Non-Stoichiometry Effects on the Extreme Magnetoresistance in Weyl Semimetal WTe_2

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe_2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistance is strongly dependent on the residual resistivity ratio(i.e., the degree of non-stoichiometry),which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe_2.     

新型hollandite结构化合物BiIr_4Se_8单晶的生长,结构与基本物性研究（英文）

通过助溶剂法制得新型单晶BiIr_4Se_8.能量色散X射线谱确定样品元素比例约为Bi:Ir:Se≈1:4:8.利用粉末与单晶X射线衍射技术确定了单晶属于单斜晶系,具有扭曲的hollandite结构,其中的一维通道被Bi原子占据.300K以下的电阻与磁化率测试表明,样品属于半导体,且表现抗磁性.Bi在一维通道的无序暗示该材料是一种潜在的热电材料.这种结构容易受掺杂与压力的影响,为进一步探索5d过渡金属化合物中复杂的物理现象提供了良好的平台.     

层状过渡金属硫代亚磷酸盐材料的磁性研究

采用化学气相输运的方法生长了一系列的MPS_3(M=Mn,Fe,Ni)单晶样品.X射线衍射和电子能谱测试结果表明生长出来的样品是纯相并且单晶质量较好.MPS_3单晶样品在低温下均为反铁磁性.当磁场平行于面内时,磁化率—温度曲线在奈尔点以上存在一个较宽的峰值,可能与准二维磁交换导致的短程序有关.这些现象表明MPS_3体系是一个很好的研究二维材料磁性的平台.此前理论与实验结果显示该体系具有宽带隙,电阻率也很大.因此,MPS_3体系在二维层状材料介电方面有很大的应用前景.