Controlling the carrier concentration of the high-temperature superconductor Bi_2Sr_2CaCu_2O_(8+δ) in angle-resolved photoemission spectroscopy experiments

摘要

We study the variation of the electronic properties at the surface of a high-temperature superconductor as a function of vacuum conditions in angle-resolved photoemission spectroscopy experiments. Normally, under inadequate ultrahigh vacuum (UHV) conditions the carrier concentration of Bi_2Sr_2CaCu_2O_(8+δ)(Bi2212) increases with time due to the absorption of oxygen from CO_2/CO molecules that are prime contaminants present in UHV systems. We find that in an optimal vacuum environment at low temperatures, the surface of Bi2212 is quite stable (the carrier concentration remains constant); however at elevated temperatures the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. These two effects can be used to control the carrier concentration in situ. Our finding opens the possibility of studying the electronic properties of the cuprates as a function of doping across the phase diagram on the same surface of sample (i.e., with the same impurities and nondopant defects). We envision that this method could be utilized in other surface sensitive techniques such as scanning tunneling microscopy/spectroscopy.