Effect of quenched impurities on long-range order in systems with a frustrated ground state

Abstract

Destruction of long-range order (LRO) in interacting systems with a frustrated ground state due to quenched dilution is discussed. In such systems there is an additional contribution to the disordering process when initially frustrated bonds become satisfied as dilution removes the competing bonds. It is therefore expected that at $T=0$, LRO vanishes at an impurity concentration ${q}_{L}$ which is lower than the corresponding percolation threshold impurity concentration ${q}_{c}$. To study this phenomenon the anisotropic Ising antiferromagnet on a triangular lattice with quenched site dilution is analyzed. An estimate for ${q}_{L}$ is obtained by means of series-expansion methods. This model may describe the magnetic phase of oxygen adsorbed on graphite which has been of considerable interest in recent years.