Revisiting 9Be Nuclear Magnetic Resonance in UBe13: Itinerant-Localized Duality and Possible Fermi Surface Reconstruction at High Magnetic Field

TL;DR

This study revisits 9Be NMR in UBe13, revealing high-field spectral changes, duality evidence, and possible Fermi surface reconstruction through detailed measurements and simulations.

Contribution

It provides a new set of parameters for high-field NMR spectra and links spectral anomalies to Fermi surface changes and duality in UBe13.

Findings

Reproduced complex NMR line profiles at high magnetic fields.

Identified the influence of classical dipolar fields on NMR spectra.

Detected anomalies in Knight shift indicating Fermi surface reconstruction.

Abstract

We report on new results of 9Be nuclear magnetic resonance (NMR) measurements conducted on a single crystal of the heavy fermion superconductor UBe13. Our previous 2007 study [J. Phys. Soc. Jpn. 76 204705 (2007)] determined NMR and electric field gradient (EFG) parameters that successfully reproduced the NMR spectra at low magnetic fields. However, these parameters did not accurately describe the angular dependence of the NMR spectra at high magnetic fields. To address this discrepancy, we have now performed a more comprehensive investigation, measuring the magnetic field dependence of the 9Be-NMR spectra across a field range of 0.5 T to 8 T, as well as the magnetic field angle dependence at 0.5 T and 6 T. Through detailed simulations that take into account the non-symmorphic space group of UBe13, we have determined a new set of parameters capable of reproducing the complex NMR line profiles observed at high magnetic fields. Notably, our analysis reveals the significant influence of classical dipolar fields. A comparison between the Knight shift (KS) and the classical dipolar shift provides microscopic supporting evidence for the nature of an itinerant-localized duality in UBe13. Furthermore, the magnetic field dependence of the KS exhibits anomalies around 6 T, suggesting a reconstruction of a part of the multiple Fermi surfaces in the high magnetic field region.