Seebeck effect inFe1+xTe1−ySeysingle crystals

Abstract

We present measurements of resistivity and thermopower S of Fe 1+x Te 1−y Se y single crystalline samples with y = 0, 0.1, 0.2, 0.3, and 0.45 in zero field and in a magnetic field B = 8 T. We find that the shape of thermopower curves appears quite peculiar in respect to that measured in other Fe-based superconducting families. We propose a qualitative analysis of the temperature behavior of S, where the samples are described as almost compensated semimetals: different electron and hole bands with similar carrier concentrations compete and their relative contribution to the thermoelectric transport depends on the respective filling, mobility, and coupling with phonons. For y Ն 0.2, superconductivity occurs and the optimum Se-doping level for a maximum T c of 13 K turns out to be y = 0.3. At low temperatures, evidence of a contribution to S by an excitation-drag mechanism is found while at high temperatures a strikingly flat behavior of S is explained within a narrowband Hubbard model.

Theoretical and experimental investigation of magnetotransport in iron chalcogenides

“…The Fe 1.05 Te sample reaches a steady negative value of approximately −6 µV K −1 at high temperatures. Such saturation of S at high temperatures was first pointed out in [17] as a feature of the 11 family, in contrast to other Fe-based pnictides, and is typical of narrow-band materials. Indeed, in such materials, at sufficiently high temperatures the kinetic terms contributing to S can be neglected and the value of S can be calculated by simple combinatorial arguments, considering only the density of carriers, as described by the Heikes law [18][19][20].…”

Coupling of electronic and magnetic properties in Fe1+y(Te1−xSeHu1, Liu2, Qian3 et al. 2013Phys. Rev. B

“…For a multiple-band system, RH is not only dependent on carrier density, but is also associated with charge carriers' mobility. Multiple-band signature of Fe1+y(Te1-xSex) has indeed been probed in thermopower measurements 25,32 .…”

Strong correlation and low carrier density inFe1+yTe0.6Se0.4as seen from its the

“…A set-up with cernox thermometers in a He 4 cryostat was used in a superconducting magnet up to 12 T, and afterwards in a DC resistive magnet up to 28 T. The magnetic field was applied perpendicular to the [applied] heat-current and the [measured] electric-field vectors. [12]. The application of a magnetic field shifts and broadens the superconducting transition, but not the amplitude of the normal state Seebeck response.…”