arXiv subjects

W. M. Li

Publications and source records attributed to W. M. Li.

4 recordsLinked to original sources

arXiv2023

Simulation study of intra-beam scattering effect in the HALF storage ring with Piwinski model

The Hefei Advanced Light Facility (HALF) will be a VUV and soft X-ray diffraction-limited storage ring (DLSR), and its high density of electron bunches makes the intra-beam scattering (IBS) effect very serious. In this paper, an IBS module used in the IMPACT code is developed, where the scattering process of IBS is described by the Piwinski model in Monte Carlo sampling. For benchmarking, the IMPACT code with IBS module is compared with the ELEGANT code and a semi-analytic code using Bane's model. Then, the results of IBS effect in the HALF storage ring studied by this new code are presented. With various countermeasures, the IBS impact can be controlled to a certain extent, and the expected beam emittance is approximately 59 pm.rad.

physics.acc-ph↗

arXiv2019

Superconductivity in a unique type of copper oxide

The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics.High Tc cuprates crystallize into layered perovskite structure featuring copper oxygen octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high Tc cuprates are elongated along the c axis, leading to a 3dx2-y2 orbital at the top of the band structure wherein the doped holes reside.This scenario gives rise to two dimensional characteristics in high Tc cuprates that favor d wave pairing symmetry. Here we report superconductivity in a cuprate Ba2CuO4-y wherein the local octahedron is in a very exceptional compressed version.The Ba2CuO4-y compound was synthesized at high pressure at high temperatures, and shows bulk superconductivity with critical temperature Tc above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the Tc for the isostructural counterparts based on classical La2CuO4. X-ray absorption measurements indicate the heavily doped nature of the Ba2CuO4-y superconductor. In compressed octahedron the 3d3z2-r2 orbital will be lifted above the 3dx2-y2 orbital, leading to significant three dimensional nature in addition to the conventional 3dx2-y2 orbital. This work sheds important new light on advancing our comprehensive understanding of the superconducting mechanism of high Tc in cuprate materials.

cond-mat.supr-con↗

arXiv2016

Superconductivity in HfTe5 Induced via Pressures

Recently, ZrTe5 and HfTe5 are theoretically studied to be the most promising layered topological insulators since they are both interlayer weakly bonded materials and also with a large bulk gap in the single layer. It paves a new way for the study of novel topological quantum phenomenon tuned via external parameters. Here, we report the discovery of superconductivity and properties evolution in HfTe5 single crystal induced via pressures. Our experiments indicated that anomaly resistance peak moves to low temperature first before reverses to high temperature followed by disappearance which is opposite to the low pressure effect on ZrTe5. HfTe5 became superconductive above ~5.5 GPa up to at least 35 GPa in the measured range. The highest superconducting transition temperature (Tc) around 5 K was achieved at 20 GPa. High pressure Raman revealed that new modes appeared around pressure where superconductivity occurs. Crystal structure studies shown that the superconductivity is related to the phase transition from Cmcm structure to monoclinic C2/m structure. The second phase transition from C2/m to P-1 structure occurs at 12 GPa. The combination of transport, structure measurement and theoretical calculations enable a completely phase diagram of HfTe5 at high pressures.

cond-mat.supr-con↗

arXiv2014

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3

Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

cond-mat.supr-con↗