Strongly correlated two-dimensional plasma explored from entropy measurements

Abstract

Charged plasma and Fermi liquid are two distinct states of electronic matter intrinsic to dilute two-dimensional electron systems at elevated and low temperatures, respectively. Probing their thermodynamics represents challenge because of lack of an adequate technique. Here, we report a thermodynamic method to measure the entropy per electron in gated structures. Our technique appears to be three orders of magnitude superior in sensitivity to a.c. calorimetry, allowing entropy measurements with only 10 8 electrons. This enables us to investigate the correlated plasma regime, previously inaccessible experimentally in twodimensional electron systems in semiconductors. In experiments with clean two-dimensional electron system in silicon-based structures, we traced entropy evolution from the plasma to Fermi liquid regime by varying electron density. We reveal that the correlated plasma regime can be mapped onto the ordinary non-degenerate Fermi gas with an interaction-enhanced temperature-dependent effective mass. Our method opens up new horizons in studies of low-dimensional electron systems.

On the Heat Capacity of a Quasi-Two-Dimensional Electron Gas

“…According to Figure 2(a), at sufficiently low temperatures, the specific heat varies abruptly, i.e., practically repeating the dependence of the density of states (see Figure 1(a)). This is also seen from the analytical result (20). The peak width of derivative d / dT at the resonance point is also small ∼ T and is not noticeable in the graph.…”

“…Under certain conditions, the effects of size quantization appear in the observed thermodynamic quantities even in the absence of a magnetic field [16][17][18][19][20][21][22][23].…”

Two-loop renormalization of the Finkel’stein theory: The specific heat

“…Observed temperature and electron density dependence of resistivity resembles the expected behavior of resistivity near a 2D metal-insulator transition and was found to be in reasonable agreement with the predictions of the two-parameter scaling theory [38][39][40]. However, recent thermodynamics and transport measurements in Si metal-oxide-semiconductor field effect transistor suggest that the observed strong temperature and electron concentration dependence of resistivity occurs in the regime of nondegenerate Fermi system and, consequently, has nothing to do with the metal-insulator quantum phase transition [41][42][43][44][45]. These new experimental results call for development of the transport theory of nondegenerate strongly interacting 2D electron system, on the one hand, and more detailed understanding of the 2D metal-insulator transition within NLSM approach, on the other hand.…”

Measurements of the magnetic properties of conduction electrons

“…In Refs. [23,24,238,255] the measured oscillations of the thermodynamic parameters for 2D electron system were compared with theory. The shape of the measured quantum oscillations in [121,256] turned out to be described in the best way using the Lorentzian distribution with field independent Γ, and by using ζ as an adjustable parameter.…”