Role of spin-orbit coupling effects in rare-earth metallic tetra-borides: a first principle study

Ismail Sk () and Nandan Pakhira ()
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Ismail Sk: Bajkul Milani Mahavidyalaya
Nandan Pakhira: Kazi Nazrul University

The European Physical Journal B: Condensed Matter and Complex Systems, 2023, vol. 96, issue 3, 1-12

Abstract: Abstract Recent observation of magnetization plateau in rare-earth metallic tetra-borides, $$\text {RB}_{4}$$ RB 4 , have drawn lot of attention to this class of materials. In this article, using first principle electronic structure methods (DFT) implemented in Quantum Espresso (QE), we have studied hither-to neglected strong spin-orbit coupling (SOC) effects present in these systems on the electronic structure of these system in the non-magnetic ground state. The calculations were done under GGA and GGA+SO approximations. In the electronic band structure, strong SOC effect lifts degeneracy at various symmetry points. The projected density of states consists of 3 distinct spectral peaks well below the Fermi energy and separated from the continuum density of states around the Fermi energy. The discrete peaks arise due to rare-earth $${\varvec{s}}$$ s , rare-earth $${\varvec{p}}$$ p + B $${\varvec{p}}$$ p and B $${\varvec{p}}$$ p while the continuum states around the Fermi level arises due to hybridized B $${\varvec{p}}$$ p , rare-earth $${\varvec{p}}$$ p and $${\varvec{d}}$$ d orbitals. Upon inclusion of SOC the peak arising due to rare-earth p gets split into two peaks corresponding to $${\varvec{j}}={\textbf {0.5}}$$ j = 0.5 and $${\varvec{j}}={\textbf {1.5}}$$ j = 1.5 configurations. The splitting gap ( $${\varvec{\Delta }} {\varvec{E}}_{\text {gap}}$$ Δ E gap ) between $${\varvec{j}}={\textbf {0.5}}$$ j = 0.5 and $${\varvec{j}}={\textbf {1.5}}$$ j = 1.5 manifold shows power law ( $${\varvec{\Delta }} {\varvec{E}}_{\text {gap}}\varvec{\propto } {\varvec{Z}}^{{\varvec{n}}}$$ Δ E gap ∝ Z n , $${\varvec{Z}}$$ Z is the atomic number of the rare-earth atom involved) behaviour with n =4.82. In case of $$\text {LaB}_{4}$$ LaB 4 , in the presence of SOC, spin-split $${\textbf {4}}{\varvec{f}}$$ 4 f orbitals contributes to density of states at the Fermi level while the density of states at the Fermi level largely remains unaffected for all other materials under consideration. Graphic abstract

Date: 2023
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DOI: 10.1140/epjb/s10051-023-00500-7

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