Xiyu Zhu

Superconductivity at 25 K in hole-doped (La1-xSrx)OFeAs

By partially substituting the tri-valence element La with di-valence element Sr in LaOFeAs, we introduced holes into the system. For the first time, we successfully synthesized the hole-doped new superconductors (La1- xSrx)OFeAs. The maximum superconducting transition temperature at about 25 K was observed at a doping level of x=0.13. It is evidenced by Hall effect measurements that the conduction in this type of material is dominated by hole-like charge carriers, rather than electron-like ones. Together with the data of the electron-doped system La(O1- xFx)FeAs, a generic phase diagram is depicted and is revealed to be similar to that of the cuprate superconductors.

Transition of stoichiometric Sr2VO3FeAs to a superconducting state at 37.2 K

The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K was successfully fabricated. It has a layered structure with the space group of p4/nmm and with the lattice constants a=3.9296 A degrees and c=15.6732 A degrees. The observed large diamagnetization signal and zero resistance demonstrated the bulk superconductivity. The broadening of resistive transition was measured under different magnetic fields revealing a rather high upper critical field. The results also suggest a large vortex liquid region that reflects high anisotropy of the system. The Hall-effect measurements revealed dominantly electronlike charge carriers in this material. The superconductivity in the present system may be induced by oxygen deficiency or the multiple valence states of vanadium.

Upper critical field, Hall effect and magnetoresistance in the iron-based layered superconductor LaFeAsO0.9F0.1-δ

By using a two-step method, we successfully synthesized the new iron-based superconductor LaFeAsO0.9F0.1−δ. The resistive transition curves under different magnetic fields were measured, leading to the determination of the upper critical field Hc2(T) of this new superconductor. The value of Hc2 at zero temperature is estimated to be about 50 T roughly. In addition, the Hall effect and magnetoresistance were measured in a wide temperature region. A negative Hall coefficient RH has been found, implying a dominant conduction mainly by electron-like charge carriers in this material. The charge carrier density determined at 100 K is about 9.8 × 1020 cm−3, which is close to the cuprate superconductors. It is further found that the magnetoresistance does not follow Kohlers law. Meanwhile, the different temperature-dependent behaviors of resistivity, Hall coefficient and magnetoresistance have anomalous properties at about 230 K, which may be induced by some exotic scattering mechanism.By using a two-step method, we successfully synthesized the iron based new superconductor LaO

Superconductivity at 36 K in gadolinium-arsenide oxides GdO 1− x F x FeAs

_{0.9}

Point-contact spectroscopy of iron-based layered superconductor LaO0.9F0.1-δFeAs

F

High-Tc superconductivity induced by doping rare-earth elements into CaFeAsF

_{0.1-x}

Sr 3 Sc 2 Fe 2 As 2 O 5 as a possible parent compound for FeAs-based superconductors

FeAs. The Hall effect and magnetoresistance were measured in wide temperature region. A negative Hall coefficient R_H has been found implying a dominant conduction by electron-like charge carriers in this material. The charge carrier density determined at 100K is about 9.8E20 cm-3, which is close to the cuprate superconductors. It is further found that the magnetoresistance does not follow the Kohlers law. Meanwhile, the Hall coefficient, the resistivity at 0T, and magnetoresistance all have an anomalous property at about 240K, which may be induced by the multi-band effect or by some exotic scattering mechanism.

SrFeAsF as a parent compound for iron pnictide superconductors

In this paper we report the fabrication and superconducting properties of GdO1−xFxFeAs. It was found that when x is equal to 0.17, GdO0.83F0.17FeAs is a superconductor with the onset transition temperature Tcon ≈ 36.6 K. Resistivity anomaly near 130 K was observed for all samples up to x = 0.17, and such a phenomenon is similar to that of LaO1−xFxFeAs. Hall coefficient indicates that GdO1−xFxFeAs is conducted by electron-like charge carriers.

Growth and characterization of A1-xKxFe2As2 (A = Ba, Sr) single crystals with x = 0-0.4

We present point-contact spectroscopy data for junctions between a normal metal and the newly discovered F-doped superconductor LaO0.9F0.1??FeAs (F-LaOFeAs). A zero-bias conductance peak was observed and its shape and magnitude suggest the presence of Andreev bound states at the surface of F-LaOFeAs, which provides a possible evidence of an unconventional pairing symmetry with a nodal gap function. The maximum gap value ?0?3.9?0.7?meV was determined from the measured spectra, in good agreement with the recent experiments on specific heat and lower critical field.

Transport properties and anisotropy of Rb1-xFe2-ySe2 single crystals

We have successfully synthesized the fluoride-arsenide compounds Ca1?xRExFeAsF (RE=Nd,?Pr; x=0,0.6). The X-ray powder diffraction confirmed that the main phases of our samples are Ca1?xRExFeAsF with the ZrCuSiAs structure. By measuring resistivity, superconductivity was observed at 56?K in Nd-doped and 52?K in Pr-doped samples with x=0.6. Bulk superconductivity was also proved by the DC magnetization measurements in both samples. Hall effect measurements revealed hole-like charge carriers in the parent compound CaFeAsF with a clear resistivity anomaly below 118?K, while the Hall coefficient RH in the normal state is negative for the superconducting samples Ca0.4Nd0.6FeAsF and Ca0.4Pr0.6FeAsF. This indicates that the rare-earth element doping introduces electrons into CaFeAsF, which induces high-temperature superconductivity.