Topological Properties in Selected Transition-Metal Pnictides and Chalcogenides

Author

Ramakanta Chapai, Louisiana State University and Agricultural and Mechanical CollegeFollow

Degree

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Document Type

Dissertation

Abstract

With the continued discovery of topological properties in condensed matter, several members of transition-metal pnictides and chalcogenides (TMPCs) compounds have been testbeds for various exotic particles such as Dirac, Weyl and Majorana fermions. In this dissertation, we have chosen four material systems: PdSb₂, PdTe₂, PtTe₂, and PdTe in the TMPC family, and explored their physical properties under a variety of stimuli (e.g. temperature, magnetic field, and pressure). We examined the topological behavior of these selected systems by analyzing the de Haas-van Alphen (dHvA) oscillations observed in the magnetization and magnetic torque.

From our magneto-transport measurements, we found that the non-symmorphic PdSb₂ with six-fold degeneracy exhibits a large magnetoresistance (MR) with continuous increase up to 35 T. The MR obeys Kohler's law indicating charge carrier compensation which is further confirmed from the Hall effect measurements. Five bands are identified from the analysis of the dHvA oscillations, two of them possessing a non-trivial Berry phase. These are two of the six-fold degenerate bands at the Fermi level (E_F).

In trigonal PdTe₂ with four-fold degeneracy, the observed dHvA oscillations provided evidence of non-trivial topology which is consistent with the presence of a Dirac cone near E_F. However, in PtTe₂ which is isostructural with PdTe₂, the dHvA oscillations we observed are dominated by topologically trivial bands. Unlike in PdTe₂, the Dirac cone in PtTe₂ is predicted to lie far below E_F which is likely a reason for the trivial topology we found in PtTe₂. While both are multiband systems, our magneto-transport measurements revealed the charge compensation in PtTe₂ but not in PdTe₂. The angular dependence of the dHvA oscillations rendered a 3D nature of the Fermi surface in both PdTe₂ and PtTe₂ despite their layered structure.

For the hexagonal PdTe, superconductivity is observed with T_c ~ 4.5 K. Below T_c, the electronic specific heat decreases obeying a power-law suggesting the presence of nodes in the superconducting energy gap, a signature of unconventional superconductivity. We identified four bands from the dHvA oscillations, two of them exhibiting a non-trivial Berry phase. The unconventional superconductivity observed is in congruence with the presence of topologically non-trivial bands.

Date

3-25-2021

Recommended Citation

Chapai, Ramakanta, "Topological Properties in Selected Transition-Metal Pnictides and Chalcogenides" (2021). LSU Doctoral Dissertations. 5503.
https://repository.lsu.edu/gradschool_dissertations/5503

Committee Chair

Jin, Rongying

DOI

10.31390/gradschool_dissertations.5503