Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parent Ca${}_{1-x}$La${}_x$FeAs${}_2$ across its structural phase transition

Abstract

The newly discovered 112-type ferropnictide superconductors contain chains of As atoms that break the tetragonal symmetry between the $a$ and $b$ axes. This feature eliminates the need for uniaxial strain that is usually required to stabilize large single domains in the electronic nematic state that exists in the vicinity of magnetic order in the iron-based superconductors. We report detailed structural symmetry measurements of 112-type Ca${}_{0.73}$La${}_{0.27}$FeAs${}_2$ using rotational anisotropy optical second harmonic generation. This technique is complementary to diffraction experiments and enables a precise determination of the point group symmetry of a crystal. By combining our measurements with density functional theory calculations, we uncover a strong optical second harmonic response of bulk electric dipole origin from the Fe and Ca $3d$-derived states that enables us to assign $C_2$ as the crystallographic point group. This makes the 112-type materials high-temperature superconductors without a center of inversion, allowing for the possible mixing of singlet and triplet Cooper pairs in the superconducting state. We also perform pump-probe transient reflectivity experiments that reveal a 4.6 THz phonon mode associated with the out-of-plane motion of As atoms in the FeAs layers. We do not observe any suppression of the optical second harmonic response or shift in the phonon frequency upon cooling through the reported monoclinic-to-triclinic transition at 58 K. This allows us to identify $C_1$ as the low-temperature crystallographic point group but suggests that structural changes induced by long-range magnetic order are subtle and do not significantly affect electronic states near the Fermi level.

References in corpus (24)

• Superconductivity in Iron Compounds
• High-temperature superconductivity in iron-based materials
• Evidence for an electron nematic phase transition in underdoped iron pnictide superconductors
• Theory of Electron Nematic Order in LaOFeAs
• Symmetry breaking orbital anisotropy on detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition
• Anomalous suppression of the orthorhombic distortion in superconducting Ba[Fe(1-x)Cox]2As2
• Effects of nematic fluctuations on the elastic properties of iron arsenide superconductors
• Magnetism in Fe-based superconductors
• Evidence of an odd-parity hidden order in a spin-orbit coupled correlated iridate
• Superconductivity in Ca1-xLaxFeAs2: A Novel 112-Type Iron Pnictide with Arsenic Zigzag Bonds
• Discovery of New Layered Iron Arsenide Superconductor (Ca,Pr)FeAs2
• A structural distortion induced magneto-elastic locking in Sr${}_2$IrO${}_4$ revealed through nonlinear optical harmonic generation
• Enhanced Superconductivity up to 43 K by P/Sb Doping of Ca1-xLaxFeAs2
• Synthesis and physical properties of Ca1-xRExFeAs2 with RE = La ~ Gd
• Doping-Enhanced Antiferromagnetism in Ca1-xLaxFeAs2
• Structural and magnetic phase transitions in Ca${}_{0.73}$La${}_{0.27}$FeAs${}_2$ with electron overdoped FeAs layers
• High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position sensitive detection
• A Low Temperature Nonlinear Optical Rotational Anisotropy Spectrometer for the Determination of Crystallographic and Electronic Symmetries
• Electronic nematic correlations in the stress free tetragonal state of BaFe${}_{2-x}$Ni${}_x$As${}_2$
• Anisotropic Superconductivity of Ca1-xLaxFeAs2 (x ~ 0.18) Single Crystal
• Raman spectra in iron-based quaternary CeO${}_{1-x}$F${}_x$FeAs and LaO${}_{1-x}$F${}_x$FeAs
• Raman Scattering Study of the Lattice Dynamics of Superconducting LiFeAs
• Optical properties of the iron-pnictide analog BaMn2As2
• Spin dependent electron-phonon interaction in SmFeAsO by low-temperature Raman spectroscopy

Cited by in corpus (7)

• A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd${}_2$Re${}_2$O${}_7$
• Correlated materials design: prospects and challenges
• Electronic nematicity in FeSe: a first-principles perspective
• Superconductivity and Dirac Fermions in 112-phase Pnictides
• Phase stability and large in-plane resistivity in the 112-type iron-based superconductor Ca${}_{1-x}$La${}_x$FeAs${}_2$
• Thermodynamic electric quadrupole moments of nematic phases from first-principles calculation
• Site-Selective Antimony Doping in Arsenic Zigzag Chains of 112-type Ca1-xLaxFeAs2