Local orthorhombic lattice distortions in the paramagnetic tetragonal phase of superconducting NaFe1−xNixAs

Abstract

Understanding the interplay between nematicity, magnetism and superconductivity is pivotal for elucidating the physics of iron-based superconductors. Here we use neutron scattering to probe magnetic and nematic orders throughout the phase diagram of NaFe1−xNixAs, finding that while both static antiferromagnetic and nematic orders compete with superconductivity, the onset temperatures for these two orders remain well separated approaching the putative quantum critical points. We uncover local orthorhombic distortions that persist well above the tetragonal-to-orthorhombic structural transition temperature Ts in underdoped samples and extend well into the overdoped regime that exhibits neither magnetic nor structural phase transitions. These unexpected local orthorhombic distortions display Curie–Weiss temperature dependence and become suppressed below the superconducting transition temperature Tc, suggesting that they result from the large nematic susceptibility near optimal superconductivity. Our results account for observations of rotational symmetry breaking above Ts, and attest to the presence of significant nematic fluctuations near optimal superconductivity.

Weaker nematic phase connected to the first order antiferromagnetic phase transition in SrFe2As2 compared to BaFe2As2Tam1, Wang2, Zhang3 et al. 2019Phys. Rev. BSelf Cite9280View full textAdd to dashboardCite

“…Theoretically, the electronic nematic phase and associated resistivity anisotropy is expected to only occur below the tetragonal-to-orthorhombic phase transition temperature T s [7]. Although recent neutron pair distribution function and Lamor diffraction experiments on dif-ferent classes of iron pnictides including Sr 1−x Na x Fe 2 As 2 [35] and NaFe 1−x Ni x As [36] reveal clear evidence for local orthorhombic lattice distortions in temperatures well above T s , these local lattice distortions are evenly distributed along the two orthorhombic lattice directions and therefore not expected to induce resistivity anisotropy. The clear presence of resistivity [12,13], spin excitation [19][20][21][22], and orbital population anisotropy [37] in the paramagnetic phase of iron pnictides can arise from the interaction of applied uniaxial pressure with nematic susceptibility and associated spin excitations through magnetoelastic coupling [38].…”

Structure, phonons, and orbital degrees of freedom in Fe2Mo3O8

“…The increase in the strain broadening S 202 can have a similar origin [27] and does not indicate macroscopic symmetry lowering. Indeed, in systems with the symmetry lowering an anisotropic strain broadening will usually precede the symmetry-lowering phase transition and diverge upon approaching the transition from above [28]. This does not happen in Fe 2 Mo 3 O 8 , where the high-resolution synchrotron data collected both right above and well below T N reveal only a weak broadening of the h0l reflections [ Fig.…”

Edwards-Anderson parameter and local Ising-nematicity in FeSe revealed via NMR spectral broadening

“…T result implies that the strong specific-heat peak in zero-field at is a novel combined structural, magnetic and superconduct first-order transition, in which a re-entrance of the C 2 -SD phase occurs. How exactly a magnetic field tunes the system fr 14 (symbols) for the thermal expansion distortion corrected for the effect of the applied force, d 0 , for the samp (see Supplementary Figs 1 and 2 for details on the measurement of th…”

“…In the iron-based superconductors, signatures of C 4 symmetry breaking and short-range nematic order have often been found well above the bulk nematic phase transition temperature [12][13][14][15], especially from local probe measurements using scanning tunneling microscopy (STM) [16] and nuclear magnetic resonance (NMR) [17][18][19][20][21][22][23][24]. More recently, x-ray and neutron pair distribution function (PDF) studies have revealed the locally orthorhombic nature of the tetragonal paramagnetic phase in the (Sr,Na)Fe 2 As 2 system [25].…”