Busy with birds in the springtime

Crowell, Laura

doi:10.1080/03634529309378940

Cited by 3 publications

(6 citation statements)

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“…M and τ d in Eqs ( 4) and (7), as well as the universal function f 6) . This procedure can be described as follows.…”

Section: Polaron Hopping Monte Carlo Simulationsmentioning

confidence: 99%

“…For instance, Mn atoms play a dual role as acceptor sites and magnetic ions in GaAs resulting in the very unusual magnetic properties of this material [5,17]. Giant negative magnetoresistance has been observed [5,6,7] below the metal-insulator transition point of GaAs : Mn, which clearly displays the VRH behavior with no sign of the hard magneto-polaron gap. The absence of this gap in the electrical conduction experiments can be understood by taking into account local fluctuations of the bound polaron shifts.…”

Section: Introductionmentioning

confidence: 99%

“…Giant negative magnetoresistance in the variable-range hopping region apparently has been observed in recently discovered dilute magnetic semiconductors, such as GaAs:Mn [5,6,7] and MnGe [21] below the metal-insulator transition point. In all these materials, magnetoresistance is described by Eq.…”

Section: Application To Giant Magnetoresistancementioning

confidence: 99%

“…The temperature dependence of the VRH conductivity is described by stretched exponents σ ∝ exp (−T /T 0 ) p and depending on the value of p can be attributed to one of the two major regimes such as the Mott (p = 1/4) and the Shklovskii-Efros (p = 1/2) regimes [1,2]. Several observations of giant and colossal negative VRH magnetoresistance in systems with strong spin disorder such as dilute magnetic semiconductors (DMS) have been reported recently [5,6,7]. It seems rather natural to attribute VRH magnetoresistance to spin polarons that are believed to be a major cause of negative magnetoresistance in DMS [8,9,10].…”

Section: Introductionmentioning

confidence: 99%

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Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

2003

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We analize electrical conductivity controlled by hopping of bound spin polarons in disordered solids with wide distributions of electron energies and polaron shifts (barriers). By means of percolation theory and Monte Carlo simulations we have shown that in such materials at low temperatures, when hopping occurs in the vicinity of the Fermi level, a hard polaron gap does not manifest itself in the transport properties. This happens because as temperature decreases the hopping polaron trades the decreasing electron and polaron barriers for increasing hopping distance.As a result, in the absence of the Coulomb correlation effects, in this variable-range variable-barrier hopping regime, the electrical resistivity, ρ, as a function of temperature, T , obeys a non-activation law: ln (ρ/ρ 0 ) = T /T p with p = 2/(d + 2), where d is the dimensionality of the system. It differs from the standard Mott law for which p = 1/(d + 1). Also, we studied the effects of upper and lower boundaries in the polaron shift distribution on hopping conduction, which may result in a partial re-entrance of the hard polaron gap. We discuss possible applications to the problem of giant negative magnetoresistance in dilute magnetic semiconductors and nanocomposites where for paramanetic materials p = 3/(d + 2).

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“…M and τ d in Eqs ( 4) and (7), as well as the universal function f 6) . This procedure can be described as follows.…”

Section: Polaron Hopping Monte Carlo Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Application To Giant Magnetoresistancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

2003

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“…an effective cross sectional area as to the emission of gravitons, and defined as a physical wave vector. L. Crowell stated that GW would undergo massive red shifting, [28,29] Needless to state, the value of to consider would be for the GHz band of GW [26,27].…”

Section: The Role Critical Density Plays In Analyzing the Frequency Pmentioning

confidence: 99%

What the Null Energy Condition (and When It May Be Violated) Tells Us about Gravitational Wave Frequencies in/for Relic Cosmology?

Beckwith

2011

JMP

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We introduce a criterion as to the range of HFGW generated by early universe conditions. The 1 to 10 Giga Hertz range is constructed initially starting with what Grupen writes as far as what to expect of GW frequencies which can be detected assuming a sensitivity of 7×h~10<sup>-27</sup> . From there we examine the implications of an earlier Hubble parameter at the start of inflation, and a phase transition treatment of pre to post Planckian inflation physics via use of inflatons. We close with an analysis of how gravitational constant G may vary with time, the tie in with the NEC condition and how to select a range of relic GW frequencies. The gravitational frequencies in turn may enable resolving a mis match between the datum that the entropy of the center of the galaxy black hole is greater than the entropy of the present four dimensional universe as we can infer and measure

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Charge and spin transport in spin valves with anisotropic spin relaxation

2007

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We investigate effects of spin-orbit splitting on electronic transport in a spin valve consisting of a large quantum dot defined on a two-dimensional electron gas with two ferromagnetic contacts. In the presence of both structure and bulk inversion asymmetry a giant anisotropy in the spin-relaxation times has been predicted. We show how such an anisotropy affects the electronic transport properties such as the angular magnetoresistance and the spin-transfer torque. Counterintuitively, anisotropic spin-relaxation processes sometimes enhance the spin accumulation.

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Busy with birds in the springtime

Cited by 3 publications

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Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

Variable-range hopping of spin polarons: Magnetoresistance in a modified Mott regime

What the Null Energy Condition (and When It May Be Violated) Tells Us about Gravitational Wave Frequencies in/for Relic Cosmology?

Charge and spin transport in spin valves with anisotropic spin relaxation

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