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Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system
S Das Sarma1, M P Lilly, E H Hwang
1Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
Physical Review Letters
|May 21, 2005
Summary
The 2D metal-insulator transition in n-GaAs is driven by density fluctuations, not a quantum critical point. This percolation transition occurs due to screening breakdown in the disordered electron system.
Area of Science:
- Condensed matter physics
- Materials science
Background:
- Understanding the 2D metal-insulator transition is crucial for novel electronic devices.
- High-mobility semiconductor heterostructures provide a platform for studying fundamental electron phenomena.
Purpose of the Study:
- To investigate the mechanism driving the 2D metal-insulator transition in undoped n-GaAs heterostructures.
- To determine if the transition is governed by quantum criticality or other factors.
Main Methods:
- Low-temperature analysis of 2D conductivity.
- Investigating density dependence in n-GaAs heterostructures.
- Comparing experimental conductivity exponents to theoretical models.
Main Results:
- The 2D metal-insulator transition is identified as a percolation transition.
- The transition is driven by density inhomogeneity and screening breakdown.
- The measured conductivity exponent (approx. 1.4) aligns with the 2D percolation exponent (4/3).
Conclusions:
- The experimental data contradict the existence of a zero-temperature quantum critical point.
- Density inhomogeneity and percolation are the primary drivers of the transition in this system.
- Screening breakdown in the charged impurity background plays a key role.
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