"Elastocaloric signature of nematic fluctuations"

Matthias S. Ikeda: Thanapat Worasaran, Elliott W. Rosenberg, Johanna C. Palmstrom, Steven A. Kivelson, and Ian R. Fisher; PNAS, 09/09/21.

Additional Authors: Thanapat Worasaran, Elliott W. Rosenberg, Johanna C. Palmstrom, Steven A. Kivelson, and Ian R. Fisher

Abstract:

The elastocaloric effect (ECE) relates changes in entropy to changes in strain experienced by a material. As such, ECE measurements can provide valuable information about the entropy landscape proximate to strain-tuned phase transitions. For ordered states that break only point symmetries, bilinear coupling of the order parameter with strain implies that the ECE can also provide a window on fluctuations above the critical temperature and hence, in principle, can also provide a thermodynamic measure of the associated susceptibility. To demonstrate this, we use the ECE to sensitively reveal the presence of nematic fluctuations in the archetypal Fe-based superconductor Ba(Fe1xCox)2As2. By performing these measurements simultaneously with elastoresistivity in a multimodal fashion, we are able to make a direct and unambiguous comparison of these closely related thermodynamic and transport properties, both of which are sensitive to nematic fluctuations. As a result, we have uncovered an unanticipated doping dependence of the nemato-elastic coupling and of the magnitude of the scattering of low-energy quasi-particles by nematic fluctuations—while the former weakens, the latter increases dramatically with increasing doping.