Negative differential conductivity and oscillations in the lifetime of nonequilibrium phonons in bismuth

A region with negative differential conductivity is observed in the stationary current-voltage characteristic of bismuth in the sound generation regime. The existence of such conductivity is related to cooling of the electron gas with increasing electric field intensity. It is found that the relaxation time upon transition to the phonon generation regime depends nonmonotonically on magnetic field and is insensitive to change in electric field within the limits of experimental error. On this basis it is concluded that the phonon–electron interaction plays a dominant role in the process of instability stabilization in bismuth. The most probable frequency range (107 Hz at H ∼ 10 kOe) generated by “supersonic” electrons is indicated.

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