000133405 001__ 133405
000133405 005__ 20240412150654.0
000133405 0247_ $$2doi$$a10.1073/pnas.2316101121
000133405 0248_ $$2sideral$$a138082
000133405 037__ $$aART-2024-138082
000133405 041__ $$aeng
000133405 100__ $$aLavroff, Robert H.
000133405 245__ $$aChemical bonding dictates drastic critical temperature difference in two seemingly identical superconductors
000133405 260__ $$c2024
000133405 5060_ $$aAccess copy available to the general public$$fUnrestricted
000133405 5203_ $$aThough YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6’s greater Fermi-level (Ef) density of states and higher electron–phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B–B bonds and bring this π-system lower in energy than the σ B–B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity.
000133405 536__ $$9info:eu-repo/grantAgreement/ES/MICINN/PID2021-122763NB-I00
000133405 540__ $$9info:eu-repo/semantics/openAccess$$aby-nc-nd$$uhttp://creativecommons.org/licenses/by-nc-nd/3.0/es/
000133405 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/publishedVersion
000133405 700__ $$0(orcid)0000-0001-6089-6126$$aMunarriz, Julen$$uUniversidad de Zaragoza
000133405 700__ $$aDickerson, Claire E.
000133405 700__ $$aMunoz, Francisco
000133405 700__ $$aAlexandrova, Anastassia N.
000133405 7102_ $$12012$$2755$$aUniversidad de Zaragoza$$bDpto. Química Física$$cÁrea Química Física
000133405 773__ $$g121, 14 (2024), e2316101121 [11 pp.]$$pProc. Natl. Acad. Sci.$$tProceedings of the National Academy of Sciences of the United States of America$$x0027-8424
000133405 8564_ $$s3444350$$uhttps://zaguan.unizar.es/record/133405/files/texto_completo.pdf$$yVersión publicada
000133405 8564_ $$s3873415$$uhttps://zaguan.unizar.es/record/133405/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada
000133405 909CO $$ooai:zaguan.unizar.es:133405$$particulos$$pdriver
000133405 951__ $$a2024-04-12-13:59:40
000133405 980__ $$aARTICLE