Scaling of an anomalous metal-insulator transition in a two-dimensional system in silicon at<i>B</i>=0

We have studied the temperature dependence of resistivity, \ensuremath{\rho}, for a two-dimensional electron system in silicon at low electron densities ${\mathit{n}}_{\mathit{s}}$\ensuremath{\sim}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, near the metal-insulator transition. The resistivity was empirically found to scale with a single parameter ${\mathit{T}}_{0}$, which approaches zero at some critical electron density ${\mathit{n}}_{\mathit{c}}$ and increases as a power ${\mathit{T}}_{0}$\ensuremath{\propto}\ensuremath{\Vert}${\mathit{n}}_{\mathit{s}}$-${\mathit{n}}_{\mathit{c}}$${\mathrm{\ensuremath{\Vert}}}^{\mathrm{\ensuremath{\beta}}}$ with \ensuremath{\beta}=1.6\ifmmode\pm\else\textpm\fi{}0.1 both in metallic (${\mathit{n}}_{\mathit{s}}$&gt;${\mathit{n}}_{\mathit{c}}$) and insulating (${\mathit{n}}_{\mathit{s}}$${\mathit{n}}_{\mathit{c}}$) regions. This dependence was found to be sample independent. We have also studied the diagonal resistivity at Landau-level filling factor \ensuremath{\nu}=3/2, where the system is known to be in a true metallic state at high magnetic field and in an insulating state at low magnetic field. The temperature dependencies of resistivity at B=0 and \ensuremath{\nu}=3/2 were found to be identical. These behaviors suggest a true metal-insulator transition in the two-dimensional electron system in silicon at B=0, in contrast with the well-known scaling theory.