Determination of the surface states from the ultrafast electronic states in a thermoelectric material

We reveal the electronic structure in Yb Cd₂Sb₂,a thermoelectric material,by angle-resolved photoemission spectroscopy(ARPES)and time-resolved ARPES(tr ARPES).Specifically,three bulk bands at the vicinity of the Fermi level are evidenced near the Brillouin zone center,consistent with the density functional theory(DFT)calculation.It is interesting that the spin-unpolarized bulk bands respond unexpectedly to right-and left-handed circularly polarized probe.In addition,a hole band of surface states,which is not sensitive to the polarization of the probe beam and is not expected from the DFT calculation,is identified.We find that the non-equilibrium quasiparticle recovery rate is much smaller in the surface states than that of the bulk states.Our results demonstrate that the surface states can be distinguished from the bulk ones from a view of time scale in the nonequilibrium physics.     

熔融织构YBa2Cu3O7-δ晶体中磁通涡旋锁定转变反常行为研究

通过改变磁场与c轴方向夹角测量了熔融织构YBa₂Cu₃O_7-δ (YBCO)晶体的磁力矩信号响应, 观察到了磁通涡旋系统的锁定(lock-in)转变行为以及锁定转变角正比于外磁场强度的反常现象. 基于Ginzburg-Landau理论和磁通涡旋线Kink结构模型, 对上述锁定转变反常现象进行了分析讨论, 提出了熔融织构YBCO晶体中存在平行于a-b面的延展性关联缺陷结构假设, 导出了锁定转变临界角与温度和磁场之间的关系, 理论分析模型结果与实验测量结果基本符合.     

Y211相粒径对YBCO单畴块材的生长及磁通俘获场的影响

本文研究了Y211相粒径对YBCO单畴块材的生长及磁通俘获场性能的影响.能量色散谱(EDS)分析结果显示:YBCO熔体中的Y离子浓度随着Y211相粒径减小而增加.差示扫描量热法(DSC)热分析结果表明:YBCO熔体的起始结晶温度随着Y211相粒径减小而升高.前驱粉Y123/Y211中使用粒径细化的Y211相能使YBCO单畴块材的磁通俘获场明显增强.上述实验分析结果意味着使用细化的Y211粉体将有助于大尺寸、高性能单畴样品的制备.