A novel method, invented to measure the minute thermodynamic magnetization of dilute two dimensional fermions, is applied to electrons in a silicon inversion layer. The interplay between the ferromagnetic interaction and disorder enhances the low temperature susceptibility up to 7.5 folds compared with the Pauli susceptibility of non-interacting electrons. The magnetization peaks in the vicinity of the density, where transition to strong localization takes place. At the same density, the susceptibility approaches the free spins value (Curie susceptibility), indicating an almost perfect compensation of the kinetic energy toll associated with spin polarization by the energy gained from the Coulomb correlation. Yet, the balance favors a paramagnetic phase over spontaneous magnetization in the whole density range.
Cooling of two-dimensional electrons in silicon-metal-oxide semiconductor field effect transistors is studied experimentally. Cooling to the lattice is found to be more effective than expected from the bulk electron-phonon coupling in silicon. The extracted heat transfer rate to phonons at low temperatures depends cubically on electron temperature, suggesting that another coupling mechanism (such as piezoelectric coupling, absent in bulk silicon) dominates over the deformation potential. According to our findings, at 100 mK, the electrons farther than ∼ 100 µm from the contacts are mostly cooled by phonons. Using long devices and low excitation voltage we measure electron resistivity down to electron temperature ∼ 100 mK and find that some of the "metallic" curves, reported earlier, turn insulating below ∼ 300 mK. This finding renders the definition of the proposed 2D metal-insulator transition questionable. Previous low temperature measurements in silicon devices are analyzed and thumb rules for evaluating their electron temperatures are provided.Since the scaling theory for non-interacting electrons was constructed in the late seventies [1], it was conjectured that a realistic two-dimensional electron system is insulating in the sense that its resistance diverges at low temperatures due to quantum interference and interaction effects. As the temperature is reduced, a logarithmic resistance increase due to weak localization is expected, followed by an exponential resistance divergence once strong localization commences [1]. It was later suggested [2] that strong Coulomb interaction may counteract localization and lead to the existence of a two dimensional metallic state and a metal-insulator transition at zero temperature.Early experiments on various types of two dimensional electron gases (2DEG) supported localization. For a comprehensive review of early theoretical and experimental results see Refs. [3,4]. It was therefore unexpected when the existence of a two dimensional metallic phase in high mobility silicon Metal Oxide Semiconductor Field Effect Transistors (MOSFET) was reported in 1994 [5,6]. The ultimate signature of such a metallic phase is resistance saturation to some residual value as the temperature approaches zero [7,8]. Since T = 0 is experimentally inaccessible, all claims for a metallic phase rely on extrapolation from finite temperatures. Two traps lurk an experimentalist in this procedure: (a) The assumption that the observed resistance saturation indeed persists to zero temperature may turn wrong. (b) The electron temperature may (and does indeed) depart from the lattice or bath temperature, T b , as T b → 0. The latter point is particularly acute in silicon MOSFETs due to the high intrinsic contact resistance and the weak electron-phonon coupling.The experiments described here focus on the second point. Using the sample itself as a thermometer we analyze electron cooling as a function of mixing chamber temperature and excitation voltage. The main findings are: (a) Electron cooling to the l...
The "metallic" characteristics of high density holes in GaAs/AlGaAs heterostructures are attributed to inelastic scattering between the two split heavy hole bands. Landau fan diagrams and weak field magnetoresistance are employed to measure the interband scattering rate. The inelastic rate is found to depend on temperature with an activation energy similar to that characterizing the longitudinal resistance. It is argued that acoustic plasmon mediated Coulomb scattering might be responsible for the Arrhenius dependence on temperature. The absence of standard Coulomb scattering characterized by a power-law dependence upon temperature is pointed out.
We investigate effects of short range interactions on the addition spectra of quantum dots using a disordered Hubbard model. A correlation function S(q) is defined on the inverse compressibility versus filling data, and computed numerically for small lattices. Two regimes of interaction strength are identified: the even/odd fluctuations regime typical of Fermi liquid ground states, and a regime of structureless S(q) at strong interactions. We propose to understand the latter regime in terms of magnetically correlated localized spins. PACS: 73.20.DxCoulomb interactions and disorder in electronic systems have posed a major challenge to condensed matter physics for quite some time.Quantum dots with discrete electronic spectra offer a new avenue to this problem. A direct probe to the ground state energy is given by Coulomb blockade peaks in the conductance as the gate voltage is varied [1][2][3][4]. Theory of spectral fluctuations of non interacting electrons has made much progress during the last decade due to the advent of semiclassical approximations, random matrix theory and the non linear sigma model approach [1,5]. However since Coulomb interactions are essential for the "Coulomb blockade" effect, one may wonder as to the validity of non interacting approximations to quantum dots in general. In particular: Is the ground state qualitatively similar or different than a Fock state of the lowest single electron orbitals?To gain insight into this question, we consider a system of interacting electrons on a finite tight binding lattice with onsite disorder. The inverse compressibility at consecutive fillings iswhere E(N ) is the ground state energy of a dot with N electrons. (We assume weakly coupled leads such that N is well defined within the area of the dot.) By varying a gate potential ϕ, the dot's energy is modified to E ϕ N = E(N ) − eϕN . Conductance peaks through the leads are observed at E ϕ (N ) = E ϕ (N + 1), i.e. at potentials eϕ N = E(N + 1) − E(N ). Thus differences between the peak potentials ϕ N yield direct measurements of ∆(N ) which can be defined as e 2 times the discrete inverse capacitance of the dot.We shall model the single electron part of the dot's Hamiltonian by a site-disordered tight binding model
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.