Electronic nematicity above the structural and superconducting transition in BaFe2(As1−xP x )2

Abstract

Strongly interacting electrons can exhibit novel collective phases, among which the electronic nematic phases are perhaps the most surprising as they spontaneously break rotational symmetry of the underlying crystal lattice.1 The electron nematicity has been recently observed in the iron-pnictide 2-6 and cuprate 7-9 hightemperature superconductors. Whether such a tendency of electrons to self-organise unidirectionally has a common feature in these superconductors is, however, a highly controversial issue. In the cuprates, the nematicity has been suggested as a possible source of the pseudogap phase, 7-9 whilst in the iron-pnictides, it has been commonly associated with the tetragonalto-orthorhombic structural phase transition at T s . Here, we provide the first thermodynamic evidence in BaFe 2 (As 1−x P x ) 2 that the nematicity develops well above the structural transition and persists to the nonmagnetic superconducting regime, resulting in a new phase diagram strikingly similar to the pseudogap phase diagram in the cuprates.9,10 Our highly sensitive magnetic anisotropy measurements using microcantilever torque-magnetometry under in-plane field rotation reveal pronounced two-fold oscillations, which break the tetragonal symmetry. Combined with complementary high-resolution synchrotron X-ray and resistivity measurements, our results consistently identify two distinct temperaturesone at T * , signifying a true nematic transition, and the other at T s (< T * ), which we show to be not a true phase transition, but rather what we refer to as a "meta-nematic transition", in analogy to the well-known metamagnetic transition in the theory of magnetism. Our observation of the extended nematic phase above the superconducting dome establishes that the nematicity has primarily an electronic origin, inherent in the normal state of high-temperature superconductors.In the iron pnictides, the antiferromagnetic transition is closely intertwined with the structural phase transition from tetragonal (T) to orthorhombic (O) crystal symmetry. Although recent experiments, including neutron scattering, 2 ARPES, 3,11 STM, 4 and transport measurements, 5,6 have provided evidence for electronic anisotropy, these measurements were carried out either in the low-temperature orthorhombic phase, 2,4,11 where the crystal lattice structure has already broken C 4 symmetry, or in the tetragonal phase under uniaxial strain 3,5,6 that also breaks this symmetry. Therefore, the question remains open whether the electronic anisotropy can exist above the structural transition without an external driving force, including under the superconducting (SC) dome. In the past, the nematic transition in the pnictides has been associated either with the orbital ordering, [12][13][14][15][16][17][18] or with the spontaneous breaking of the Z 2 Ising symmetry between two collinear magnetic ordering wave-vectors Q = (π, 0) and (0, π).19-22 Therefore determining the nature of the nematicity is a key to understanding the microscopic origin of the lattice and magnetic...

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

“…they belong to different space groups) the orthorhombic phases realized below the structural transitions in, for example, LaFeAsO, where the transition is from the tetragonal P 4/nmm to the orthorhombic Cmma (# 67) structure [48]. Similarly, in the 122 compounds that have a tetragonal structure with the ThCr 2 Si 2 type (space group F mmm) at high temperature, an electronic nematic phase breaks the four-fold rotational symmetry and hence induces the structural transition to an orthorhombic space group [49][50][51]. In the case of Ca 1−x La x FeAs 2 , the monoclinic structure is stable up to at least 450 K [14], and no transition to the tetragonal phase is reported.…”

Comprehensive scenario for single-crystal growth and doping dependence of resistivity and anisotropic upper critical fields in (Ba1−xKx)FeLiu1, Tanatar2, Straszheim3 et al. 2014Phys. Rev. B6415722View full textAdd to dashboardCite

“…In the transformation range, ρ(T ) can be described with a second-order polynomial, with the magnitude * yliu@ameslab.gov † tanatar@ameslab.gov of T -linear term scaling with superconducting T c [12]. In iron-based superconductors, this scenario works very well in isoelectron doped BaP122 [16][17][18]. Here maximum T c is indeed observed at x = 0.33, close to doping-tuned magnetic QCP, and signatures of QCP are found in both normal [16][17][18] and superconducting [19] states, with resistivity at optimal doping being T linear for both in-plane [16] and interplane [20] transport.…”

“Checkerboard Stripe” Electronic State on Cleaved Surface of NdO0.7F0.3BiS2 Probed by Scanning Tunneling Microscopy

“…Another example is the high-temperature superconductivity in copper oxides 10 and iron-pnictides 11 . The superconductivity in these materials often coexists with or emerges in the proximity of some electronic ordered states [12][13][14][15][16][17][18] , which break the C 4 -symmetry of the underlying crystal lattice. Explorations of the relation between SC and the electronic ordered states have offered interesting information for understanding of the mechanisms of unconventional superconductivity.…”