Impact of uniaxial pressure on structural and magnetic phase transitions in electron-doped iron pnictides

Abstract

We use neutron resonance spin echo and Larmor diffraction to study the effect of uniaxial pressure on the tetragonal-to-orthorhombic structural (Ts) and antiferromagnetic (AF) phase transitions in iron pnictides BaFe2−xNixAs2 (x = 0, 0.03, 0.12), SrFe1.97Ni0.03As2, and BaFe2(As0.7P0.3)2. In antiferromagnetically ordered BaFe2−xNixAs2 and SrFe1.97Ni0.03As2 with TN and Ts (TN ≤ Ts), a uniaxial pressure necessary to detwin the sample also increases TN , smears out the structural transition, and induces an orthorhombic lattice distortion at all temperatures. By comparing temperature and doping dependence of the pressure induced lattice parameter changes with the elastoresistance and nematic susceptibility obtained from transport and ultrasonic measurements, we conclude that the in-plane resistivity anisotropy found in the paramagnetic state of electron underdoped iron pnictides depends sensitively on the nature of the magnetic phase transition and a strong coupling between the uniaxial pressure induced lattice distortion and electronic nematic susceptibility.

Electronic nematic correlations in the stress-free tetragonal state ofBaFe2−xNixAs2

“…2]. Although these results would naively suggest that resistivity anisotropy is an intrinsic property of the paramagnetic tetragonal phase of BaFe 2−x T x As 2 consistent with the presence of an ideal electronic nematic state [1], our neutron Larmor diffraction measurements using three-axes spin echo spectrometer (TRISP) at Heinz Maier-Leibnitz, Garching, Germany [27][28][29][30] on temperature dependence of the lattice spacing (d) and its distortion (∆d) in lightly electron-doped iron pnictides reveal that the lattice distortion increases on cooling, passes smoothly across T s , and enhances dramatically on approaching T N with no [12]. The spin excitation anisotropy temperatures under uniaxial strain are marked as T * [20].…”

“…1(b) and the flat-cone option of the IN8 triple-axis spectrometer at ILL [37]. In addition, we performed neutron Larmor diffraction measurement on BaFe 1.97 Ni 0.03 As 2 using the TRISP spectrome- (1, 0, 5) ter [27][28][29][30]. We first describe neutron diffraction experiments on IN8 designed to study the detwinning ratio and its temperature dependence in strained and stress free BaFe 2 As 2 , as these results will allow us to determine if the detwinning ratio is maintained after releasing the uniaxial strain below T N .…”

Spin anisotropy due to spin-orbit coupling in optimally hole-dopedBa0.67K0.33Fe2As2

“…Furthermore, by measuring the splitting of the electronic states at high-symmetry points in reciprocal space 18 , angle-resolved photoemission spectroscopy (ARPES) measurements find that spin-orbit coupling (SOC) is present in both electron-and hole-doped iron pnictides with a similar energy scale ∼ 10 meV 19 . Also common to both optimally electron-doped BaFe 2−x T M x As 2 20,21 and hole-doped Ba 1−x K x Fe 2 As 2 22,23 is the presence of electronic nematic fluctuations, as revealed by the elastoresistance -i.e. the rate of change of the resistivity anisotropy with respect to applied in-plane uniaxial strain [ Fig.…”

Orbital selective neutron spin resonance in underdoped superconducting NaFe0.985Co0.015As

“…The clear spin excitation anisotropy above T s is likely due to the applied uniaxial pressure as discussed in Refs. 47,48 . As a function of decreasing temperature, the magnetic scattering anisotropy starts to build up below T * , saturates at temperatures slightly below T N , and shows no anomaly across T c .…”