Quest for nematicity in iron-based superconductors
Final Report Abstract
In the completed project, dilatometric investigations and 3 point bending measurements were carried out on iron-based superconductors and related systems, with which the interaction of the structural, magnetic and electronic degrees of freedom was investigated. Measurements of the specific heat, magnetization and thermal expansion, magnetostriction and Young's modulus using capacitance dilatometry on single crystals show the importance of structural and elastic changes for understanding unconventional superconductivity in La(Fe,Co)AsO, Sr1-xNaxFe2As2, LiFeAs and Fe(Se,S,Te). In addition to the creation of the Phase diagrams and the determination of the order parameter of the tetragonal-orthorhombic phase transition, the measurements of the Young's modulus by means of a 3-point bending method, which was established for these measurements, are in the foreground. These confirm the shear modulus C66 as a soft mode of the pseudo-ferroelastic phase transition and enable the study of electronic nematic fluctuations, which were measured for La(Fe,Co)AsO for the first time. Quantitative analysis reveals a discrepancy for La(Fe,Co)AsO compared to elastoresistance data, which challenges current analyses. Studies on Fe(Se,S) show that superconductivity and orthorhombicity reinforce each other. Measurements of the specific heat of pure FeSe provide information about the development of the superconducting phase and the order parameter. Overall, the importance of high-quality samples was confirmed during the course of the project, since the analysis of the results was made more difficult by degradation effects and defects in a large number of investigations on LiFeAs materials. The very nice and meaningful results, especially for La(Fe,Co)AsO ,FeSe and Sr1−xNaxFe2As2 were only possible due to the excellent sample quality of the single crystals produced by the project partners. Also the 3-point bending method for determining the shear modulus and ultimately the nematic susceptibility was implemented, it has been successful applied on the investigation of URu2Si2 hidden-order (HO) correlation length. In addition to measurements of iron pnicides superconducting materials, other materials like single crystalline α-RuCl3 and intermetallic compounds R2PdSi3 (R = Ho, Dy) are successfully investigated by dilatometry techniques, indicating the dilatometry and 3 point bending technique are powerful thermodynamic tools.
Publications
- Spectral Evidence for Emergent Order in Ba1-xNaxFe2As2. Physical Review Letters, 2018. 121(12): p. 127001
Yi, M.,Wang,L., et al.
(See online at https://doi.org/10.1103/PhysRevLett.121.127001) - Uniaxial and hydrostatic pressure effects in α-RuCl3 single crystals via thermal-expansion measurements. Journal of Physics: Condensed Matter, 2018. 30(38): p. 385702
He, M., Wang,L.,et al.
(See online at https://doi.org/10.1088/1361-648x/aada1e) - Calorimetric evidence of nodal gaps in the nematic superconductor FeSe. Physical Review B, 2019. 99(3): p. 035157
Hardy, F., Wang,L,. et al.
(See online at https://doi.org/10.1103/PhysRevB.99.035157) - Competing Electronic Phases near the Onset of Superconductivity in Holedoped SrFe2As2. Journal of the Physical Society of Japan, 2019. 88(10): p. 104710
Wang, L., et al.
(See online at https://doi.org/10.7566/JPSJ.88.104710) - Nematicity and structure in LaFe1-xCoxAsO. Journal of Magnetism and Magnetic Materials, 2019. 482: p. 50-53
Wang, L., et al.
(See online at https://doi.org/10.1016/j.jmmm.2019.02.061) - The Complex Electronic Phase Diagram of Single-Crystalline R2PdSi3 (R = Ho, Dy) Studied by Thermal Expansion and Magnetostriction. Journal of the Physical Society of Japan, 2019. 88(9): p. 094709.7
Wang, L., et al.
(See online at https://doi.org/10.7566/JPSJ.88.094709) - Electronic Nematicity in URu2Si2 Revisited. Physical Review Letters, 2020. 124(25): p. 257601
Wang, L., et al.
(See online at https://doi.org/10.1103/PhysRevLett.124.257601) - Revisiting the phase diagram of LaFe1-xCoxAsO in single crystals by thermodynamic methods. Physical Review B, 2021. 103(17): p. 174506
Scaravaggi, F.,Wang,L., et al.
(See online at https://doi.org/10.1103/PhysRevB.103.174506) - Rotational symmetry breaking at the incommensurate charge-densitywave transition in Ba(Ni,Co)2(As,P)2 Possible nematic phase induced by charge/orbital fluctuations. Physical Review B, 2021. 104(18): p. 184509
Merz, M., Wang,L., et al.
(See online at https://doi.org/10.1103/PhysRevB.104.184509)
