Spin Susceptibility of an Ultra-Low-Density Two-Dimensional Electron System

Abstract

We determine the spin susceptibility in a two-dimensional electron system in GaAs/AlGaAs over a wide range of low densities from 2x10(9) cm(-2) to 4x10(10) cm(-2). Our data can be fitted to an equation that describes the density dependence as well as the polarization dependence of the spin susceptibility. It can account for the anomalous g factors reported recently in GaAs electron and hole systems. The paramagnetic spin susceptibility increases with decreasing density as expected from theoretical calculations.

Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

“…Considering the band values m * ∼ = 0.2 and g * ∼ = 0.65, 53 this implies an enhancement of g * m * by a factor of about 1.5. Such an enhancement is about a factor of two smaller than the g * m * enhancement reported for 2D electrons in Si-MOSFETs, 15 GaAs, 19 or AlAs 27 at comparable values of r s . The reason for this absence of enhancement might again be the holes' band structure and large effective spin.…”

“…In the highly interacting, dilute regime (r s > ∼ 3), χ * and m * are typically enhanced compared to the band values and increase with increasing r s , as confirmed both theoretically [1][2][3][4][5][6][7][8] and experimentally. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Besides r s , the spin and/or valley degrees of freedom also play an important role in the re-normalization of m * and χ * since they modify the exchange interaction. 5,6,17,[24][25][26][27] In particular, it was recently demonstrated that when a 2D electron system is fully spin and valley polarized, m * is suppressed compared to its band value.…”

Exchange energy enhancedg-factors obtained from Landau fan diagrams at low magnetic fields

“…In lower magnetic field and in lower electron density, the ratios of the electron-electron and electron-hole energies to the cyclotron energy increase, and phenomena due to the electron-electron and electron-hole interactions are expected to be more prominent. In fact, it has been found in GaAs/AlGaAs heterostructures and in Si inversion layers that the electron effective mass (m * e ) and spin susceptibility of electrons χ = m * e g * increase with a decrease in electron density, [5][6][7][8] where g * is the electron effective g factor.…”

Density-dependent spin susceptibility and effective mass in interacting quasi-two-dimensional electron systems

“…There has been a number of experimental papers appearing in the recent literature reporting the lowtemperature ( 100mK) measurement of the susceptibility 3,4,5,6,7,8,9 and effective mass 10,11 in 2D electron systems as a function of carrier density in the r s ≈ 1 − 10 parameter range. Although some aspects of the data in different experiments (and more importantly, the interpretation of the data) have been controversial -most especially on the issue of whether there is a spontaneous density-driven ferromagnetic spin polarization transition at low carrier densities in 2D systems -the experimental reports convincingly establish a strong enhancement in both the spin susceptibility and effective mass as a function of decreasing (increasing) carrier density n (interaction parameter r s ).…”

“…The 2D systems have the distinct advantage of the density being a tunable parameter so that the density dependence of the Fermi liquid renormalization can be studied directly. In this paper, we theoretically consider the density-dependent many-body renormalization of the 2D electronic spin susceptibility and effective mass, a subject of considerable recent experimental activity 3,4,5,6,7,8,9,10,11 in a number of different semiconductor heterostructures with confined 2D electron systems.…”