Low Energy Charge Excitation in Copper Oxide Superconductors

氧化铜超导体中的低能电荷激发

• 批准号: 17340109
• 负责人: TAJIMA Setsuko
• 金额: $ 10.18万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2005
• 资助国家: 日本
• 起止时间: 2005 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17340109/
• 关键词: High Temperature Superconductor; Copper Oxides; Terahertz Spectroscopy; Inhomogeneous Electronic State; サブミリ波領域分光

Single crystals of (Y, Ca)Ba_2Cu_3O_y were grown by a pulling technique and then detwinned by annealing in oxygen atmosphere under uniaxial pressure, followed by post-annealing in O_2 for controlling carrier concentration. In this way, we have obtained samples large enough for Terahertz spectroscopy (〜3x3 mm^2). As to the method for reflectivity measurement in the low frequency region, we have changed from the original plan of usual method with use of BWO tube as a light source to the new method of time domain spectroscopy (TDS) with use of Ti-Sapphire ultra-fast pulse laser. The TDS method is usually carried out with a geometry of transmittance measurement, while there are many difficulties in measurement with a reflectance geometry. The low temperature measurement for samples within a cryostat also gives some additional difficulties. In order to overcome these difficulties, we have improved an optical system as well as a sample holder. The test measurement for a gold mirror and (La,Sr)_2CuO_4 superconductor gave us a satisfactory result.We also measured far-infrared reflectivity spectra of detwinned (Y, Ca)Ba_2Cu_3O_y with polarization parallel to a-and/or b-axes. The a-axis spectrum is expected to represent the charge response within the CuO_2-plane. Compared to the a-axis spectrum for optimally doped YBa_2Cu_3O_y, the spectrum for carrier overdoped sample was found to show lower reflectivity (<100%) even at T≪T_c, which suggests a presence of unpaired carriers. It was also found that this low reflectivity tendency becomes more pronounced in the further overdoped (Y, Ca)Ba_2Cu_3O_y. A possible origin for the unpaired carriers is that some pair-breaking is driven by carrier overdoping or that the phase separation of superconducting and non-superconducting regions takes place. This is very important findings to understand the electronic phase diagram of high-T_c superconductors.

用提拉法生长了（Y，Ca）Ba_2Cu_3O_y单晶，并通过单轴压力下氧气氛退火去孪晶，然后在O_2中进行后退火以控制载流子浓度。通过这种方式，我们已经获得了足够大的太赫兹光谱样品（1.3x3 mm^2）。在低频区反射率的测量方法上，我们从原来的以返波管为光源的常规方法，改变为采用钛宝石超快脉冲激光的时域光谱法。TDS方法通常采用透射测量的几何结构，而采用反射测量的几何结构存在许多困难。低温恒温器内样品的低温测量也带来了一些额外的困难。为了克服这些困难，我们改进了光学系统以及样品保持器。对金镜和（La，Sr）_2CuO_4超导体的实验测量得到了满意的结果，并测量了（Y，Ca）Ba_2Cu_3O_y的退孪晶远红外反射率谱，其偏振方向平行于a轴和/或b轴。a轴谱代表CuO_2面内的电荷响应。与最佳掺杂YBa_2Cu_3O_y的a轴光谱相比，即使在T T_c下，载流子过掺杂样品的光谱也显示出较低的反射率（<100%），这表明存在未成对的载流子。在进一步过掺杂的（Y，Ca）Ba_2Cu_3O_y中，这种低反射率的趋势变得更加明显。不成对载流子的一个可能起源是载流子过掺杂导致的成对断裂，或者超导区和非超导区发生了相分离。这对理解高温超导体的电子相图具有重要意义。

项目成果

Mn substitution effect on superconducting properties of MgB_2 single crystals

Mn取代对MgB_2单晶超导性能的影响

• 发表时间: 2006
• 期刊: Physica C 445-448
• 作者: T.Hiramachi;T.Masui;S.Tajima;R.Lortz;T.Kakeshita;J.Lee;S.Tajima;H.Uchiyama;K.M.Kojima;T.Kakeshita;H.Uchiyama;N.Suemitsu
• 通讯作者: N.Suemitsu

Effects of carbon incorporation on doping state of YBa_2Cu_3O_y

碳掺入对YBa_2Cu_3O_y掺杂状态的影响

• 发表时间: 2005
• 期刊: Physica C 421
• 作者: T.Kakeshita;S.Lee;S.Tajima;S.Tajima;T.Masui;Y.G.Naidyuk;A.Yamamoto
• 通讯作者: A.Yamamoto

Polarization dependence of the electronic Raman spectra of Ca-substituted YBCO single crystals: As a probe of s-wave mixing in the superconducting gap

Ca取代YBCO单晶电子拉曼光谱的偏振依赖性：作为超导间隙中横波混频的探针

• 发表时间: 2007
• 期刊: Physica C 463-465
• 作者: Cheng;X.;F. Niu;P. G. Silver;S. Horiuchi;K. Takai;Y. Iio;and H. Ito;T. Hiramachi et at.
• 通讯作者: T. Hiramachi et at.

Muon spin relaxation studies of magnetic-field-induced effects in high-Tc superconductors.

• DOI: 10.1103/physrevlett.95.157001
• 发表时间: 2004-10
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: A. Savici;A. Fukaya;I. M. Gat-Malureanu;T. Ito;P. L. Russo;Y. Uemura;Christopher R Wiebe;P. Kyriakou;G. MacDougall;M. Rovers;G. Luke;K. Kojima;M. Goto;S. Uchida;R. Kadono;K. Yamada;S. Tajima;T. Masui;H. Eisaki;N. Kaneko;M. Greven;G. Gu

Optimization of oxygenation process in YBCO tapes fabricated by TFA-MOD method

TFA-MOD法制备YBCO带材氧化工艺优化

• 发表时间: 2005
• 期刊: Physica C 426-431
• 作者: T.Kakeshita;S.Lee;S.Tajima;S.Tajima;T.Masui;Y.G.Naidyuk;A.Yamamoto;S.Tsuda;K.Ishii;A.T.Savici;K.Nakao;N.Chikumoto
• 通讯作者: N.Chikumoto