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Study on the Physical Properties of High-Tc Superconductors by Interlayer Tunneling Spectroscopy

高温超导体物理性质的层间隧道光谱研究

基本信息

批准号：
12640344
负责人：
SUZUKI Minoru
金额：
$ 1.98万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

1. Epitaxial Growth of La_<1.9>Sr_<0.1>CuO_4 Superconducting Thin Films by Magnetron SputteringLa_<1.9>Sr_<0.1>CuO_4 (001) superconducting thin films are grown on SrTiO3 (100) substrates by rf magnetron sputtering at substrate temperatures of 730 to 770 C. The films are metallic and exhibit superconducting transition at 29 K.2. Reduction in Contact Resistance of Au Electrodes onto La_<1.9>Sr_<0.1>CuO_4 (001) Thin FilmsBy means of in situ sputter-cleaning and Au evaporation combined with rapid thermal annealing, the contact resistance is reduced to, 1x10^<-50>Ωcm^2, which is applicable to the small mesa upper electrode.3. Fabrication and Tunneling Characteristics of Small MesasSmall mesas are fabricated by Ar ion milling and photolithography on the surface of thin films with a lateral dimension of 10x10mm and a thickness of 13 nm, which corresponds to 20 CuO_2 layers. The Mesas exhibit metallic behavior with a resistivity of 13 Ωcm at 300 K. The mesas show current-voltage characteristics of a resistively shunted junction.4. Short Pulse Tunneling Spectroscopy Using Bi_2Sr_2CaCu_2O_<8+8> Intrinsic Josephson JunctionsUsing small mesas fabricated on top of cleaved surface of Bi_2Sr_2CaCu_2O_<8+8> single crystals with different doping levels, it is found that the superconducting gap and the pseudogap is definitely different. This is particularly clear in the underdoped specimens. This experimental result implies that the fluctuation model of high-T_c superconductivity-is ruled out.5. Extension of Energy Range for Short Pulse Interlayer Tunneling SpectroscopyPulse wave form reformation from a rectangular to a combined wave form consisting of rectangular and half-period sinusoidal wave form leads to a significant improvement of break-down voltage from 100 mV for a single junction in the conventional case to greater than 200 mV. Almost no breakage of specimen takes place during measurements within this range.

1.磁控溅射法外延生长La_<1.9>Sr_<0.1>CuO_4超导薄膜<1.9><0.1>采用射频磁控溅射法在SrTiO_3（100）衬底上生长La_Sr_ CuO_4（001）超导薄膜，衬底温度为730 ~ 770 ℃。薄膜是金属的，并表现出超导转变在29 K。降低La_<1.9>Sr_<0.1>CuO_4（001）薄膜上Au电极的接触电阻采用原位清洗和Au蒸发结合快速热退火的方法，使接触电阻降低到1 × 10 ^<-50>Ω cm ^2，适用于小梅萨上电极.用Ar离子刻蚀和光刻技术在横向尺寸为10 × 10 mm、厚度为13 nm的CuO_2薄膜表面上制备了20层CuO_2层的小台面。在300 K时，Mesa的电阻率为13 Ωcm，表现出金属性.台面显示了反向分流结的电流-电压特性.利用Bi_2Sr_2CaCu_2O_（8+8）本征Josephson结的短脉冲隧道谱研究在不同掺杂水平的Bi_2Sr_2CaCu_2O_（8+8）单晶解理面上制作小台面，发现超导带隙和赝带隙明显不同。这在低掺杂样品中特别明显。这一实验结果表明，高T_c超导的涨落模型被排除.短脉冲层间隧道能谱能量范围的扩展脉冲波形由矩形波改造为矩形波和半周期正弦波的组合波形，使单结击穿电压由传统情况下的100 mV提高到200 mV以上。在此范围内的测量过程中，几乎不会发生试样断裂。