Spectroscopic evidence for strong quantum spin fluctuations with itinerant character in ${\mathrm{YFe}}_2{\mathrm{Ge}}_2$

We report x-ray absorption and photoemission spectroscopy of the electronic structure in the normal state of metallic ${\mathrm{YFe}}_2{\mathrm{Ge}}_2$. The data reveal evidence for large fluctuating spin moments on the Fe sites, as indicated by exchange multiplets appearing in the Fe $3s$ core-level photoemission spectra, even though the compound does not show magnetic order. The magnitude of the multiplet splitting is comparable to that observed in the normal state of the Fe-pnictide superconductors. This shows a connection between ${\mathrm{YFe}}_2{\mathrm{Ge}}_2$ and the Fe-based superconductors even though it contains neither pnictogens nor chalcogens. The implication is that the chemical range of compounds showing at least one of the characteristic magnetic signatures of the Fe-based superconductors is broader than previously thought.

Figure 1

(a) $\mathrm{Fe}2p$ core-level PES spectrum excited with photon energy $h\nu =907.5\mathrm{eV}$. (b) $\mathrm{Fe}{\mathrm{L}}_{23}$ XAS spectrum. Note the marked similarities with corresponding spectra excited in Fe-based high temperature superconductors, as reported in Ref. [9].

Figure 2

VB measured with photon energy $h\nu =907.5\mathrm{eV}$. Note the high DOS at $E_F$, denoted with the vertical dashed line. Also shown are the calculated total DOS, and the $\mathrm{Fe}3d$, $\mathrm{Ge}4s$, and $\mathrm{Ge}4p$ partial DOS.

Figure 3

(a) Fe $3s$ and (b) Ge $3s$ core-level PES spectra excited with photon energy $h\nu =907.5\mathrm{eV}$. The value of the energy separation of the multiplet is $\Delta E_{3s}=3.15\mathrm{eV}$.