Quantum liquid versus electron solid around ν=1/5 Landau-level filling

In the high-magnetic-field low-disorder limit the ground state at ν=1/5 Landau-level filling is an incompressible quantum liquid. This is determined by observing vanishing resistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$ as the temperature T→0. At filling factors below ν=1/5 as well as in a narrow region above ν=1/5, ${\mathrm{\rho }}_{\mathit{x}\mathit{x}}$ diverges exponentially as T→0. This contrasts the T dependence at any higher ν. We conclude that the quantum liquid at ν=1/5 is surrounded by a different phase. In as much as the exponential divergencies are indicative of an electron solid this phase is reentrant in a narrow region above ν=1/5.