Electronic states and quadrupole orders in the 1-2-20 systems Pr$T_{2}$Al$_{20}$ ($T$=Ti, V) are investigated on the basis of the first-principles band calculation. As the de Haas-van Alphen experiments reveal that the Pr-4$f$ electrons in the systems are sufficiently localized and irrelevant for the Fermi surface, we derive the low-energy effective tight-binding models consists of 196 orbitals of conduction electrons so as to reproduce the first-principles electronic structures of La$T_{2}$Al$_{20}$ ($T$=Ti, V) without contribution from the 4$f$ electrons. Based on the effective models, we calculate the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the quadrupole moments of the Pr ions mediated by the conduction electrons. The obtained results indicate that the wave vector of the expected quadrupole order is ${bm{Q}}=left(0,0,0right)$ for PrTi$_{2}$Al$_{20}$ while it is ${bm{Q}}=left(pi/a,pi/a,0right)$ for PrV$_{2}$Al$_{20}$ as consistent with experimental observations in PrTi$_{2}$Al$_{20}$ and PrV$_{2}$Al$_{20}$ which exhibit ferro- and antiferro-quadrupole orders, respectively.
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