Universal magnetic-field-driven metal-insulator-metal transformations in graphite and bismuth

Applied magnetic field induces metal-insulator and reentrant insulator-metal transitions in both graphite and rhombohedral bismuth. The corresponding transition boundaries plotted on the magnetic field\char22{}temperature $(B\text{\ensuremath{-}}T)$ plane nearly coincide for these semimetals and can be best described by power laws $T\ensuremath{\sim}{(B\text{\ensuremath{-}}{B}_{c})}^{\ensuremath{\kappa}}$, where ${B}_{c}$ is a critical field at $T=0$ and $\ensuremath{\kappa}=0.45\ifmmode\pm\else\textpm\fi{}0.05$. We show that insulator-metal-insulator (I-M-I) transformations take place in the Landau level quantization regime and illustrate how the insulator-metal transformation in graphite samples with a moderate anisotropy transforms into a cascade of I-M-I transitions, related to the quantum Hall effect in strongly anisotropic, quasi-two-dimensional graphite samples. We discuss the possible coupling of superconducting and excitonic correlations with the observed phenomena, as well as the signatures of quantum phase transitions associated with the M-I and I-M transformations.