Starts 15 Sep 2017 14:10
Ends 15 Sep 2017 15:25
Central European Time
Leonardo Building - Luigi Stasi Seminar Room

Most superconductors are made using standard techniques involving inorganic components and modifications are made according to a standard set of simple chemical replacements. However, organic chemistry is potentially much more flexible and the addition of molecules into superconductors offers a new route to controlling properties. This has led to the field of organic superconductors and I will outline some of the results that have been achieved in this field [1-3]. I will also describe some new superconductors which have been made using a low- temperature intercalation method that is capable of inserting molecular species in between superconducting FeSe layers. It results in a large increase in superconducting transition temperature - more than a factor of 4 [4,5]. In this talk, I will review recent progress and describe new results on Lix[(NH2)y(NH3)1−y]zFe2Se2 (z = 1, 2) which have been carried out in order to study the effect on the superconducting properties of intercalating additional ammonia, via reversible adsorption and desorption. The reactions were carried out in situ on the muon beamline so that the superfluid stiffness could be measured using transverse-field muon-spin rotation experiment on a single sample, first having undergone exposure to 1 bar of ammonia at 250 K, and then again following desorption. These results illustrate some of the possibilities, but also the difficulties, of using molecules in developing new superconductors.

(Work performed in collaboration with S. J. Clarke and coworkers at Oxford, RAL and Durham, UK.)

[1] T. Ishiguro, K. Yamaji, G. Saito, Organic Superconductors, second ed., Springer-Verlag, Berlin, (1998)
[2] F. L. Pratt and S. J. Blundell, Phys. Rev. Lett. 94, 097006 (2005)
[3] J. G. Analytis, A. Ardavan, S. J. Blundell, R. L. Owen, E. F. Garman, C. Jeynes and B. J. Powell, Phys. Rev. Lett. 96, 177002 (2006)
[4] M. Burrard-Lucas, D. G. Free, S. J. Sedlmaier, J. D. Wright, S. J.Cassidy, Y. Hara, A. J. Corkett, T. Lancaster, P. J. Baker, S. J. Blundell, and S. J. Clarke, Nat. Mater. 12, 15 (2013)
[5] H. Sun, D. N. Woodruff, S. J. Cassidy, G. M. Allcroft, S. J. Sedlmaier, A. L. Thompson, P. A. Bingham, S. D. Forder, S. Cartenet, N. Mary, S. Ramos, F. R. Foronda, B. H. Williams, X. Li, S. J. Blundell, and S. J. Clarke, Inorg. Chem. 54, 1958 (2015)