Superconducting properties of well-shapedMgB2single crystals

We report measurements of the transport and the magnetic properties of high-quality, sub-millimeter-sized ${\mathrm{MgB}}_2$ single crystals with clear hexagonal-plate shapes. The low-field magnetization and the magnetic hysteresis curves show the bulk pinning of these crystals to be very weak. The Debye temperature of ${\Theta }_D\sim 1100\hspace{0.5em}\mathrm{K},$ obtained from the zero-field resistance curve, suggests that the normal-state transport properties are dominated by electron-phonon interactions. The resistivity ratio between 40 K and 300 K was about 5, and the upper critical field anisotropy ratio was $3.0\pm 0.2$ at temperatures around 32 K.