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Lattice Trailing the Electrons
Superconducting order recedes with decreased chemical doping in a typical iron-based superconductor family. Thus, the symmetry of the material is broken by almost simultaneous antiferromagnetic and structural phase transitions. However, some pnictides also exhibit an electronic nematic transition manifested by anisotropy of the electrical resistance. Because this anisotropy occurs at the same time as the structural transition, it is not clear whether it is a consequence of the broken crystal lattice symmetry or its cause. Chu et al. (p. 710) performed constant strain experiments on the series Ba(Fe1−xCox)2As2, which can distinguish between the two scenarios, and confirm that the electrons drive the lattice transition.
Abstract
Within the Landau paradigm of continuous phase transitions, ordered states of matter are characterized by a broken symmetry. Although the broken symmetry is usually evident, determining the driving force behind the phase transition can be complicated by coupling between distinct order parameters. We show how measurement of the divergent nematic susceptibility of the iron pnictide superconductor Ba(Fe1−xCox)2As2 distinguishes an electronic nematic phase transition from a simple ferroelastic distortion. These measurements also indicate an electronic nematic quantum phase transition near the composition with optimal superconducting transition temperature.
