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Register a new userEnergy-Dependent Enhancement of the Electron-Coupling Spectrum of the Underdoped Bi2Sr2CaCu2O8+d Superconductor
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We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O8+d from high-resolution angle-resolved photoemission spectra by two deconvolution-free robust methods. As hole concentration decreases, the coupling spectral weight at low energies ~<15 meV shows a twofold and nearly band-independent enhancement, while that around ~65 meV increases moderately, and that in ~>130 meV decreases leading to a crossover of dominant coupling excitation between them. Our results suggest the competition among multiple screening effects, and provide important clues to the source of sufficiently strong low-energy coupling, {lambda}LE ~ 1, in underdoped system.
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Laser-based angle-resolved photoemission measurements with super-high resolution have been carried out on an optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_8$ high temperature superconductor. New high energy features at $sim$115 meV and $sim$150 meV, besides the prominent $sim$70 meV one, are found to develop in the nodal electron self-energy in the superconducting state. These high energy features, which can not be attributed to electron coupling with single phonon or magnetic resonance mode, point to the existence of a new form of electron coupling in high temperature superconductors.
We use inelastic neutron scattering to explore the evolution of the low energy spin dynamics in the electron-doped cuprate Pr0.88LaCe0.12CuO4-d (PLCCO) as the system is tuned from its nonsuperconducting, as-grown antiferromagnetic (AF) state into an optimally-doped superconductor (Tc~24 K) without static AF order. The low temperature, low energy response of the spin excitations in under-doped samples is coupled to the presence of the AF phase, whereas the low-energy magnetic response for samples near optimal Tc exhibits spin fluctuations surprisingly insensitive to the sample temperature. This evolution of the low energy excitations is consistent with the influence of a quantum critical point in the phase diagram of PLCCO associated with the suppression of the static AF order. We carried out scaling analysis of the data and discuss the influence of quantum critical dynamics in the observed excitation spectrum.
We performed inelastic neutron experiments on underdoped La_2-xSr_xCuO_4(x=0.10, T_c=28.6K) using a time-of-flight neutron scattering technique. Four incommensurate peaks on the two-dimensional reciprocal plane disperse inwards toward an antiferromagnetic zone center as the energy increases. These peaks merge into a single peak at an energy E_cross around w=40+-3meV. Beyond E_cross, the peak starts to broaden and ``hourglass-like excitations are observed. The E_cross in the underdoped sample is smaller than that reported for the optimally doped La_1.84Sr_0.16CuO_4. The reduction of the E_cross is explained by the doping-independent slope of the downward dispersion below the E_cross combined with the smaller incommensurability in the underdoped sample. In the energy spectrum of chi(w), we observed a similar peak-dip-hump structure in the energy region of 10~45meV to that reported for the optimally doped sample. We discuss the relation between the hourglass-shaped dispersion and the peak-dip-hump energy spectrum.
New tunneling data are reported in underdoped Bi2Sr2CaCu2O8-d using superconductor-insulator-superconductor break junctions. Energy gaps, Delta, of 51+2, 54+2 and 57+3 meV are observed for three crystals with Tc=77, 74, and 70 K respectively. These energy gaps are nearly three times larger than for overdoped crystals with similar Tc. Detailed examination of tunneling spectra over a wide doping range from underdoped to overdoped, including the Josephson IcRn product, indicate that these energy gaps are predominantly of superconducting origin.
We study the low-energy density of states of Dirac fermions in disordered d-wave superconductor. At zero energy, a finite density of states is obtained via the mechanism of dynamical mass generation in an effective (1+1)-dimensional relativistic field theory.
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