Principal thermodynamic properties of quasi-two-dimensional carriers under in-plane magnetic field.

An external magnetic field, H, applied parallel to a quasi-two-dimensional carrier system modifies quantitatively and qualitatively the density of states. We examine how this affects primary thermodynamic properties, namely, the entropy, S, the internal and free energy, U and F, the magnetization, M, and the magnetic susceptibility, χ(m), using a self-consistent numerical approach. Although M is mainly in the opposite direction to H, the system is not linear. Hence, surprisingly, [Formula: see text] swings between negative and positive values, i.e. a diamagnetic to paramagnetic transition of entirely orbital origin is predicted. This phenomenon is important compared to the ideal de Haas-van Alphen effect, i.e. the corresponding phenomenon under perpendicular magnetic field. By augmenting temperature, the diamagnetic to paramagnetic transition fades away. The overall behaviour of entropy is also foreseen and consistently interpreted. While the entropy contribution to the free energy is very small at low temperatures, entropy shows a clear dependence on the external magnetic field.