Strain-derivative of thermoelectric properties: a sensitive probe for nematicity

• Published in: arXiv.org 2020-08
• Main Authors: Caglieris, Federico, Wuttke, Christoph, Hong, Xiaochen, Sykora, Steffen, Kappenberger, Rhea, Aswartham, Saicharan, Wurmehl, Sabine, Büchner, Bernd, Hess, Christian
• Format: Article
• Language: English
• Subjects: Anisotropy; Carrier mobility; Condensed matter physics; Iron; Magnetic transitions; Phenomenology; Superconductivity; Transport properties; Unconventional superconductors; Variation
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1905.11660

The nematic instability of iron-based superconductors is an undebatable ingredient of the physics of iron-based superconductors. Yet, its origin remains enigmatic as it involves a fermiology with an intricate interplay of lattice-, orbital- and spin- degrees of freedom. It is well known that thermoelectric transport is an excellent probe for revealing even subtle signatures of instabilities and pertinent fluctuations. In this paper, we report a strong response of the thermoelectric transport properties of two underdoped 1111 iron-based superconductors to a vanishingly small strain. By introducing the strain-derivative of the Seebeck and the Nernst coefficients, we provide a novel description of the nematic order parameter, proving the existence of an anisotropic Peltier-tensor beside an anisotropic conductivity-tensor. Our measurements reveal that the transport nematic phenomenology is the result of the combined effect of both an anisotropic scattering time and Fermi surface distortions, pointing out that in a realistic description, abreast of the spin-fluctuations also the orbital character is a fundamental ingredient. In addition, we show that nematic fluctuations universally relax in a Curie-Weiss fashion above T_S in all the elasto-transport measurements and we provide evidences that nematicity must be band-selective.