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Register a new userUniversal inhomogeneous magnetic-field response in the normal state of cuprate high-Tc superconductors
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We report the results of a muon spin rotation (muSR) study of the bulk of Bi{2+x}Sr{2-x}CaCu2O{8+delta}, as well as pure and Ca-doped YBa2Cu3Oy, which together with prior measurements reveal a universal inhomogeneous magnetic-field response of hole-doped cuprates extending to temperatures far above the critical temperature (Tc). The primary features of our data are incompatible with the spatially inhomogeneous response being dominated by known charge density wave (CDW) and spin density wave (SDW) orders. Instead the normal-state inhomogeneous line broadening is found to scale with the maximum value Tc^max for each cuprate family, indicating it is controlled by the same energy scale as Tc. Since the degree of chemical disorder varies widely among the cuprates we have measured, the observed scaling constitutes evidence for an intrinsic electronic tendency toward inhomogeneity above Tc.
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We measure the temperature and frequency dependence of the complex Hall angle for normal state YBa$_2$Cu$_3$O$_7$ films from dc to far-infrared frequencies (20-250 cm$^{-1}$) using a new modulated polarization technique. We determine that the functional dependence of the Hall angle on scattering does not fit the expected Lorentzian response. We find spectral evidence supporting models of the Hall effect where the scattering $Gamma_H$ is linear in T, suggesting that a single relaxation rate, linear in temperature, governs transport in the cuprates.
Upon doping, Mott insulators often exhibit symmetry breaking where charge carriers and their spins organize into patterns known as stripes. For high-Tc superconducting cuprates, stripes are widely suspected to exist in a fluctuating form. Here, we use numerically exact determinant quantum Monte Carlo calculations to demonstrate dynamical stripe correlations in the three-band Hubbard model, which represents the local electronic structure of the Cu-O plane. Our results, which are robust to varying parameters, cluster size, and boundary condition, strongly support the interpretation of a variety of experimental observations in terms of the physics of fluctuating stripes, including the hourglass magnetic dispersion and the Yamada plot of incommensurability vs. doping. These findings provide a novel perspective on the intertwined orders emerging from the cuprates normal state.
We formulate an effective low energy theory for the fermionic excitations in d-wave superconductors in the presence of periodic vortex lattices. These can be modeled by an effective free Dirac Hamiltonian with renormalized velocities and possibly a small mass term. In the presence of random nonmagnetic impurities this will result in universal (i.e. field and disorder strength independent) thermal and spin conductivities with values different from those occurring in the Meissner state.
HTS show many puzzling anomalies in their normal state properties. Among them are: - the presence of a peak in the c-axis resistance and its growth in external magnetic field - the anomalous negative magnetoresistance observed above Tc - the deviation from the Korringa law in the temperature dependence of the NMR relaxation rate - the opening of a large pseudo-gap in the c-axis optical conductivity well above Tc - the gap-like tunneling anomalies observed above Tc - the anomalies in the thermoelectric power above Tc We show how all these effects can be explained by the enhanced role played in quasi-2D systems by the fluctuation decrease of the one-electron density of states (DOS) at the Fermi level, and its competition with other fluctuation contributions (AL, MT). The full fluctuation theory in HTS is reviewed and its resuls compared with experimental data.
We report on results of our theoretical study of the in-plane infrared conductivity of the high-Tc cuprate superconductors using the model where charged planar quasiparticles are coupled to spin fluctuations. The computations include both the renormalization of the quasiparticles and the corresponding modification of the current-current vertex function (vertex correction), which ensures gauge invariance of the theory and local charge conservation in the system. The incorporation of the vertex corrections leads to an increase of the total intraband optical spectral weight (SW) at finite frequencies, a SW transfer from far infrared to mid infrared, a significant reduction of the SW of the superconducting condensate, and an amplification of characteristic features in the superconducting state spectra of the inverse scattering rate 1/tau. We also discuss the role of selfconsistency and propose a new interpretation of a kink occurring in the experimental low temperature spectra of 1/tau around 1000cm^{-1}.
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