Figure 2: Entropy per electron in zero perpendicular field.
From: Strongly correlated two-dimensional plasma explored from entropy measurements
(a) The entropy per electron ∂S/∂n versus density (symbols) for various temperatures, sample Si-UW2. Inset: the same data versus dimensionless density (EF/T), the solid curve is the expectation for the Fermi gas with the Si band parameters, the dashed curve is the expectation for the FL with negative ∂m*/∂n (see text); (b) the effective mass m* versus density. The black curve corresponds to the approximation of m* from the Shubnikov-de-Haas measurements4. Symbols are the m*(n,T) data determined using equation (4) from the measured ∂S/∂n values. Different symbols correspond to different temperatures (shown in the inset). Scaling of the effective mass versus effective interaction parameter 
is shown in the inset(see text). (c) The signal ∂S/∂n(n) at 3.2 K for Si-UW2 is shown with filled symbols: at zero field (black boxes), B||=5.5 T (blue triangles) and 9 T (red boxes). Empty symbols (right axis) are the corresponding effective masses at B=0 (black) and B||=9 T (red). The bars illustrate schematically the band diagram for two spin subbands in the regions A, B and C. Vertical dashed lines depict schematic borders between the regions A, B and C. (d) The entropy of the 2D electron system measured in Si-UW2 for three temperatures (symbols). Inset: temperature dependence of the entropy for n=10.5 × 1011 cm−2 (EF=75 K) and 3.9 × 1011 cm−2 (EF=30 K). Dashed curves denote the upper estimate for the entropy.
