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

Highlights: • Electrical (magneto)transport, heat capacity measured on single crystals of CaIr₂Ge₂. • Sub-quadratic magnetoresistance, unsaturated at 9 T, reaches only up to 11 % in 2 K. • Metallic-like electronic structure of bulk CaIr₂Ge₂ calculated from first principles. • Anisotropic and gapped Dirac cone revealed in the band structure at the Fermi level. • Short relaxation times of charge carriers and small electronic mobilities estimated. -- 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.