Abstract
Combined experimental and theoretical studies are reported of the Fermi surface, band structure, generalized magnetic susceptibility, electron-phonon enhancement factor λ and superconducting transition temperature TT of LaB6. Whereas the unusually large λ values, ranging from 1.0 to 2.5, are expected to result in high TT values, TT is observed to be only 0.122°K. These results further emphasize the need for appropriate theoretical formulations for these systems.
Highlights
The strong covalent bonding in crystalline phases of boron compounds. which is responsible for their being extremely hard. refracting, and stable materials, makes these compounds attractive as possible high-temperature superconductors
Approximate eigenvalues and eigenfunctions of the HFS Hamiltonian are generated by means of a DMV which has been previously applied to a number of energy band problems [l 1, 121
We have not included the effects of matrix elements, we believe that the weak momentum dependence of the 5d La wave function would not greatly reduce X“ (q)near the dominant [1111 peak. The existence of this peak suggests two important conclusions for further experimental observations, (1) in systems like La& which are not magnetic, the peak leads to “soft” phonon modes and large electron-phonon coupling; (2) in rare-earth systems with felectrons the peak leads to a simple rock-salt commensurate antiferromagnetic ordering
Summary
The strong covalent bonding in crystalline phases of boron compounds. which is responsible for their being extremely hard. refracting, and stable materials, makes these compounds attractive as possible high-temperature superconductors. The strong covalent bonding in crystalline phases of boron compounds. Refracting, and stable materials, makes these compounds attractive as possible high-temperature superconductors. Superconducting transition temperature T, of high-purity single crystals of LaB,. (1.0 to 2.5) and expect that T, would be large (naively, the use of the McMillan equation results in T,ranging from 27 to 61’K). This striking failure of theory is related to the very different phonon spectra -“hard” boron-based modes and ‘‘soft’’ lathanum-based modes in LaB,-compared with those of Nb used in the derivation of the McMillan equation.
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