Superconducting interaction charge in thallium-based high-TC cuprates: Roles of cation oxidation state and electronegativity

Abstract

Superconductivity in the Tl-based cuprates encompasses a notably broad range of measured optimal transition temperatures T C0 , ranging from lowest in the charge-depleted Tl-1201 compounds (Tl 1-x (Ba/Sr) 1+y La 1-y CuO 5-δ ), such as Tl 0.7 LaSrCuO 5 (37 K) and TlBa 1.2 La 0.8 CuO 5 (45.4 K), to highest in the Tl-1223 compound TlBa 2 Ca 2 Cu 3 O 9±δ (133.5 K). Seven Tl-based cuprates are considered and compared using the model of superconductive pairing via electronic interactions between two physically separated charge reservoirs, whereis determined by the superconducting interaction charge fraction σ, the number η of CuO 2 layers, and the basal-plane area A, each per formula unit, and the transverse distance ζ between interacting layers. Herein it is demonstrated that σ follows from the elemental electronegativity and the oxidation state of Tl, and other structurally analogous cations. The comparatively lower elemental electronegativity of Tl, in conjunction with its oxidation state, explains the higher σ and T C0 values in the Tl-based compounds relative to their Bi-based cuprate homologues. A derivation of σ is introduced for the optimal Tl 2 Ba 2 Ca η-1 Cu η O 2η+4 (for η = 1, 2, 3) compounds, which exhibit a Tl oxidation state at or near +3, obtaining the fundamental value σ 0 = 0.228 previously established for YBa 2 Cu 3 O 6.92 . Also reported is the marked enhancement in σ associated with Tl +1 and analogous inner-layer cations relative to higher-valence cations. For a model proposition of σ = σ 0 , the fractional Tl +1 content of the mixed-valence compound, TlBa 2 Ca 2 Cu 3 O 9±δ , is predicted to be 1/3 at optimization, in agreement with existing data. Charge depletion is illustrated for the two Tl-1201 compounds, where σ < σ 0 values are determined according to substitution of Ba , and/or Tl depletion. Additionally, statistical analysis of calculated and experimental transition temperatures of 48 optimal superconductors shows an absence of bias in determining σ, A, and ζ.

Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling

“…In all, nine compounds are found to be optimal, satisfying criteria of negligible pairbreaking and optimal doping: for Na 0.16 (PC) y TiNCl, Na 0.16 (BC) y TiNCl, Li 0.08 -ZrNCl, Li 0.13 (DMF) y ZrNCl, Na 0.25 HfNCl, Li 0.2 HfNCl, Eu 0.08 (NH 3 ) y HfNCl, Ca 0.11 (NH 3 ) y -HfNCl, and Li 0.2 (NH 3 ) y HfNCl, the calculated T C0 agrees with the measured T C to within 0.8-K rms deviation. Combining these with previous results [23,[37][38][39], the rms deviation between calculated T C0 and measured T C is 1.35 K for 48 compounds from seven different high-T C families.…”

“…Materials free of pair breaking and possessing the optimal cation doping necessarily exhibit T C = T C0 to within uncertainties. Note that the pairing model outlined in [23] and elsewhere [37][38][39] generally defines T C by the resistive zero when available, but given the broadened transitions typically prevalent in these materials, the magnetic onset T C value (preferably field-cooled) is acceptable. In any case, the suppression of T C below T C0 evident in the remaining compounds can then be attributed to pair-breaking phenomena and treated accordingly.…”

High-TCsuperconductivity in Cs3C60compounds governed by local Cs–C60Coulomb interactions

“…The presence of these two disparate charge reservoirs is the probable source of differing conclusions regarding the ground-state symmetry in some high-T C superconductors [30]. At the time of this writing, this model has already been validated with a statistical deviation between the calculated and measured T C0 of ±1.35 K for 48 different layered materials from seven superconducting families (cuprates, ruthenates, rutheno-cuprates, iron-pnictides and ET-based [bis(ethylenedithio)tetrathiafulvalene] organics [27,31,32]; iron-chalcogenides [33]; intercalated group-4-metal nitride-halides [34,35]) with measured T C meas values ranging from ~7 to 150 K.…”

“…For optimal cuprate compounds where the doping is not known, σ is calculated by scaling to σ 0 = 0.228 of YBa 2 Cu 3 O 6.92 , as discussed in [27,31,32], along with the role played by electronegativity [32].…”

High-TC Superconductivity in Hydrogen Clathrates Mediated by Coulomb Interactions Between Hydrogen and Central-Atom Electrons

“…Rule (1b) from[40] (see also[51]) reads that "The doping is shared equally between the hole and electron reservoirs, resulting in a factor of 1/2. "…”