Nonexponential Relaxations in a Two-Dimensional Electron System in Silicon

Abstract

The relaxations of conductivity have been studied in a strongly disordered two-dimensional (2D) electron system in Si after excitation far from equilibrium by a rapid change of carrier density ns at low temperatures T. The dramatic and precise dependence of the relaxations on ns and T strongly suggests (a) the transition to a glassy phase as T-->0, and (b) the Coulomb interactions between 2D electrons play a dominant role in the observed out-of-equilibrium dynamics.

Nonequilibrium Relaxations and Aging Effects in a Two-Dimensional Coulomb Glass

“…Such scaling has been observed in spin glasses above T g [12]. The dependence / expn 1=2 s (-a proportionality constant) [9] is a strong indication for the relevance of Coulomb interactions between 2D electrons [13] in the n s < n g regime. The most puzzling feature of the relaxation in Ref.…”

“…Furthermore, studies of the relaxations of the conductivity [9], following a rapid change of n s , show that the equilibration time eq [11] diverges exponentially as temperature T ! 0, suggesting a glass transition at T g 0.…”

“…The same devices were used in Ref. [9], and they were also very similar to the samples used in noise studies [7]. The density n s is controlled by the gate voltage V g , such that n s 10 11 cm ÿ2 4:31V g V ÿ V T , where the threshold voltage for forming the 2D layer V T 6:3 V for V sub ÿ2 V; n g 10 11 cm ÿ2 7:5 and n c 10 11 cm ÿ2 4:5 [9].…”

Intermediate phase at the metal-insulator boundary in a magnetically doped two-dimensional electron system

“…Indeed, such manifestations of glassiness and evidence for an intermediate metallic phase have been found recently in a 2DES in Si metal-oxidesemiconductor field-effect transistors ͑MOSFETs͒. [5][6][7] There is also growing evidence that phase separation is responsible for several striking effects in bulk transition metal oxides, such as manganites, 8 cuprates, 9 and similar complex magnetic materials. 10 In that context, magnetically doped 2DESs ͑M2DESs͒ in semiconductor heterostructures constitute an ideal system for studying both magnetism and reduced dimensionality effects near the MIT.…”

Aging of solid 4He under torsional oscillation at low temperatures

“…For example, measurements [47] carried out on a disordered twodimensional electron system in silicon metal-oxidesemiconductor show that when the applied gate voltage is suddenly decreased the conductivity undergoes a rapid undershoot before recovering slowly towards steady value. Unlike our system, however, collapse of the observed time dependent conductivity [48] when plotted against the ratio / w tt is similar to the simple aging behavior in spin glasses.…”