Effective models for gapped phases of strongly correlated quantum lattice models

Understand

We present a robust scheme to derive effective models non-perturbatively for quantum lattice models when at least one degree of freedom is gapped.

• A combination of graph theory and the method of continuous unitary transformations (gCUTs) is shown to efficiently capture all zero-temperature fluctuations in a controlled spatial range.
• The gCUT can be used either for effective quasi-particle descriptions or for effective low-energy descriptions in case of infinitely degenerate subspaces.
• We illustrate the method for 1d and 2d lattice models yielding convincing results in the thermodynamic limit.