Hole carrier in MgB2 characterized by Hall measurements

The longitudinal resistivity ${\mathrm{(\rho }}_{\mathrm{xx}})$ and Hall coefficient ${\mathrm{(R}}_H)$ were measured for ${\mathrm{MgB}}_{\mathrm{2}}$ sintered under high pressure. We found that $R_H$ is positive like cuprate high-$T_c$ superconductors, and decreases as the temperature increases for 40 K $\text{<T<300\hspace{0.05em}}\mathrm{K}.$ The cotangent of the Hall angle was found to follow ${\mathrm{a+bT}}^2$ behavior from $T_c$ to 300 K. At $\text{T=100\hspace{0.05em}}\mathrm{K},$ $R_H{\text{=4.1×10}}^{\text{−11}} {\mathrm{m}}^{\mathrm{3}}\mathrm{/C}$ from which the hole carrier density was determined to be ${\text{1.5×10}}^{23}/{\mathrm{cm}}^{\mathrm{3}}.$ This carrier density is 1–2 orders of magnitude larger than those of ${\mathrm{Nb}}_{\mathrm{3}}\mathrm{Sn}$ and optimally doped ${\mathrm{YBa}}_{\mathrm{2}}{\mathrm{Cu}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{y}}$ superconductors.