Computational materials design of attractive Fermion system with large negative effective Ueff in the hole-doped Delafossite of CuAlO2, AgAlO2 and AuAlO2: Charge-excitation induced Ueff < 0

• General design rules for negative Ueff systems are proposed.
• Negative Ueff systems in hole-doped Delafossite are designed.
• Our calculations show that CuAlO2, AgAlO2 and AuAlO2 have large negative Ueff values.
• We propose a new design method for high-TC superconductors.

On the basis of general design rules for negative effective U(Ueff) systems by controlling purely-electronic and attractive Fermion mechanisms, we perform computational materials design (CMD®) for the negative Ueff system in hole-doped two-dimensional (2D) Delafossite CuAlO2, AgAlO2 and AuAlO2 by ab initio calculations with local density approximation (LDA) and self-interaction corrected-LDA (SIC-LDA). It is found that the large negative Ueff in the hole-doped attractive Fermion systems for CuAlO2 (UeffLDA=−4.53 eV and UeffSIC−LDA=−4.20 eV), AgAlO2 (UeffLDA=−4.88 eV and UeffSIC−LDA=−4.55 eV) and AuAlO2 (UeffLDA=−4.14 eV and UeffSIC−LDA=−3.55 eV). These values are 10 times larger than that in hole-doped three-dimensional (3D) CuFeS2 (Ueff=−0.44Ueff=−0.44 eV). For future calculations of Tc and phase diagram by quantum Monte Carlo simulations, we propose the negative Ueff Hubbard model with the anti-bonding single π-band model for CuAlO2, AgAlO2 and AuAlO2 using the mapped parameters obtained from ab initio electronic structure calculations. Based on the theory of negative Ueff Hubbard model (Noziéres and Schmitt-Rink, 1985), we discuss |Ueff| dependence of superconducting critical temperature (Tc) in the 2D Delafossite of CuAlO2, AgAlO2 and AuAlO2 and 3D Chalcopyrite of CuFeS2, which shows the interesting chemical trend, i.e., Tc   increases exponentially (Tc∝exp[−1/|Ueff|]Tc∝exp[−1/|Ueff|]) in the weak coupling regime |Ueff(−0.44eV)|W(1.7eV), for the hole-doped CuAlO2.