Orbital Symmetry and Orbital Excitations in High-$T_c$ Superconductors

Abstract

We discuss a few possibilities of high-$T_c$ superconductivity with more than one orbital symmetry contributing to the pairing. First, we show that the high energies of orbital excitations in various cuprates suggest a simplified model with a single orbital of $x^2-y^2$ symmetry doped by holes. Next, several routes towards involving both $e_g$ orbital symmetries for doped holes are discussed: (i) some give superconductivity in a CuO${}_2$ monolayer on Bi2212 superconductors, Sr${}_2$CuO${}_{4-\delta }$, Ba${}_2$CuO${}_{4-\delta }$, while (ii) others as nickelate heterostructures or Eu${}_{2-x}$Sr${}_x$NiO${}_4$, could in principle realize it as well. At low electron filling of Ru ions, spin-orbital entangled states of $t_{2g}$ symmetry contribute in Sr${}_2$RuO${}_4$. Finally, electrons with both $t_{2g}$ and $e_g$ orbital symmetries contribute to the superconducting properties and nematicity of Fe-based superconductors, pnictides or FeSe. Some of them provide examples of orbital-selective Cooper pairing.

12 pages, 3 figures; in: Special Issue "From Cuprates to Room Temperature Superconductors", dedicated to the anniversary of Professor K. Alex Müller

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Cited by in corpus (9)

• Charge and spin order dichotomy in NdNiO${}_2$ driven by SrTiO${}_3$ capping layer
• Multi-Band Superconductivity and the Steep Band -- Flat Band Scenario
• Interplay between Zhang-Rice singlets and high-spin states in a model for doped NiO${}_2$ planes
• Resonant Inelastic X-ray Scattering Study of Electron-Exciton Coupling in High-Tc Cuprates
• Second Dome of Superconductivity in YBa${}_2$Cu${}_3$O${}_7$ at High Pressure
• Band crossover and magnetic phase diagram of high-Tc superconducting compound Ba2CuO4-δ
• Evolution of Spin-Orbital Entanglement with Increasing Ising Spin-Orbit Coupling
• Freestanding perovskite and infinite-layer nickelate membranes
• X-raying Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O: disentangling elemental contributions in a prototypical high-entropy oxide