Anisotropic Multiband Many-Body Interactions in ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$

We present a comprehensive de Haas–van Alphen study on the nonmagnetic borocarbide superconductor ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$. The analysis of the angular-dependent effective masses for different bands in combination with full-potential density functional calculations allowed us to determine the mass-enhancement factors, $\lambda$, for the different electronic bands and their wave-vector dependences. Our data clearly show the anisotropic multiband character of the superconductivity in ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$.

Figure 1

Band structure (upper panel) and FSs of ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$. The bands are labeled according to different FSs: circle (red)—ball, diamond (blue)—cube, triangle (green)—cushion, cross (orange)—branched FS. The FS in the third panel was shifted by ($\pi /a$, $\pi /a$, 0) to present simply connected sheets.

Figure 2

Angular dependence of the dHvA frequencies. The solid lines are obtained by use of FPLO calculations. The calculated dHvA frequency for the spherical FS, $F_{\alpha }$, is somewhat larger than measured. For the cubic, $F_{ϵ}$, the cushion-like, $F_{\eta }$, and the “branched” FSs, $F_{\sigma 1}$ and $F_{\sigma 2}$, excellent agreement between theory and experiment is found. For the open circles, no corresponding FS could be assigned.

Figure 3

Experimentally obtained effective masses of the cushion-, cubic-, and ball-like FSs (closed symbols). The solid lines represent the calculated effective masses.

Figure 4

Angular dependence of the mass-enhancement factor $\lambda$ separated for three closed FSs and for the “branched” FS in one orientation. The inset shows the $T$ dependence of the $F_{\alpha }$ frequency for a crystallographic orientation close to the [001] axis together with a LK fit.