Fermi pockets and quantum oscillations in specific heat of YBCO in the presence of disorder

We investigate a chiral d-density wave (CDDW) mean field model Hamiltonian in the momentum space suitable for the hole-doped cuprates, such as YBCO, in the pseudo-gap phase to obtain the Fermi surface(FS)topologies, including the anisotropy parameter(\'Epsilon) and the elastic scattering by disorder potential (|v0|). For \'Epsilon = 0, the chemical potential {\mu} = - 0.27 eV for 10% doping level, and |v0| \geq |t| (where |t| = 0.25 eV is the first neighbor hopping), at zero/non-zero magnetic field (B), the FS on the first Brillouin zone are found to correspond to Fermi pockets around anti-nodal regions and barely visible patches around nodal regions. For \'Epsilon \neq 0, we find Pomeranchuk distortion of FS. We next relate our findings regarding FS to the magneto-quantum oscillations in the electronic specific heat. Since the nodal quasi-particle energy values for B = 0 are found to be greater than {\mu} for |v0| \geq |t|, the origin of the oscillations for non-zero B corresponds to the Fermi pockets around anti-nodal regions. The oscillations are shown to take place for 17 T \leq B \leq 53 T and beyond in the weak disorder regime (|v0|=0.25eV) only.