Electronic structure of UTe$_2$ under pressure

Abstract

A heavy-fermion paramagnet UTe$_2$ has been a strong candidate for a spin-triplet superconductor. Experiments on UTe$_2$ under pressure have been vigorously conducted, and rich phase diagrams have been suggested. Multiple superconducting phases exist in the pressure region of $0 \leq P < 1.8 \mathrm{\;GPa}$, and an antiferromagnetic ordered state is observed in the high pressure region $P > 1.8 \mathrm{\;GPa}$. However, under pressure, the underlying electronic structure in the normal state has not been clarified, although knowledge of electronic structures is essential for studying magnetic and superconducting states. As an indispensable step toward understanding the phase diagram of UTe$_2$, we study the electronic structure under hydrostatic and uniaxial stresses based on the density functional theory with and without employing structural optimization. It is shown that the low-energy band structure and Fermi surfaces are not sensitive to pressure for parameters where itinerant $f$-electrons are not essential. However, we find a significant pressure dependence for a certain Coulomb interaction $U$ of the GGA+$U$ calculation, where the large weight of $f$-electrons appears at the Fermi level. An increase in the density of states at the Fermi level is observed under pressure, which is attributed to compressive stress along the [010] crystallographic axis.