Two-magnon excitations

Key words Raman scattering, stripe ordering, phonon and two-magnon excitations... 

In eq. (5) the first term stands for the Drude free-carrier conductivity with plasma frequency 0>pD and scattering rate 1/r. The second term accounts for the additional contributions to the conductivity that are modeled with Lorentzian oscillators centered at frequency ft) with plasma frequency tOj, and damping yp. These additional contributions are assigned to two-magnon excitations, interband transitions, polarons and unpurity states. 

These results show evidence for not simple two-magnon nature of the band at -730 cm"1. Perhaps possible effects connected with the interaction between spin excitations and collective motion of charge domain-walls21,37 are necessary to be taken into account. 

Fig. 6. Diagram of the two-magnon Raman scattering process in the cuprates (a) initial antiferromagnetic spin configuration on the Cu sites (b) incident photon excitation of a spin-up Cu(3d ) hole to an intermediate-state 0(2p) orbital (c) double spin flip due to direct spin exchange between the spin-up hole on the intermediate-state 0(2p) site and a spin-down hole on a nearest-neighbor Cu site (d) hopping of a spin-down hole from the 0(2p) intermediate state to the original copper site, emitting the scattered photon.

The Raman spectra in La2Cu04 is presented in Figure 7.4(a) below the Neel temperature [30]. The polarization configuration is chosen to be the Big symmetry. A peak structure is observed around 3000 cm with a broad width. This is identified as the two magnon Raman scattering. Consider the antiferromagnetic order of the S = 2 spins in Cu02 plane and focus on a Cu(/)-0-Cu(/) bond where i and j indicate Cu sites. The incident photon excites an electron with up spin from... 

The broken symmetry of the SDW ground state characterized by a magnetic modulation at wave vector Q in (TMTSF)2X, X = PF6, N03, and so on, is responsible for the activated behavior of the conductivity through the single-particle gap 2A. However, two kinds of collective excitations arise in the SDW condensate. They are, first, the magnon exci-... 

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