Metal–insulator transition in two-dimensional electron systems

Abstract

The interplay between strong Coulomb interactions and randomness has been a long-standing problem in condensed matter physics. According to the scaling theory of localization, in two-dimensional systems of noninteracting or weakly interacting electrons, the ever-present randomness causes the resistance to rise as the temperature is decreased, leading to an insulating ground state. However, new evidence has emerged within the past decade indicating a transition from insulating to metallic phase in two-dimensional systems of strongly interacting electrons. We review earlier experiments that demonstrate the unexpected presence of a metallic phase in two dimensions, and present an overview of recent experiments with emphasis on the anomalous magnetic properties that have been observed in the vicinity of the transition.

Conductivity of a spin-polarized two-dimensional electron liquid in the ballistic regime

“…In theory, 13 the ratio A * ͑B sat ͒ / A * ͑0͒ ͑for a two-valley 2D system͒ is formally equal to ͑1+4F 0 ͒ / ͑1 + ␣F 0 ͒, 25 once the effective mass, as well as the g factor, are independent of the degree of spin polarization. 1,2 Here the interaction parameter F 0 is responsible for the renormalization of the g factor through g =2/͑1+F 0 ͒, the coefficient ␣ =8 if T Ͻ⌬ v and ␣ =16 if T Ͼ⌬ v , and ⌬ v is the valley splitting. For negative F 0 , the observed slope ratio ͑Fig.…”

Impact of short-range scattering on the metallic transport of strongly correlated two-dimensional holes in GaAs quantum wells

“…We have studied the transport of high mobility 2D holes in 20nm wide GaAs quantum wells (QWs) with varying short-range disorder strength by changing the Al fraction x in the Al x Ga 1-x As barrier. Via varying the short range interface roughness and alloy scattering, it is observed that increasing x suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short-range versus long-range disorder in the 2D metallic transport in this correlated 2D hole system with interaction parameter r s~ 20.PACS Numbers: 71.30.+h, 73.63.Hs For the past thirty years, two-dimensional (2D) quantum systems have been a rich area of concentrated study for both theorists and experimentalists to explore the interplay between Coulomb interaction and disorder effects [1][2][3][4]. In the case of 2D electrons with ultra-low density and weak disorder, the quantum and strongly interacting nature of the systems becomes so prominent that various complex quantum phases and phase transitions may exist according to theory [5][6][7][8][9][10][11].…”

“…In the case of 2D electrons with ultra-low density and weak disorder, the quantum and strongly interacting nature of the systems becomes so prominent that various complex quantum phases and phase transitions may exist according to theory [5][6][7][8][9][10][11]. Obtaining a clear understanding of such strongly correlated 2D systems thus remains to be extremely important in the field of many-body physics.In 2D electron or hole samples with high mobility, an intriguing metal to insulator transition (MIT) was observed in zero magnetic field (B=0) with the carrier density as the tuning parameter [2,3,12]. Although strong electron-electron interactions are believed to be an essential factor in the origin of this MIT in 2D, the effects of disorder seem to be non-negligible and must be incorporated in order to reconcile the subtle differences in all the 2D MIT experiments over a range of disorder and interaction strength [2,3,[13][14][15].…”

“…PACS Numbers: 71.30.+h, 73.63.Hs For the past thirty years, two-dimensional (2D) quantum systems have been a rich area of concentrated study for both theorists and experimentalists to explore the interplay between Coulomb interaction and disorder effects [1][2][3][4]. In the case of 2D electrons with ultra-low density and weak disorder, the quantum and strongly interacting nature of the systems becomes so prominent that various complex quantum phases and phase transitions may exist according to theory [5][6][7][8][9][10][11].…”

“…In 2D electron or hole samples with high mobility, an intriguing metal to insulator transition (MIT) was observed in zero magnetic field (B=0) with the carrier density as the tuning parameter [2,3,12]. Although strong electron-electron interactions are believed to be an essential factor in the origin of this MIT in 2D, the effects of disorder seem to be non-negligible and must be incorporated in order to reconcile the subtle differences in all the 2D MIT experiments over a range of disorder and interaction strength [2,3,[13][14][15].…”