Anomalous magnetoresistance in the spinel superconductor LiTi2O4

TL;DR

This study investigates the transport properties of high-quality LiTi2O4 thin films, revealing unusual magnetoresistance behavior and suggesting strong electron correlations influence its superconductivity.

Contribution

First systematic transport and tunneling spectroscopy analysis of epitaxial LiTi2O4 thin films, uncovering novel magnetoresistance phenomena linked to spin fluctuations and orbital effects.

Findings

Unusual magnetoresistance changes from positive to negative with temperature.

Energy gap decreases quadratically with magnetic field.

Charge carrier concentration remains constant across temperatures.

Abstract

Transition-metal oxides offer an opportunity to explore unconventional superconductors, where the superconductivity (SC) is often interrelated with novel phenomena such as spin/charge order, fluctuations, and Fermi surface instability (1-3). LiTi2O4 (LTO) is a unique compound in that it is the only known spinel oxide superconductor. In addition to electron-phonon coupling, electron-electron and spin fluctuation contributions have been suggested as playing important roles in the microscopic mechanism for its superconductivity (4-8). However, the lack of high quality single crystals has thus far prevented systematic investigation of their transport properties (9). Here, we report a careful study of transport and tunneling spectroscopy in epitaxial LTO thin films. In the superconducting state, the energy gap was found to decrease as a quadratic function of magnetic field. In the normal state, an unusual magnetoresistance (MR) was observed where it changes from anisotropic positive to isotropic negative as the temperature is increased. A constant charge carrier concentration without any abrupt change in lattice parameters as a function of temperature suggests that the isotropic MR stems from the suppression of spin scattering/fluctuations, while the anisotropic term originates from an orbital contribution. These observations point to an important role strong correlations play in this unique superconductor.