Interplay of magnetic and structural transitions in iron-based pnictide superconductors

Abstract

The interplay between the structural and magnetic phase transitions occurring in the Fe-based pnictide superconductors is studied within a Ginzburg-Landau approach. We show that the magnetoelastic coupling between the corresponding order parameters is behind the salient features observed in the phase diagram of these systems. This naturally explains the coincidence of transition temperatures observed in some cases as well as the character (first or second-order) of the transitions. We also show that magnetoelastic coupling is the key ingredient determining the collinearity of the magnetic ordering, and we propose an experimental criterion to distinguish between a pure elastic from a spin-nematic-driven structural transition.PACS numbers: 74.70. Xa, 74.90.+n, 75.80.+q Introduction.-The discovery of an unconventional high-temperature superconductivity in the F-doped arsenic-oxide LaFeAsO 1 has given rise to a great interest on iron pnictide compounds. To date several families of Fe-based superconductors have been discovered, and the superconducting transition temperature has been raised to above 50 K.2 All of these systems display an intriguing competition between structural, magnetic and superconducting transitions.2,3 The parent compounds of the so-called 1111 and 111 families undergo a structural transition (ST) followed by a magnetic transition (MT) at a lower temperature, 4 whereas in the 122 and 11 cases these two transitions take place simultaneously. [5][6][7] In any case these orderings are quickly suppressed by doping or by applying pressure, which eventually gives rise to superconductivity. The role, if any, of magnetic and elastic degrees of freedom in inducing this superconductivity is currently an open question. There is already a growing body of theoretical works advocating for spin fluctuation mediated superconductivity, 8 but the isotope effect observed in both magnetism and superconductivity suggests that the elastic medium also plays a role.9 It is therefore compelling to understand the connection between the ST and the MT in these systems.

In-plane uniaxial stress effects on the structural and electronic properties of BaFe2As2and CaFe2AsTomić1, Jeschke2, Fernandes3 et al. 2013Phys. Rev. B285231View full textAdd to dashboardCite

“…6 also found an enhancement of the magnetic transition temperature T N in the same detwinned samples. Phenomenological models 14,30,36 attribute this effect to changes in the magnetic fluctuation spectrum of the paramagnetic phase promoted by the uniaxial stress. In this regard, it would be interesting in future ab initio studies to systematically investigate the changes in the nesting feature of the Fermi surface (Fig.…”

“…This may have important impact on the coupled magnetic and structural transitions displayed by these compounds, as discussed in Refs. 11,36,37, and as such deserves further investigation in the future. a+b .…”

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca1−xLaxFeAs2

“…Below, we show that this is not the case. Even though there have been various studies which wrote down the Landau theory for these systems, such as references [70][71][72], to the best of our knowledge there are no studies which emphasize the difference between ferro-and antiferro-orbital orders and their connection with the nematicity.…”

Observation of the magnetic C4 phase in Ca1−xNaxFe2As2

“…5,10,11,[43][44][45] In Fig. 7 (e) the magnetic order parameter (m) is plotted as a function of the structural order parameter (δ) for all three systems at base temperature.…”