (3CFOS) is analysed theoretically. The Fourier spectrum of the structural function of the 3CFOS is numerically calculated. The positions of reciprocal vectors are in good agreement with the theoretical prediction. The intensities of the second harmonic (SH) and third-harmonic (TH) are calculated relative to the depletion of the fundamental. The dependence of the SH and TH intensity on structural parameters is discussed. Numerical calculation shows that, compared with two-component Fibonacci optical superlattice (2CFOS), there are more plentiful harmonic spectrum and adjustable structure parameters in 3CFOS. By chosen the reciprocal vectors and adjusted the structure parameters, the higher transform efficiency of THG is obtained.

Fabrication and characteristics of high-capacity LiNi0.8Co0.15Al0.05O2 with monodisperse yolk–shell spherical precursors by a facile method

The structure of yolk–shell microspheres is attractive because it exhibits excellent structural stability during lithiation; monodispersed crumpled yolk–shell spherical precursors of LiNi0.8Co0.15Al0.05O2 were obtained via a general and simple supersonic atomization method. After mixing with LiNO3, this cathode material showed a high discharge capacity of about 225.9 mA h g−1 and a good cycle performance at 0.2 C, which is higher than previously reported studies.

Composition dependent phase transition and its induced hysteretic effect in the thermal conductivity of WxMo1−xTe2

Recently, transition metal dichalcogenide (TMD) materials have shown promise in electronics and optoelectronics applications. Most of their properties are closely related to their abundant structural phases and phase transitions. For more practical applications in the future, it is necessary to tune the phase transitions in this material system. Here, we demonstrate the modulation of phase transitions in miscible WxMo1−xTe2 samples by appropriate alloying. The temperature dependent thermal conductivity along the c-axis, which strongly relates to the phase structures and the defect level, has been measured using the time-domain thermoreflectance method. In addition, a tunable hysteretic effect, induced by phase transitions, is observed in both thermal and electrical transport properties and confirmed by the consistent hysteresis in the Raman spectroscopic study. This hysteretic effect can be applied to realize phase-change storage devices. Furthermore, we provide a phase diagram to illustrate the compositi...

Construction of 3D Metallic Nanostructures on an Arbitrarily Shaped Substrate

Constructing conductive/magnetic nanowire arrays with 3D features by electrodeposition remains challenging. An unprecedented fabrication approach that allows to construct metallic (cobalt) nanowires on an arbitrarily shaped surface is reported. The spatial separation of nanowires varies from 70 to 3000 nm and the line width changes from 50 to 250 nm depending on growth conditions.

Observation of spin-orbit magnetoresistance in metallic thin films on magnetic insulators

A new type of spin-orbit magnetoresistance effect is observed in Cu/YIG with interface decorated with nanosize Pt islands. A magnetoresistance (MR) effect induced by the Rashba spin-orbit interaction was predicted, but not yet observed, in bilayers consisting of normal metal and ferromagnetic insulator. We present an experimental observation of this new type of spin-orbit MR (SOMR) effect in the Cu[Pt]/Y3Fe5O12 (YIG) bilayer structure, where the Cu/YIG interface is decorated with nanosize Pt islands. This new MR is apparently not caused by the bulk spin-orbit interaction because of the negligible spin-orbit interaction in Cu and the discontinuity of the Pt islands. This SOMR disappears when the Pt islands are absent or located away from the Cu/YIG interface; therefore, we can unambiguously ascribe it to the Rashba spin-orbit interaction at the interface enhanced by the Pt decoration. The numerical Boltzmann simulations are consistent with the experimental SOMR results in the angular dependence of magnetic field and the Cu thickness dependence. Our finding demonstrates the realization of the spin manipulation by interface engineering.