The lower endpoint of a two-liquid coexistence region. In the lower-critical case, demixing can be induced by heating above the endpoint.

A boundary giving the equilibrium limit of one solid solution against coexistence with another solid phase. Moving along a solvus during cooling changes equilibrium solid compositions even after all liquid has disappeared.

The experiment follows phonon peaks as both momentum and energy transfer are varied. In inelastic neutron scattering, $\mathbf{q}={\mathbf{k}}_i-{\mathbf{k}}_f$ locates the lattice modulation and $\hslash \omega =E_i-E_f$ measures the mode energy, so a softened mode can be distinguished from static diffraction alone. Measurements on deuterated TTF-TCNQ between $60$ and $300\mathrm{K}$ found a growing Kohn anomaly near $2k_F$ below about $150\mathrm{K}$ as the $54\mathrm{K}$ transition was approached.^[ref]

Suppression of a transition when its required final fermion state is already occupied. In a low-temperature Fermi gas, an otherwise allowed collision must place outgoing particles in empty states; occupation restricts its available phase space. This does not mean that fermions cease interacting.

One identical fermion in each of two input modes remains one in each output after a lossless two-mode unitary transformation. The fully occupied two-mode state transforms by the determinant phase. Pauli exclusion prevents double occupation of either specified mode.

Path independence requires the same line integral for every admissible path between fixed endpoints, not merely a few selected paths. For example, the smooth field $\mathbf{F}=(y-z,0,0)$ vanishes on the entire plane $y=z$. Every path in that plane from $(0,0,0)$ to $(1,1,1)$ therefore has zero integral. Yet the path through $(0,1,0)$ and $(1,1,0)$ has integral one: only the horizontal middle segment contributes. The curl is $(0,-1,-1)$, confirming that the field is not conservative. Special paths can hide a nonconservative component.