Spin-Independent Origin of the Strongly Enhanced Effective Mass in a Dilute 2D Electron System

We accurately measure the effective mass in a dilute two-dimensional electron system in silicon by analyzing the temperature dependence of the Shubnikov–de Haas oscillations in the low-temperature limit. A sharp increase of the effective mass with decreasing electron density is observed. We find that the enhanced effective mass is independent of the degree of spin polarization, which points to a spin-independent origin of the mass enhancement and is in contradiction with existing theories.

Figure 1

Change of the amplitude of the weak-field SdH oscillations with temperature at $n_s=1.17\times {10}^{11}{\mathrm{c}\mathrm{m}}^{-2}$ for oscillation numbers $\nu =hc{n}_s/e{B}_{\perp }=10$ (dots) and $\nu =14$ (squares). The value of $T$ for the $\nu =10$ data is divided by the factor of 1.4. The solid line is a fit using Eq. (1).

Figure 2

Dependence of the effective mass on electron density in the spin-unpolarized system. Also shown by a dashed line are the data obtained using the method of Refs. 9, 13.

Figure 3

The effective mass vs the degree of spin polarization for the following electron densities in units of ${10}^{11}{\mathrm{c}\mathrm{m}}^{-2}$: 1.32 (dots), 1.47 (squares), 2.07 (diamonds), and 2.67 (triangles). The dashed lines are guides to the eye.

Figure 4

Behavior of the Dingle temperature extracted from SdH oscillations (dots) and that calculated from the transport scattering time (dashed line) with electron density in the spin-unpolarized system (a) and with the degree of spin polarization (b). In (b) the electron density is equal to $1.47\times {10}^{11}{\mathrm{c}\mathrm{m}}^{-2}$.