Possible high- Tc superconductivity due to incipient narrow bands originating from hidden ladders in Ruddlesden-Popper compounds

Abstract

We introduce the concept of "hidden ladders" for the bilayer Ruddlesden-Popper type compounds: While the crystal structure is bilayer, dxz (dyz) orbitals in the relevant t2g sector of the transition metal form a two-leg ladder along x (y), since the dxz (dyz) electrons primarily hop in the leg (x, y) direction along with the rung (z) direction. This leads us to propose that Sr3Mo2O7 and Sr3Cr2O7 are candidates for the hidden-ladder material, with the right position of EF from a first-principles band calculation. Based on the analysis of Eliashberg equation, we predict the possible occurrence of high temperature superconductivity in these non-copper materials arising from the interband pair-scattering processes between a wide band and an "incipient" narrow band on the ladder.

Hidden Ladder in SrMoO3/SrTiO3 Superlattices: Experiments and Theoretical Calculations

“…[18][19][20] Recently, Ogura et al have proposed a new type of materials that possess wide and incipient-narrow bands, bilayer Ruddlesden-Popper (RP) compounds, Sr 3 Mo 2 O 7 and Sr 3 Cr 2 O 7 (Mo 4+ , Cr 4+ , d 2 ) . 21) Although the bilayer RP structures are apparently not ladder-shaped ( Fig. 1), they have electronic structures similar to the two-leg ladder cuprate.…”

“…This results from the anisotropy of the d xz and d yz orbitals; the d xz and d yz orbitals can broadly be treated separately and form the two-leg ladders along the x and y directions, respectively. 21) Theoretical calculations on the basis of the fluctuation exchange approximation have shown the potential for high-T c superconductivity in this "hidden ladder" system. 21) Unfortunately, no sign of superconductivity has been observed experimentally in Sr 3 Cr 2 O 7 and Sr 3 Mo 2 O 7 , 22,23) although the incipient band is located close to the Fermi level.…”

“…For Sr 3 Cr 2 O 7 , orbital ordering accompanied by an antiferromagnetic order at 210 K may prevent superconductivity, 22) while in the case of Sr 3 Mo 2 O 7 , oxygen deficiency is likely to be the main cause. 21) For example, Sr 3 Mo 2 O 7 grown under high pressure has the oxygen content of ∼ 6.3. 21) Some efforts have been made to control of the partial pressure of oxygen, 23,24) but it appears there remains ambiguity in the chemical composition.…”

“…21) For example, Sr 3 Mo 2 O 7 grown under high pressure has the oxygen content of ∼ 6.3. 21) Some efforts have been made to control of the partial pressure of oxygen, 23,24) but it appears there remains ambiguity in the chemical composition.…”

Superconducting mechanism for the cuprate Ba2CuO3+δ based on a multiorbital Lieb lattice model

“…Recently, such a band lying just above or below the Fermi level is referred to as an "incipient band" and has received attention, especially in the context of the iron-based superconductors [27][28][29][30][31][32][33][34][35]38], where hole bands lying just below the Fermi level are observed in some materials [30,31,[68][69][70][71][72][73][74][75]. In a wider context, the possibility of the occurrence or strong enhancement of superconductivity due to an incipient band has long been proposed for multiband Hubbard models on various types of lattices [23,26,36,37,[39][40][41][42][43][44][76][77][78][79][80][81][82]. A salient feature in these cases is that the gap function typically exhibits nodeless "s±-wave" symmetry.…”