arXiv subjects

Yingxu Li

Publications and source records attributed to Yingxu Li.

5 recordsLinked to original sources

arXiv2020

Room-temperature quasi-continuous-wave pentacene maser pumped by an invasive Ce:YAG luminescent concentrator

We present in this work a quasi-continuous-wave (CW) pentacene maser operating at 1.45 GHz in the Earth's magnetic field at room temperature with a duration of $\sim$4 ms and an output power of up to -25 dBm. The maser is optically pumped by a cerium-doped YAG (Ce:YAG) luminescent concentrator (LC) whose wedge-shaped output is embedded inside a 0.1% pentacene-doped para-terphenyl (Pc:Ptp) crystal. The pumped crystal is located inside a ring of strontium titanate (STO) that supports a TE$_{01δ}$ mode of high magnetic Purcell factor. Combined with simulations, our results indicate that CW operation of pentacene masers at room-temperature is perfectly feasible so long as excessive heating of the crystal is avoided.

physics.app-ph↗

arXiv2017

Magneto-elastic coupling model of deformable anisotropic superconductors

We develop a magneto-elastic (ME) coupling model for the interaction between the vortex lattice and crystal elasticity. The theory extends the Kogan-Clem's anisotropic Ginzburg-Landau (GL) model to include the elasticity effect. The anisotropies in superconductivity and elasticity are simultaneously considered in the GL theory frame. We compare the field and angular dependences of the magnetization to the relevant experiments. The contribution of the ME interaction to the magnetization is comparable to the vortex-lattice energy, in materials with relatively strong pressure dependence of the critical temperature. The theory can give the appropriate slope of the field dependence of magnetization near the upper critical field. The magnetization ratio along different vortex frame axes is independent with the ME interaction. The theoretical description of the magnetization ratio is applicable only if the applied field moderately close to the upper critical field.

cond-mat.supr-con↗

arXiv2016

Anisotropic critical-state model of type-II superconducting slabs

We introduce a critical-state model incorporating the anisotropy of flux-line pinning to analyze the critical states developing in an anisotropic biaxial superconducting slab exposed to a uniform perpendicular magnetic field and to two crossed in-plane magnetic fields which are applied successively. The theory is an extension of the anisotropic collective pinning theory developed by Mikitik and Brandt. The anisotropic flux-line pinning enters into the critical states by generating the angular dependence of the critical current density and by deviating the direction of the electric field from the current in the plane perpendicular to the vortex line. We find that an enhanced in-plane anisotropy moderates the gradients of the magnitudes of the magnetic field and the electric field along the slab thickness, however increases the gradients of their rotations.

cond-mat.supr-con↗

arXiv2015

Scaling laws for the critical current density in anisotropic biaxial superconductors

To understand the anisotropy of flux pinning and critical current density in technological superconductors, the scaling law for the anisotropy of single-vortex collective pinning in uniaxial superconductors is extended to flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the critical current density is described by a unified function with the magnetic field of the scaled isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

cond-mat.supr-con↗

arXiv2015

Superconducting properties variation with A15 composition in Nb3Sn

We extend the Ginzburg-Landau-Abrikosov-Gor'kov (GLAG) theory to account for the variation of the upper critical field Hc2 with Sn content in A15-type Nb3Sn. Hc2 at the vicinity of the critical temperature Tc is related quantitatively to the electrical resistivity, specific heat capacity coefficient and Tc, with inclusion of the electron-phonon coupling correction, Pauli paramagnetic limiting and martensitic phase transformation of A15 lattices. Hc2 near Tc is then extrapolated to Hc2(0) at temperature 0K, and Hc2(0) versus tin content agrees well with experiments. We find that, as Sn content gradually approaches the stoichiometry, Nb3Sn undergoes a transition from the dirty limit to clean limit, split by the phase transformation boundary. The H-T phase boundary and the pinning force show different behaviors in the cubic and tetragonal phase. Applying the theoretical formulas in the technical Nb3Sn wire, we obtain the dependence of the composition gradient on the superconducting properties variation in the A15 layer, as well as the curved tail at vicinity of Hc2 in the Kramer plot of the Nb3Sn wire. This gives a better understanding of the inhomogeneous-composition inducing discrepancy between the results by the state-of-art scaling laws and experiments.

cond-mat.supr-con↗