Seminars Archive

Angle-resolved Photoemission Spectroscopy study of Iron Pnictide Superconductors

Abstract
One of the challenging topics in the condensed matter physics is to obtain a detailed understanding of the microscopic mechanism that is responsible for the emergence of hightemperature (Tc) superconductivity (SC). In this context, the recent discovery of high-Tc superconductivity in Fe-based compounds becomes the focus of extensive research where SC can be easily controlled by external parameters such as chemical substitutions or pressure. These materials show complex phase diagrams and range of fascinating properties regarding the interplay among structure, magnetism and SC. The electronic band structure and the Fermi surface (FS) topology are critical to understand the underlying physics. Angle-resolved photoemission spectroscopy (ARPES) is a powerful technique to directly probe the electronic dispersion of materials. In this talk, I will discuss our recent ARPES results of BaFe2As2 with Co and Ru substitutions [1-4]. Although the phase diagrams show similarities, they control the superconductivity in very different ways. In case of Co, even small substitutions induce large changes not only in the size of the FS pockets but also in the FS topology, which closely linked to the SC [1-3]. However, Ru substitution does not change the value of the chemical potential. Interestingly, there are no measured significant changes in the shape of the FS or in the Fermi velocity [4]. These findings make the Ru case special and challenging to the previous FS nesting related scenarios on the mechanisms of the SC. More recently, we revealed that the band structure of Ba(Fe1-xRux)2As2 changes significantly as a function of sample temperature. The hole and electron pockets are well nested at low temperature, which likely drives the spin density wave and resulting antiferromagnetic order in these compounds [5]. [1] C. Liu, et al., Nature Physics, 6, 419 (2010). [2] C. Liu, A. D. Palczewski, R. S. Dhaka, et al., Physical Review B, 84, 020509(R) (2011). [3] R. S. Dhaka, et al., Physical Review B, 87, 214516 (2013). [4] R. S. Dhaka, et al., Physical Review Letters, 107, 267002 (2011). [5] R. S. Dhaka, et al., Physical Review Letters, 110, 067002 (2013).