Magnetotransport properties and pseudogap phase diagram of superconducting EuBa2Cu3Oy thin films: the influence of Eu substitution

Abstract

This research explores and debates magnetotransport properties and the pseudogap phase diagram of high-temperature superconducting EuBa _2 Cu _3 O _y (EBCO) films through ρ _xx ( T ) and ρ _xy ( T ) measurements. The mixed state transport properties of samples with higher doped levels show a power-law field-dependence of activation energy U , U ∝ H ^−α with α = 0.52 ± 0.05, while the slightly doped samples reveal a logarithmic field-dependence of U . In addition, for the first time, all samples in the underdoped region display an unusual power-law behavior of U ∝ p ^γ with γ = −5.90 ± 0.28, which is qualitatively explained. A sign reversal of transverse resistivity in the mixed state is also present in the nearly optimum-doped samples, which have strong pinning energies. In the normal state, the cotangent of the Hall angle shows a wide range quadratic temperature dependence for all the samples, which can be described by Anderson’s theory. The values of spin excitation bandwidth W are coincident between two results obtained from the hidden Fermi-liquid theory and from the Hall angle for the slightly overdoped sample. Moreover, the phase diagram of EBCO, containing the superconducting transition temperatures, the T * and T ** temperatures in the pseudogap (PG) phase, and the antiferromagnetic transition temperatures θ _N , in the whole underdoped region has been completed and compared with those for YBa _2 Cu _3 O _y (YBCO). The findings demonstrate that EBCO has lower T * and T ** values, versus those of YBCO in the same doping region. The observed smaller magnitude of PG for EBCO is explained by considering the oxygen vibrational amplitudes in Cu−O−Cu bonds, which agrees with the inference based on the fluctuating bond model. The influence of Eu substitution is examined and discussed.

Keywords

• high-Tc superconductor
• activation energy
• Hall angle
• phase diagram