SPEAKER: Hanho Lee
Advisor: R. Greene
TITLE: Epitaxial Growth of Ba(Fe1-xCox)2As2 and LiFeAs thin films on SrTiO3 (001) using Pulsed Laser Deposition in Ultrahigh Vacuum: A Scanning Tunneling Microscopy Study
ABSTRACT: We report on in situ scanning tunneling microscopy (STM) investigation of superconducting iron pnictide thin films grown by pulsed laser deposition (PLD) under ultrahigh vacuum. Epitaxial thin films of Ba(Fe1-xCox)2As2 and LiFeAs were grown on SrTiO3 (001) substrates and examined in an STM chamber directly connected to the growth chamber. The crystallinity of the epitaxial thin films was monitored using reflection high-energy electron diffraction (RHEED) and low energy electron diffraction (LEED) during and after deposition. Surface reconstruction and missing-row-structure were observed in the Ba(Fe1-xCox)2As2 films. The LiFeAs films revealed (1x1) structure. These thin films showed superconducting behavior in the scanning tunneling spectroscopy and four probe transport measurements.
SPEAKER: Jon Collini
Advisor: J. Paglione
TITLE: The 1-2-2 Superconductors and Future Pressure Work on Ba1-xSrxNi2As2
ABSTRACT: For nearly a decade, the Fe-based 1-2-2 superconductors have generated a large amount of scientific attention and are partly responsible for the recent resurgence in superconducting materials. Related to these Fe 1-2-2 materials is the (Ba,Sr)Ni2As2 series, which shares many structural elements with it's Fe-based counterpart but exhibits vastly different quantum behaviors at low temperature. We will discuss the current history on the 1-2-2 superconductors (both Fe and Ni based), highlighting work done here are CNAM and abroad on the topic, as well as, recent work done at University of Illinois (UI). This will be done to motive a future experiment at UI in collaboration with CNAM, in which a pressure/temperature phase diagram will be mapped for (Ba,Sr)Ni2As2 using x-rays and a diamond anvil pressure cell.