Controlling sign problems in spin models using tensor renormalization

Understand

We consider the sign problem for classical spin models at complex $\beta =1/g_0^2$ on $L\times L$ lattices.

• We show that the tensor renormalization group method allows reliable calculations for larger Im$\beta$ than the reweighting Monte Carlo method.
• For the Ising model with complex $\beta$ we compare our results with the exact Onsager-Kaufman solution at finite volume.
• The Fisher zeros can be determined precisely with the TRG method.