Sergey Lee

Growth, Structure Analysis and Anisotropic Superconducting Properties of MgB2 Single Crystals

Here we report the growth of sub-millimeter MgB 2 single crystals of various shapes under high pressure in Mg–B–N system. Structure refinement using a single-crystal X-ray diffraction analysis gives lattice parameters a =3.0851(5) A and c =3.5201(5) A with small reliability factors ( R w =0.025, R =0.018), which enables us to analyze the Fourier and Fourier difference maps. The maps clearly show the B sp 2 orbitals and covalency of the B–B bonds. The sharp superconducting transitions at T c =38.1–38.3 K were obtained in both magnetization (Δ T c =0.6 K) and resistivity (Δ T c <0.3 K) measurements. Resistivity measurements with magnetic fields applied parallel and perpendicular to the Mg and B sheets reveal the anisotropic nature of this compound, with upper critical field anisotropy ratio of about 2.7.

Enhancement of Irreversibility Field in Carbon-substituted MgB2 Single Crystals

We report on a detailed study of the irreversibility field H irr of single crystals of Mg(B 1- x C x ) 2 ( x =0, 2, 3.5, 5 and 7.5%) in strong magnetic fields of up to 40 T. Highly sensitive torque measurements revealed that H irr is greatly enhanced by a factor of two (µ 0 H irr (0) ≃33 T with x =5%) by carbon substitution compared with that of the pristine MgB 2 , owing to a reduction in in-plane coherence length. We also observed the temperature-dependent H irr anisotropy for all carbon contents. This strongly suggests that the two-gap superconductivity of MgB 2 is less influenced by a small amount of carbon substitution. We discuss these results by focusing on the impact of carrier doping and impurity scattering on a two-gap superconductor.We report the detailed study of the irreversibility field {\hirr} of single crystals of Mg(B

Crystal growth and characterization of MgB2: the relation between structural and superconducting properties

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Exponential temperature dependence of the penetration depth in single crystal MgB2.

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Superconductivity-induced resonant Raman scattering in multilayer high- T c superconductors

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The electrical transport properties of high quality Bi-2223 crystal

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Crystal growth of Bi2Sr2Ca2Cu3O10+x and (Bi,Pb)2Sr2Ca2Cu3O10+x by the KCl flux method

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Electronic structure of B 2 p σ and p π states in MgB 2 , AlB 2 , and ZrB 2 single crystals

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A Raman scattering study of superconductivity in MgB2

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Mn Substitution Effect in Two-Gap Superconductor MgB2

=0, 2, 3.5, 5 and 7%) in strong magnetic fields of up to 40 T. High sensitive torque measurements revealed that the {\hirr} is greatly enhanced by a factor of two (