Self-energy effects in electronic Raman spectra of doped cuprates due to magnetic fluctuations

We present results for magnetic excitations in doped copper oxides using the random phase approximation and itinerant electrons. In the [1,0] direction the observed excitations resemble dispersive quasiparticles both in the normal and in the superconducting state, similarly to recent resonant inelastic x-ray scattering experiments. In the [1,1] direction the excitations form, except for the critical region near the antiferromagnetic wave vector $\mathbf{Q}=(\pi ,\pi )$, only very broad continua. Using the obtained spin propagators we calculate electron self-energies and their effects on electronic Raman spectra. We show that the recently observed additional peak at about twice the pair breaking in $B_{1g}$ symmetry below $T_c$ in HgBa${}_2$CuO${}_{4+\delta }$ can be explained as a self-energy effect where a broken Cooper pair and a magnetic excitation appear as final states. The absence of this peak in $B_{2g}$ symmetry, which probes mainly electrons near the nodal direction, is explained by their small self-energies compared to those in the antinodal direction.

Figure 1

${\chi }^{\prime \prime }(\mathbf{k},\omega )$ along the $[1,1]$ direction in the normal (top) and superconducting (bottom) state at $T=0$.

Figure 2

${\chi }^{\prime \prime }(\mathbf{k},\omega )$ along the $[1,0]$ direction in the normal (top) and superconducting (bottom) state at $T=0$.

Figure 3

Imaginary part of the self-energy (top) and spectral function (bottom) for the momentum on the Fermi line in the $[1,1]$ direction in the normal and superconducting states.

Figure 4

Imaginary part of the self-energy (top) and spectral function (bottom) for the momentum on the Fermi line in the $(\pi ,0)-(\pi ,\pi )$ direction in the normal and superconducting states.

Figure 5

Raman spectra with $B_{1g}$ symmetry (top plot) and $B_{2g}$ and $A_{1g}$ symmetries (bottom plot) in the normal (dashed lines) and superconducting (solid lines) states.