La_(2-x)Sr_xCuO_4体系正常态的低温反常输运与载流子的局域化

Abnormal Transport Behaviors and Carrier Localization at Low Temperatures in the Normal State of La_(2-x)Sr_xCuO_4 System

对 L a2 - x Srx Cu O4 系列 (x =0 .0 6～ 0 .2 0 )样品的电阻率和霍尔系数等输运特性进行了系统研究。电阻率随温度变化的实验结果表明 ,对低掺杂样品 ,在正常态区域 (T >Tc) ,随 Sr掺杂量的增加 ,各样品在低温区超导转变温度附近均发生了金属 -绝缘体转变 ,且转变温度 TMI 随掺杂量的增加逐渐降低 ;对于最佳掺杂样品 ,其金属 -绝缘体转变行为变得非常不明显 ,到 x =0 .18时完全消失。对正常态样品的霍尔系数而言 ,随温度的降低逐渐增大 ,且随 Sr掺杂量的增加显示减小。表明载流子浓度随掺杂量的增加而增加。在低掺杂时 ,接近 Tc的温区内霍尔系数 RH迅速增大 ,随着掺杂量的增加 Tc附近霍尔系数的增大变缓。霍尔系数在 Tc附近的增大 ,表明低温区载流子浓度减少。电阻率和霍尔系数在低温区电输运的这种反常行为可从载流子的局域化角度给予初步解释。

Transport characteristics was systematically studied for La 2-x Sr xCuO 4 system (x=0.06～0.20) with excellent tetragonal phase structures. The normal state resistivity at low temperatures reveals a metal-insulator transition from underdoping to optimum doping, and the transition temperature T MI  decreases with the increase of Sr doped content. The metal-insulator transition is unconspicuous in the optimum doped sample and vanished completely in x=0.18 sample. The hall coefficient R H increases rapidly with the decrease of temperature, and its value decreases drastically with the increase of Sr doped content. The results indicate that the carrier density increases with the increase of Sr doped content. The value of R H near T c increases drastically, and the increment decreases with the increase of Sr doped content. The increase of the hall coefficient R H near T c means that the decrease of carrier density at low temperatures, which suggest that the abnormal transport behaviors of the normal state La 2-x Sr xCuO 4 superconductors at low temperatures are related with the carrier localization near T c.