Unconventional polaronic ground state in superconducting LiTi2O4

Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel LiB<sub>2</sub>O<sub>4</sub> materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi<sub>2</sub>O<sub>4</sub> and heavy fermion behavior in LiV<sub>2</sub>O<sub>4</sub>. To date, however, LiTi<sub>2</sub>O<sub>4</sub> has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic ground states. Here, we present a multimodal investigation of LiTi<sub>2</sub>O<sub>4</sub>, combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state with spectroscopic signatures that underlie co-dominant electron-phonon coupling and electron-electron correlations also found in the lightly doped cuprates. The cooperation between the two interaction scales distinguishes LiTi<sub>2</sub>O<sub>4</sub> from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi<sub>2</sub>O<sub>4</sub>. Our work deepens our understanding of the rare interplay of electron-electron correlations and electron-phonon coupling in unconventional superconducting systems. In particular, our work identifies the geometrically frustrated, mixed-valence spinel family as an under-explored platform for discovering unconventional, correlated ground states.

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Publication Details

Journal
Nature Communications
Published
2026-01-06
DOI
https://doi.org/10.1038/s41467-025-68068-7
Primary Topic
Advanced Condensed Matter Physics
Type
article
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article

Unconventional polaronic ground state in superconducting LiTi2O4

Katja C. Nowack, Harrison LaBollita, Zubia Hasan, V. K. Bhartiya et al.
Nature Communications
Advanced Condensed Matter Physics
article

Unconventional polaronic ground state in superconducting LiTi2O4

Katja C. Nowack, Harrison LaBollita, Zubia Hasan, V. K. Bhartiya, Andreas Suter, Austin Kaczmarek, Zaher Salman, Julia A. Mundy, Shekhar Sharma, Mirian García‐Fernández, Jonathan Pelliciari, Alexander J. Grutter, Matthew R. Barone, Valentina Bisogni, Suk Hyun Sung, Darrell G. Schlom, Purnima P. Balakrishnan, K. -J. Zhou, Antía S. Botana, A. de la Torre, Grace A. Pan, Brendan D. Faeth, Charles M. Brooks, Alpha T. N’Diaye, Edward Mercer, Thomas Prokscha, Ismail El Baggari
article en

Abstract

Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel LiB<sub>2</sub>O<sub>4</sub> materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi<sub>2</sub>O<sub>4</sub> and heavy fermion behavior in LiV<sub>2</sub>O<sub>4</sub>. To date, however, LiTi<sub>2</sub>O<sub>4</sub> has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic ground states. Here, we present a multimodal investigation of LiTi<sub>2</sub>O<sub>4</sub>, combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state with spectroscopic signatures that underlie co-dominant electron-phonon coupling and electron-electron correlations also found in the lightly doped cuprates. The cooperation between the two interaction scales distinguishes LiTi<sub>2</sub>O<sub>4</sub> from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi<sub>2</sub>O<sub>4</sub>. Our work deepens our understanding of the rare interplay of electron-electron correlations and electron-phonon coupling in unconventional superconducting systems. In particular, our work identifies the geometrically frustrated, mixed-valence spinel family as an under-explored platform for discovering unconventional, correlated ground states.

Nature CommunicationsVol. 17(1)
Northeastern University (US), Harvard University (US), Lawrence Berkeley National Laboratory (US), Brookhaven National Laboratory (US), Cornell University (US), Harvard University Press (US), Diamond Light Source (GB), Interface (United States) (US), NIST Center for Neutron Research (US), Arizona State University (US), Leibniz Institute for Crystal Growth (DE)
Openalex Percentile: Top 92%
Advanced Condensed Matter Physics
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