Intrinsic defects and local charge ordering of single-crystal FeTe

Iron chalcogenides have been widely studied due to their intriguing superconducting and magnetic properties. We investigate the intrinsic defects existing in single-crystal FeTe via scanning tunneling microscopy (STM). The cleavage surfaces of FeTe show that Te vacancies exist primarily at the top or bottom Te sites. It is known that FeTe presents charge ordering with 2a periodicity (a = lattice constant), as driven by the bicollinear antiferromagnetic (AFM) order at the Fe layer. Numerous studies confirmed that the Neel temperature of FeTe varies from TN = 60–70 K. Interestingly, we find that the STM topography images exhibit local charge orderings with 2a periodicity at 79 K, which is slightly above the TN. This result suggests that the AFM phase might still survive locally with fluctuations up to temperatures slightly above TN without macroscopic ordering. Our work provides important information that captures the moment of phase transition between AFM and paramagnetic ordering in the FeTe system.