Calculate the effective mass m* of electron with the momentum k- G/2 in a weak periodic potential U(r) = 2U0 cos(27x/a) for which the energy spectrum E(k) is given by Eq. (1.3.22) of Lect. 4. The mass m* is defined by the behavior of E(k) at k x G/2: h?q? E(k) = Em - G G 2m* Can m* be smaller or larger than the free electron mass?

Calculate the effective mass m* of electron with the momentum k- G/2 in a weak periodic potential U(r) = 2U0 cos(27x/a) for which the energy spectrum E(k) is given by Eq. (1.3.22) of Lect. 4. The mass m* is defined by the behavior of E(k) at k x G/2: h?q? E(k) = Em - G G 2m* Can m* be smaller or larger than the free electron mass?

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