Valley degeneracy in tunneling current

[Noki Lee]

I'm trying to understand the valley degeneracy to calculate the tunneling current.

Here is the equation of tunneling current.$$I_T=q\frac {g_sg_v} {L} \sum_{k} v_g(k)(f_v-f_c)T$$

$g_v$ is valley degeneracy. I thought it comes from the symmetry of structures, depending on a certain point in k-space like below

$$I_T=q\frac {g_s} {L} \sum_{k} g_v(k)v_g(k)(f_v-f_c)T$$

How can I count the number of valley degeneracy?
And what I'm misunderstanding?

 

[azntoon]

The valley degeneracy factor, g_v, is a measure of the number of valleys, or distinct energy minima, in the band structure of the material. It is related to the symmetry of the crystal lattice and the number of distinct energy minima that exist in the Brillouin zone. In general, it is determined by counting the number of distinct points in the Brillouin zone where the band has a minimum energy. This number may be equal to 1, 2, 3, or more, depending on the material and its lattice structure. For example, in a two-dimensional honeycomb lattice, the band structure includes two distinct valleys at the corners of the Brillouin zone (K and K'), so the valley degeneracy factor, g_v, would be equal to 2.