A new experimental setup is designed for the measurement of Seebeck and Nernst coefficients on the single crystal flakes and polycrystalline samples. The setup utilizes the multifunctional probe assembly of the physical property measurement system by Quantum Design, Inc. and can measure in the temperature range of 1.8 K–380 K up to 8 T magnetic fields. The experimental measurement was fully automated through a computer using the code written in LabVIEW software. The setup is capable of measurements on samples as small as 2 × 1 mm2 in size and thickness as small as a few micrometers, which is quite important for the crystal flakes grown using the vapor transport method. The determination of the coefficients is based on the quasi-static approach, with the thermal gradient of 0.2 K–1.2 K across the sample in the measured temperature range of 1.8 K–300 K. The sensitivity of the instrument is better than 0.1 µV/K, and the accuracy is better than ∼0.5 µV/K, which can be further improved with the better quality of electrical contacts on the sample. The Seebeck and Nernst coefficient measurements performed on some well-studied semimetallic (bismuth), thermoelectric (Bi2Se3), and superconducting (FeTe0.5Se0.5) systems are also presented.
A detailed investigation on the structural and magnetotransport properties of iron‐intercalated Bi2Se3 single crystals is presented. The X‐ray diffraction and Raman studies confirm the intercalation of Fe in the van der Waals gaps between the layers. The electrical resistivity of the compounds decreases upon intercalation, and Hall resistivity shows the enhancement of the charge carriers upon intercalation. The magnetoresistance (MR) shows the non‐saturating linear behavior at higher magnetic field and low temperature. Intercalation of Fe increases the onset of the linear MR behavior, indicating the reduction in quantum effects. The Kohler scaling used on the MR data indicates single scattering process for all these compounds in the measured temperature range of 3–300 K.
We present the magneto-transport and the thermoelectric (Seebeck and Nernst coefficient) studies of the Nb-doped Bi2Se3 topological superconductor. The angle-dependent magnetoresistance study highlights the anisotropy of upper critical field (Hc2) for in-plane and out-of-plane magnetic field orientation with the anisotropy parameter Γ ~1.3. The estimated value of the carrier concentration (~1019 cm-3) for Nb0.20Bi2Se3 is one order larger than for Bi2Se3. Doping of Nb shows a significant decrease in the Seebeck coefficient value and the estimated Fermi temperature of the three-dimensional Fermi surface at the centre of Brillouin zone in the zero-temperature limit enhances by ~4 times in comparison to pristine Bi2Se3 . We have observed a large value (~2.3 μV K-1 T-1) of Nernst coefficient for Bi2Se3 at room temperature which decreases with Nb doping (~0.5 μV K-1 T-1).
The discovery of the planar Hall effect in the topological semimetals has generated extensive research interest recently. We present the planar Hall effect studies on Cu intercalated type-II Dirac semimetal PdTe2 in order to understand the role of chiral anomaly. We observed a positive field dependence of electrical resistivity in both perpendicular and parallel field directions, causing a non-zero anisotropy. The planar Hall signal and anisotropic resistivity oscillate with the in-plane angle with an oscillation period of π. However, the positive longitudinal magnetoresistance, which shows almost linear field dependence at low temperatures, rules out the chiral anomaly as an origin of the planar Hall effect. In addition, Cu0.05PdTe2 is found to exhibit a tilted prolate shaped orbits in parametric plot between transverse and longitudinal resistivities. Our study suggests that for the type-II Dirac semimetal materials with positive longitudinal magnetoresistance, the origin of the planar Hall effect cannot be asserted with certainty to the topological or non-topological origins without considering the anisotropy of the Fermi surface.
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