Fig. 1: The elasto-thermoelectric transport technique.
From: Strain derivative of thermoelectric properties as a sensitive probe for nematicity
a Schematic of our experimental setup. The relative size of the sample and the piezo-stack in the sketch is exaggerated: the actual size of the piezo device is 9 × 5 × 5 mm3, while the sample is around 1 × 1 × 0.04 mm3. The sample is mounted on a piezoelectric device, which expands or contracts according to the green arrows. The thermal circuit is realized with a heater and a cold foot connected to the thermal mass. The temperature gradient is measured using a chromel-Au thermocouple while two couples of electrodes measure the Seebeck voltage ΔVS and the Nernst voltage ΔVN. The applied strain ϵ is measured with a strain gauge glued on the back side of the piezo. d The sample is oriented with the tetragonal a-axis tilted of 45 degrees with respect to the piezo straining axis, so that the distortion occurs along the putative orthorhombic axis. Fe1 and Fe2 are the iron atoms in the Fe-As planes. b, e Time-dependence of the applied heat power WH (bottom panel), applied strain ϵ (middle panel) and resulting Seebeck (b) and Nernst (e) signals at representative temperatures and magnetic fields for a LaFeAsO compound. c Strain dependence of the Seebeck anisotropy ΔS = S(ϵ) − S(ϵ = 0) for a single crystal of LaFeAsO at T = 155 K and T = 200 K. f Strain dependence of the Nernst anisotropy Δν = ν(ϵ) − ν(ϵ = 0) for a single crystal of LaFeAsO at T = 157 K and B = ±14 T.
