Abstract
was predicted to be a high-temperature superconductor upon electron doping since it highly resembles the cuprates in crystal structure, electronic structure, and magnetic coupling constants. Here, we report a scanning tunneling microscopy/spectroscopy (STM/STS) study of with surface electron doping by depositing potassium (K) atoms. We find that as the electron doping increases, the system gradually evolves from an insulating state to a normal metallic state, via a pseudogaplike phase, and a phase with a sharp, V-shaped low-energy gap with about 95% loss of density of state (DOS) at . At certain K coverage (0.5–0.6 monolayer), the magnitude of the low-energy gap is 25–30 meV, and it closes at around 50 K. Our observations show that the electron-doped remarkably resembles hole-doped cuprate superconductors.
- Received 17 June 2015
DOI:https://doi.org/10.1103/PhysRevX.5.041018
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Published by the American Physical Society
Popular Summary
, a transition-metal oxide, strongly resembles high-temperature-superconducting cuprates in its structure and Mott insulator nature, and it is predicted to be a high-temperature superconductor upon electron doping. However, no experimental evidence of superconductivity has been reported up until now. Here, we present low-temperature scanning tunneling microscopy and spectroscopy of electron-doped subjected to in situ surface potassium (K) dosing. We also provide an indication of possible superconductivity in this system.
We evaporate K atoms onto the surface of and hold our experimental setup at a temperature of 4.5 K. We observe a sharp, V-shaped gap with about 95% spectral weight suppression and visible coherence peaks in with 0.5–0.7 monolayer (ML) K coverage. We also demonstrate that, given increased surface K coverage, the electronic state of evolves from a Mott insulating state to a normal metallic state with more than 1 ML K coverage via a pseudogaplike state and a V-shape-gapped state, sequentially. The remarkable analogy between this system and the hole-doped cuprates, particularly in the tunneling spectral line shapes, characteristic temperatures, gap energy scales, and the evolution of various electronic states with doping, hints at possible superconductivity in , which is consistent with previous theoretical predictions. Efforts are currently underway to look for further evidence of superconductivity in such as magnetic vortex, zero resistance, and the Meissner effect. If confirmed, superconductivity in would help to build a universal theme of high-temperature superconductivity and solve a long-standing mystery.
We expect that our findings will pave the way for a more thorough understanding of the electronic properties of .