YbBi2单晶的电磁特性研究

本文主要研究了YbBi₂单晶的电阻温度特性、磁化强度和温度的关系以及2K时的磁化特性.实验发现YbBi₂单晶具有金属特征;在1.8K以上没有表现出超导电性;其净电阻率之比高达380;YbBi₂单晶是一种顺磁质;电阻温度特性曲线和磁化强度与温度关系都表明:YbBi₂单晶在55K左右发生了明显的相变.     

Bi-2212单晶本征Josephson结的制备及其非线性行为

采用自助熔剂固态反应法制作了Bi2Sr2CaCu2O8+x单晶,使用光刻蚀和Ar离子刻蚀技术在Bi-2212单晶表面制作了台阶结构的Josephson本征结.用三引线和四引线法分别测量了该样品零场下c轴方向的电阻-温度(R-T)关系和恒定温度(14.4K)时的I-V特征曲线.I-V曲线具有典型的多分支非线性行为,并对该实验结果进行了讨论.     

立方C15b型YbCu_(5-x)In_x(0≤x≤1)中的原子混合价态与价态转移

利用电弧熔炼方法制备了YbCu5-xInx(x=0.2,0.4,0.6,0.8,1)稀土金属相间化合物样品.多晶X射线衍射分析表明样品具有立方C15b型结构,并发现其晶胞参数随In含量的增加而线性增加.利用SQUID技术测量了样品在4.2K和300K之间的磁化强度与温度变化曲线,结果表明YbCu4In在40K附近显示出明显的具有一级相变特征的Yb离子价态转移现象;在150K以上YbCu5-xInx样品显示居里-外斯型(Curie-Weiss)型顺磁行为,Yb离子为局域三价态(Yb3+,4f13,J=7/2,μeff=4.54μB),这和先前报道的文献一致.     

Bi2Sr2CaCu2O8单晶的穿透深度研究

从Bi2Sr2CaCu2O8(Bi-2212)单晶临界温度下的可逆磁化强度数据中,考虑高温超导混合态涡旋线涨落对磁化强度的影响,得到穿透深度λab(T,H)的温度和磁场依赖关系.发现在温度远低于Tc时λab与温度存在T2关系.λab随磁场的增加而增加,且绝对零度下的穿透深度λab(0,H)随磁场H的变化符合经验式λab(0,H)=λ0[1+(H/H0)β] ,这里λ0、H0和β为常数.     

零电阻温度高于100K的纯Bi-Sr-Ca-Cu-O材料的制备及其超导电性

采用固相反应法制备名义组分为 Bi_3Sr_2Ca_2Cu_3Oy(3223),Bi_2Sr_2Ca_3Cu_3Oy(2223),Bi_2Sr_2Ca_6Cu_7Oy(2267)的纯 Bi-Sr-Ca-Cu-O 体系的样品.对样品进行了物相分析.电阻率和磁化率测量,结果表明:①组分为3223,2223样品的零电阻温度分别为110.5K 和101K,样品的零电阻温度 T_(ce)与其高 T_c 相的含量并无十分明显的联系;②样品中富 Bi 比富 Ca 更有利于提高零电阻温度.作者认为,样品中富 Bi 有利于改善晶界的导电性能,是提高零电阻温度的主要因素.     

零电阻温度高于100K的纯Bi-Sr-Ca-Cu-O材料的制备及其超导电性

采用固相反应法制备名义组分为 Bi_3Sr_2Ca_2Cu_3Oy(3223),Bi_2Sr_2Ca_3Cu_3Oy(2223),Bi_2Sr_2Ca_6Cu_7Oy(2267)的纯 Bi-Sr-Ca-Cu-O 体系的样品.对样品进行了物相分析.电阻率和磁化率测量,结果表明:①组分为3223,2223样品的零电阻温度分别为110.5K 和101K,样品的零电阻温度 T_(ce)与其高 T_c 相的含量并无十分明显的联系;②样品中富 Bi 比富 Ca 更有利于提高零电阻温度.作者认为,样品中富 Bi 有利于改善晶界的导电性能,是提高零电阻温度的主要因素.     

Bi(Pb)-Sr-Ca-Cu-O(F)超导薄膜

本文介绍用电阻加热、单源混合分层蒸镀的方法制备掺 Pb 的 Bi-Sr-Ca-Cu-O(F)薄膜.我们用钼舟作加热源,用称量法控制膜的组份,采用金属 Bi、Pb、Cu 以及晶体 SrF_2和CaF_2 作原材料,把它们混合放入钼舟内加热蒸发.衬底为单晶 MgO(100).在热处理过程中通入湿氧和干氧,烧结温度850℃,获得了起始转变温度116K,零电阻温度103K 的超导薄膜.     

Bi2Sr2CaCu2O8超导单晶中的电阻反常行为

测量了Bi2 Sr2 CaCu2 O8单晶的ab面和c轴方向电阻 ,在其超导转变温度附近发现了反常的电阻峰出现 .其随外磁场 (>10 0Gs)和电流的增加而逐渐消失 .文章认为这个反常的电阻峰是由于单晶中超导相的不均匀分布而导致的准再进入行为 .     

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.     

