电子型超导体Sm1.85Ce0.15CuO4单晶的赝能隙行为研究

测量了在O2中退火不同时间的Sm1.85Ce0.15CuO4单晶样品的热电势S与电阻率ρ的温度依赖关系.所有的样品电阻率高温下呈现线性温度依赖行为.未退火的样品在148K发生超导转变,而退火后的样品在低温下发生金属半导体相变,其超导电性消失,表明退火引起了载流子浓度下降,体系进入欠掺杂态.随着温度降低,所有的样品ST和ρT曲线在200K附近(T)都发生斜率的改变,可以用赝能隙现象解释.热电势S在低温下出现一个正的曳引峰,意味着载流子符号发生改变,由电子型转变为空穴型 关键词： 电子型超导体 热电势 赝能隙     

Specific heat of the electronic superconductor Pr1.85Ce0.15CuO4

We have investigated the specific heat of the ceramic Pr_1.85Ce_0.15CuO₄ in the temperature range 2–800K in magnetic fields up to 8 T. We have determined the magnitude of the specific-heat discontinuity at the superconducting transition ΔC/T _c and estimate the coefficient of the electronic specific heat. In the temperature interval 5–800K we have separated out the phonon contribution to the specific heat, determined the temperature dependence of the characteristic Debye temperature Θ, and calculated the mean frequencies (moments) of the phonon spectrum. We compare the parameter values obtained in this way with data for the compound La_1.85Sr_0.15CuO₄ having similar crystal structure, but hole conductivity. The magnitude of the specific-heat discontinuity and consequently the effective electron mass in the “electronic” superconductor Pr_1.85Ce_0.15CuO₄ is several times smaller than in the “hole” superconductor La_1.85Sr_0.15CuO₄. The phonon spectrum in Pr_1.85Ce_0.15CuO₄ in the low-energy region is somewhat “more rigid,” and in the high-energy region somewhat “softer” than in La_1.85Sr_0.15CuO₄. Fiz. Tverd. Tela (St. Petersburg) 41, 1154–1159 (July 1999)     

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr1.85Ce0.15CuO4-y

63Cu nuclear magnetic resonance spin-echo decay rate (T-12) measurements are reported for the normal and superconducting states of a single crystal of Pr(1.85)Ce(0.15)CuO(4-y) in a magnetic field B(0)=9 T over the temperature range 2相似文献   

Neutron-spin resonance in the optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta

We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta above and below its superconducting transition temperature Tc=25 K. In addition to gradually opening a spin pseudogap at the antiferromagnetic ordering wave vector Q=(1/2,1/2,0), the effect of superconductivity is to form a resonance centered also at Q=(1/2,1/2,0) but at energies above the spin pseudogap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr0.88LaCe0.12CuO4. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-Tc superconductivity.     

电子型最佳掺杂高温超导体Nd1.85Ce0.15CuO4-δ中的磁激发谱

文章作者用非弹性中子散射探测了电子型最佳掺杂高温超导体Nd1.85Ce0.15CuO4-δ(Tc=25K)的磁激发谱.当样品的温度从正常态逐渐降低至超导态时,在以波矢Q=(π,,π0)为中心的区域,系统打开了一个小于4m eV的自旋隙,与此同时,在9.5m eV附近出现了一个"中子-自旋磁共振峰",并且"共振峰"的强度随温度的变化关系类似于超导序参量在超导相变发生时的变化,这一点与以前发现的各种空穴型超导体以及电子型超导体Pr0.88LaCe0.12CuO4中的"共振峰"的性质极为相似.因此可以说明"共振峰"是所有高温超导体的共性,并且对高温超导电性的形成有着非常关键的作用.     

THERMOELECTRIC POWER IN (Gd,Sm)1.85Ce0.15CuO4 SYSTEM

Thermoelectric power measurements are reported for seven samples with different x in the Gd_1.85-xSm_xCe_0.15CuO₄ system at temperatures ranging from 80K to 300K. For Sm-rich superconducting samples, thermoelectric power S has a small negative value and is almost temperature independent. As the content of Sm decreases, the absolute value of S increases and a broad valley appears in the S(T) curve. The results which can be interpreted in terms of a two-channel model support the existence of mid-gap states with Fermi level close to the minimum of the density of states as well as the coexistence of electron and hole carriers. It is suggested that a linear temperature dependence of S with a small negative slope is close to the intrinsic behavior in the a-b plane of normal states for superconducting samples.     

Anisotropy of the superconducting transition in magnetic fields in a Nd1.85Ce0.15CuO4 single crystal

The anisotropy of superconducting properties of a Nd_1.85Ce_0.15CuO₄ single crystal is studied by resistance measurements over the temperature range 2–30 K in magnetic fields of 0, 1, 2, 4, and 6 T parallel to the a-b plane. A strong anisotropy of T _c (H) and H _c 2(T) is observed for different orientations of magnetic field in the a-b plane. This anisotropy leads to a twofold symmetry of T _c (H) and H _c 2(T), and the gap node direction is determined. An analysis of experimental data shows that this result can be attributed to a change in the local symmetry of the copper atom environment, which manifests itself as a reduction from tetragonal to orthorhombic symmetry in the low-temperature region. The comparison with La_1.85Sr_0.15CuO₄ suggests that the mechanisms of superconductivity in electron and hole doped superconductors are similar, and the difference observed in the experiment is related to the structural features of these materials.     

Spontaneous strain in high-temperature superconductor La1.85Sr0.15CuO4

The lattice parameters of La_1.85Sr_0.15CuO₄ were measured by an x-ray Rietveld method between 15 K and room temperature. A change in a lattice parameter could be detected at superconducting phase transition. It is pointed out, for the first time, that the change can be attributed to a spontaneous strain in the superconducting phase caused by coupling between a superconducting order parameter and the strain.