An Investigation of Particle-Hole Asymmetry in the Cuprates via Electronic Raman Scattering

In this paper we examine the effects of electron-hole asymmetry as a consequence of strong correlations on the electronic Raman scattering in the normal state of copper oxide high temperature superconductors. Using determinant quantum Monte Carlo simulations of the single-band Hubbard model, we construct the electronic Raman response from single particle Greens functions and explore the differences in the spectra for electron and hole doping away from half filling. The theoretical results are compared to new and existing Raman scattering experiments on hole-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ and electron-doped Nd$_{2-x}$Ce$_{x}$CuO$_{4}$. These findings suggest that the Hubbard model with fixed interaction strength qualitatively captures the doping and temperature dependence of the Raman spectra for both electron and hole doped systems, indicating that the Hubbard parameter U does not need to be doping dependent to capture the essence of this asymmetry.

Temporal response of nonequilibrium correlated electrons

In this work we examine the time-resolved, instantaneous current response for the spinless Falicov-Kimball model at half-filling, on both sides of the Mott-Hubbard metal-insulator transition, driven by a strong electric field pump pulse. The results are obtained using an exact, nonequilibrium, many-body impurity solution specifically designed to treat the out-of-equilibrium evolution of electrons in time-dependent fields. We provide a brief introduction to the method and its computational details. We find that the current develops Bloch oscillations, similar to the case of DC driving fields, with an additional amplitude modulation, characterized by beats and induced by correlation effects. Correlations primarily manifest themselves through an overall reduction in magnitude and shift in the onset time of the current response with increasing interaction strength.

Insights on the cuprate high energy anomaly observed in ARPES

Recently, angle-resolved photoemission spectroscopy has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy waterfall or high energy anomaly (HEA). The anomaly is present for both hole- and electron-doped cuprates as well as the half-filled parent insulators with different energy scales arising on either side of the phase diagram. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. creating a waterfall-like appearance, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram. We find that the anomaly demarcates a transition, or cross-over, from a quasiparticle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character.

Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors

Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy waterfall or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the by-product of matrix element effects, but rather represents a cross-over from a quasiparticle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the waterfall-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.

Time-resolved photoemission of correlated electrons driven out of equilibrium

We describe the temporal evolution of the time-resolved photoemission response of the spinless Falicov-Kimball model driven out of equilibrium by strong applied fields. The model is one of the few possessing a metal-insulator transition and admitting an exact solution in the time domain. The nonequilibrium dynamics, evaluated using an extension of dynamical mean-field theory, show how the driven system differs from two common viewpoints - a quasiequilibrium system at an elevated effective temperature (the hot electron model) or a rapid interaction quench (melting of the Mott gap) - due to the rearrangement of electronic states and redistribution of spectral weight. The results demonstrate the inherent trade-off between energy and time resolution accompanying the finite width probe pulses, characteristic of those employed in pump-probe time-domain experiments, which can be used to focus attention on different aspects of the dynamics near the transition.