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Quantum Materials : Jeudi 24 Juin à 14h

Victor PORÉE, (PSI Villigen, Switzerland)

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Title: « Nature of the magnetic ground state in cerium-based pyrochlores »


Rare-earth pyrochlore frustrated magnets have played a central role in the study of three- dimensional quantum spin liquids (QSL) over the last years [1]. Indeed, magnetic dipole moments on a tetrahedron adopting a 2-in-2-out ice configuration can, under certain conditions, give rise to a so-called quantum spin ice state. Recent experimental studies on cerium pyrochlores have further boosted the interest for this elusive state of matter [2,3,4]. Interestingly, the Kramers trivalent cerium moments were found to evade magnetic order down to the lowest temperature accessible, but the exact nature of its magnetic ground state was not yet identified.

A detailed analysis of weak diffuse scattering in diffraction patterns together with low-energy time-of-flight spectroscopy data, both taken on a large powder sample of Ce2Sn2O7, allowed us to unveil the formation of a quantum liquid of magnetic octupoles [5]. This novel magnetic ground state can be described using a pseudo-spin with both magnetic dipole and magnetic octupole components. Upon cooling, the octupolar degrees of freedom become dominant under the effect of octupole-octupole couplings. To further characterize these multipolar interactions, single crystal experiments are highly urged. However, the difficulty to synthesis single crystals motivates the investigation of other Ce3+-based pyrochlore compounds like Ce2Hf2O7.

[1] – J.G. Rau, M.J.P Gingras, Annual Review of Condensed Matter Physics 10:1, 357-386 (2019); [2] – R. Sibille & al., Physical Review Letters 115, 097202 (2015); [3] – J. Gaudet & al., Physical Review Letters 122, 187201 (2019); [4] – B. Gao & al., Nature Physics 15, 1052-1057 (2019); [5] – R. Sibille et al., Nature Physics 16, 546–552(2020)