arXiv subjects

Xiaxin Ding

Publications and source records attributed to Xiaxin Ding.

25 records · Page 2Linked to original sources

arXiv2015

The Josephson current in Fe-based superconducting junctions: theory and experiment

We present theory of dc Josephson effect in contacts between Fe-based and spin-singlet $s$-wave superconductors. The method is based on the calculation of temperature Green's function in the junction within the tight-binding model. We calculate the phase dependencies of the Josephson current for different orientations of the junction relative to the crystallographic axes of Fe-based superconductor. Further, we consider the dependence of the Josephson current on the thickness of an insulating layer and on temperature. Experimental data for PbIn/Ba$_{1-x}$K$_{x}$(FeAs)$_2$ point-contact Josephson junctions are consistent with theoretical predictions for $s_{\pm}$ symmetry of an order parameter in this material. The proposed method can be further applied to calculations of the dc Josephson current in contacts with other new unconventional multiorbital superconductors, such as $Sr_2RuO_4$ and superconducting topological insulator $Cu_xBi_2Se_3$.

cond-mat.supr-con↗

arXiv2014

Strong and nonmonotonic temperature dependence of Hall coefficient in superconducting K$_x$Fe$_{2-y}$Se$_2$ single crystals

In-plane resistivity, magnetoresistance and Hall effect measurements have been conducted on quenched K$_x$Fe$_{2-y}$Se$_2$ single crystals in order to analysis the normal-state transport properties. It is found that the Kohler's rule is well obeyed below about 80 K, but clearly violated above 80 K. Measurements of the Hall coefficient reveal a strong but non-monotonic temperature dependence with a maximum at about 80 K, in contrast to any other FeAs-based superconductors. With the two-band model analysis on the Hall coefficient, we conclude that a gap may open below 65 K. The data above 65 K are interpreted as a temperature induced crossover from a metallic state at a low temperature to an orbital-selective Mott phase at a high temperature. This is consistent with the recent data of angle resolved photoemission spectroscopy. These results call for a refined theoretical understanding, especially when the hole pockets are absent or become trivial in K$_x$Fe$_{2-y}$Se$_2$ superconductors.

cond-mat.supr-con↗

arXiv2013

Impurity effect and suppression to superconductivity in Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn)

We report the successful growth and the impurity scattering effect of single crystals of Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn). The temperature dependence of DC magnetization at high magnetic fields is measured for different concentrations of Cu and Mn. Detailed analysis based on the Curie-Weiss law indicates that the Cu doping weakens the average magnetic moments, while doping Mn enhances the local magnetic moments greatly, suggesting that the former may be non- or very weak magnetic impurities, and the latter give rise to magnetic impurities. However, it is found that both doping Cu and Mn will enhance the residual resistivity and suppress the superconductivity at the same rate in the low doping region, being consistent with the prediction of the S$^{\pm}$ model. For the Cu-doped system, the superconductivity is suppressed completely at a residual resistivity $ρ_0$ = 0.87 m$Ω$ cm at which a strong localization effect is observed. However, in the case of Mn doping, the behavior of suppression to \emph{T}$_{c}$ changes from a fast speed to a slow one and keeps superconductive even up to a residual resistivity of 2.86 m$Ω$ cm. Clearly the magnetic Mn impurities are even not as detrimental as the non- or very weak magnetic Cu impurities to superconductivity in the high doping regime.

cond-mat.supr-con↗

arXiv2013

Orbital-Selective Mottness in KxFe2-ySe2 Superconductors Revealed by Pump-Probe Spectroscopy

We report transient optical signatures of the orbital-selective Mottness in superconducting KxFe2-ySe2 crystals by using dual-color pump-probe spectroscopy. Besides multi-exponential decay recovery dynamics of photo-induced quasiparticles, a damped oscillatory component due to coherent acoustic phonons emerges when the superconducting phase is suppressed by increasing the temperature or excitation power. The oscillatory component diminishes with significant enhancement of a slow decay component upon raising temperature to 150-160 K. These results are in consistence with the picture of orbital-selective Mott phase transition, indicating a vital role played by electron correlation in the iron-based superconductors.

cond-mat.supr-con↗

arXiv2012

Multi-Band Exotic Superconductivity in the New Superconductor Bi4O4S3

Resistivity, Hall effect and magnetization have been investigated on the new superconductor Bi4O4S3. A weak insulating behavior has been induced in the normal state when the superconductivity is suppressed. Hall effect measurements illustrate clearly a multiband feature dominated by electron charge carriers, which is further supported by the magnetoresistance data. Interestingly, a kink appears on the temperature dependence of resistivity at about 4 K at all high magnetic fields when the bulk superconductivity is completely suppressed. This kink can be well traced back to the upper critical field Hc2(T) in the low field region, and is explained as the possible evidence of residual Cooper pairs on the one dimensional chains.

cond-mat.supr-con↗

arXiv2012

Transport properties, upper critical field and anisotropy of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals

The temperature and angle dependent resistivity of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals were measured in magnetic fields up to 14 T. The temperature dependent resistivity with the magnetic field aligned parallel to c-axis and ab-planes allow us to derive the slope of d$H_{c2}^{ab}/dT$ and d$H_{c2}^c/dT$ near $T_c$ yielding an anisotropy ratio $Γ=dH_{c2}^{ab}/dT/dH_{c2}^c/dT \approx$ 2. By scaling the curves of resistivity vs. angle measured at a fixed temperature but different magnetic fields within the framework of the anisotropic Ginzburg-Landau theory, we obtained the anisotropy in an alternative way. Again we found that the anisotropy $(m_c/m_{ab})^{1/2}$ was close to 2. This value is very similar to that in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (K-doped Ba122) and Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ (Co-doped Ba122). This suggests that the 3D warping effect of the Fermi surface in Ru-doped samples may not be stronger than that in the K-doped or Co-doped Ba122 samples, therefore the possible nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect of the Fermi surface.

cond-mat.supr-con↗

arXiv2012

Distinct behaviors of suppression to superconductivity in $LaRu_3Si_2$ induced by Fe and Co dopants

In the superconductor LaRu$_3$Si$_2$ with the Kagome lattice of Ru, we have successfully doped the Ru with Fe and Co atoms. Contrasting behaviors of suppression to superconductivity is discovered between the Fe and the Co dopants: Fe-impurities can suppress the superconductivity completely at a doping level of only 3%, while the superconductivity is suppressed slowly with the Co dopants. A systematic magnetization measurements indicate that the doped Fe impurities lead to spin-polarized electrons yielding magnetic moments with the magnitude of 1.6 $μ_B$\ per Fe, while the electrons given by the Co dopants have the same density of states for spin-up and spin-down leading to much weaker magnetic moments. It is the strong local magnetic moments given by the Fe-dopants that suppress the superconductivity. The band structure calculation further supports this conclusion.

cond-mat.supr-con↗