Magnetic order arises from interactions between electronic spins. This introduces correlation in the quantum mechanical wavefunction, which renders a theoretical description highly challenging. One tyically resorts to the Heisenberg model, which captures the essential physics, but even that model cannot be solved without certain approximations.
Very recently, it was demonstrated that the two-dimensional material CrI3 exhibits magnetic order below 45 K. This is the first example ever of a magnetic 2D material and the microscopic mechanism that is responsible for magnetic order is linked to the magnetic anisotropy in the material.
In the present project we will study the 2D Heisenberg model with anisotropy relevant for CrI3. We combine quantum mechanical calculations with statistical physics to obtain a theoretical estimate of the critical temperature. In particular, we will use the method of Schwinger bosons that maps the spin operators on to a set of bosonic operators that create and anihilate spin exciations. The resulting equations can be handled in a mean field framework if a holonomic constraint on the operators is included.
Electronic structure methods in solid state physics