A. A. Shashkin

Sharp increase of the effective mass near the critical density in a metallic two-dimensional electron system

We find that at intermediate temperatures, the metallic temperature dependence of the conductivity σ(T) of two-dimensional electrons in silicon is described well by a recent interaction-based theory of Zala et al. [Phys. Rev. B 64, 214204 (2001)]. The tendency of the slope σ - 1 dσ/dT to diverge near the critical electron density is in agreement with the previously suggested ferromagnetic instability in this electron system. Comparing theory and experiment, we arrive at a conclusion that the instability, unexpectedly, originates from the sharp enhancement of the effective mass, while the effective Lande g factor remains nearly constant and close to its value in bulk silicon.

Indication of the ferromagnetic instability in a dilute two-dimensional electron system.

The magnetic field B(c), in which the electrons become fully spin polarized, is found to be proportional to the deviation of the electron density from the zero-field metal-insulator transition in a two-dimensional electron system in silicon. The tendency of B(c) to vanish at a finite electron density suggests a ferromagnetic instability in this strongly correlated electron system.

Metal–insulator transitions and the effects of electron–electron interactions in two-dimensional electron systems

Experimental results on metal–insulator transitions and the anomalous properties of strongly interacting two-dimensional electron systems are reviewed and critically analyzed. Special attention is given to recent results on strongly enhanced spin susceptibility and effective mass in low-disordered silicon MOSFETs.

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.

Canted antiferromagnetic phase in a double quantum well in a tilted quantizing magnetic field.

We investigate the double-layer electron system in a parabolic quantum well at filling factor nu=2 in a tilted magnetic field using capacitance spectroscopy. The competition between two ground states is found at the Zeeman splitting appreciably smaller than the symmetric-antisymmetric splitting. Although at the transition point the system breaks up into domains of the two competing states, the activation energy turns out to be finite, signaling the occurrence of a new insulator-insulator quantum phase transition. We interpret the obtained results in terms of a predicted canted antiferromagnetic phase.

Pauli spin susceptibility of a strongly correlated two-dimensional electron liquid

Thermodynamic measurements reveal that the Pauli spin susceptibility of strongly correlated two-dimensional electrons in silicon grows critically at low electron densities--behavior that is characteristic of the existence of a phase transition.

Strong enhancement of the valley splitting in a two-dimensional electron system in silicon

Using magnetocapacitance data, we directly determine the chemical potential jump in a strongly correlated two-dimensional electron system in silicon when the filling factor traverses the valley gap at

Destruction of localized electron pairs above the magnetic-field-driven superconductor-insulator transition in amorphous In-O films

\ensuremath{\nu}=1

Critical Behavior of a Strongly Interacting 2D Electron System

and

Scaling Analysis of the Magnetic Field-Tuned Quantum Transition in Superconducting Amorphous In-O Films 1

\ensuremath{\nu}=3.