Nematic phase of Iron Based Superconductors probed by Nernst effect
Final Report Abstract
The topic of this project was the investigation of the nematic phase of iron-based superconductors by means of an original experimental setup, which combines the standard equipment for the realization of thermoelectric transport properties with a device for the application of uniaxial strain. We succeeded in building the experimental apparatus for the measurement of the elasto-transport properties, corresponding to the first objective of the project. In particular, starting from the state-of-art technique for the elasto-resistance, we upgraded the setup in order to measure the elasto-thermoelectric properties, namely the strain-derivative of the Seebeck and the Nernst coefficient. In addition, we started implementing a 3-piezos device to gain an order of magnitude in the applicable strain. The realization of this experimental setup opens new interesting perspectives concerning the application of the elasto-thermoelectric technique to the study of other classes of materials. In particular, in close vicinity of any electronic and structural instability, the strain-derivatives of the thermoelectric transport properties are expected to be strongly reacting, offering a novel experimental tool for fundamental investigations. We performed our experiments on various samples belonging to the 122, 1111 and 11 families of ironbased superconductors, across the nematic transition. In particular, we systematically performed measurements of Nernst effect and elasto-resistance in order to compare the evolution of the nematic susceptibility, as probed with two different techniques. Moreover, we successfully measured the elasto-Seebeck and elasto-Nernst for selected samples of the 1111 and 11 family. As a main result, not only we demonstrated the practicability of this new technique, but we obtained also original information about the nematic phenomenology in iron-based superconductors, in accordance to the second objective of the project. In particular, our measurements provided the following outcomes: i) multiple quantum critical points can exist into the phase diagram of iron-based superconductors; ii) the Nernst effect is extremely sensitive to nematic fluctuations; iii) the orbital degree of freedom plays a fundamental role and it is crucial towards the understanding of the electronic origin of the nematicity; iv) the nematicity is band-selective; v) the elasto-thermoelectric properties offers a new insight into the nematic phenomenology, resulting generally non-equivalent to the elasto-resistivity mesaurements.
Publications
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Evolution of the Nematic Susceptibility in LaFe1-xCoxAsO, Phys. Rev. Lett. 125, 067001 (2020)
Xiaochen Hong, Federico Caglieris, Rhea Kappenberger, Sabine Wurmehl, Saicharan Aswartham, Francesco Scaravaggi, Piotr Lepucki, Anja U. B. Wolter, Hans-Joachim Grafe, Bernd Büchner, and Christian Hess
