Fermionic algebraic quantum spin liquid in an octa-kagome frustrated antiferromagnet

We investigate the ground state and finite-temperature properties of the spin-1/2 Heisenberg antiferromagnet on an infinite octa-kagome lattice by utilizing state-of-the-art tensor network-based numerical methods. It is shown that the ground state has a vanishing local magnetization and possesses a $1/2$-magnetization plateau with an up-down-up-up spin configuration. A quantum phase transition at the critical coupling ratio ${J}_d/{J}_t=0.6$ is found. When $0<{J}_d/{J}_t<0.6$, the system is in a valence bond state, where an obvious zero-magnetization plateau is observed, implying a gapful spin excitation; when ${J}_d/{J}_t>0.6$, the system exhibits a gapless excitation, in which the dimer-dimer correlation is found decaying in a power law, while the spin-spin and chiral-chiral correlation functions decay exponentially. At the isotropic point (${J}_d/{J}_t=1$), we unveil that at low temperature $T$, the specific heat depends linearly on $T$, and the susceptibility tends to a constant for $T\ensuremath{\rightarrow}0$, giving rise to a Wilson ratio around unity, implying that the system under interest is a fermionic algebraic quantum spin liquid.