The effect of Ca and Th substitution on the crystal-field spectrum of the high-T_csuperconductor HoBa₂Cu₃O_x

Abstract

The inelastic neutron scattering technique was employed to study the transitions between the low-lying levels of the ground-state J -multiplet of the Ho 3+ ions in Ho 1−y Ca y Ba 2 Cu 3 O x (x ≈ 6.3, 7.0; y ≈ 0.1, 0.2) and Ho 1−y Th y Ba 2 Cu 3 O x (x ≈ 6.3; y ≈ 0.07, 0.13) split by the crystalline electric field. For oxygen-rich Ca-doped samples, the observed energy spectra exhibit a fine structure, which reflects the behaviour of the local hole density near the doping centre. For the first time this experimental observation unambiguously confirms that the charge inhomogeneity, which was found to be a characteristic feature of the underdoped cuprates, still exists in the deeply overdoped regime with T c = 56 K. On the other hand, the modification of the crystal-field spectra observed for the oxygendeficient samples with both Ca 2+ and Th 4+ substitutions for Ho 3+ is found to result from distortions of the copper-oxygen polyhedron around the Ho 3+ ion in the direct neighbourhood of the implanted ions, rather than from the dopinginduced variation of the carrier concentration in the CuO 2 planes.

Alternative crystal field parameters for rare-earth ions obtained from various techniques: IV. Comparative analysis of crystal field parameters obtained from inelastic neutron scattering and related studies of RE ions (RE=Er3+, Ho3+, Nd3+, Pr3+) in REBa2Cu3O7−δ high-Tc superconductors

“…The notations used in the four related papers by Mirmelstein, Golosova and coworkers [5,[40][41][42] is discussed jointly in this Section. The papers [5,40,41] dealt with both Er and Ho ions, whereas the paper [42] dealt with only Ho ions and is discussed in Section 3.2.…”

“…The papers [5,40,41] dealt with both Er and Ho ions, whereas the paper [42] dealt with only Ho ions and is discussed in Section 3.2. A model of the crystal field generated by a periodic array of charged tapes (PACTs) was developed in [5] to consider charge ordering occurring in the CuO 2 planes due to doping and describe the variation of the CF parameters versus oxygen stoichiometery.…”

“…A model of the crystal field generated by a periodic array of charged tapes (PACTs) was developed in [5] to consider charge ordering occurring in the CuO 2 planes due to doping and describe the variation of the CF parameters versus oxygen stoichiometery. The PACTs model has been used to analyze the CF interaction in REBa 2 Cu 3 O 7Àd (RE = Er, Ho) high-T c copper oxides observed by INS [5,[40][41][42]. The modified Stevens notation, in which the reduced matrix elements (expressed in the original symbols used in [5]) H n = 1, i.e.…”

“…The modified Stevens notation, in which the reduced matrix elements (expressed in the original symbols used in [5]) H n = 1, i.e. B nm = B nm (Stevens)/H n , was adopted in [5,40,41], whereas the Wybourne notation in [42].…”

“…with the Stevens multiplicative factors H n = 1. Properly converted CFP sets [40][41][42] are included in Table 1a and b for Er 3+ and Ho 3+ , respectively. The difference between the CFPs for the overdoped (OvD) clusters and the optimally doped (OpD) ones was considered in [40] based on the relation: [B 20 (OvD) À B 20 (OpD)] ffi À[B 22 (OvD) À B 22 (OpD)].…”