Quantum criticality in many-body parafermion chains

Abstract

We construct local generalizations of 3-state Potts models with exotic critical points. We analytically show that these are described by non-diagonal modular invariant partition functions of products of Z_3Z3 parafermion or u(1)_6u(1)6 conformal field theories (CFTs). These correspond either to non-trivial permutation invariants or block diagonal invariants, that one can understand in terms of anyon condensation. In terms of lattice parafermion operators, the constructed models correspond to parafermion chains with many-body terms. Our construction is based on how the partition function of a CFT depends on symmetry sectors and boundary conditions. This enables to write the partition function corresponding to one modular invariant as a linear combination of another over different sectors and boundary conditions, which translates to a general recipe how to write down a microscopic model, tuned to criticality. We show that the scheme can also be extended to construct critical generalizations of kk-state clock type models.

Phase diagram of an extended parafermion chain

“…The result (19) represents two decoupled (o/e) quantum Potts chains. Consequently, at U = −1 the model possesses a second-order phase transition corresponding to a CFT with c = 4/5 + 4/5 = 8/5 (see also Reference [55]) depicted by C 2 in Figure 2, separating a trivial from a topological phase.…”

Phase diagram of an extended parafermion chain

“…The result (19) represents two decoupled (o/e) quantum Potts chains. Consequently, at U = −1 the model possesses a second-order phase transition corresponding to a CFT with c = 4/5 + 4/5 = 8/5 (see also Reference [46]) depicted by C 2 in Figure 2, separating a trivial from a topological phase.…”