CONFINED COHERENCE IN STRONGLY CORRELATED ANISOTROPIC METALS

We present a detailed discussion of both theoretical and experimental evidence in favour of the existence of states of 'confined coherence' in metals of sufficiently high anisotropy and with sufficiently strong correlations. The defining property of such a state is that single el ectron coherence is confined to lower dimensional subspaces (planes or chains) so that it is impossible to observe interference effects betw een histories which involve electrons :moving between these subspaces. The most dramatic experimental manifestation of such a state is the c oexistence of incoherent non-metallic transport in one or two directio ns (transverse to the lower dimensional subspaces) with coherent trans port ill at least one ether direction (within the subspaces). The magn itude of the Fermi surface warping due to transverse (intersubspace) m omentum plays the role of an order parameter (in a state of confined c oherence, this order parameter vanishes) and the effect can occur in a pure system at zero temperature. Our theoretical approach is to treat an anisotropic two (2D)- or three (3D)-dimensional electronic system as a collection of one (1D)- or two-dimensional electron liquids coupl ed by weak interliquid single-particle hopping. We find that a necessa ry condition for the destruction of coherent interliquid transport is that the intraliquid state be a non-Fermi liquid. We present a very de tailed discussion of coupled 1D Luttinger liquids and the reasons for believing in the existence of a phase of confined coherence in that mo del. This provides a paradigm for incoherent transport between weakly coupled 2D non-Fermi liquids, the case relevant to the experiments of which we are aware. Specifically, anomalous transport data in the (nor mal state of the) cuprate superconductors and in the low temperature m etallic state of the highly anisotropic organic conductor (TMTSF)(2)PF 6 cannot be understood within a Fermi liquid framework, and, we argue, the only plausible way to understand that transport is in terms of a state of confined coherence.