Electronic nematic phases have been proposed to occur in various correlated electron systems and were recently claimed to have been detected in scanning tunneling microscopy (STM) conductance maps of the pseudogap states of the cuprate high-temperatu
re superconductor Bi2Sr2CaCu2O8+x (Bi-2212). We investigate the influence of anisotropic STM tip structures on such measurements and establish, with a model calculation, the presence of a tunneling interference effect within an STM junction that induces energy-dependent symmetry-breaking features in the conductance maps. We experimentally confirm this phenomenon on different correlated electron systems, including measurements in the pseudogap state of Bi-2212, showing that the apparent nematic behavior of the imaged crystal lattice is likely not due to nematic order but is related to how a realistic STM tip probes the band structure of a material. We further establish that this interference effect can be used as a sensitive probe of changes in the momentum structure of the samples quasiparticles as a function of energy.
The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high-pressure. In CeFeAsO polycrystals, the magnetic phases involving the Fe and Ce ions coexist up to 15 GPa, with no signs of pressure-induced s
uperconductivity up to 50 GPa. For the CeFePO single crystals, pressure stabilizes the Kondo screening of the Ce 4f-electron magnetic moments.
