Alexei E. Koshelev

Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439

Multiple-band electronic structure and proximity to antiferromagnetic (AF) instability are the key properties of iron-based superconductors. Parent materials of most compounds are AF metals. Several compounds demonstrate anomalous magnetotransport properties both in paramagnetic and AF states such as linear magnetoresistance and strong field dependence of the Hall resistivity. We explore the influence of Fermi-surface reconstruction and scattering on AF fluctuations of transport of multiple-band metals both above and below the magnetic transition [1,2]. 

In the AF state, the Fermi surface is reconstructed near the nesting lines leading to the appearance of sharp tips. It is difficult for quasiparticles to pass through these points during their orbital motion in magnetic field, because they must turn sharply.  As the area of the Fermi surface affected by these turning points increases proportionally to magnetic field, this leads to the linear magnetoresistance [1]. The crossover between the quadratic and linear regimes takes place at the field scale set by the SDW gap and scattering rate.

A salient feature of scattering on AF fluctuations in paramagnetic state is that it is strongly enhanced at the Fermi surface locations where the nesting is perfect (``hot spots'' or ``hot lines''). In the paramagnetic state, such enhanced scattering rate near the ``hot lines'' leads to anomalous behavior of transport in the magnetic field [2]. The magnetic field dependences are characterized by the two field scales. The lower scale is set by the width of the ``hot spots'' and is proportional to temperature while the higher scale is set by the total scattering amplitude. In the range in between these two scales the longitudinal conductivity has a linear dependence on the magnetic field and the Hall conductivity has quadratic dependence. The linear dependence of the diagonal component reflects the growth of the Fermi-surface area affected by "hot spots" proportional to the magnetic field. The developed theoretical framework is utilized for modeling of magnetotransport in the compound BaFe₂(As_{1 − x}P_x)₂ displaying linear magnetoresistance at high fields for a broad range of doping levels [3].

[1] Alexei E. Koshelev, Linear magnetoconductivity in multiband spin-density-wave metals with nonideal nesting, Phys. Rev. B 88, 060412(R) (2013).

[2] Alexei E. Koshelev, Magnetotransport of multiple-band nearly-antiferromagnetic metals due to

“hot-spot” scattering, Phys. Rev. B 94, 125154, (2016).

[3] Nikola Maksimovic, Ian M. Hayes, Vikram Nagarajan, and James G. Analytis, Alexei E. Koshelev, John Singleton, Yeonbae Lee, and Thomas Schenkel,Magnetoresistance scaling and the origin of H-linear and T-linear resistivity in BaFe₂(As_1-xP_x)₂, Phys. Rev. X 10, 041062 (2020).