We report on a new type of orbital symmetry breaking in the CoO 2 triangular lattice with hole doped t 2g bands. Unrestricted Hartree-Fock calculations on a multi-orbital d-p Hamiltonian show that, in the lightly hole doped t 2g bands, the é g orbitals are fully occupied with a circular charge distribution, and the doped holes in the a 1g band form a hole pocket sandwiched by two concentric Fermi surfaces with sixfold (and almost continuous) rotational symmetry. This symmetric state has an instability to an anisotropic state with twofold rotational symmetry, where the hole pocket is split into two pieces. This transition is governed by the anisotropic interaction between the a 1g and é g orbitals.
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