Interpretation of nuclear quadrupole resonance spectra in doped La2CuO4

The nuclear quadrupole resonance (NQR) spectrum of strontium-doped La2CuO4 surprisingly resembles the NQR spectrum of La2CuO4 doped with excess oxygen, both spectra being dominated by a main (A) peak and one principal satellite (B) peak at similar frequencies. Using first-principles cluster calculations, this is investigated here by calculating the electric field gradient (EFG) at the central copper site of the cluster after replacing a lanthanum atom in the cluster with a strontium atom or adding an interstitial oxygen to the cluster. In each case the EFG was increased by approximately 10% leading unexpectedly to the explanation that the NQR spectra are only accidentally similar and the origins are quite different.