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Dragana Popović

Publications and source records attributed to Dragana Popović.

7 recordsLinked to original sources
PubMed2006

Nonexponential relaxations in a two-dimensional electron system in silicon.

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.

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PubMed2004

Magnetic-field dependence of the anomalous noise behavior in a two-dimensional electron system in silicon.

Studies of low-frequency resistance noise show that the dramatic change in the dynamics of the two-dimensional electron system (2DES) in Si that occurs near the metal-insulator transition (MIT) persists in high parallel magnetic fields B such that the 2DES is fully spin polarized. This strongly suggests that charge, as opposed to spin, degrees of freedom are responsible for this effect. In the metallic phase, however, noise is suppressed by a parallel B, pointing to the role of spins. At low B, the temperature dependence of conductivity in the metallic phase provides evidence for a MIT.

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PubMed2002

Universal behavior of the resistance noise across the metal-insulator transition in silicon inversion layers.

Studies of low-frequency resistance noise show that the glassy freezing of the two-dimensional (2D) electron system in the vicinity of the metal-insulator transition occurs in all Si inversion layers. The size of the metallic glass phase, which separates the 2D metal and the (glassy) insulator, depends strongly on disorder, becoming extremely small in high-mobility samples. The behavior of the second spectrum, an important fourth-order noise statistic, indicates the presence of long-range correlations between fluctuators in the glassy phase, consistent with the hierarchical picture of glassy dynamics.

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PubMed2002

Ising quantum Hall ferromagnet in magnetically doped quantum wells.

We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T(C) as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance "spikes" at T-->T(C) corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.

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PubMed2002

Onset of glassy dynamics in a two-dimensional electron system in silicon.

The fluctuations of conductivity sigma with time have been studied in a two-dimensional electron system in low-mobility Si inversion layers. The noise power spectrum is approximately 1/f(alpha) with alpha exhibiting a sharp jump at an electron density n(s) = n(g). A huge increase in the relative variance of sigma is observed as n(s) is reduced below n(g), reflecting a dramatic slowing down of the electron dynamics. This is attributed to the freezing of the electron glass. The data strongly suggest that glassy dynamics persists in the metallic phase.

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PubMed2002

Effects of a parallel magnetic field on the metal-insulator transition in a dilute two-dimensional electron system.

The temperature dependence of conductivity sigma(T) of a two-dimensional electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a metal-insulator transition at a critical electron density n(c)(0), and dsigma/dT>0 in the metallic phase. At low fields ( B < or approximately equal to 2 T), n(c) increases as n(c)(B)-n(c)(0) proportional, variant Bbeta ( beta approximately 1), and the zero-temperature conductivity scales as sigma(n(s),B,T = 0)/sigma(n(s),0,0) = f(B(beta)/delta(n)), where delta(n) = [n(s)-n(c)(0)]/n(c)(0) and n(s) is electron density, as expected for a quantum phase transition. The metallic phase persists in fields of up to 18 T, consistent with the saturation of n(c) at high fields.

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