Nuclear spin-lattice relaxation in superlattices

The nuclear spin-lattice relaxation rate in a superlattice subjected to a strong magnetic field H parallel to its axis is studied theoretically. The energy conservation law allows flip-flop spin-reversal processes due to the hyperfine interaction between the nuclear and electron spins only in some intervals of H. In particular, the width of the highest occupied superlattice subband Δ must exceed the spin splitting of Landau levels, which results in the relaxation offset at some critical magnetic field H₂. At H2 and low temperatures, the relaxation rate T₁^-1 versus H dependence has giant oscillations depending on the Fermi level position. The behavior of T₁ can be changed by the tilting of the magnetic field, decreasing the Landau level separation at a constant spin-splitting. At some critical tilt angle, these two quantities become equal and inter-Landau-level processes come into action which drastically increases the relaxation rate.