Scanning tunneling microscopy and spectroscopy on pnictide superconductors
Freek Massee - May 03 2010
Using scanning tunneling microscopy (STM), we try to uncover (some of) the mysteries behind the superconductivity
in the recently discovered iron based superconductors, the pnictides. First we investigate the cleavage surface
of the '122' family of superconductors, which provides essential information for all surface sensitive techniques
such as angle resolved photoemission (ARPES) and STM. Then we go on to show some of the surprising properties of
the superconducting state: a strong spatial variation of the superconducting gap size on length scales of a few
nanometers in the BaFe2-xCoxAs2 system. Since this seems at first glance difficult to reconcile with a very sharp
transition temperature of less than 1 K, a pseudogap scenario, like has been observed in the cuprate high temperature
superconductors, might also exist in the pnictides. However, temperature dependent spectroscopy excludes this
possibility since all superconducting gaps of different size close at Tc. A different hypothesis is the presence of
Co atoms in the superconducting Fe layers, which is essential for the system to become superconducting.
Comparison to a different system without Co doping seems to confirm this idea.