arXiv subjects

R. L. Meng

Publications and source records attributed to R. L. Meng.

24 records · Page 2Linked to original sources

arXiv2001

Nonstoichiometry, Defects and Transport Properties in MgB2

The local composition Mg:B of MgB2 powder was systematically changed through annealing. Correlations were observed between the Mg loss and the lattice parameters a/c and the microstrain of MgB2. Direct wavelength-dispersive-spectrum and XRD measurements on ceramic samples with different residual resistivity ratios suggested that the transport property of MgB2 might be affected by this Mg-deficiency, but oxygen-related defects may play a more important role.

cond-mat.supr-con↗

arXiv2001

Hydrostatic Pressure Effect on the Superconducting Transition Temperature of MgB2

The pressure effect on the superconducting transition temperature of MgB2 has been determined using gas pressure up to 1 GPa. The transition temperature Tc was found to decrease linearly at a constant rate over the whole pressure range. The recently observed dramatic decrease of dTc/dp at the 40 K freezing pressure (0.5 GPa) cannot be confirmed. The pressure coefficient was also found to be independent of the hydrostatic or nonhydrostatic He environment. The differences in recently reported values of dTc/dp may be attributed to variations in the sample conditions, e.g. stoichiometry.

cond-mat.supr-con↗

arXiv2001

Thermoelectric power and transport properties of pure and Al-doped MgB2

We have measured the thermoelectric power, S, and resistivity, rho, of pure and Al-doped MgB2. S is positive and increases linearly with temperature above the superconducting transition temperature, Tc. Deviations from the linear dependence appear at higher temperature, T>T0 approx 160 K. Tc and T0 both decrease with Al doping whereas the slope of S(T) in the linear range increases with the Al content. The data are discussed in terms of doping induced changes of the Fermi surface and the density of states at the Fermi level.

cond-mat.supr-con↗

arXiv2001

High Pressure Study on MgB2

The hydrostatic pressure effect on the newly discovered superconductor MgB2 has been determined. The transition temperature Tc was found to decrease linearly at a large rate of -1.6 K/GPa, in good quantitative agreement with the ensuing calculated value of -1.4 K/GPa within the BCS framework by Loa and Syassen, using the full-potential linearlized augmented plane-wave method. The relative pressure coefficient, dlnTc/dp, for MgB2 also falls between the known values for conventional sp- and d-superconductors. The observation, therefore, suggests that electron-phonon interaction plays a significant role in the superconductivity of the compound.

cond-mat.supr-con↗

arXiv2000

A Possible Crypto-Superconducting Structure in a Superconducting Ferromagnet

We have measured the dc and ac electrical and magnetic properties in various magnetic fields of the recently reported superconducting ferromagnet RuSr2GdCu2O8. Our reversible magnetization measurements demonstrate the absence of a bulk Meissner state in the compound below the superconducting transition temperature. Several scenarios that might account for the absence of a bulk Meissner state, including the possible presence of a sponge-like non-uniform superconducting or a crypto-superconducting structure in the chemically uniform Ru-1212, have been proposed and discussed.

cond-mat.supr-con↗

arXiv1999

Absence of a Bulk Meissner State in RuSr2GdCu2O8

We have systematically investigated the magnetic, electrical, and structural properties of RuSr2GdCu2O8, in which a long-range ferromagnetic order and superconductivity have been previously reported to coexist. Based on the reversible magnetization results, we conclude that the bulk Meissner state does not exist in this compound and that the condensation energy associated with superconductivity is negligible. The absence of a bulk Meissner state and the superconductivity detected are thus attributed to the possible appearance of a sponge-like crypto-superconducting fine structure in RuSr2GdCu2O8 samples that are found to be chemically homogeneous to 1-2 mu m and electrically uniform to \~ 10 mu m across the sample.

cond-mat.supr-con↗