Tilted Dirac cone gapped due to spin-orbit coupling and transport properties of a 3D metallic system CaIr2Ge2

Abstract

We present results of electrical transport (resistance, magnetoresistance, Hall effect) and heat capacity measurements performed on single crystals of the tetragonal compound, CaIr2Ge2. Their analysis is supported by the electronic structure data (band dispersion, density of states, Fermi surface), calculated for this three-dimensional (3D) system from first principles, using the full-potential local-orbital code. Interestingly, we have found the highly anisotropic Dirac cone at the Fermi level, in the bulk band structure, being gapped due to the strong p-d hybridization and spin-orbit coupling effects. However, this feature seems to have insignificant influence on the transport properties studied. The compound appears to be metallic-like with a rather low Sommerfeld coefficient (3.23 mJ mol−1 K−2) and non-superconducting even down to 0.1 K. In turn, the transverse magnetoresistance curves do not saturate with magnetic field up to 9 T revealing sub-quadratic scaling but relatively small values (up to 11 % in 2 K) as for Dirac semimetals. We may ascribe these properties to small values of the estimated relaxation time of charge carriers (~10−13 s) and, therefore, small electronic mobilities. Moreover, the angular magnetoresistance exhibits very small anisotropy (~ 1.7 %), in line with weakly anisotropic large 3D Fermi surface sheets, predicted by our calculations.