Two-Level System — Schottky Anomaly

kBT/ε = 1.05

Populations

E₀ = 0
p₀ = 0.50
E₁ = ε
p₁ = 0.50

Mean Energy ⟨E⟩/ε

Heat Capacity C/kB vs kBT/ε

Partition Function Z

The heat capacity peaks at kBT ≈ 0.417 ε (βε ≈ 2.399) — the Schottky anomaly. At low T the system is frozen in the ground state; at high T both levels are equally populated and C → 0.