The temperature dependencies of the coupled superconducting gaps, observed in Fe-As based superconducting compounds is calculated and a universal temperature scaling observed which is only present if the coupled order parameters both have s-wave symmetry. Predictions for possible isotope effects on the transition temperature are made if phonons are involved in the pairing or polaronic effects are of importance. Comparison to experimental data is given where these are available.
Novel Isotope Effects on the Pairing Pseudogap in High-$T_{c}$ Cuprates: Evidences for Polaronic Metal and Precursor BCS-Like Pairing of Large Polarons
Investigation of isotope effects on superconducting transition temperature (Tc) is one of the useful methods to examine whether electron-phonon interaction is essential for pairing mechanisms. The layered BiCh2-based (Ch: S, Se) superconductor family is a candidate for unconventional superconductors, because unconventional isotope effects have previously been observed in La(O,F)BiSSe and Bi4O4S3. In this study, we investigated the isotope effects of 32S and 34S in the high-pressure phase of (Sr,La)FBiS2, which has a monoclinic crystal structure and a higher Tc of 10 K under high pressures, and…
In the present paper, the impact of small Fermi energy on the selected parameters of the superconducting state in Ba$_{1-x}$K$_{x}$BiO$_{3}$ (BKBO) is studied at $x \in (0.3, 0.4, 0.5)$. This is done by employing the adiabatic and non-adiabatic Eliashberg equations in context of the available experimental data. It is found that the retardation, strong-coupling and the non-adiabatic effects notably influence superconducting phase in BKBO. In particular, the electron-electron interaction, approximated here by the Coulomb pseudopotential, is argued to be reduced by the non-adiabatic effects that …
Multiple Gaps and Superfluid Density from Interband Pairing in Iron Oxypnictides
我们研究了铁氧磷属化合物的四带模型，其中的超导性质被假定为由类空穴和类电子费米面之间的带间耦合决定。我们发现，合理的参数可以解释的角度分辨的光电子能谱显示多个间隙在Ba $_{1-x}$ K $_x$ Fe $_2$ As $_2$，和超流密度的温度依赖性。同时，超流密度的零温值与载流子数呈常规的比例关系。
Pairing interactions and pairing mechanism in high temperature copper oxide superconductors
在未掺杂的母体铜氧化物的极化子结合能E_{p}已被确定为约1.0 eV的反铁磁有序温度的非常规氧同位素效应。推导出的E_{p}值与由独立光学数据估计的值和由测量的介电常数理论估计的值在定量上是一致的。在最佳掺杂的铜酸盐中观察到的面内超载流子质量上的大量氧同位素效应表明极化子被束缚到库珀对中。我们还确定了声子模式，强烈耦合到传导电子的角度分辨的光电子能谱，隧穿光谱，和光学数据。我们一贯表明，有一个非常强的电子-声子耦合功能，在声子能量约20毫电子伏沿波腹方向，这种耦合变得越来越弱的对角方向。我们进一步指出，铜酸盐的高温超导电性是由强的电子-声子耦合、极化子效应以及与2 eV Cu-O电荷转移涨落的显著耦合引起的。
Doped strontium titanate SrTiO$_3$ (STO) is one of the most dilute superconductors known today. The fact that superconductivity occurs at very low carrier concentrations is one of the two reasons that the pairing mechanism is not yet understood, the other is the role played by the proximity to a ferroelectric instability. In undoped STO, ferroelectric order can in fact be stabilized by substituting $^{16}$O with its heavier isotope $^{18}$O. Here we explore the superconducting properties of doped and isotope-substituted SrTi$(^{18}$O$_{y}^{16}$O$_{1-y})_{3-δ}$ for $0\le y \le 0.81$ and carrier…
We have investigated the Se isotope effect in layered bismuth chalcogenide (BiCh2-based) superconductor LaO0.6F0.4Bi(S,Se)2 with 76Se and 80Se. For all examined samples, the Se concentration, which is linked to the superconducting properties, is successfully controlled within x = 1.09-1.14 in LaO0.6F0.4BiS2-xSex. From the magnetization and electrical resistivity measurements, changes in Tc are not observed for the LaO0.6F0.4Bi(S,Se)2 samples with 76Se and 80Se isotopes. Our results suggest that pairing in the BiCh2-based superconductors is not mediated by phonons, and unconventional supercondu…
