Probing the Coulomb Interaction of the Unconventional Superconductor ${\mathrm{PuCoGa}}_5$ by Phonon Spectroscopy

The phonon dispersion curves of the superconductor ${\mathrm{PuCoGa}}_5$ were studied by inelastic x-ray scattering at room temperature. The experimental data agree well with ab initio lattice dynamics calculations. An accurate description of the phonon spectrum is obtained only when a local Coulomb repulsion $U\approx 3\mathrm{eV}$ among $5f$ electrons is taken into account.

Figure 1

IXS phonon spectra of ${\mathrm{PuCoGa}}_5$ measured at $T=297\mathrm{K}$. The full symbols correspond to mode measured at $\mathbf{Q}=(0,4,3-q)$ and the empty symbols at $\mathbf{Q}=(0,4,1-q)$. The dashed lines indicate the dispersion of the corresponding TA and TO modes.

Figure 2

Dispersion relations for the [100] direction. The experimental data (full circles) are compared with ab initio calculations for $U=0$ and 3 eV. Branches are classified according to the irreducible representations along [100].

Figure 3

Dispersion relation for the [001] direction. The experimental data (full circles) are compared with ab initio calculation for $U=0$ and 3 eV. Branches are classified according to the irreducible representations along [001].

Figure 4

Measured (full circles) and calculated (lines) phonon dispersion relations with $U=3\mathrm{eV}$ along the principal symmetry directions for ${\mathrm{PuCoGa}}_5$.