Electronic Structure and the Fermi Surface of ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$ and ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$

Using a relativistic linear augmented-plane-wave method, we clarify energy band structures and Fermi surfaces of recently discovered plutonium-based superconductor ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$ and the isostructural material ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$. For ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, we find several cylindrical sheets of Fermi surfaces with large volume, similar to $\mathrm{C}\mathrm{e}M{\mathrm{I}\mathrm{n}}_5$, while for ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, the Fermi surfaces are found to be similar to those of $\mathrm{U}M{\mathrm{G}\mathrm{a}}_5$. These similarities are discussed based on the $j$-$j$ coupling scheme, suggesting some hints for the superconducting mechanism in ${\mathrm{H}\mathrm{o}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$-type $f$-electron compounds.

Figure 1

(a) Energy band structure for ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$ obtained by the RLAPW method. Calculated Fermi surfaces of ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$ for (b) 15th band hole sheets, (c) 16th band hole sheets, (d) 17th band electron sheets, and (e) 18th band electron sheets. Colors indicate the amount of $5f$ angular momentum character on each Fermi surface sheet and redshift indicates the increase of the $f$ character. The center of the Brillouin zone is set at the $\Gamma$ point.

Figure 2

Energy band structure around $E_{\mathrm{F}}$ for (a) ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$, (b) ${\mathrm{U}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, (c) ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, and (d) ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$. In (a), (b), and (d), red and blue curves indicate the upper and lower bands to construct the hole and electron Fermi-surface sheets, respectively. Those are 14th (red) and 15th (blue) for ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$, 15th (red) and 16th (blue) for ${\mathrm{U}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, and 16th (red) and 17th (blue) for ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$. Note that for (c) ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, the bands to construct the two hole sheets, 15th and 16th, are specified by red and blue curves, respectively. (e) Configurations for $f$ electrons accommodated in three Kramers doublets. Up (down) arrow denotes pseudo-spin-up (-down).

Figure 3

Calculated Fermi surfaces of (a) ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$, (b) ${\mathrm{U}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$, and (c) ${\mathrm{N}\mathrm{p}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$.

Figure 4

(a) Energy band structures for ${\mathrm{P}\mathrm{u}\mathrm{C}\mathrm{o}\mathrm{G}\mathrm{a}}_5$ for the tight-binding model (solid curves) and the RLAPW results (dashed curves). Fermi surfaces discussed here are (b) 16th, (c) 17th, and (d) 18th band sheets. Solid and broken curves denote the tight-binding and RLAPW results, respectively.