Journal Article

Unconventional polaronic ground state in superconducting LiTi 2 O 4

Brooks, Charles M, LaBollita, Harrison, N'Diaye, Alpha T, Sharma, Shekhar, Bhartiya, Vivek, El Baggari, Ismail, Zhou, Ke-Jin, Barone, Matthew R, Sung, Suk Hyun, Salman, Zaher, Botana, Antia S, Faeth, Brendan D, Mercer, Edward, Garcia-Fernandez, Mirian, Bisogni, Valentina, Kaczmarek, Austin, Pan, Grace A, Prokscha, Thomas, Pelliciari, Jonathan, de la Torre, Alberto, Hasan, Zubia, Nowack, Katja C, Suter, Andreas, Grutter, Alexander J, Mundy, Julia A, Balakrishnan, Purnima P, Schlom, Darrell G

2026

Overview

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 O materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi O and heavy fermion behavior in LiV O . To date, however, LiTi O 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 O , 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 O from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi O . 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.