Figure 2.

The electronic-specific heat coefficient γ(n) in Si:P. The experimental data are from ref. 16, as is the dashed line, representing noninteracting electrons in a rigid band with the same effective mass value as in the pure crystal. The solid line is a smooth curve drawn through the experimental points, except that a break in slope has been placed at n = n_cb for the reasons discussed in the text. Note that for n > n_cb, the observed specific heat is parallel to, but larger than, the expected crystalline value, which corresponds to mass enhancement, which can be attributed to electron–electron interactions that drive the metallic carriers in extended states to blob and filament internal surfaces, where the internal electric fields are least screened. The plateau between n_c and n_cb has a quasi-spinodal character that represents the latent first-order nature of the phase transition. This first-order effect has been retained in the continuous phase transition because of its fractal nature (3).