A Possible Mechanism for Pseudo-Gap in Cuprates

The electron spectrum in the normal phase of cuprates is analyzed in terms of the boson-fermion model. It is argued that the existence of the uncondensed pairs and the quasi-two-dimensional nature of the crystal structure are responsible for the pseudo-gap above T_C observed recently.Comment: 19 pages, Plain Te

Boson-Fermion Model of High-T_C Superconductivity ----A Progress Report

This is an invited lecture at the XXII International School of Theoretical Physics, Ustron, Poland, 9/10-9/15, 1998. The boson-fermion model of high T_C superconductivity is reviewed. Its applications to the pseudo-gap and DC transport coefficients are discussed.Comment: 14 pages, 3 figures; A few changes in the quotation

Color Superconductivity of QCD at High Baryon Density

At sufficiently high baryon density, a quark matter is expected to become a color superconductor because of the pairing forces mediated by gluons. The theoretical aspect of this novel phase of the strong interaction is reviewed with the emphasis on the perturbation theory of QCD at high chemical potential and low temperature. The derivation of the scaling formula of the superconducting transition temperature at weak coupling is explained in detail. The Ginzburg-Landau theory of the color superconductivity is also discussed.Comment: 52 pages, 10 figures, Lecture notes at CCAST domestic workshop "Progresses in Color Superconductivity", Beijing, China, Dec.8-Dec.11, 200

The Meissner Effect in a Two Flavor LOFF Color Superconductor

We calculate the magnetic polarization tensor of the photon and of the gluons in a two flavor color superconductor with a LOFF pairing that consists of a single plane wave. We show that at zero temperature and within the range of the values of the displacement of the Fermi sea that favors the LOFF state, all the eigenvalues of the magnetic polarization tensor are positive. Therefore the chromomagnetic instabilities pertaining to a gapless color superconductor disappear.Comment: 20 pages and 7 figures, Latex, typos were corrected, references adde

Chromomagnetic Instability and the LOFF state in a two flavor Color Superconductor

We explore the relation between the chromomagnetic instability of a homogeneous two flavor color superconductor and the LOFF state. We perturb the free energy of the 2SC by generating a small net momentum for the quark pair. We find that the imaginary Meissner mass of a particular gluon implies that the LOFF state is energetically favored.Comment: 11 pages, no figures, latex, discussion on charge neutrality, new references were adde

On T-violation signals originating from magnetic orders through double exchange mechanism

The photon self energy tensor in a crystal with double exchange and ferromagnetic or canting magnetic orders is analyzed at zero temperature with emphasis on the signal of the time-reversal invariance breaking. Three comparable contributions, spin susceptibility, local magnetic field and spin-orbit coupling are estimated and the prospect of their experimental detection is discussed.Comment: 21 page

Physical properties of the double exchange and its relevance to the specific heat of double perovskite materials

In response to the experimental discovery of double perovskite Ru- base material, The magnetic and electronic properties of the double exchange mechanism are studied theoretically. The electron band structure and the spin wave spectrum response at zero temperature with the canting background are computed from the first principle Hamiltonian. The long range Coulomb interaction between charge carriers is found to be crucial in stabilizing the canting order. A Monte Carlo simulation is performed on de-Gennes's effective magnetic Hamiltonian with classical spin approximation. The peaks of the specific heat as a function of temperature, which correspond to FM(AF) and canting transitions, and its response to the external magnetic field are consistent with the observation. For certain region of parameters, a more complex canting order than layer type is found at sufficiently low temperature. The effective interaction between carriers via exchanging a magnon wave is found to be rather similar to that via exchanging an acoustic phonon. The pros and cons to a genuine superconducting order in this system is analyzed.Comment: 42 page

Some Comments on the Holographic Heavy Quark Potential in a Thermal Bath

The heavy quark potential of a thermal Yang-Mills theory in strong coupling limit is explored in terms of the holographic principle. With a fairly general AdS/QCD metric the heavy quark potential displays a kink-like screening in the plasma phase. This behavior may conflict the causality of a field theory that is mathematically equivalent to the thermal Yang-Mills.Comment: 9 pages, 5 figures, more references added, typo fixe

A Possible Higher Order Correction to the chiral Vortical Conductivity in a Gauge Field Plasma

The two loop contributions to the chiral vortical conductivity are considered. The Kubo formula together with the anomalous Ward identity of the axial vector current suggest that there may be a nonzero correction to the coefficient of the $T^2$ term of the conductivity.Comment: 6 pages, 2 figues, in latex, minor changes with typos fixed and a few references adde

(Inverse) Magnetic Catalysis in Bose-Einstein Condensation of Neutral Bound Pairs

The Bose-Einstein condensation of bound pairs made of oppositely charged fermions in a magnetic field is investigated. We find that the condensation temperature shows the magnetic catalysis effect in weak coupling and the inverse magnetic catalysis effect in strong coupling. The different responses to the magnetic field can be attributed to the competition between the dimensional reduction by Landau orbitals in pairing dynamics and the anisotropy of the kinetic spectrum of fluctuations (bound pairs in the normal phase)Comment: 12 pages, 4 figures, in Latex with further explanations, references added and typos fixe