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Computational Nano-materials Design: From Spintronics, Photovoltaics to High-Tc Superconductors

Event Details

Event Dates: 

Friday, March 29, 2013 - 8:00am

Seminar Location: 

  • Duane Physics Room D142

Speaker Name(s): 

Hiroshi Katayama-Yoshida

Speaker Affiliation(s): 

Osaka University, Japan
Seminar Type/Subject

Scientific Seminar Type: 

  • Condensed Matter Seminar

Event Details & Abstract: 

Based on ab initio electronic structure calculation and multi-scale simulation, we discuss the self-organized spinodal nano-decomposition in dilute magnetic semiconductors (DMS), photovoltaic solar-cells such as Cd(Te,S), Cd(Te,Se), CuInSe2, Cu(In,Ga)Se2, Cu2ZnSn(S,Se)4, spincaloritronics in Cu-Ni alloy nano-superstructures, water-splitting ZnO-GaN alloy, Mn-doped GaN-based artificial photosynthesis, NiO-based Re-RAM, and, MgO-based d0-ferromagnetism. By controlling the dimensionality (2D and 3D) in the crystal growth, crystal growth speed, and seeding in the spinidal nano-decomposition, we can grow shape-controlled quantum-dot (Dairiseki-Phase) and quantum nano-wire (Konbu-Phase).  New functionalities by spinodal nano-decomposition, such as a thermoelectric power materials, high-blocking temperature in super-paramagnetism, fast electron-hole separation in nano-scale Type-II semiconductors, and multi-exciton formation in photovoltaic solar-cells can be realized. We compare our recent computational nano-materials design with the recent available experimental data.Finally, we would like to discuss how to design the High-Tc (room temperature) superconductors based on ab initio electronic structure calculation and multi-scale simulations. We discuss the design of reasonably higher-Tc (Tc~50K) superconductors by electron-phonon interaction mechanism by hole-doped delafossite CuAlO2, AgAlO2, AuAlO2, and CuBO2. Then, we will discuss the additional purely electronic attractive interactions by (i) the exchange-correlation-induced negative effective correlation energy U (d4 and d6) and (ii) charge-excitation-induced (or valence-fluctuation-induced) negative effective U (s1 and d9).  These system show the negative effective U by purely electronic attractive interactions (U~-2.6 eV for CuAlO2 ).  We can map the calculated result (ab initio electronic band structure and negative effective U) of delafosite CuAlO2, AgAlO2 and AuAlO2 to the negative U Hubbard model.  We can calculate the phase diagram and Tc based on the multi-scale simulation by Monte Carlo method. Then, we can design the high-Tc superconductors (Tc up to 1000K). (1). K. Sato et al., Rev. of Mod. Phys., 82, (2010) 1633.(2). Y. Tani, et al., Appl. Phys. Express 3, (2010) 101201.; ibid, 4, (2011) 021201. J. of Non-Crystalline Solids, 358, (2012).; Jpn. J. of Appl. Phys., 51, (2012) 050202.(3). Nguyen Dang Vu, et al., Appl. Phys. Express, 4, (2011) 015203.(4). M. Oshitani, et al., Appl. Phys. Express, 4, (2011) 022302.; ibid 4 (2011) 049201.(5). M. Seike et al., Jpn. J. Appl. Phys.50 (2011) 090204.; ibid 51 (2012) 050201.(6). K. Oka et al., J. Am. Chem. Soc. 134 (2012) 2535.(7). A. Nakanishi et al., Solid State Commun.152, (2012) 24; ibid. 152, (2012) 2078.(8). H. Katayama-Yoshida et al., Appl. Phys. Exp. 1, 081703 (2008).