BiS2 compounds: Properties, Effective Low-Energy Models and RPA Results

When: Wednesday, March 12, 2014 at 3:00 pm
Where: DA 114
Speaker: George Martins
Organization: Oakland University, Rochester, MI
Sponsor: Condensed Matter Seminar

“Someone once said: ‘Research is to see what everybody has seen and to think what nobody has thought’. Yet, physicists, when interpreting data, sometimes scratch their heads and ask ‘What is Nature trying to tell us?’ In hindsight, it is easy to confirm the former and answer the latter. High-temperature superconductivity (HTS) has for quite a while been an area of research that has had physicists obsessively staring at data and painfully scratching their heads. Intriguing new data has flooded and revitalized this field in the last 5 years: 2008 saw the emergence of Iron-based HTS. Like the ‘old’ cuprates, the new so-called iron-pnictides are two-dimensional materials involving d-type electrons. Differences and similarities abound between these copper and iron compounds, posing again the question above: ‘What is Nature…’ Will 2012 mark the year of new questions? In this talk [G. B. Martins, A. Moreo, and E. Dagotto, 'RPA analysis of a two-orbital model for the BiS2-based superconductors', PRB 87, 081102(R) (2013)], we will start from the premise that the newly discovered material LaOBiS2 displays HTS (or, equivalently, unconventional superconductivity), by assuming that the pairing mechanism is provided by strong spin fluctuations. We use the Random Phase Approximation, exactly as used for Iron materials, and make predictions for the symmetry of the paired electrons. The intriguing new thing here is that the electrons forming the pairs originate from p-type orbitals. And this is indeed new!! If it turns out that unconventional superconductivity occurs in BIS2 compounds (and there is already experimental evidence pointing in this direction) one HAS to ask again: ‘What is Nature trying to tell us?’”

Host: Assistant Professor Adrian Feiguin