Oxygen<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>K</mml:mi></mml:math>-edge shift at the Verwey transition of magnetite

The temperature dependence of the $\mathrm{O}\phantom{\rule{0.2em}{0ex}}K$-edge threshold has been investigated in a temperature range encompassing the Verwey transition. Both above and below ${T}_{V}$ the $\mathrm{O}\phantom{\rule{0.2em}{0ex}}K$-edge threshold changes linear with temperature whereas there is discontinuous energy shift of $13\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at ${T}_{V}$. A comparison of our results to published low and high energy photoemission experiments suggests the presence of an asymmetric gap with respect to the Fermi level. This explains present fundamental differences between photoemission and infrared derived gap energies, and supports the polaronic image of the electrical conductivity of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ above the Verwey transition temperature.