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arXiv · 2208.02155

Element-specific probe of quantum criticality in $\mathrm{CeCoIn_{5}}$

A. Khansili·R. Sharma·R. Hissariya·I. Baev·J. Schwarz·F. Kielgast·M. Nissen·M. Martins·M. -J. Huang·M. Hoesch·V. K. Paidi·J. van Lierop·A. Rydh·S. K. Mishra
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Abstract

Employing the elemental sensitivity of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), we study the valence and magnetic order in the heavy fermion superconductor CeCoIn$_5$. We probe spin population of the f-electrons in Ce and d-electrons in Co as a function of temperature (down to 0.1 K) and magnetic field (up to 6 T). From the XAS we find a pronounced contribution of Ce$^{4+}$ component at low temperature and a clear temperature dependence of the Ce valence below 5 K, suggesting enhanced valence fluctuations, an indication for the presence of a nearby quantum critical point (QCP). We observe no significant corresponding change with magnetic field. The XMCD displays a weak signal for Ce becoming clear only at 6 T. This splitting of the Kramers doublet ground state of Ce$^{3+}$ is significantly smaller than expected for independent but screened ions, indicating strong antiferromagnetic pair interactions. The unconventional character of superconductivity in CeCoIn$_5$ is evident in the extremely large specific heat step at the superconducting transition.

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A. Khansili, R. Sharma, R. Hissariya, I. Baev, J. Schwarz, F. Kielgast, M. Nissen, M. Martins, M. -J. Huang, M. Hoesch, V. K. Paidi, J. van Lierop, A. Rydh, S. K. Mishra. 2022-08-03. Element-specific probe of quantum criticality in $\mathrm{CeCoIn_{5}}$. https://arxiv.org/abs/2208.02155

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