Phase diagram of depleted Heisenberg model for CaV4O9

TL;DR

This study maps the phase diagram of the 1/5-depleted Heisenberg model for CaV4O9 using quantum Monte Carlo, revealing how small frustrating interactions can induce a quantum disordered phase.

Contribution

It provides the first detailed numerical phase diagram of the depleted Heisenberg model relevant to CaV4O9, highlighting the effects of frustration on magnetic order.

Findings

Long-range order persists at isotropic coupling.

Small frustrating interactions can induce a quantum disordered phase.

The model explains the spin gap behavior of CaV4O9.

Abstract

We have numerically investigated the 1/5-depleted Heisenberg square lattice representing CaV4O9 using the Quantum Monte Carlo loop algorithm. We have determined the phase diagram of the model as a function of the ratio of the two different couplings: bonds within a plaquette and dimer bonds between plaquettes. By calculating both the spin gap and the staggered magnetization we determine the range of stability of the long range ordered (LRO) phase. At isotropic coupling LRO survives the depletion. But the close vicinity of the isotropic point to the spin gap phase leads us to the conclusion that already a small frustrating next nearest neighbor interaction can drive the system into the quantum disordered phase and thus explain the spin gap behavior of CaV4O9.