Magnetic-field-driven quantum critical behavior in graphite and bismuth

We study magnetotransport properties of graphite and rhombohedral bismuth samples and found that in both materials applied magnetic field induces the metal–insulator- (MIT) and reentrant insulator–metal-type (IMT) transformations. The corresponding transition boundaries plotted on the magnetic field–temperature (B − T) plane nearly coincide for these semimetals and can be best described by power laws T ∼ (B − Bc)κ, where Bc is a critical field at T = 0 and κ = 0.45 ± 0.05. We show that insulator–metal–insulator (I–M–I) transformations take place in the Landau level quantization regime and illustrate how the IMT in quasi-3D graphite transforms into a cascade of I–M–I transitions, related to the quantum Hall effect in quasi-2D graphite samples. We discuss the possible coupling of superconducting and excitonic correlations with the observed phenomena, as well as signatures of quantum phase transitions associated with the M–I and I–M transformations.