Acoustic phonon branch
= Acoustic phonon branch
An acoustic phonon branch has $\omega(k)\to0$ as $k\to0$. Its long-wavelength <group velocity> is the <speed of sound>.
= Acoustic phonon branch
An acoustic phonon branch has $\omega(k)\to0$ as $k\to0$. Its long-wavelength <group velocity> is the <speed of sound>.