G. Vongehlen, NON-HERMITIAN TRICRITICALITY IN THE BLUME-CAPEL MODEL WITH IMAGINARY FIELD, International journal of modern physics b, 8(25-26), 1994, pp. 3507-3529
Using finite-size-scaling methods, we study the quantum chain version
of the spin-1-Blume-Capel model coupled to an imaginary field. The aim
is to realize simple non-unitary minimal conformal field theories in
an Ising-type spin model. We find that the first ground-state level cr
ossing in the high-temperature phase leads to a second-order phase tra
nsition of the Yang-Lee universality class (central charge c = 22/5).
The Yang-Lee transition region ends at a line of a new type of tricrit
icality, where the three lowest energy levels become degenerate. The a
nalysis of the spectrum at two points on this line gives good evidence
that this line realizes the universality class of the M2, 7-conformal
theory with c = -68/7.