用于光纤电流传感器的掺Bi稀土铁石榴石单晶生长与磁光性能

用熔盐法生长了两种Bi替代的高法拉第旋转、温度稳定的稀土铁石榴石磁光单晶Bi-HoYbIG和Bi-GdYIG,测试分析了其在近红外波段的磁光性能及其温度特性。Ho3-z-y,YbyiBixFe512(x＝1.03,y=1.20)单晶的比法拉第旋转角为-891°/cm(λ=1.31μm)和-767°/cm(λ＝1.55μm),Y3-z-yGdyBixFe5O12(x=0.46,y=0.24)单晶的值为－1067°／cm(λ=1.31μm)和-882°／cm(λ=1.55μm),两者都比纯YIG晶体高出许多。而且这两种晶体的法拉第旋转角随温度变化较小,在250～400K范围内,其温度灵敏度S分别为4. 60×10-4／K和4. 20×10-4/K。分析表明,Bi的掺入能大大提高晶体的法拉第旋转角,而yb3+、Gd3+等离子的掺入可以有效降低Bi3+替代磁光单晶的法拉第旋转的温度灵敏性,Bi-HoYbiG和Bi-GdYIG等磁光晶体非常适合作为高灵敏度、温度稳定的光纤电流传感器中的法拉第转子材料。     

Single crystal growth,structural and transport properties of bad metal RhSb_2

We have successfully grown an arsenopyrite marcasite type RhSb2 single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb2 shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with ne = 8.62 × 10¹⁸ cm^-3 at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with ab-initio band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb_2. In addition, a large thermopower S(T) about -140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.     

新型超导体MgB_2的热电势和电阻率研究

测量了MgB-2的热电势和电阻率与温度的依赖关系.在100K—300K区间,热电势呈近似线性温度依赖关系,其斜率为正,表明载流子为空穴型且与能带贡献的图像相一致.与此对应,在此温区电阻率呈T2依赖关系.在100K以下,热电势和电阻率各自转变了其高温区的温度依赖关系.热电势在超导转变温度Te(零电阻36.6K)到100K间有一宽峰,具有声子曳引峰的特征,表明电子-声子相互作用很强.估算了一些重要的参数,如带米能EF、能带宽度等.     

Anomalous pressure dependence of the superconducting transition temperature of beta-pyrochlore AOs2O6 oxides

High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A = Cs,Rb,K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T(c) first increases with increasing pressure in every compound and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa), and 10 K (0.6 GPa) for A = Cs, Rb, and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficient A of the T(2) term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T(c).     

Kinetic coefficients of the semiconducting phase of FeSi2 at low temperatures

The results of studying the kinetic coefficients of β-FeSi₂ in the temperature range 4.2–300 K are considered. The resistivity decreases upon heating in the entire temperature range under investigation. The temperature dependences of the resistivity and thermal conductivity exhibit a break at ～20 K. In the range of 4.2–20 K, the resistivity is a linear function of temperature. The thermo-emf increases rapidly upon cooling and attains values exceeding 15 mV/K. The temperature dependence of the thermo-emf exhibits a break at ～40 K. The observed set of temperature dependences of the kinetic coefficients apparently cannot be explained by a superposition of the known effects only. A new effect probably exists that is associated with a strong electron-phonon interaction in FeSi₂ and which requires a further investigation.     

Electrical resistivities of the uranium carbides

Electrical resistivities of arc-melted uranium carbides, UC, UC₂, U₂C₃ and UC + UC₂, were measured over the temperature range between 4 and 1900 K. The monocarbide, dicarbide and the mixture of carbides showed metallic character in their resistivity dependence on temperature above 30 K, while below this the resistivities were constant. U₂C₃ showed a knee in the resistivity curve at 54.0 K corresponding to a magnetic transition. Above 1100 K, the resistivity of U₂C₃ did not vary with temperature. The resistivity of the mixture (UC + UC₂ with U₂C₃ precipitates) showed an arrest between 800 and 950 K.     

新型超导体MgB2的热电势和电阻率研究

测量了MgB₂的热电势和电阻率与温度的依赖关系.在100K—300K区间,热电势呈近似线性温度依赖关系,其斜率为正,表明载流子为空穴型且与能带贡献的图像相一致.与此对应,在此温区电阻率呈T²依赖关系.在100K以下,热电势和电阻率各自转变了其高温区的温度依赖关系.热电势在超导转变温度T_c(零电阻366K)到100K间有一宽峰,具有声子曳引峰的特征,表明电子-声子相互作用很强.估算了一些重要的参数,如带米能E_F、能带宽度 关键词： 新型超导体 热电势 电阻率     

Temperature-dependent transport in suspended graphene

The resistivity of ultraclean suspended graphene is strongly temperature (T) dependent for 50.5 x 10(11) cm(-2), the resistivity increases with increasing T and is linear above 50 K, suggesting carrier scattering from acoustic phonons. At T=240 K the mobility is approximately 120,000 cm2/V s, higher than in any known semiconductor. At the charge neutral point we observe a nonuniversal conductivity that decreases with decreasing T, consistent with a density inhomogeneity <10(8) cm(-2).     

Electronic properties of Zr-doped TiSe2

Electrical resistivity measurements on substitutionally-Zr-doped TiSe₂ show that the 202 K phase transition in pure TiSe₂ is suppressed by 14 atomic percent Zr. This is the concentration at which the samples are estimated to undergo a semimetal-semiconductor transformation. These results, together with limited electrical resistivity measurements on Te-doped TiSe₂, indicate that both electrons and holes are necessary for the 202 K phase transition to occur.     

Anomalous electrical properties of linear chain mercury compounds

The electrical resistivity of Hg_2.86AsF₆ has been studied as a function of temperature. At room temperature, the resistivity along the chain direction is 10^?4 Ω-cm with an anisotropy of about 10². This incommensurate linear chain system remains metallic at low temperatures with resistance ratio ?_ab(300 K)/ ?_ab(1.4 K) ? 3000 and still increasing with no apparent sign of residual resistivity. A large anisotropic magnetic field dependence of the resistivity is observed below 30 K. Near 4 K, the c-axis resistance drops abruptly more than three orders of magnitude, apparently to zero, while ?_ab is continuous. The c-axis transition is suppressed in a small magnetic field.