Spin polarization and exchange-correlation effects in transport properties of two-dimensional electron systems in silicon

Abstract

We show that the parallel magnetic field-induced increase in the critical electron density for the Anderson transition in a strongly interacting two-dimensional electron system is caused by the effects of exchange and correlations. If the transition occurs when electron spins are only partially polarized, additional increase in the magnetic field is necessary to achieve the full spin polarization in the insulating state due to the exchange effects.PACS numbers: 71.10.-w, 71.27.+a, 71.30.+h The metal-insulator transition (MIT) in twodimensional (2D) electron systems, studied experimentally and theoretically in 1970s [1], was declared nonexistent after negative logarithmic quantum corrections to the conductivity had been found (for a review, see Ref.[2]). The reasoning was as follows. In an infinite 2D system, upon decreasing temperature, negative quantum logarithmic corrections to the conductivity will eventually become comparable to the conductivity itself. After this, conductivity will decrease exponentially. Therefore, the system will inevitably become an insulator no matter how high the initial value of the conductivity is. However, it has later been shown both theoretically [3][4][5][6] and experimentally [7,8] that this conclusion may be wrong in 2D systems with strong electron-electron interactions.Since there has been a certain amount of confusion and controversy in the literature regarding the zero-temperature MIT in infinite 2D systems (see, e.g., Ref.[9]), here we will consider a disorder-driven Anderson MIT at finite (although low) temperatures and in finite 2D systems. (As correctly stated in Ref. [10], the question about the true MIT is "a rather academic question as what has actually been measured experimentally corresponds to rather high energy physics".) Attempts to describe the experimentally observed behavior of the critical density for the MIT in silicon metaloxide-semiconductor field-effect transistors (MOSFETs) as a function of a parallel to the interface magnetic field, B, were made by quite a few theoretical groups [10][11][12][13][14][15]. Nevertheless, the satisfactory explanation of experimental results is still absent. Monte Carlo calculations and finite size scaling techniques [10,11] show that the spin polarization in strongly-correlated electron systems favors localization. Using the appraisal Ioffe-Regel criterion to calculate the critical density in the Born approximation with two fitting parameters, the authors of Ref. [12] have achieved a satisfactory agreement with the experiment, but correlation effects have not been taken into account and their negligibility in the case of strong electron-electron interactions has not been established. Doubts in the applicability of the percolation scenario to the transition in Si MOSFETs [13] are expressed in Ref. [12]. The increase of the effective mass with decreasing electron density suggests that the effect of interactions is the dominant driving force for the experimentally observed MIT due to fermion condensation [14] or the Wigner-...

Recent Developments in the Field of the Metal-Insulator Transition in Two Dimensions

“…Another effect of the parallel magnetic field is that it wipes out the strong metallic temperature dependence of the resistance at electron densities just above n c and suppresses the metallic regime [7,17,19,[25][26][27]. In Fig.…”

Chapter 2. Metal-Insulator Transition in a Strongly Correlated Two-Dimensional Electron System

“…It is interesting to compare the ratio n c (B * )/n c (0) ≈ 1.2 of the measured critical densities for the MIT to that calculated in Ref. [28]. According to the calculations, the increase of the critical electron density for the Anderson transition in a strongly interacting 2D electron system with increasing B is due to the exchange and correlation effects, and the ratio between the critical electron densities for fully spin-polarized and unpolarized electron systems is independent of the density of impurities and is equal to ≈ 1.33.…”

New Reentrant Insulating Phases in Strongly Interacting 2D Systems with Low Disorder

“…In the zero field MIT, it was established that an in-plane magnetic field causes large positive magneto-resistance and drives the system toward the insulating phase [8,9,42,43]. Recent in-plane field magneto-transport experiments revealed that the resistivity of dilute 2D electrons in Si-MOSFET in the insulating state are the same for zero field and in the presence of an in-plane field that polarizes the spins [43], a behavior different from the metallic phase of the 2D MIT [8,9,42]. It would be thus very insightful to study the effect in-plane magnetic field induced spinpolarization effect on the RIPs and examine how the in-plane field affects the transition between the RIPs and metallic liquid.…”