The Metalliclike Conductivity of a Two-Dimensional Hole System

Abstract

We report on a zero magnetic field transport study of a two-dimensional, variable-density, hole system in GaAs. As the density is varied we observe, for the first time in GaAsbased materials, a crossover from an insulating behavior at low-density, to a metallic-like behavior at high-density, where the metallic behavior is characterized by a large drop in the resistivity as the temperature is lowered. These results are in agreement with recent experiments on Si-based twodimensional systems by Kravchenko et al.[1] and others [2][3][4][5]. We show that, in the metallic region, the resistivity is dominated by an exponential temperature-dependence with a characteristic temperature which is proportional to the hole density, and appear to reach a constant value at lower temperatures. 71.30.+hThe study of the transport properties of twodimensional electron systems (2DES's) revealed numerous unique features associated with their reduced dimensionality. A central question is whether a metal-insulator transition (MIT) can occur in two-dimensions (2D). Using scaling arguments Abrahams et al. [6] stated that non-interacting electrons in 2D systems are localized at zero temperature (T ) for any level of disorder, and a MIT is not expected to occur at zero magnetic-field (B). This work motivated several experimental studies which investigated the T dependence of the resistivity (ρ) of low-mobility 2DES in Si metal-oxide semiconductor filedeffect transistors (MOSFET's) [7,8] and in In 2 O 3−x films [9]. The resistivity was found to increase with decreasing T , and its T -dependence changed from weak to strong as the density of the 2DES was lowered, or the disorder increased. These experiments seemed to confirm the theoretical notion that no metallic phase exists in 2D.However, several recent studies presented evidence to the contrary. In these studies 2DES's in Si MOSFET's [1,2] and Si/SiGe heterostructure [3][4][5] were used, and the resistivity was measured as a function of T for various carrier-densities. These studies demonstrated a clear crossover from metallic to insulating behavior at low T . Further, in the metallic region, the resistivity was shown to decrease with decreasing T by as much as a factor of eight, while in the insulating region the resistivity increases sharply with decreasing T . The authors of refs.[1] took these results as evidence for the existence of a MIT in 2D, and several theoretical works have tried to associate them with modified scaling [10] or raised the possibility of superconductivity [11,12]. The disagreement between these new results and earlier ones are generally attributed to the higher mobility in these samples (reaching a value as high as 75, 000 cm 2 /V ·s) and to the high effective mass of electrons in Si (m = 0.19m 0 ) which, according to the authors, combine to accentuate the effect of carrier-carrier interactions. It was therefore suggested [13] that due to the heavy mass of holes in GaAs (0.6m 0 , 0.38m 0 ) [14,15] and the superior quality of molecular beam epitaxy (MBE) growth, a ...

Singular or non-Fermi liquids

“…71-73 is for Si-MOSFET samples. The data for GaAs heterostructures, and Si in other geometries is qualitatively similar [120,62,63,210,119,184]. Fig.…”

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

“…The electronic contribution to the resistance behaves nonmonotonically, first increasing and then decreasing as T is lowered past a characteristic temperature T 0 , which is comparable to T F . This feature, better observed in low density 2D systems, occurs when carriers become semi-degenerate and has been observed in the three most commonly studied 2D systems: p-GaAs [19][20][21][22], n-Si [23,24] and n-GaAs [25,26]. The mechanism of this non-monotonic R xx (T) has been a key point in several leading theories of the 2D metallic transport [7,8,[27][28][29] and is the subject of this experimental study.…”

Spin–valley phase diagram of the two-dimensional metal–insulator transition

“…While behavior similar to that of Ref. [2] has now been reported for a wide variety of 2D carrier systems such as n-AlAs [4], n-GaAs [5], n-Si/SiGe [6,7], p-GaAs [8,9,10], and p-Si/SiGe [11,12], the origin of the metallic state and its transition into the insulating phase remain major puzzles in solid state physics.…”