Pressure-induced Structural Phase Transition and New Superconducting Phase in UTe2

We report on the crystal structure and electronic properties of the heavy fermion superconductor UTe2 at high pressure up to 11 GPa, as investigated by X-ray diffraction and electrical resistivity experiments. The X-ray diffraction measurements under high pressure using a synchrotron light source reveal anisotropic linear compressibility of the unit cell up to 3.5 GPa, while a pressure-induced structural phase transition is observed above PO-T similar to 3.5-4 GPa at room temperature, where the body-centered orthorhombic crystal structure with the space group Immm changes into a bodycentered tetragonal structure with the space group I4/mmm. The molar volume drops abruptly at PO-T, while the distance between the first-nearest neighbor of U atoms, dU-U, increases, implying a switch from the heavy electronic states to the weakly correlated electronic states. Surprisingly, a new superconducting phase at pressures higher than 7 GPa was detected at Tsc > 2 K with a relatively low upper-critical field, Hc2(0). The resistivity above 3.5 GPa, thus, in the highpressure tetragonal phase, shows a large drop below 230 K, which may also be related to a considerable change from the heavy electronic states to the weakly correlated electronic states.

Automated summary

We investigated the crystal structure and electronic properties of the heavy fermion superconductor UTe2 at high pressure using X-ray diffraction and electrical resistivity experiments. The X-ray diffraction measurements reveal that the unit cell has anisotropic linear compressibility up to 3.5 GPa, and a pressure-induced structural phase transition occurs above 3.5-4 GPa at room temperature. The molar volume decreases abruptly, while the distance between neighboring U atoms increases, indicating a transition from heavy electronic states to weakly correlated ones. Surprisingly, a new superconducting phase with a relatively low upper-critical field was detected at pressures above 7 GPa.