We performed point-contact spectroscopy tunneling measurements on single crystal ${\mathrm{BaPb}}_{1-x}{\mathrm{Bi}}_x{\mathrm{O}}_3$ for $0\le x\le 0.28$ at temperatures $T=2–40\mathrm{K}$ and find a suppression in the density of states at low bias voltages that is characteristic of disordered metals. Both the correlation gap and the zero-temperature conductivity are zero at a critical concentration $x_c=0.30$. Not only does this suggests that a disorder driven metal-insulator transition occurs before the onset of the charge disproportionated charge density wave insulator, but we also explore whether a scaling theory is applicable. In addition, we estimate the disorder-free critical temperature and compare these results to ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{BiO}}_3$.

• Received 17 November 2013

DOI:https://doi.org/10.1103/PhysRevLett.113.177004