Fig. 1
From: Observation of gapless collective charge fluctuations in an Anderson insulating state
(a), \(^{27}\)Al (\(I=5/2\)) NMR spectrum measured at 120 K under an external field of 5.716 T for two field orientations. The symmetric satellite pairs reflect axial symmetry about the c direction at the Al site, yielding a well-defined quadrupole frequency \(\nu _Q\) for \(^{27}\)Al. The inset depicts the crystal structure of CuAlO\(_2\). (b–c), Central transition lines (\(\frac{1}{2} \leftrightarrow -\frac{1}{2}\)) of \(^{27}\)Al (b) and \(^{63}\)Cu (c). (d–e), Temperature dependence of the Knight shift \(\mathcal {K}\) (d) and FWHM (e) for the \(^{27}\)Al and \(^{63}\)Cu central transitions. Both \(\mathcal {K}\) and FWHM remain nearly constant down to \(T_0=50\) K for both nuclei.
