Quantum Potts Models on the Sierpi\'nski Pyramid

Phase transition of the two- and three-state quantum Potts models on the Sierpi\'nski pyramid are studied by means of a tensor network framework, the higher-order tensor renormalization group method. Critical values of the transverse magnetic field and the magnetic exponent $\beta$ are evaluated. Despite the fact that the Hausdorff dimension of the Sierpi\'nski pyramid is exactly two $( = \log_2^{~} 4)$, the obtained critical properties show that the effective dimension is lower than two.