Spin fluctuations in disordered interacting electrons (original) (raw)
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Physical Review B, 1986
The response of a disordered interacting electron gas to a time and spatially varying magnetic field is discussed. Local spin conservation leads to a generalized Ward identity, which together with global spin conservation implies that the dynamic magnetic susceptibility P(q, 0}must obey a simple diffusive form. The same identity, when combined with the general perturbative structure of g{q,0), also relates the renormalization of static susceptibility g and the spin diffusion constant D, to the renormalization of the charge diffusion constant and the Fermi-liquid interaction amplitudes. These relations are shown to be consistent with perturbations to first order in t t =1/[(2n) NOD] j but only after nontrivial cancellations. Thus the Ward identity allows both easy derivation of P(q, Q) from the renormalized theory and a consistency check on the scaling equations. By using the renormalization-group equations for these parameters, it is shown that there is strong enhancement of g" and decrease in D, with lowering temperature. The significance of this with respect to the metal-insulator transition is discussed.
Magnetic properties of interacting, disordered electron systems in d=2 dimensions
2011
We compute the magnetic susceptibilities of interacting electrons in the presence of disorder on a two-dimensional square lattice by means of quantum Monte Carlo simulations. Clear evidence is found that at sufficiently low temperatures disorder can lead to an enhancement of the ferromagnetic susceptibility. We show that it is not related to the transition from a metal to an Anderson insulator in two dimensions, but is a rather general low temperature property of interacting, disordered electronic systems.
No indications of metal-insulator transition for systems of interacting electrons in two dimensions
Physical Review B, 2001
The influence of Coulomb interaction on transport properties of spinless electrons in small disordered two dimensional systems is studied within a tight binding model. Spatial correlations, inverse participation ratio, and multifractal spectrum of the zero temperature local tunneling amplitude as well as the DC Kubo conductance are traced as function of the interaction strength U . When U is increased, all of the above quantities are shifted rather smoothly towards localized behavior, indicating the absence of an interaction driven insulator-metal transition.
Interacting Electrons in a Two-Dimensional Disordered Environment: Effect of a Zeeman Magnetic Field
Physical Review Letters, 2003
The effect of a Zeeman magnetic field coupled to the spin of the electrons on the conducting properties of the disordered Hubbard model is studied. Using the Determinant Quantum Monte Carlo method, the temperature-and magnetic-fielddependent conductivity is calculated, as well as the degree of spin polarization. We find that the Zeeman magnetic field suppresses the metallic behavior present for certain values of interaction-and disorder-strength, and is able to induce a metal-insulator transition at a critical field strength. It is argued that the qualitative features of magnetoconductance in this microscopic model containing both repulsive interactions and disorder are in agreement with experimental findings in two-dimensional electron-and hole-gases in semiconductor structures.
Interaction-driven metal-insulator transitions in disordered fermion systems
Physical Review B, 1984
We study the effects of electron-electron interactions in disordered metals in and close to two dimensions (2D). We consider physical situations in which localization effects are suppressed. The field-theoretical renormalization-group (RG) calculation performed recently by Finkelstein is interpreted and rederived in terms of perturbative results. Surprisingly, except for the density of states, the scaling behavior is independent of the interaction range. We further extend the model to several new universality classes. In the presence of a strong magnetic field the metal is unstable in 2D and undergoes a metal-insulator transition in d =2+e. The conductivity exponent, defined by 0.-(nn,)i", is universal with p = 1+0(e) but N(EF) depends not only on the range of the interaction but also on its strength for short-ranged interactions. In 2D the conductivity has a universal temperature dependence [5o(T)=crn(2-2ln2)ln(Tr), o&-e /2+iii] if the interaction is Coulombic. If magnetic impurities (or strong spin-orbit scattering with a weak magnetic field) are present instead, the noninteracting fixed point is stable for short-ranged interactions (p=-,). For the Coulomb interaction the interaction is relevant and drives a metal-insulator transition in d =2+@ with universal critical properties (p=1). In 2D the conductivity also has a universal temperature dependence [5o(T) =o&ln(Tw)]. We also discuss the behavior of the dielectric constant on the insulator side and the frequency (temperature) dependence of the conductivity at criticality. Remarks are made on the relationship of the above to experiments.
Metal-insulator transition by suppression of spin fluctuations
EPL (Europhysics Letters), 2009
PACS 71.27.+a -Strongly correlated electron systems; heavy fermions PACS 71.30.+h -Metal-insulator transitions and other electronic transitions PACS 75.20.Hr -Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
Journal de Physique, 1989
2014 Des fluctuations universelles de conductance (UCF) de l'ordre de e2/h, ont été récemment observées à basse température dans des métaux désordonnés mésoscopiques, indépendamment de la taille de l'échantillon et du degré de désordre. L'explication théorique qui suivit supposait que les impuretés, source du désordre, étaient indépendantes les unes des autres. Nous réexaminons ce problème avec l'hypothèse plus réaliste que les impuretés sont en fait corrélées et d'autant plus que leur concentration est plus élevée. Nous montrons ainsi que les UCF sont modifiées par ces interactions : le résultat e2/h est multiplié par un facteur numérique plus grand ou plus petit que un, suivant que les impuretés se repoussent ou s'attirent. Les modifications dépendent, en particulier, de la concentration en impuretés et donc du degré de désordre. Par conséquent le caractère universal des fluctuations de conductance n'est plus vrai dans les systèmes réalistes. De nouvelles expériences seraient utiles pour tester cette théorie en comparant des cas où les interactions sont répulsives ou attractives. Abstract. 2014 Low temperature universal conductance fluctuations (UCF) of the order of e2/h have been recently observed in mesoscopic disordered metals, independent of sample size and degree of disorder. The theoretical explanation which followed assumed that the impurities, at the source of the disorder, were independent of each other. We reexamine this problem using the more realistic assumption that the impurities are, in fact, correlated and more and more so for increasing concentration. We show that the UCF are modified by these interactions : the e2/h result is multiplied by a numerical factor larger or smaller than one, depending on whether the impurities repel or attract each other. The modifications do depend, in particular, on the impurity concentration and thus on the degree of disorder. Therefore the universal character of the conductance fluctuations breaks down in realistic systems. Further experiments would be useful to test the present theory by comparing cases where the interactions are repulsive or attractive.
2006
Recent thermodynamic measurements on two-dimensional (2D) electron systems have found diverging behavior in the magnetic susceptibility and appearance of ferromagnetism with decreasing electron density. The critical densities for these phenomena coincide with the metal-insulator transition recorded in transport measurements. Based on density functional calculations within the local spin-density approximation, we have investigated the compressibility and magnetic susceptibility of a 2D electron gas in the presence of remote impurities. A correlation between the minimum in the inverse capacitance (∂µ/∂n) and the maximum of magnetization and magnetic susceptibility is found. Based on values we obtain for the inverse participation ratio, this seems to be also the MIT point.