\hbar k (or equivalently h \over \lambda ).
\mathcal{L} = { 1 \over \omega } \mathcal{E}_c \left ( \mid \psi_R \mid^2 - \mid \psi_L \mid^2 \right ) = { \hbar \over V } \left ( \mid \psi_R \mid^2 - \mid \psi_L \mid^2 \right ) .