Year: 2022
Type: article
Abstract: Using the Ioffe-Regel-Mott criterion for strong localization crossover in disordered doped two-dimensional (2D) electron systems, we theoretically study the relationships between the three key experimentally determined localization quantities: critical density ${n}_{\mathrm{c}}$, critical resistance ${\ensuremath{\rho}}_{\mathrm{c}}$, and sample quality defined by the effective impurity density (as experimentally diagnosed by the sample mobility ${\ensuremath{\mu}}_{\mathrm{m}}$ at densities much higher than critical densities). Our results unify experimental results for 2D metal-insulator transitions (MITs) in Si systems over a 50-year period (1970--2020), showing that ${n}_{\mathrm{c}}$ $({\ensuremath{\rho}}_{\mathrm{c}})$ decreases (increases) with increasing sample quality, explaining why the early experiments in the 1970s, using low-quality samples $[{\ensuremath{\mu}}_{\mathrm{m}}\ensuremath{\sim}{10}^{3}$ ${\mathrm{cm}}^{2}/(\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{s})]$, reported strong localization crossover at ${n}_{\mathrm{c}}\ensuremath{\sim}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ with ${\ensuremath{\rho}}_{\mathrm{c}}\ensuremath{\sim}{10}^{3}$ $\mathrm{\ensuremath{\Omega}}$ whereas recent experiments (after 1995), using high-quality samples $[{\ensuremath{\mu}}_{\mathrm{m}}>{10}^{4}$ ${\mathrm{cm}}^{2}/(\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{s})]$, report ${n}_{\mathrm{c}}\ensuremath{\sim}{10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ with ${\ensuremath{\rho}}_{\mathrm{c}}>{10}^{4}$ $\mathrm{\ensuremath{\Omega}}$. Our theory establishes the 2D MIT to be primarily a screened Coulomb disorder-driven strong localization crossover phenomenon, which happens at different sample-dependent critical density and critical resistance values, thus unifying Si 2D MIT phenomena over a 50-year period.
Source: Physical Review Materials
Authors: Seongjin Ahn, Sankar Das Sarma
Institutions: Joint Quantum Institute, University of Maryland, College Park
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4296137903