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Quantum Critical Behavior and Superconductivity in new multi-site Cerium Heavy Fermion Compound Ce3PtIn11

The recent discovered heavy Fermion (HF) system Ce3PtIn11 [1] brought in a barely explored aspect in these heavy fermion compounds. The majority of the cerium HF compounds studied to date have been compounds which have only one crystallographic site for the cerium ions. This situation makes it fairly easy and straightforward to understand the electronic nature of the cerium ion. On the contrary, in compounds with two or more inequivalent sites, the local environment of these two– or more kinds of cerium atoms will vary, i. e., different exchange interaction of each of the two or more kinds of Ce 4f state with the conduction electrons of the surrounding ligands. This may lead to a variety of new and complex phenomena in these multi–site cerium compounds where different ground states coexist on a microscopic scale. Such is well illustrated in cubic Ce3Pd20Si6, which will be shortly addressed in the presentation, where one Ce-site exhibits dipolar (TN ≈ 0.3 K) and the second site quadrupolar antiferromagnetic (AFM) order (TQ ≈ 0.5 K) [2–4]. The compound arouse special attention displaying a field induced QCP (TN → 0 for Bc ≈ 0.9 T) of Kondo breakdown type which separates two different ordered phases [5].
We will focus on our work on the new multi–site cerium HF compound, Ce3PtIn11. The material belongs to the CenTmIn3n+2m class of materials which comprises a numerous amount of compounds including CeCoIn5, CeRhIn5 and Ce2RhIn8. The compound is structurally equal to Ce3PdIn11 (space group P4/mmm) replacing Pd by Pt [1]. The lattice constants appear to be slightly reduced holding a = 4.6874(4) Å and c = 16.8422(12) Å. There are two non-equivalent Ce-sites. Ce2 resides the Wyckoff 1a place which has local C4v symmetry. The ion is experiences CeIn3 environment. The Ce1-site occupies the 2g position (D4h symmetry). Its surroundings is identical to Ce-atoms in Ce2PtIn8 albeit with smaller interatomic distances. At ambient condition the material shows remarkable properties: in the absence of magnetic field, Ce3PtIn11 undergoes two successive magnetic transitions at T1 = 2.2 K and TN = 2.04 K, respectively, and becomes superconducting below Tc = 0.35 K.
We attribute this prospective coexistence of superconductivity (SC) and magnetism to different Ce-sites. We reveal the pressure - temperature phase diagram and show that Ce3PtIn11 exhibits
a magnetic QCP at pc ≈ 1.3 GPa. The superconducting transition temperature exhibits a maximum here suggesting an unconventional pairing mechanism closely connected to the QCP. In this sense, Ce3PtIn11 is unique, allowing at ambient conditions (i) studying of complex behavior between different Ce-sites within a unit cell, and (ii) investigating the interplay of SC and magnetism, two commonly believed antagonistic ground states.
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