电子型超导体Sm_(2-x)Ce_xCuO_4(0.00≤x≤0.21)的异常热电势与电阻率  

Anomalous thermopower and resistivity of the electron-doped superconductor Sm_(2-x)Ce_xCuO_4(0.00≤x≤0.21)

作　　者：余旻[1] 杨宏顺[1] 柴一晟[1] 阮可青[1] 李鹏程[1] 李志权[1] 陈兆甲[1] 曹烈兆[1] 

机构地区：[1]中国科学技术大学结构分析开放实验室,物理系合肥230026

出　　处：《物理学报》2002年第3期674-678,共5页Acta Physica Sinica

基　　金：国家重点基础研究项目 (批准号 :G199906 46 )资助的课题~~

摘　　要：测量了Sm2 -xCexCuO4(0 0 0≤x≤ 0 2 1)多晶样品的热电势S和电阻率 ρ的温度依赖关系 .在缘绝体—金属转变边界处 ,观测到热电势从绝缘体区明显的弱温度依赖关系到金属区线性温度依赖关系的转变 .当Ce的含量由0 0 9增加到 0 2 1时 ,高温下S的斜率发生由负到正的转变 ,这是能带的填充能级发生改变时电子型和空穴型载流子的贡献发生竞争的表现 ,由电子型向空穴型的过渡发生在x =0 17处 .S和 ρ在 2 0 0K以下的斜率变化是载流子局域化造成的 .x=0 0 6— 0 2 1的样品在 5 0K处观察到一个正的曳引峰 .室温下的热电势S3 0 0K 和S0 (高温区热电势线性外推到 0K的值 )与Ce含量在绝缘体、欠掺杂和过掺杂区域有不同的依赖关系 .过掺杂区域很小的S3 0 0K 和S0意味着一个宽带的费米液体的贡献 ,同时 ρ满足T2 关系 ,二者相一致 .The temperature-dependence of thermopower S and resistivity ρ for Sm 2-xCe xCuO 4 polycrystalline samples with 0.00≤x≤0.21 has been measured. A definite change of thermopower from weakly temperature-dependent to the linearly temperature-dependent above 200K is observed on the insulator-metal transition border. The slope of the high-temperature thermopower changes from negative to positive when the Ce concentration increases from 0.09 to 0.21, suggesting a competition between electron-type and hole-type contributions for charge carriers when the filling level in the energy band is changed. The crossover of charge carriers from electron-type to hole-type hoccurs at x=0.17. The change of slope of thermopower and resistivity below about 200K is corresponding to the localization of carriers. A positive excitation-drag contribution for thermopower near 50K is observed in samples with 0.06≤x≤0.21, indicating that the sign of the carriers is changed. The room-temperature and zero-offset thermopowers present three different Ce concentration relationships in the insulator underdoped and overdoped regions, respectively. The small value and the weak Ce content dependence of S 300K and S 0 in the overdoped region indicate that the contribution is from a wide band contribution of the Fermi-liquid, which is supported by the resistivity result(obeying T 2 law in the overdoped region).

关 键 词：电子型超导体 输运性质 热电势 电阻率 Sm2-xCexCuO4 超导铜氧化合物 

分 类 号：TM26[一般工业技术—材料科学与工程]