Spin-roton excitations in the cuprate superconductors

Zheng-Yu Weng, Tsinghua University.

Abstract: We identify a new kind of elementary excitations in the superconducting state of a doped Mott insulator, called spin-rotons. They will play a central role in deciding the superconducting transition temperature, resulting in a simple Tc formula: Tc=Eg/γkB with γ≈6 and Eg as the characteristic energy scale of the spin-rotons. We show that the singlet (S=0) and triplet (S=1) rotons are degenerate in energy, hinting the spin-charge separation, which can be probed by A1g Raman scattering and neutron scattering, respectively, and are in excellent agreement with the high-Tc cuprates. Finally how such excitations appear in the superconducting wave function will be discussed.