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Magnetoelastic Transitions in Iron-based Superconductors: Bulk and Thin Films

Materials Science Seminar
Andres Cano, ESRF, Grenoble, France
April 23, 2013 11:00AM to 12:00PM
Building 223, Room S105
The surprising discovery of superconductivity in fluorine-doped arsenic-oxide LaO1-xFxFeAs [1] has established a new class of high-temperature superconductors [2]. The normal state of these systems displays an intriguing interplay between structural and magnetic transitions that persists in the superconducting region of the phase diagram. In the seminar I will discuss how this interplay is largely dominated by symmetry-specific magnetoelastic couplings [3]. I will show, in particular, that i) the existence of tricritical points in the generic phase diagram [4] and ii) the variations of transition temperatures induced by uniaxial pressure [5] are two direct consequences of these couplings. In addition, I will discuss specific results for thin films [6]. Here, this magnetostructural interplay combined with epitaxial strain can radically modify the Kittel law for the size of the structural domains as a function of the film thickness. The new regime that appears in the ultrathin limit gives an access to the response functions of the nematic order parameter that complements bulk experiments [7].

[1] Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008).
[2] For reviews, see e.g. D. Johnston, Adv. Phys. 59, 803 (2010); M. D. Lumsden and A. D. Christianson, J. Phys.: Condens. Matter 22, 203203 (2010); G. Stewart, Rev. Mod. Phys. 83, 1589 (2011).
[3] A. Cano, M. Civelli, I. Eremin, and I. Paul, Phys. Rev. B 82, 020408(R) (2010); I. Paul, A. Cano and K. Sengupta, ibid. 83, 115109 (2011); A. Cano and I. Paul, ibid. 85, 155133 (2012).
[4] Kim et al., Phys. Rev. B 83, 134522 (2011).
[5] Dhital et al., Phys. Rev. Lett. 108, 087001 (2012).
[6] A. Cano, Phys. Rev. B 84, 012504 (2011).
[7] J.-H. Chu, et al. Science, 337, 710-712 (2012).