1 research outputs found
Phase transition and anomalous electronic behavior in layered dichalcogenide CuS (covellite) probed by NQR
Nuclear quadrupole resonance (NQR) on copper nuclei has been applied for
studies of the electronic properties of quasi-two-dimensional low-temperature
superconductor CuS (covellite) in the temperature region between 1.47 and 290
K. Two NQR signals corresponding to two non-equivalent sites of copper in the
structure, Cu(1) and Cu(2), has been found. The temperature dependences of
copper quadrupole frequencies, line-widths and spin-lattice relaxation rates,
which so far had never been investigated so precisely for this material,
altogether demonstrate the structural phase transition near 55 K, which
accompanies transformations of electronic spectrum not typical for simple
metals. The analysis of NQR results and their comparison with literature data
show that the valence of copper ions at both sites is intermediate in character
between monovalent and divalent states with the dominant of the former. It has
been found that there is a strong hybridization of Cu(1) and Cu(2) conduction
bands at low temperatures, indicating that the charge delocalization between
these ions takes place even in 2D regime. Based on our data, the occurrence of
energy gap, charge fluctuations and charge-density waves, as well as the nature
of phase transition in CuS are discussed. It is concluded that some physical
properties of CuS are similar to those of high-temperature superconductors
(HTSC) in normal state.Comment: to be publishe