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arXiv · 1711.03984

Dynamical susceptibility of a near-critical non-conserved order parameter and B2g Raman response in Fe-based superconductors

Avraham Klein·Samuel Lederer·Debanjan Chowdhury·Erez Berg·Andrey Chubukov
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Abstract

We analyze the dynamical response of a two-dimensional system of itinerant fermions coupled to a scalar boson $ϕ$, which undergoes a continuous transition towards nematic order with $d-$wave form-factor. We consider two cases: (a) when $ϕ$ is a soft collective mode of fermions near a Pomeranchuk instability, and (b) when it is an independent critical degree of freedom, such as a composite spin order parameter near an Ising-nematic transition. In both cases, the order-parameter is not a conserved quantity and the $d-$wave fermionic polarization $Π(q, Ω)$ remains finite even at $q=0$. The polarization $Π(0, Ω)$ has similar behavior in the two cases, but the relations between $Π(0, Ω)$ and the bosonic susceptibility $χ(0, Ω)$ are different, leading to different forms of $χ^{\prime \prime} (0, Ω)$, as measured by Raman scattering. We compare our results with polarization-resolved Raman data for the Fe-based superconductors FeSe$_{1-x}$S$_x$, NaFe$_{1-x}$Co$_x$As and BaFe$_2$As$_2$. We argue that the data for FeSe$_{1-x}$S$_x$ are well described within Pomeranchuk scenario, while the data for NaFe$_{1-x}$Co$_x$As and BaFe$_2$As$_2$ are better described within the "independent" scenario involving a composite spin order.

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Avraham Klein, Samuel Lederer, Debanjan Chowdhury, Erez Berg, Andrey Chubukov. 2017-11-10. Dynamical susceptibility of a near-critical non-conserved order parameter and B2g Raman response in Fe-based superconductors. https://doi.org/10.1103/physrevb.98.041101

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