Anomalous beating phase of the oscillating interlayer magnetoresistance in layered metals

We analyze the beating behavior of the magnetic quantum oscillations in a layered metal under the conditions when the cyclotron energy ωc is comparable to the interlayer transfer energy t. Using a simple semiclassical model, we show that the positions of the beats in the interlayer resistance are considerably shifted from those in the magnetization oscillations. The shift is determined by the ratio ωc/t that may lead to significant deviations from the conventional periodicity of the beats in the scale of inverse magnetic field. A comparative study of the Shubnikov--de Haas and de Haas--van Alphen oscillations in the layered organic metal β-(BEDT-TTF)₂IBr₂ is performed and shown to be consistent with the theoretical prediction.