= Ellipsoidal cyclotron mass
{title2=$m_c^2=\det M/(\widehat{\mathbf B}^TM\widehat{\mathbf B})$}
For a positive definite parabolic <effective mass> tensor $M$, the <Lorentz force> equation is $M\dot{\mathbf v}=e\mathbf B\times\mathbf v$. Its nonzero eigenfrequencies are $\pm eB/m_c$, giving the displayed mass. With principal values $(m_t,m_t,m_l)$, a field along the long valley axis gives $m_c=m_t$; a perpendicular field gives $\sqrt{m_tm_l}$. For equally oriented cubic valleys viewed along $[111]$, all valleys give $m_c=\sqrt{3m_t^2m_l/(2m_t+m_l)}$.
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