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

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. The composition of CeCoIn 5 was examined through scanning electron microscope (SEM) with energy-dispersive x-ray spectroscopy (EDX). Figure S1 shows the chemical composition and microscopic surface of a crystal. The measurement was performed at various locations in the crystal surface to confirm the suitable composition and homogeneity. The average chemical composition, shown in Table I, is consistent with the expected composition for CeCoIn 5 (Ce: Co: In = 1: 1: 5) within uncertainties of the EDX technique.

[1]  R. McDonald,et al.  Evidence for a delocalization quantum phase transition without symmetry breaking in CeCoIn5 , 2021, Science.

[2]  L. Tjeng,et al.  Orientation of the ground-state orbital inCeCoIn5andCeRhIn5 , 2019, Physical Review B.

[3]  Charles A. Roberts,et al.  Role of Ce4fhybridization in the origin of magnetism in nanoceria , 2018, Physical Review B.

[4]  M. Martins,et al.  New experimental perspectives for soft x-ray absorption spectroscopies at ultra-low temperatures below 50 mK and in high magnetic fields up to 7 T. , 2016, The Review of scientific instruments.

[5]  Jinghua Guo,et al.  Influence of crystal structure, ligand environment and morphology on Co L-edge XAS spectral characteristics in cobalt compounds. , 2015, Journal of synchrotron radiation.

[6]  P. Coleman Heavy Fermions and the Kondo Lattice: a 21st Century Perspective , 2015, 1509.05769.

[7]  E. Stilp,et al.  Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(In1−xCdx)5 , 2015, Scientific Reports.

[8]  J. Martínez,et al.  Magnetic properties of a Kramers doublet. An univocal bridge between experimental results and theoretical predictions. , 2015, Journal of magnetic resonance.

[9]  P. Dai Antiferromagnetic order and spin dynamics in iron-based superconductors , 2015, 1503.02340.

[10]  Y. Ikeda,et al.  Role of valence fluctuations in the superconductivity of Ce122 compounds. , 2014, Physical review letters.

[11]  D. Johnston,et al.  Elaboration of the α-model derived from the BCS theory of superconductivity , 2013, 1304.2275.

[12]  D. Scalapino A common thread: The pairing interaction for unconventional superconductors , 2012, 1207.4093.

[13]  M. Norman,et al.  The Challenge of Unconventional Superconductivity , 2011, Science.

[14]  F. D. de Groot,et al.  The CTM4XAS program for EELS and XAS spectral shape analysis of transition metal L edges. , 2010, Micron.

[15]  E. Bauer,et al.  Superconducting quantum critical point in CeCoIn(5-x)Sn(x). , 2010, Physical review letters.

[16]  P. Coleman,et al.  Frustration and the Kondo Effect in Heavy Fermion Materials , 2010, 1007.1723.

[17]  T. Yokoyama,et al.  Unconventional superconductivity on a topological insulator. , 2009, Physical Review Letters.

[18]  E. Bauer,et al.  Coupled Superconducting and Magnetic Order in CeCoIn5 , 2008, Science.

[19]  M. Yokoyama,et al.  Change of antiferromagnetic structure near a quantum critical point in CeRh 1-x Co x In 5 , 2008, 0805.1957.

[20]  Philipp Gegenwart,et al.  Quantum criticality in heavy-fermion metals , 2007, 0712.2045.

[21]  Z. Fisk,et al.  Reversible tuning of the heavy-fermion ground state in CeCoIn5. , 2006, Physical review letters.

[22]  E. Bauer,et al.  Structural tuning of unconventional superconductivity in PuMGa5 (M=Co,Rh). , 2004, Physical review letters.

[23]  E. Bauer,et al.  Superconductivity in CeCoIn5-xSnx: veil over an ordered state or novel quantum critical point? , 2004, Physical review letters.

[24]  E. Bauer,et al.  Anderson lattice behavior in Yb1-xLuxAl3 , 2004 .

[25]  K. Kern,et al.  Ferromagnetism in one-dimensional monatomic metal chains , 2002, Nature.

[26]  V. Sidorov,et al.  Superconductivity and quantum criticality in CeCoIn5. , 2002, Physical review letters.

[27]  Z. Fisk,et al.  Heavy-fermion superconductivity in CeCoIn5 at 2.3 K , 2001, cond-mat/0103168.

[28]  Z. Fisk,et al.  A new heavy-fermion superconductor CeIrIn5: A relative of the cuprates? , 2000, cond-mat/0012261.

[29]  C. C. Tsuei,et al.  Pairing symmetry in cuprate superconductors , 2000 .

[30]  I. R. Walker,et al.  The normal and superconducting states of CeIn3 near the border of antiferromagnetic order , 1997 .

[31]  Bertran,et al.  4f orbital and spin magnetism in cerium intermetallic compounds studied by magnetic circular x-ray dichroism. , 1994, Physical review. B, Condensed matter.

[32]  Thole,et al.  X-ray circular dichroism as a probe of orbital magnetization. , 1992, Physical review letters.

[33]  Thole,et al.  Strong magnetic dichroism predicted in the M4,5 x-ray absorption spectra of magnetic rare-earth materials. , 1985, Physical review letters.

[34]  S. Doniach The Kondo lattice and weak antiferromagnetism , 1977 .

[35]  Vladimir A. Stephanovich,et al.  Theory of Heavy-Fermion Compounds , 2015 .

[36]  W. Marsden I and J , 2012 .

[37]  A. Yaresko,et al.  X-ray magnetic circular dichroism in CeFe2 : First-principles calculations , 2008 .