Orbital Nematic Instability in Two-Orbital Hubbard Model:   Renormalization-Group + Constrained RPA Analysis
  Motivated by the nematic electronic fluid phase in Sr_{3}Ru_{2}O_{7}, we develop a combined scheme of the renormalization-group method and the random-phase-approximation-type method, and analyze orbital susceptibilities of the (d_{xz},d_{yz})-orbital Hubbard model with high accuracy. It is confirmed that the present model exhibits a ferro-orbital instability near the magnetic or superconducting quantum criticality, due to the Aslamazov-Larkin-type vertex corrections. This mechanism of orbital nematic order presents a natural explanation for the nematic order in Sr_{3}Ru_{2}O_{7}, and is expected to be realized in various multiorbital systems, such as Fe-based superconductors. 
Masahisa Tsuchiizu, Yusuke Ohno, Seiichiro Onari, Hiroshi Kontani
cond-mat.str-el cond-mat.supr-con