# What are some examples of systems which have non-zero entropy at zero temperature?

At zero temperature, the entropy of generic systems need not vanish, but often seems to in practice. I would like to know some concrete examples where $$S\neq 0$$ at $$T=0$$.

A very high-energy flavored scenario where $$S\neq 0$$ at $$T=0$$ is the case of extremal black holes, where $$S=\frac{\rm Area}{4G_N}\neq 0$$. I believe glassy systems (and frustrated systems, more generally) also have non-trivial zero-$$T$$ entropy.

What are some additional systems which have $$S\neq 0$$ at $$T=0$$? References are appreciated.