123 research outputs found
Quantum magnetoresistance of Weyl semimetals with strong Coulomb disorder
We study the effects a strong Coulomb disorder on the transverse
magnetoresistance in Weyl semimetals at low temperatures. Using the
diagrammatic technique and the Keldysh model to sum up the leading terms in the
diagrammatic expansion, we find that the linear magnetoresistance exhibits a
strong renormalization due to the long-range nature of the Coulomb interaction
, where is
the distance between the zeroth and the first Landau levels, measures the strength of the impurity potential in terms of
the impurity concentration and the Fermi velocity , and is the effective fine structure constant of the material. As
disorder becomes even stronger (but still in the parametric range, where the
Coulomb interaction can be treated as a long-range one), we find that the
magnetoresistivity becomes quadratic in the magnetic field
Effects of anisotropy on the high field magnetoresistance of Weyl semimetals
We study the effects of anisotropy on the magnetoresistance of Weyl
semimetals (WSMs) in the ultraquantum regime. We utilize the fact that many
Weyl semimetals are approximately axially anisotropic. We find that anisotropy
manifests itself in the strong dependence of the magnetoresistance on the polar
and azimuthal angles determining the orientation of the anisotropy axis with
respect to the applied magnetic field and electric current. We also predict
that the ratio of magnetoresistances in the geometries, where the magnetic
field and anisotropy axes are aligned and where they are orthogonal, scales as
where and are the corresponding
Fermi velocities
Pecularities of Hall effect in GaAs/{\delta}<Mn>/GaAs/In\timesGa1-\timesAs/GaAs (\times {\approx} 0.2) heterostructures with high Mn content
Transport properties of GaAs/{\delta}/GaAs/In\timesGa1-\timesAs/GaAs
structures containing InxGa1-xAs (\times {\approx} 0.2) quantum well (QW) and
Mn delta layer (DL) with relatively high, about one Mn monolayer (ML) content,
are studied. In these structures DL is separated from QW by GaAs spacer with
the thickness ds = 2-5 nm. All structures possess a dielectric character of
conductivity and demonstrate a maximum in the resistance temperature dependence
Rxx(T) at the temperature {\approx} 46K which is usually associated with the
Curie temperature Tc of ferromagnetic (FM) transition in DL. However, it is
found that the Hall effect concentration of holes pH in QW does not decrease
below TC as one ordinary expects in similar systems. On the contrary, the
dependence pH(T) experiences a minimum at T = 80-100 K depending on the spacer
thickness, then increases at low temperatures more strongly than ds is smaller
and reaches a giant value pH = (1-2)\cdot10^13 cm^(-2). Obtained results are
interpreted in the terms of magnetic proximity effect of DL on QW, leading to
induce spin polarization of the holes in QW. Strong structural and magnetic
disorder in DL and QW, leading to the phase segregation in them is taken into
consideration. The high pH value is explained as a result of compensation of
the positive sign normal Hall effect component by the negative sign anomalous
Hall effect component.Comment: 19 pages, 6 figure
Charge inhomogeneities and transport in semiconductor heterostructures with a manganese -layer
We study experimentally and theoretically the effects of disorder, nonlinear
screening, and magnetism in semiconductor heterostructures containing a
-layer of Mn, where the charge carriers are confined within a quantum
well and hence both ferromagnetism and transport are two-dimensional (2D) and
differ qualitatively from their bulk counterparts. Anomalies in the electrical
resistance observed in both metallic and insulating structures can be
interpreted as a signature of significant ferromagnetic correlations. The
insulating samples turn out to be the most interesting as they can give us
valuable insights into the mechanisms of ferromagnetism in these
heterostructures. At low charge carrier densities, we show how the interplay of
disorder and nonlinear screening can result in the organization of the carriers
in the 2D transport channel into charge droplets separated by insulating
barriers. Based on such a droplet picture and including the effect of magnetic
correlations, we analyze the transport properties of this set of droplets,
compare it with experimental data, and find a good agreement between the model
calculations and experiment. Our analysis shows that the peak or shoulder-like
features observed in temperature dependence of resistance of 2D
heterostructures -doped by Mn lie significantly below the Curie
temperature unlike the three-dimensional case, where it lies above and
close to . We also discuss the consequences of our description for
understanding the mechanisms of ferromagnetism in the heterostructures under
study.Comment: 13 pages, 12 figures, RevTe
Quantum Size Effect transition in percolating nanocomposite films
We report on unique electronic properties in Fe-SiO2 nanocomposite thin films
in the vicinity of the percolation threshold. The electronic transport is
dominated by quantum corrections to the metallic conduction of the Infinite
Cluster (IC). At low temperature, mesoscopic effects revealed on the
conductivity, Hall effect experiments and low frequency electrical noise
(random telegraph noise and 1/f noise) strongly support the existence of a
temperature-induced Quantum Size Effect (QSE) transition in the metallic
conduction path. Below a critical temperature related to the geometrical
constriction sizes of the IC, the electronic conductivity is mainly governed by
active tunnel conductance across barriers in the metallic network. The high 1/f
noise level and the random telegraph noise are consistently explained by random
potential modulation of the barriers transmittance due to local Coulomb
charges. Our results provide evidence that a lowering of the temperature is
somehow equivalent to a decrease of the metal fraction in the vicinity of the
percolation limit.Comment: 21 pages, 8 figure
Magnetoresistance and Anomalous Hall Effect of InSb Doped with Mn
Transport properties of polycrystalline (In, Mn)Sb samples are investigated. Behavior of the temperature and magnetic field dependencies of the resistivity, anomalous Hall coefficient and magnetoresistivity at low temperatures points out the influence of Mn complexes, Mn ions and nano- and microsizes MnSb precipitates on charge transport.
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