Random magnetic field and quasi-particle transports in the mixed state of high T_{c} cuprates

By a singular gauge transformation, the quasi-particle transport in the mixed state of high T_{c} cuprates is mapped into charge-neutral composite Dirac fermion moving in short-range correlated random scalar and long-range correlated vector potential. A fully quantum mechanical approach to longitudinal and transverse thermal conductivities is presented. The semi-classical Volovik effect is presented in a quantum mechanical way. The quasi-particle scattering from the random magnetic field which was completely missed in all the previous semi-classical approaches is the dominant scattering mechanism at sufficiant high magnetic field. The implications for experiments are discussed.Comment: 4+ pages, 1 figure. To appear in Phys. Rev. Let

On gauge-invariant Green function in 2+1 dimensional QED

Both the gauge-invariant fermion Green function and gauge-dependent conventional Green function in $2+1$ dimensional QED are studied in the large $N$ limit. In temporal gauge, the infra-red divergence of gauge-dependent Green function is found to be regulariable, the anomalous dimension is found to be $\eta= \frac{64}{3 \pi^{2} N}$. This anomalous dimension was argued to be the same as that of gauge-invariant Green function. However, in Coulomb gauge, the infra-red divergence of the gauge-dependent Green function is found to be un-regulariable, anomalous dimension is even not defined, but the infra-red divergence is shown to be cancelled in any gauge-invariant physical quantities. The gauge-invariant Green function is also studied directly in Lorentz covariant gauge and the anomalous dimension is found to be the same as that calculated in temporal gauge.Comment: 8 pages, 6 figures, to appear in Phys. Rev.