Electronic phase separation in TmBa2Cu4O8

The NQR spectra of Cu(2) in the superconductor TmBa₂Cu₄O₈ are studied at temperatures from 300 to 4.2 K. In analyzing the spectra it is assumed that the NQR line of each isotope contains two Gaussian components — narrow (n) and broad (b). It is discovered that the NQR frequencies have a minimum at the temperature T*=150 K. The frequencies of the components of the spectrum are close at temperatures from T* to 4.2 K and differ substantially at temperatures T>T*. Both components are broadened as the temperature decreases, but this broadening occurs especially rapidly at temperatures T<T*. The relative intensity of the narrow component I _n/(I _n+I _b) equals 1/6 for T=225−160 K, increases abruptly at T=T*, and remains constant (1/3) at temperatures T from 125 to 4.2 K. Analysis of the experimental data showed that the anomalous temperature dependences of the Cu(2) NQR spectra could be due to electronic phase separation (stratification) in the CuO₂ planes at temperatures T⩽T*. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 214–219 (10 February 1996)