Abstract
The charge and spin dynamics of the structurally simplest iron-based superconductor, FeSe, may hold the key to understanding the physics of high temperature superconductors in general. Unlike the iron pnictides, FeSe lacks long range magnetic order in spite of a similar structural transition around 90 K. Here, we report results of Raman scattering experiments as a function of temperature and polarization and simulations based on exact diagonalization of a frustrated spin model. Both experiment and theory find a persistent low energy peak close to 500 cm−1 in B1g symmetry, which softens slightly around 100 K, that we assign to spin excitations. By comparing with results from neutron scattering, this study provides evidence for nearly frustrated stripe order in FeSe.
Highlights
The charge and spin dynamics of the structurally simplest iron-based superconductor, FeSe, may hold the key to understanding the physics of high temperature superconductors in general
By comparing experimental and simulated Raman data we find a persistent low-energy peak at roughly 500 cm−1 in B1g symmetry, which softens slightly around 100 K
For A1g, A2g, and B2g symmetry we show spectra at 40, 90, and 300 K (Fig. 1b–d)
Summary
The charge and spin dynamics of the structurally simplest iron-based superconductor, FeSe, may hold the key to understanding the physics of high temperature superconductors in general. We report results of Raman scattering experiments as a function of temperature and polarization and simulations based on exact diagonalization of a frustrated spin model. Both experiment and theory find a persistent low energy peak close to 500 cm−1 in B1g symmetry, which softens slightly around 100 K, that we assign to spin excitations. Some systems have a nearly ordered localized moment close to 2μB5, such as FeTe or rare-earth iron selenides, whereas the moments of AFe2As2-based compounds (A = Ba, Sr, Eu or Ca) are slightly below 1μB6 and display aspects of itinerant spindensity-wave (SDW) magnetism with a gap in the electronic excitation spectrum[7]. The resulting exchange coupling energies between nearest (J1) and nearest neighbor (J2) iron atoms have the same order of magnitude, and small changes in the pnictogen (chalcogen) height above the Fe plane influence the ratio J2/J1, such that various orders are energetically very close[12]
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