Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling

We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.     

Multifractality and conformal invariance at 2D metal-insulator transition in the spin-orbit symmetry class

We study the multifractality (MF) of critical wave functions at boundaries and corners at the metal-insulator transition (MIT) for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the MF exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole sample even in the thermodynamic limit.     

Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots

In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.     

Metal-insulator transition in Bi-doped,amorphous Ga:Ar mixtures: Influence of spin-orbit scattering

Doping amorphous Ga_xAr_1?x mixtures with the strong spin-orbit scatterer Bi has a dramatic effect on the metal-insulator transition (MIT) occurring in this system at a critical metal atomic concentration x_c: (i) the MIT is shifted from x′_c = 0.36 ± 0.01 (corresponding to a critical metal volume fraction v′_c = 0.19 ± 0.01) of the undoped system to a lower value of x_c = 0.25 ± 0.01 (v_c = 0.14 ± 0.01) for (Ga_0.9Bi_0.1)_xAr_1?x and (ii) the critical exponent v and g of the dc conductivity and Hall coefficient, respectively, change from v′ = 0.5 ± 0.1 and g′ = 0 for the undoped samples to v = 1.3 ± 0.3 and g = 0.5 ± 0.1 for (Ga_0.9Bi_0.1)_xAr_1?x.     

Critical fidelity at the metal-insulator transition

Using a Wigner Lorentzian random matrix ensemble, we study the fidelity, F(t), of systems at the Anderson metal-insulator transition, subject to small perturbations that preserve the criticality. We find that there are three decay regimes as perturbation strength increases: the first two are associated with a Gaussian and an exponential decay, respectively, and can be described using linear response theory. For stronger perturbations F(t) decays algebraically as F(t) approximately t(-D2(mu)), where D2(mu) is the correlation dimension of the local density of states.     

Tuning the tricritical point with spin-orbit coupling in polarized fermionic condensates

We investigate a two-component atomic Fermi gas with population imbalance in the presence of Rashba-type spin-orbit coupling (SOC). As a competition between SOC and population imbalance, the finite-temperature phase diagram reveals a large variety of new features, including the expanding of the superfluid state regime and the shrinking of both the phase separation and the normal regimes. For sufficiently strong SOC, the phase separation region disappears, giving way to the superfluid state. We find that the tricritical point moves toward a regime of low temperature, high magnetic field, and high polarization as the SOC increases.     

The metal-insulator transition and the phase transition in metal-ammonia solutions

The ground state of impurity metal (sodium) atoms in liquid ammonia close to the solvated state of the free electrons is considered. It is shown that the critical solubility point lying on the metal side of the metal-insulator transition is determined by the Coulomb interaction between the ions and electrons in the overlapping impurity states, classically accessible spheres of which form an infinite percolation cluster. The percolation conductivity via the impurity states is estimated. The estimate agrees with the experimental data near the critical solubility point. Zh. éksp. Teor. Fiz. 111, 938–948 (March 1997)     

Superconductivity and metal-insulator transition in amorphous Si1−xAux system

Electrical conductivity of metallic amorphous Si_1?xAu_x films was measured down to 10 mK. Superconducting transition was observed in a certain range of Au content. In the normal state, the temperature variation of electrical conductivity showed √T-dependence at higher temperatures and ln T-dependence at lower temperatures. This crossover is interpreted as being due to a change of sample dimensionality.     

Coherent backscattering near the two-dimensional metal-insulator transition

We have studied corrections to conductivity due to the coherent backscattering in low-disordered two-dimensional electron systems in silicon for a range of electron densities including the vicinity of the metal-insulator transition, where the dramatic increase of the spin susceptibility has been observed earlier. We show that the corrections, which exist deeper in the metallic phase, weaken upon approaching the transition and practically vanish at the critical density, thus suggesting that the localization is suppressed near and at the transition even in zero field.     

Anderson transition in two-dimensional systems with spin-orbit coupling

We report a numerical investigation of the Anderson transition in two-dimensional systems with spin-orbit coupling. An accurate estimate of the critical exponent nu for the divergence of the localization length in this universality class has to our knowledge not been reported in the literature. Here we analyze the SU(2) model. We find that for this model corrections to scaling due to irrelevant scaling variables may be neglected permitting an accurate estimate of the exponent nu=2.73+/-0.02.