Anomalous Fisher-like zeros for the canonical partition function of   noninteracting fermions
  Noninteracting fermions, placed in a system with a continuous density of states, may have zeros in the $N$-fermion canonical partition function on the positive real $\beta$ axis (or very close to it), even for a small number of particles. This results in a singular free energy, and instability in other thermal properties of the system. In the context of trapped fermions in a harmonic oscillator, these zeros are shown to be unphysical. By contrast, similar bosonic calculations with continuous density of states yield sensible results.Noninteracting fermions, placed in a system with a continuous density of states yield sensible results. 
R. K. Bhaduri, A. MacDonald and W. van Dijk
cond-mat.stat-mech cond-mat.quant-gas