Electron delocalization and relaxation behavior in Cu-doped Bi2Se3 films

Abstract

$\mathrm{C}{\mathrm{u}}_{x}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ is known for superconductivity due to Cu intercalation in the van der Waals gaps between the quintuple layers of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ at $xg0.10$. Here we report the synthesis and transport properties of Cu-doped $\mathrm{C}{\mathrm{u}}_{x}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ films prepared by the chemical-vapor-deposition (CVD) method with $0.11\ensuremath{\ge}x\ensuremath{\ge}0$. It is found that the insulatinglike temperature-dependent resistivity of polycrystalline $\mathrm{C}{\mathrm{u}}_{x}\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ films exhibits a marked metallic downturn and an increase of carrier concentration below \ensuremath{\sim}37 K. There is also a time-dependent slow relaxation behavior in the resistance at low temperature. These effects might be related to the strong hybridization between $\mathrm{C}{\mathrm{u}}^{+}$ and $\mathrm{C}{\mathrm{u}}^{2+}$ conduction bands from the intercalated $\mathrm{C}{\mathrm{u}}^{+}$ and substituted $\mathrm{C}{\mathrm{u}}^{2+}$ sites in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ films. The findings here have important implications for the understanding and development of doping-induced superconductivity in topological insulators.