THE QUANTUM-CLASSICAL METAL

In a normal Fermi liquid, Landau's theory precludes the loss of single -fermion quantum coherence in the low-energy, low-temperature limit. F or highly anisotropic, strongly correlated metals, there is no proof t hat this remains the case, and quantum coherence for transport in some directions may be lost intrinsically. This loss of coherence should s tabilize an unusual, qualitatively anisotropic non-fermi liquid, separ ated by a zero-temperature quantum phase transition from the Fermi liq uid state and categorized by the unobservability of certain interferen ce effects. There is compelling experimental evidence for this transit ion as a function of magnetic field in the metallic phase of the organ ic conductor (TMTSF)(2)PF6 (where TMTSF is tetramethyltetraselenafulva lene).