Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4

Magnetic excitations for energies up to approximately 100 meV are studied for overdoped La(2-x)Sr(x)CuO(4) with x=0.25 and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, 20 相似文献   

La_(1．6-x)Nd_(0．4)Sr_xCuO_4超导电性的反常特性

分析并讨论了La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列单相性样品(x=0．08～0．25)的晶体结构和超导电性。结果表明,晶体结构随着Sr掺杂量的变化规律与La_(2-x)Sr_x CuO_4系列相似。超导电性方面,La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列超导转变温度均远小于相应的La_(2-x)Sr_xCuO_4系列组分。同La_(1．875)Ba_(0．125)CuO_4相似,La_(1．48)Nd_(0．4)Sr_(0．12)CuO_4处出现显著的极小值8K但高于La_(1．875)Ba_(0．125)CuO_4。La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列的超导电性明显与La_(2-x)Sr_x CuO_4系列有着不同的特性,虽然同La_(2-x) Ba_xCuO_4系列相似但仍有区别。我们从其晶体结构的反常变化的角度对La_(1．6-x)Nd_(0．4)Sr_x CuO_4系列反常的超导电性做了初步的解释。     

Anomalous millimeter-wave absorption in the superconducting phase of La2−x SrxCuO4

Direct measurements of the complex conductivity spectra of thin-film La_2−2x Sr_xCuO₄ are made at frequencies of 5–40 cm⁻¹. Narrow, intense Drude-type excitation is observed in the superconducting phase. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 406–409 (10 September 1998)     

La1.4-xNd0.6SrxCuO4中的一维电子结构

1995年,Ｔｒａｎｑｕａｄａ等通过中子散射实验首先在Ｌａ16-ｘＮｄ04ＳｒｘＣｕＯ4中观察到一维自旋-电荷密度的调制,即所谓条纹相.当ｘ=1/8,电荷条纹的周期恰好是4ａ(ａ是四方ＣｕＯ2平面的晶格常数),而自旋的调制周期是8ａ.具体说,可运动的电荷载流子被限制在很窄的一维条纹内,在电荷条纹之间是自旋反铁磁排列的绝缘区;在跨越电荷条纹时,自旋序的位相翻转.早在1989年,Ｚａａｎｅｎ等就曾预言:在掺杂过渡金属氧化物中可能存在条纹相.不过,根据平均场理论作出的上述预言所导致的直接结果是:条纹相是整体绝缘的.这与掺杂铜氧化物中的实际情…     

Metallic nonsuperconducting phase and D-wave superconductivity in Zn-substituted La1.85Sr0.15CuO4

Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La1.85Sr0.15CuO4, with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d-wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k(F)l approximately 1, and appears to be disorder driven, with the carrier concentration unaffected by doping.     

Disappearance of the resistivity peak and possibility of the conductivity peak in overdoped ferromagnets

At large charge carrier densities the resistivity peak close to the Curie point and colossal negative magnetoresistance common for degenerate ferromagnetic semiconductors disappear. Instead of them a conductivity peak and positive magnetoresistance may appear. Necessary conditions for this are an incomplete spin polarisation of charge carriers and a dominating role of the magnetoimpurity scattering.     

Theory of the electronic structure and spin susceptibility of La2−x SrxCuO4

We solve the problem of the effect of strong electron correlations on the homogeneous spin susceptibility of current carriers in CuO₂ planes. We show that the dependence of the spin susceptibility χ(T) of high-T _c superconductors of the La_2−x Sr_xCuO₄ type on temperature and the doping index x can be explained fairly well by the two-band model suggested earlier (the singlet-correlated oxygen band plus the lower Hubbard band of copper). The model has features in common with the phenomenological t-J model but cannot be reduced to the latter completely. In contrast to the t-J model, the density of states of the oxygen holes has a peak near the bottom of the band. It is the presence of this peak together with the non-Fermi-liquid properties that explain the unusual behavior of the spin susceptibility of La_2−x Sr_xCuO₄. Zh. éksp. Teor. Fiz. 112, 1763–1777 (November 1997)     

Effect of vacancies and interstitials on the dynamic properties of the La2−x SrxCuO4 superconductor

The effect of vacancies and interstitials in the CuO₂ layer on the vibrational spectrum in the La_2−x Sr_xCuO₄ system has been calculated by molecular dynamics. It is shown that the excitation probability for local ∼0.4-eV high-frequency vibrations of nonphonon origin in the vicinity of Sr impurity atoms decreases if copper vacancies are introduced at a concentration x=0.17, which corresponds to the maximum superconducting transition temperature, this decrease being still more effective (by about ten times) if interstitial atoms are present. The appearance of interstitials makes a considerable region around them (five to six nearest neighbors) quasi-amorphous. A comparison with available experimental data is made. It is concluded that the behavior of the system under irradiation is accounted for primarily by interstitials, which bring about strong perturbation in the lattice (∼1 nm) up to making it completely amorphous. Fiz. Tverd. Tela (St. Petersburg) 40, 984–988 (June 1998)     

Same superconducting criticality for underdoped and overdoped La2-xSrxCuO4 single crystals

By measuring the superconducting diamagnetic moments for an underdoped and an overdoped La2-xSrxCuO4 single crystal with equal quality and roughly equal transition temperatures, it is found that the underdoped sample has only one transition which corresponds to H(c2), but the overdoped sample has two transitions with the higher one at H(c2). Further investigation reveals the same upper-critical field H(c2) for both samples although the overall charge densities are very different, indicating the possibility of a very direct and detailed equivalence of the superconducting condensation process in the two doping limits. The second transition for the overdoped sample can be understood as the bulk coupling between the superconducting clusters produced by macroscopic phase separation.     

Direct relation between the low-energy spin excitations and superconductivity of overdoped high-Tc superconductors

The dynamic spin susceptibility, chi(")(omega), has been measured over the energy range of 2相似文献   

Magnetic-field-induced localization of quasiparticles in underdoped La(2-x)SrxCuO4 single crystals

Magnetic-field-induced ordering of electrons around vortices is a striking phenomenon recently found in high-T(c) cuprates. To identify its consequence in the quasiparticle dynamics, the magnetic-field (H) dependence of the low-temperature thermal conductivity kappa of La(2-x)SrxCuO4 crystals is studied for a wide doping range. It is found that the behavior of kappa(H) in the subkelvin region changes drastically across optimum doping, and the data for underdoped samples are indicative of unusual magnetic-field-induced localization of quasiparticles; this localization phenomenon is probably responsible for the unusual "insulating normal state" under high magnetic fields.