【作者】 潘复苏；

【导师】 石兢；

【作者基本信息】 武汉大学 ， 凝聚态物理， 2005， 硕士

【摘要】 自从人们发现了掺杂的二维反铁磁铜氧化合物的高温超导特性后,具有相似的Cu—O键的一维铜氧化合物吸引了更多的研究兴趣。尤其是具有偶数臂的梯状结构的铜氧化合物被预言和高温超导铜氧化合物一样具有自旋能隙,并且理论研究表明这种铜氧化合物在掺杂空穴的条件下可能实现超导。我们研究的Sr_14-xCa_xCu₂₄O₄₁体系是准一维的反铁磁铜氧化合物,具有双臂自旋梯子结构,在自旋链和自旋梯子中都存在自旋能隙,并且在该体系的高Ca含量的掺杂样品中观察到了超导特性。除此以外,Sr_14-xCa_xCu₂₄O₄₁还因它的独特结构体现出了许多新奇的物理特性。本论文从最基础的制备入手,用X射线衍射分析确定其晶格常数,用芯能级光电子发射谱初步研究其电子结构,并且测量其直流电阻率,磁化率和磁比热等温度特性,通过拟合和分析进一步的深入了解该体系的结构本质及其和物理特性之间的密切联系。 首先,我们用传统的固相反应法制备了两个系列的多晶样品Sr_14-xCa_xCu₂₄O₄₁。并主要针对系列Ⅰ即x（Ca）=0,0.4,3.5,6,7,8.4的样品进行系统的研究。 第二,X射线衍射分析表明系列Ⅰ中所有的样品都是单相的,并通过扫描电镜观察这些样品的表面形貌表明晶粒生长较好。通过对X射线衍射谱寻峰和程序拟合得到了系列Ⅰ中所有样品室温下的晶格常数。又因Sr_14-xCa_xCu₂₄O₄₁体系特殊的物理性质与电子结构密切相关,但到目前为止人们对该体系的电子结构所作的研究工作非常少,我们测量了系列Ⅰ样品（除x=0.4以外）的Cu2p_3/2,O1s,Ca2p_3/2和Sr3d_5/2光电子发射谱,并着重讨论了Cu离子的化合价态,得出该体系中的Cu离子主要是+2价的,只存在非常少的+3价Cu离子,Cu离子的平均化合价为+2.25可以通过氧空穴的存在来解释的结论。 第三,我们在10—300K温度范围内测量了不同磁场强度（H=1T,3T,5T）下系列Ⅰ样品（除x=0.4和7外）的磁化率,并进一步对磁化率温度曲线进行拟合。讨论了磁场强度和Ca掺杂量对磁化率尤其是对引起温度60K左右的磁化率宽峰的自旋能隙的影响,并根据拟合参数讨论磁特性与电子态之间的联系。 第四,我们测量了Sr₁₄Cu₂₄O₄₁和Sr_10.5Ca_3.5Cu₂₄O₄₁在2—12K和50—90K温区内的零磁场和磁场强度H=3T时的比热温度特性。先拟合和分析2-12K低温区的比热,给出低温比热中各比热项的系数α、γ、β值以及对应的德拜温度（?）_P、费密温度T_F更多还原

【Abstract】 After the high-temperature superconductivity was discovered in doped two-dimensional antiferromagnetic copper oxides, one dimensional cuprates with the same Cu-O bonds have attracted much interest. Particularly, ladders with even legs are predicted to have a finite spin gap reminiscent of that in underdoped high-Tc cuprates, and the theoretical works suggest a possibility of superconductivity when doped with holes. The system Sr₁4-xCa_xCu₂4O₄1 we have studied is a kind of quasi-one-dimensional antiferromagnetic copper oxide, consists of two-legs ladders （Cu₂O₃）, spin gap exists in both spin chains （CuO₂） and ladders （Cu₂O₃）. In particular, superconductivity has been found in high Ca content doped compounds of this system. In this thesis, we exhibit several experimental investigations on this kind of ladder compounds.Firstly, we prepared two series of samples with the conventional solid state reaction method. And our systematic study was aimed at the first series, namely Sr₁4-xCa_xCu₂4O₄1 compounds with x （Ca） = 0,0.4, 3.5, 6, 7, 8.4.Secondly, we confirmed all the samples of the first series are of single phase by x-ray diffraction analysis and found the crystal grains have grown well by observed the surfaced pattern with scanning electronic microscope. The unit cell parameters of all the samples of the first series at room temperature were identified through peak-seeking and fitting program. We measured the Cu 2p ₃/2、 O 1s、Ca 2p₃/2 and Sr 3d₅/2 photoelectron emission spectra and mainly discussed the valence of Cu ions. The results reveal that the valence of Cu ions in this system is mainly +2, Cu⁺3 ions is very few and the existence of O holes can explain for the average valence +2.25 of Cu ions.Thirdly, we measured the magnetic susceptibilities of the various samples of the first series （except for x（Ca）= 0.4, 7 ） under different magnetic intensities（H= 1T, 3T, 5T） within the temperature range of 10-300K. The effect of the doping of Ca and the magnetic field on the magnetic susceptibility, particularly the effect on spin gap related to the broad peak of the magnetic-field intensity around 60K is discussed. Furthermore, we fitted theexperimental data and discussed the connection between magnetic property and electronic state.Fourthly, we measured the specific heat of Sri4Cu24O4i and Srio^Ca3.5Cu2404i under different magnetic-field intensities （zero and 3 Tesla） within the temperature range of 2-12K and 50-90K respectively. The experimental data of the specific heat within 2-12K give out the coefficients of each term of specific heat （a > Y ^ ^）. Base on these results we figured out the value of Debye temperature ?o ^ Fermi temperature TF and Fermilevel EF .We found the linear term of the specific heat is abnormally large and discussedthe effect on the specific heat by the doping of Ca and the magnetic-field intensities. Furthermore, we analysed the abnormality of specific heat within 50-90K.We connected this abnormality with the spin gap dued to the formation of dimer in the O1O2 chains and suggest that the doping of Ca and the magnetic intensities don’t effect the open of spingap-Finally, we measured the dc-resistivity of Sri4Cu24O4i within the temperature range of 80-280K. The semiconductor behavior of Sri4Cu24O4i was confirmed. We identified the temperature Tp below which holes in the G12O3 ladders are localized. Accordingly, thereare two kinds of active energies: 82meV （belowTp） and 106meV （above Tp）.更多还原