Interference between One- and Two-Electron Channels in Resonant Inelastic X-Ray Scattering

Interference between scattering channels is observed in resonant inelastic x-ray scattering (RIXS) at the Ne <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>K</a:mi> </a:math> threshold. Final states with <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mo stretchy="false">|</c:mo> <c:mn>2</c:mn> <c:msup> <c:mi>p</c:mi> <c:mrow> <c:mo>−</c:mo> <c:mn>1</c:mn> </c:mrow> </c:msup> <c:mi>n</c:mi> <c:mi>p</c:mi> <c:mo stretchy="false">⟩</c:mo> </c:math> as the main configuration are populated via <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mo stretchy="false">|</g:mo> <g:mn>1</g:mn> <g:msup> <g:mi>s</g:mi> <g:mrow> <g:mo>−</g:mo> <g:mn>1</g:mn> </g:mrow> </g:msup> <g:msup> <g:mi>n</g:mi> <g:mo>′</g:mo> </g:msup> <g:mi>p</g:mi> <g:mo stretchy="false">⟩</g:mo> </g:math> resonances, where large-amplitude one-electron ( <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msup> <k:mi>n</k:mi> <k:mo>′</k:mo> </k:msup> <k:mo>=</k:mo> <k:mi>n</k:mi> </k:math> ) channels interfere with small-amplitude two-electron ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msup> <m:mi>n</m:mi> <m:mo>′</m:mo> </m:msup> <m:mo>≠</m:mo> <m:mi>n</m:mi> </m:math> ) channels. The interference is manifested in an asymmetric line profile where the two-electron resonance occurs in the tail region of the one-electron resonance. In RIXS, this slowly varying tail plays the role of the continuum for the Fano effect. The asymmetric profile is well modeled by means of a single asymmetry parameter, determined by the amplitudes of the scattering channels and the energy separation between the resonances.