${}^{11}$B and ${}^{27}$Al NMR spin-lattice relaxation and Knight shift study of Mg${}_{1-x}$Al${}_x$B${}_2$. Evidence for anisotropic Fermi surface

Abstract

We report a detailed study of ${}^{11}$B and ${}^{27}$Al NMR spin-lattice relaxation rates ($1/T_1$), as well as of ${}^{27}$Al Knight shift (K) of Mg${}_{1-x}$Al${}_x$B${}_2$, $0\le x\le 1$. The obtained ($1/T_{1}T$) and K vs. x plots are in excellent agreement with ab initio calculations. This asserts experimentally the prediction that the Fermi surface is highly anisotropic, consisting mainly of hole-type 2-D cylindrical sheets from bonding $2p_{x,y}$ boron orbitals. It is also shown that the density of states at the Fermi level decreases sharply on Al doping and the 2-D sheets collapse at $x\approx 0.55$, where the superconductive phase disappears.

References in corpus (29)

• Superconductivity of metallic boron in MgB_2
• Beyond Eliashberg superconductivity in MgB2: anharmonicity, two-phonon scattering, and multiple gaps
• Superconductivity of MgB2: Covalent Bonds Driven Metallic
• Electron-phonon interaction in the normal and superconducting states of MgB2
• Evidence for two superconducting energy gaps in MgB2 by point-contact spectroscopy
• Specific Heat of Mg ^{11}B_2
• Two Gap State Density in MgB${}_2$: A True Bulk Property or A Proximity Effect?
• Evidence for Two Superconducting Gaps in $Mg{B}_2$
• Direct evidence for a multiple superconducting gap in MgB2 from high-resolution photoemission spectroscopy
• Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
• Order parameter of MgB_2: a fully gapped superconductor
• Nature of bonding and electronic structure in MgB2, a boron intercalation superconductor
• Anisotropic superconducting properties of aligned MgB2 crystallites
• Effects of Al doping on the structural and electronic properties of Mg(1-x)Al(x)B2
• Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data
• Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNi${}_2$B${}_2$C, YNi${}_2$B${}_2$C and MgB${}_2$
• Role of Boron p-Electrons and Holes in Superconducting MgB2, and other Diborides: A Fully-Relaxed, Full-Potential Electronic Structure Study
• The complex superstructure in Mg1-xAlxB2 at x~0.5
• Crystal structure of the Mg${}_{1-x}$Al${}_x$B${}_2$ superconductors near x=0.5
• Reduction in the electron density-of-states in superconducting MgB${}_2$ disordered by $n^1$-irradiation: the ${}^{11}$B and ${}^{25}$Mg NMR estimates
• Two-Dimensional Sigma-Hole Systems in Boron Layers: A First-Principles Study on Mg_{1-x}Na_xB_2 and Mg_{1-x}Al_xB_2
• Superconducting properties and c-axis superstructure of Mg1-xAlxB2
• ${}^{11}B$ NMR and Relaxation in $Mg{B}_2$ Superconductor
• Evidence for High-frequency Phonon Mediated S-wave Superconductivity : 11B-NMR Study of Al-doped MgB2
• NMR relaxation rates and Knight shifts in MgB2
• ${}^{11}$B NMR detection of the magnetic field distribution in the mixed superconducting state of MgB${}_2$
• A magnetization and ${}^{11}$B NMR study of Mg${}_{1-x}$Al${}_x$B${}_2$ superconductors
• ^25Mg NMR study of the MgB_2 superconductor
• Anisotropy of p states and 11B nuclear spin-lattice relaxation in (Mg,Al)B2

Cited by in corpus (9)

• Electronic Structure, Electron-Phonon Coupling, and Multiband Effects in MgB2
• Band filling and interband scattering effects in MgB${}_2$: C vs Al doping
• Thermodynamics of Two - Band Superconductors: The Case of MgB${}_2$
• Inversion of two-band superconductivity at the critical electron doping of (Mg,Al)B${}_2$
• NMR relaxation time in a clean two-band superconductor
• Effect of disorder on the NMR relaxation rate in two-band superconductors
• ${}^{11}$B NMR study of pure and lightly carbon doped MgB${}_2$ superconductors
• Is Delta_{pi}-gap-only superconductivity possible in Mg_{1-x}Al_{x}B_{2} and Mg(B_{1-y}C_{y})_{2} alloys?
• Enhancing long-range order in disordered two-band s-wave superconductors