Study of B11 and C13 NMR on doped MgB2 in the normal and in the superconducting state

R. W. Bounds; E. Pavarini; M. Paolella; E. Young; I. Heinmaa; R. Stern; M. Carravetta

doi:10.1103/PhysRevB.97.014509

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Study of B11 and C13 NMR on doped MgB2 in the normal and in the superconducting state

R. W. Bounds, E. Pavarini, M. Paolella, E. Young, I. Heinmaa, R. Stern, M. Carravetta

DOI 10.1103/PhysRevB.97.014509 · Physical Review B

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Abstract

We have studied carbon-doped magnesium diboride nanoparticles using C13 and B11 NMR in the normal and superconducting states. Measurements of the line shape reveal the role of carbon as a flux-pinning center and, combined with Knight shift measurements, suggest the doping procedure favors the chemical substitution scenario. We perform ab initio calculations on a structure with a single carbon-boron substitution which yield results that match the experimental data. The C13 and B11 Knight shift data are used to extract the spin susceptibility, which indicates a BCS pairing mechanism; however, we do not observe the Hebel-Slichter coherence peak from 1/T1 data, which we hypothesize is due to a pair-breaking mechanism present in the boron planes.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	39	Pressure not reported	unknown
MgB1.95C0.05 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	37	Pressure not reported	onset