Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe1−xRuxAs)

Abstract

We report electronic transport of Dirac cones when Fe is replaced by Ru, which has an isoelectronic electron configuration to Fe, using single crystals of Ba(Fe1−xRuxAs)2. The electronic transport of parabolic bands is shown to be suppressed by scattering due to the crystal lattice distortion and the impurity effect of Ru, while that of the Dirac cone is not significantly reduced due to the intrinsic character of Dirac cones. It is clearly shown from magnetoresistance and Hall coefficient measurements that the inverse of average mobility, proportional to cyclotron effective mass, develops as the square root of the carrier number (n) of the Dirac cones. This is the unique character of the Dirac cone linear dispersion relationship. Scattering of Ru on the Dirac cones is discussed in terms of the estimated mean free path using experimental parameters.

Kondo-like mass enhancement of Dirac fermions in Ba(Fe1−xMnxAs)2

“…Since the present B * was directly tied to the quantum behavior of the Dirac cone, and µ ave is likewise influenced by the Dirac cone in the rapidly quenched Ba(FeAs) 2 series [17], the present observations, showing that B * increases and µ ave decreases, can be associated with a Kondo-like mass enhancement of the Dirac fermions in Ba(Fe 1−x Mn x As) 2 under the Abrikosov model [23] (Fig. 1(b)).…”

“…We can easily recognize a remarkable contrast between the linear evolution of 1/µ ave observed for Ba(Fe 1−x Ru x As) 2 and the positive deviation seen in Ba(Fe 1−x Mn x As) 2 . The former has been consistently explained in terms of the dependence of m * on n D in the Dirac cone [1,17]. Given the invariant n D of the Dirac cone for Ba(Fe 1−x Mn x As) 2 , m * at the lowest temperature of 2 K was evaluated using Eqs.2 and 3.…”

“…For Ba(FeAs) 2 , it has been theorized that the Fermi surface under the SDW ordered state is composed of four pockets [14]. If this is the case, the transport parameters in each pocket of the four carrier system can be merged into n e , n h , µ e , and µ h within a two carrier model [17]. We thus use the averaged mobility (µ ave = (µ e + µ h )/2) to evaluate the dependence of mobility on the carrier number of the Dirac cones.…”

“…Ba(Fe 1−x Ru x As) 2 specifically showcases this resistance to nonmagnetic substitution impurities. Under Ru substitution, isoelectronic to the Fe-3d state, the robustness of the Dirac cone leads to a suppression of backward scattering [17]. Since the Dirac cones in iron pnictides originate from the pseudospin vorticities, they should also be resistant to magnetic impurities [6], in contrast with topological insulators such as Bi 2 Se 3 where the Dirac cone is disrupted by the breaking of time reversal symmetry [18].…”

“…This introduces a lattice strain into the crystal structure. The samples obtained by such a procedure highlight the Dirac cone relative to the parabolic pockets, since the former is experimentally less sensitive to lattice distortion, while in the latter the relaxation times of the electrons are greatly decreased [17]. We will show that although LMR is observed for Ba(Fe 1−x Mn x As) 2 , the temperature dependence of the onset magnetic field for LMR (B * ) departs significantly from the trend typically expected due to the Landau Level (LL) splitting of Dirac cones at low temperatures [16].…”