Computational materials design of attractive Fermion system with large negative effective $U$ in the hole-doped Delafossite of CuAlO$_2$, AgAlO$_2$ and AuAlO$_2$

Akitaka Nakanishi; Hiroshi Katayama-Yoshida A. Nakanishi; T. Fukushima; H. Uede; H. Katayama-Yoshida

paper

Computational materials design of attractive Fermion system with large negative effective $U$ in the hole-doped Delafossite of CuAlO $_{2}$ , AgAlO $_{2}$ and AuAlO $_{2}$

arXiv:1405.3746

Abstract

In order to realize super-high-critical temperature $(T_{c})$ superconductors ( $T_{c}$ >1,000 K) based on general design rules for negative effective $U$ $(U_{e f f})$ systems by controlling purely-electronic and attractive Fermion mechanisms, we perform computational materials design for the negative $U_{e f f}$ system in hole-doped two-dimensional (2D) Delafossite CuAlO $_{2}$ , AgAlO $_{2}$ and AuAlO $_{2}$ from $ab initio$ calculations. It is found that the large negative $U_{e f f}$ in the hole-doped attractive Fermion systems for CuAlO $_{2}$ ( $U_{e f f}$ = -4.53 eV), AgAlO $_{2}$ ( $U_{e f f}$ = -4.88 eV), AuAlO $_{2}$ ( $U_{e f f}$ = -4.14 eV). These values are 10 times larger than that in hole-doped three-dimensional (3D) CuFeS $_{2}$ ( $U_{e f f}$ = -0.44 eV). For future calculations of the $T_{c}$ and phase diagram by quantum Monte Carlo simulations, we propose the negative $U_{e f f}$ Hubbard model with the anti-bonding single $π$ -band model for CuAlO $_{2}$ , AgAlO $_{2}$ and AuAlO $_{2}$ by using the parameters obtained from $ab initio$ electronic structure calculations. The behavior of $T_{c}$ in the 2D Delafossite of CuAlO $_{2}$ , AgAlO $_{2}$ and AuAlO $_{2}$ and 3D Chalcopyrite of CuFeS $_{2}$ shows the interesting chemical trend, $i.e.,$ $T_{c}$ increases exponentially in the weak coupling regime $∣ U_{e f f} ∣ < W$ ( $\sim$ 2 eV) (where $W$ is the band width of Hubbard model) for the hole-doped CuFeS $_{2}$ , and then $T_{c}$ goes through a maximum when $∣ U_{e f f} ∣ \sim W$ (2.8 eV, 3.5 eV) for the hole-doped AgAlO $_{2}$ and AuAlO $_{2}$ , and finally $T_{c}$ decreases with increasing $∣ U_{e f f} ∣$ in the strong coupling regime, where $∣ U_{e f f} ∣ > W$ (1.7 eV), for the hole-doped CuAlO $_{2}$ . In this strong coupling regime, one can expect that $T_{c}$ = 1,000 $\sim$ 2,000 K by assuming the relation of the very strong coupling as $2Δ/ k_{B} T_{c}$ = 50 $\sim$ 100 and the superconducting gap $Δ \sim ∣ U_{e f f} ∣$ = 4.53 eV $\sim$ 50,000 K.

35 pages, 12 figures

Computational materials design of attractive Fermion system with large negative effective U in the hole-doped Delafossite of CuAlO2​, AgAlO2​ and AuAlO2​

Abstract

Computational materials design of attractive Fermion system with large negative effective $U$ in the hole-doped Delafossite of CuAlO $_{2}$ , AgAlO $_{2}$ and AuAlO $_{2}$