Spin susceptibility of interacting two-dimensional electrons with anisotropic effective mass

We report measurements of the spin susceptibility in dilute (r_s up to ≈10) AlAs two-dimensional (2D) electrons occupying a single conduction-band valley with an anisotropic in-plane Fermi contour, characterized by longitudinal and transverse effective masses m_l and m_t. As the density is decreased, the spin susceptibility is significantly enhanced over its band value, reflecting the role of interaction. Yet the enhancement is suppressed compared to the results of quantum Monte Carlo based calculations that take the finite thickness of the electron layer into account but assume an isotropic effective mass equal to √m_l.m_t. Proper treatment of an interacting 2D system with an anisotropic effective mass therefore remains a theoretical challenge.