New fundamental dHvA frequency in canonical low-dimensional fermi liquids

We show that a new fundamental period $P_{f}$ of dHvA oscillations, which appears along with other "forbidden" combination frequencies in a multi-band canonical Fermi-liquid, is very robust with respect to a finite smearing of Landau levels and a background of non-quantized states. We analyse the possibility of measuring small Fermi surface pockets with the use of the "forbidden" frequencies.