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I understand the answer given in this question. It explains how we can measure the effective mass in a semiconductor.

However, I wonder what happens in the case of a multivalley semiconductor. Namely, a semiconductor in which the effective mass tensor may take a different form in distinct valleys. What effect does this give? Does it matter at all? And how can one take this into account experimentally?

Let me make a guess, just to indicate how a potential answer may look:

I would guess that, if the applied electromagnetic field respects the point group symmetries of the crystal, the measured effective mass would be some kind of superposition of the effective masses in each valley.

Furthermore, I would guess that if the electromagnetic field breaks any crystal symmetry, the valleys would become inequivalent. In this case, we would only measure the effective mass of a subset of the valleys.

I would very much appreciate an answer telling me if I am correct, in addition to a more quantitative explanation or a pointer to a more elaborate source.

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