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Register a new userSpectral measurement of the Hall angle response in normal state cuprate superconductors
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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.
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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.
We propose a weakly coupled two-band model with $d_{x^2-y^2}$ pairing symmetry to account for the anomalous temperature dependence of superfluid density $rho_s$ in electron-doped cuprate superconductors. This model gives a unified explanation to the presence of a upward curvature in $rho_s$ near $T_c$ and a weak temperature dependence of $rho_s$ in low temperatures. Our work resolves a discrepancy in the interpretation of different experimental measurements and suggests that the pairing in electron-doped cuprates has predominately $d_{x^2-y^2}$ symmetry in the whole doping range.
The study of the electromagnetic response in cuprate superconductors plays a crucial role in the understanding of the essential physics of these materials. Here the doping dependence of the electromagnetic response in cuprate superconductors is studied within the kinetic-energy driven superconducting mechanism. The kernel of the response function is evaluated based on the linear response approximation for a purely transverse vector potential, and can be broken up into its diamagnetic and paramagnetic parts. In particular, this paramagnetic part exactly cancels the corresponding diamagnetic part in the normal-state, and then the Meissner effect is obtained within the entire superconducting phase. Following this kernel of the response function, the electromagnetic response calculation in terms of the specular reflection model qualitatively reproduces many of the striking features observed in the experiments. In particular, the local magnetic-field profile follows an exponential law, while the superfluid density exhibits the nonlinear temperature behavior at the lowest temperatures, followed by the linear temperature dependence extending over the most of the superconducting temperature range. Moreover, the maximal value of the superfluid density occurs at around the critical doping $delta_{rm critical}sim 0.16$, and then decreases in both lower doped and higher doped regimes. The theory also shows that the nonlinear temperature dependence of the superfluid density at the lowest temperatures can be attributed to the nonlocal effects induced by the d-wave gap nodes on the electron Fermi surface.
We investigated the nature of the quasi-particle state in the vortex core by means of the flux-flow Hall effect measurements at 15.8 GHz. We measured the flux-flow Hall effect in cuprate superconductors, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{y}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ single crystals, whose equilibrium $B$-$T$ phase diagrams were different. As a result, we found that the Hall angle is independent of the magnetic field, and reaches an order of unity at low temperatures in BSCCO. However, in YBCO, the angle increases with increasing magnetic field even at low temperatures. We understood that this difference in the magnetic field dependence of the Hall angle is due to the difference in the influence of the pinning, which originated from the difference in the vortex state (liquid vs. solid) between the two materials. However, as a common feature, both materials showed a large tangent of the Hall angle at low temperatures, which was larger by an order of magnitude than those obtained in the effective viscous drag coefficient measurements. We discussed the origin of the discrepancy both in terms of the possible nonlinearity of the viscous drag force and possible hidden dissipation mechanisms. The unexpectedly large Hall angle of the vortex motion in cuprates revealed in our flux-flow Hall effect study poses a serious question on the fundamental understanding of the motion of the quantized vortex in superconductors, and it deserves further investigation.
We explore the electronic structure in the heavily overdoped regime of the single layer cuprate superconductor Bi1.74Pb0.38Sr1.88CuO6+delta. We found that the nodal quasiparticle behavior is dominated mostly by phonons, while the antinodal quasiparticle lineshape is dominated by spin fluctuations. Moreover, while long range spin fluctuations diminish at very high doping, the local magnetic fluctuations still dominate the quasiparticle dispersion, and the system exhibits a strange metal behavior in the entire overdoped regime.
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