Symmetry Considerations for the Detection of Second-Harmonic Generation in Cuprates in the Pseudogap phase

A proposal to test the proposed time-reversal and inversion breaking phase in the Pseudogap region of the Cuprate compounds through the variation of Second-harmonic generation intensity with temperature and polarization and angle of incidence is presented.Comment: 7 pages, 2 figures include

The Influence of Quantum Critical Fluctuations of Circulating Current Order Parameters on the Normal State Properties of Cuprates

We study a model of the quantum critical point of cuprates associated with the "circulating current" order parameter proposed by Varma. An effective action of the order parameter in the quantum disordered phase is derived using functional integral method, and the physical properties of the normal state are studied based on the action. The results derived within the ladder approximation indicate that the system is like Fermi liquid near the quantum critical point and in disordered regime up to minor corrections. This implies that the suggested marginal Fermi liquid behavior induced by the circulating current fluctuations will come in from beyond the ladder diagrams.Comment: 7pages, 1 figure included in RevTex file. To appear in Phys. Rev.

Two-impurity Kondo problem for correlated electrons

The behavior of two magnetic impurities coupled to correlated electrons in one dimension is studied using the DMRG technique for several fillings. On-site Coulomb interactions among the electrons lead to a small Kondo screening cloud and an overall suppression of magnetic order. For arbitrary electronic correlations and large inter-impurity distances R, we find a 1/R^2 decay of magnetic correlations.Comment: RevTeX (version 3.0), 4 twocolumn pages with 6 embedded figures. To appear in PRB RC, April 199

Developments in Correlated Fermions

This manuscript is based on the Summary and Overview talk given at the "The International Conference of Strongly Correlated Electronic Systems" (SCES '04), July 26-30, at Karlsruhe, Germany. After highlighting some of the principal new experimental developments in heavy fermions presented at the conference, I turn to two kinds of theoretical questions. (1) What is understood of the fermi-liquid state of the heavy fermions and what is not, but may reasonably well be understood by systematic calculations. (2) The profound issues raised by the observed correlations near the quantum critical points in the heavy fermions. The numbers and letters in the parenthesis in the text refer to the listing of the talks in the "Program and Abstracts" book of the conference

Thermal Hall conductivity of marginal Fermi liquids subject to out-of plane impurities in high-TcT_c cuprates

The effect of out-of-plane impurities on the thermal Hall conductivity $\kappa_{xy}$ of in-plane marginal-Fermi-liquid (MFL) quasiparticles in high-$T_c$ cuprates is examined by following the work on electrical Hall conductivity $\sigma_{xy}$ by Varma and Abraham [Phys. Rev. Lett. 86, 4652 (2001)]. It is shown that the effective Lorentz force exerted by these impurities is a weak function of energies of the MFL quasiparticles, resulting in nearly the same temperature dependence of $\kappa_{xy}/T$ and $\sigma_{xy}$, indicative of obedience of the Wiedemann-Franz law. The inconsistency of the theoretical result with the experimental one is speculated to be the consequence of the different amounts of out-of-plane impurities in the two YBaCuO samples used for the $\kappa_{xy}$ and $\sigma_{xy}$ measurements.Comment: 5 pages, 2 eps figures; final versio

Charge Dynamics in Cuprate Superconductors

In this lecture we present some interesting issues that arise when the dynamics of the charge carriers in the CuO$_2$ planes of the high temperature superconductors is considered. Based on the qualitative picture of doping, set by experiments and some previous calculations, we consider the strength of various inter and intra-cell charge transfer susceptibilities, the question of Coulomb screening and charge collective modes. The starting point is the usual p-d model extended by the long range Coulomb (LRC) interaction. Within this model it is possible to examine the case in which the LRC forces frustrate the electronic phase separation, the instability which is present in the model without an LRC interaction. While the static dielectric function in such systems is negative down to arbitrarily small wavevectors, the system is not unstable. We consider the dominant electronic charge susceptibilities and possible consequences for the lattice properties.Comment: 14 pages, 15 figures, latex, to be published in "From Quantum Mechanics to Technology", Lecture Notes in Physics, Springe

Hall effect in the marginal Fermi liquid regime of high-Tc superconductors

The detailed derivation of a theory for transport in quasi-two-dimensional metals, with small-angle elastic scattering and angle-independent inelastic scattering is presented. The transport equation is solved for a model Fermi surface representing a typical cuprate superconductor. Using the small-angle elastic and the inelastic scattering rates deduced from angle-resolved photoemission experiments, good quantitative agreement with the observed anomalous temperature dependence of the Hall angle in optimally doped cuprates is obtained, while the resistivity remains linear in temperature. The theory is also extended to the frequency-dependent complex Hall angle

Thirty Years of heavy Fermions: Scientific Setting for their Discovery and Partial Understanding

Heavy-Fermions provide an extreme example of the utility of the idea of continuity and analyticity in physics. Their discovery and study in the past thirty years has added a fascinating chapter to condensed matter physics. I briefly review the origins of the heavy-fermion problem out of the study of magnetic moments in metals and the study of mixed-valent rare-earth compounds. I also review the principal ideas underlying the features understood in their fermi-liquid phase as well as in their anisotropic superconductivity. The unsolved issues are also briefly mentioned.Comment: This is the text of one of the talks given at the plenary symposium entitled "Thirty years of heavy Fermions" at the beginning of the International conference on Strongly correlated Electrons in Vienna in July 200

Fermi Liquid Properties of a Two Dimensional Electron System With the Fermi Level Near a van Hove Singularity

We use a diagrammatic approach to study low energy physics of a two dimensional electron system where the Fermi level is near van-Hove singularies in the energy spectrum. We find that in most regions of the $\epsilon_F-T$ phase diagram the system behaves as a normal Fermi liquid rather than a marginal Fermi liquid. Particularly, the imaginary part of the self energy is much smaller than the excitation energy, which implies well defined quasiparticle excitations, and single particle properties are only weakly affected by the presence of the van-Hove singularities. The relevance to high temperature superconductivity is also discussed.Comment: 10 pages, 4 postscript figure

Changes in Optical Conductivity due to Readjustments in Electronic Density of States

Within the model of elastic impurity scattering, we study how changes in the energy dependence of the electronic density of states (EDOS) $N(\epsilon)$ around the Fermi energy $\epsilon_F$ are reflected in the frequency-dependent optical conductivity $\sigma(\omega)$. While conserving the total number of states in $N(\epsilon)$ we compute the induced changes in $\sigma(\omega)$ as a function of $\omega$ and in the corresponding optical scattering rate $1/\tau_{\rm op}(\omega)$. These quantities mirror some aspects of the EDOS changes but the relationship is not direct. Conservation of optical oscillator strength is found not to hold, and there is no sum rule on the optical scattering rate although one does hold for the quasiparticle scattering. Temperature as well as increases in impurity scattering lead to additional changes in optical properties not seen in the constant EDOS case. These effects have their origin in an averaging of the EDOS around the Fermi energy $\epsilon_F$ on an energy scale set by the impurity scattering.Comment: 13 pages, 7 figure