Quantum oscillations in quasi-one-dimensional metals with spin-density-wave ground states

We consider the magnetoresistance oscillation phenomena in the Bechgaard sa lts (TMTSF)(2)X, where X = ClO4, PF6, and AsF6 in pulsed magnetic fields to 51 T. Of particular importance is the observation of a new magnetoresistan ce oscillation for X = ClO4 in its quenched state. In the absence of any Fe rmi-surface reconstruction due to anion order at low temperatures, all thre e materials exhibit nonmonotonic temperature dependence of the oscillation amplitude in the spin-density-wave (SDW) state. We discuss a model where, b elow a characteristic temperature T* within the SDW state, a magnetic break down gap opens. [S0163-1829(99)00904-2].