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Where is the pi particle?

O. Tchernyshyov·M. R. Norman·A. V. Chubukov
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Abstract

We discuss the interplay of particle-particle and particle-hole spin-triplet channels in high-T_c superconductors using a quasiparticle dispersion motivated by angle-resolved photoemission. Within a generalized RPA, we find a well defined antibound state of two holes, the pi resonance of Demler and Zhang, as well as a bound state of a particle and a hole, the spin exciton. We show that the energy of the pi resonance always exceeds 2 Delta, twice the maximum d-wave gap, therefore the neutron resonance observed in the cuprates around energy Delta is most likely a spin exciton. At the same time, we speculate that the pi particle can exist at higher energies and might be observed in neutron scattering around 100 meV.

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O. Tchernyshyov, M. R. Norman, A. V. Chubukov. 2000-09-05. Where is the pi particle?. https://doi.org/10.1103/physrevb.63.144507

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