Electronic Structures and Phonon Spectra in Boronitride Superconductors LaMBN (M= Ni, Pt)

Abstract

We have investigated electronic structures and phonon spectra of newly discovered isostructural superconductors LaNiBN (T_c = 4.1 K) and LaPtBN (T_c = 6.7 K). We have found that their electronic structures are substantially three-dimensional, leading to metallicity both in NiB (PtB) and the intervening LaN layers. Our ab initio phonon calculations show that almost all phonon modes contribute to the electron-phonon coupling (EPC) mechanism, reflecting that both layers are involved in the superconductivity. For LaNiBN, we obtain an EPC strength of λ= 0.52 and a logarithmically averaged characteristic phonon frequency of ω_{log} = 376 K, leading to T_c = 3.9 K. Compared with the Ni B_{1g} mode in LaNiBN, the Pt B_{1g} mode in LaPtBN is reduced by ~70%, leading to a slightly enhanced λ= 0.56 and an ~20 % reduced ω_{log}. The estimated T_c is 5.4 K for LaPtBN, in good agreement with the experiment. We do not find any indication of magnetic instability for either LaNiBN or LaPtBN, which implies that both systems are EPC mediated superconductors. Further, we have found an interesting trend of monotonic increase of T_c with respect to the boron height in the NiB (PtB) layer of both borocarbide and boronitride superconductors, which suggests a possible way to enhance T_c in these systems.

arXiv comment8 pages

References in corpus (11)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Heavy fermion superconductivity and magnetic order in non-centrosymmetric $CeP{t}_{3}Si$
• Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln=La,Nd)
• S-wave/spin-triplet order in superconductors without inversion symmetry: Li${}_2$Pd${}_3$B and Li${}_2$Pt${}_3$B
• Crystal Symmetry, Electron-Phonon Coupling, and Superconducting Tendencies in Li${}_2$Pd${}_3$B and Li${}_2$Pt${}_3$B
• Formal Valence, $d$ Occupation, and Charge-Order Transitions
• Electron-phonon superconductivity in $A$Pt${}_3$P compounds: from weak to strong coupling
• Electron-phonon coupling in the conventional superconductor YNi${}_2$B${}_2$C at high phonon energies studied by time-of-flight neutron spectroscopy
• Electron and phonon band-structure calculations for the antipolar SrPt${}_3$P antiperovskite superconductor: Evidence of low-energy two-dimensional phonons
• Vibrational Modes in LiBC: Theory Compared with Experiment
• Magnetism in heavy-fermion U(Pt,Pd)3 studied by mSR

Cited by in corpus (1)

• BaCuS2: a superconductor with moderate electron-electron correlation