Quasi Two-dimensional Antiferromagnet SrRu$_2$O$_6$: Mechanism of Electrical Conduction

The electronic ground state in the layered antiferromagnetic compound SrRu$_2$O$_6$ is semiconducting. However, the band gap estimated from fitting of the Arrhenius model to the high temperature region (300K-200K) of the electrical- transport data in SrRu$_2$O$_6$ is typically found to be significantly smaller than the theoretically predicted value. Here we show that in high temperature region, the Arrhenius, the Variable Range Hopping (VRH) as well as modified VRH exhibit similar goodness of fit, when fitted to transport data. Interestingly, the Fluctuation-Induced Tunneling (FIT) model is observed to exhibit an excellent fit in a much wider temperature range. For SrRu$_2$O$_6$, which inherently possesses a quasi two-dimensional crystal structure, the FIT model point towards the intriguing possibility of thermal fluctuations induced tunneling of charge carriers across the conducting and insulating layers. We also explored the role of morphology and defects in a number of SrRu$_2$O$_6$ samples prepared in different batches. Data on multiple samples brings out the profound role of intrinsic defects and associated strain in the nature of electrical conduction, especially at lower temperatures.