Crystallization of heavy fermions via epitaxial strain in spinel LiV2O4 thin film

The mixed-valent spinel LiV2O4 is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2023-06, Vol.120 (24), p.e2215722120-e2215722120
Main Authors: Niemann, Ulrike, Wu, Yu-Mi, Oka, Ryosuke, Hirai, Daigorou, Wang, Yi, Suyolcu, Y Eren, Kim, Minu, van Aken, Peter A, Takagi, Hidenori
Format: Article
Language:English
Subjects:
Compressive properties
Crystallization
Elementary excitations
Fermions
Instability
Particle mass
Physical Sciences
Pyrochlores
Single crystals
Spinel
Stability
Substrates
Thin films
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Summary:The mixed-valent spinel LiV2O4 is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has remained yet elusive. A charge-ordering (CO) instability of V3+ and V4+ ions that is geometrically frustrated by the V pyrochlore sublattice from forming a long-range CO down to T = 0 K has been proposed as a prime candidate for the mechanism. Here, we uncover the hidden CO instability by applying epitaxial strain on single-crystalline LiV2O4 thin films. We find a crystallization of heavy fermions in a LiV2O4 film on MgO, where a charge-ordered insulator comprising of a stack of V3+ and V4+ layers along [001], the historical Verwey-type ordering, is stabilized by the in-plane tensile and out-of-plane compressive strains from the substrate. Our discovery of the [001] Verwey-type CO, together with previous realizations of a distinct [111] CO, evidence the close proximity of the heavy-fermion state to degenerate CO states mirroring the geometrical frustration of the V pyrochlore lattice, which supports the CO instability scenario for the mechanism behind the heavy-fermion formation.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2215722120