Conductance noise in an out-of-equilibrium two-dimensional electron system

Abstract

A study of the conductance noise in a two-dimensional electron system (2DES) in Si at low temperatures (T ) reveals the onset of large, non-Gaussian noise after cooling from an equilibrium state at a high T with a fixed carrier density ns. This behavior, which signifies the falling out of equilibrium of the 2DES as T → 0, is observed for ns < ng (ng -glass transition density). A protocol where density is changed by a small value ∆ns at low T produces the same results for the noise power spectra. However, a detailed analysis of the non-Gaussian probability density functions (PDFs) of the fluctuations reveals that ∆ns has a qualitatively different and more dramatic effect than ∆T , suggesting that ∆ns induces strong changes in the free energy landscape of the system as a result of Coulomb interactions. The results from a third, waiting-time (tw) protocol, where ns is changed temporarily during tw by a large amount, demonstrate that non-Gaussian PDFs exhibit history dependence and an evolution towards a Gaussian distribution as the system ages and slowly approaches equilibrium. By calculating the power spectra and higher-order statistics for the noise measured over a wide range of the applied voltage bias, it is established that the non-Gaussian noise is observed in the regime of Ohmic or linear response, i.e. that it is not caused by the applied bias.

Evidence for correlated dynamics near the Berezinskii-Kosterlitz-Thouless-like transition in highly underdopedLa2−xSrxCuO4

“…Therefore, the system is nonergodic on experimental time scales [54]. Similar out-of-equilibrium behavior was found in spin [26] and Coulomb glasses [28][29][30][31][32], systems that wander collectively, with time, between many metastable states. We note that here the observed change in the dynamics occurs near T c , i.e.…”

“…In the studies of glasses, it was argued [26,55], albeit not calculated theoretically, that such S 2 (f 2 , f ) should be scale invariant, or independent of f , in models in which the system wanders collectively between many metastable states related by a kinetic hierarchy. Such scale-free behavior was indeed observed in metallic spin glasses [26,55] and Coulomb glasses [27][28][29][30], both systems with long-range interactions. In contrast, a decrease of S 2 (f 2 , f ) with f at constant f 2 /f , similar to that in Fig.…”

“…Also, in complex impedance studies, disorder-induced inhomogeneity may lead to spurious effects at low f [23], and magnetic flux noise is more susceptible to surface [24] and geometrical [25] effects. In contrast, R noise has been a powerful probe of correlated dynamics in many systems [26][27][28][29][30], including lightly doped, insulating LSCO [31,32]. Being a bulk probe, it is less sensitive to surface and geometrical effects, and it measures R directly.…”

Charge avalanches and depinning in the Coulomb glass: The role of long-range interactions

“…Early work also revealed that Coulomb interactions in disordered insulators generally contribute to the formation of an extensive number of metastable states, i.e., the formation of the Coulomb glass (CG) [6][7][8]. In subsequent work, various aspects of glassy behavior of the CG were explored theoretically [9][10][11][12][13][14][15][16][17][18] and experimentally [19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Phase coexistence and dynamical behavior inNdNiO3ultrathin films

“…The contour plot shows a 'splitting' of the PDF at certain points in time, extending for up to tens of minutes. Multipeak PDFs have been observed in two dimensional electron systems in Si, and were attributed to the existence of a 'rugged' free energy landscape 57 . We describe the 'split' state as having transport processes resulting in two relaxation times, τ 1 and τ 2 , such that τ 1 >τ and τ 2 <τ .…”