Insulator-Metal Transition and Topological Superconductivity in UTe2 from a First-Principles Calculation

Abstract

We theoretically study superconductivity in UTe2, which is a recently discovered strong candidate for an oddparity spin-triplet superconductor. Theoretical studies for this compound faced difficulty because first-principles calculations predict an insulating electronic state, incompatible with superconducting instability. To overcome this problem, we take into account electron correlation effects by a GGA+U method and show the insulatormetal transition by Coulomb interaction. Using Fermi surfaces obtained as a function of U , we clarify topological properties of possible superconducting states. Fermi surface formulas for the three-dimensional winding number and three two-dimensional Z2 numbers indicate topological superconductivity at an intermediate U for all the odd-parity pairing symmetry in the Immm space group. Symmetry and topology of superconducting gap nodes are analyzed and the gap structure of UTe2 is predicted. Topologically protected low-energy excitations are highlighted, and experiments by bulk and surface probes are proposed to link Fermi surfaces and pairing symmetry. Based on the results, we also discuss multiple superconducting phases under magnetic fields, which were implied by recent experiments. arXiv:1908.04004v3 [cond-mat.supr-con] 1 Nov 2019

How to Obtain Fermi Surfaces of UTe2

“…Therefore, an insulating band structure of UTe 2 results in strong mixing between the conduction bands and 5 f electrons. The calculated insulating ground state for UTe 2 are also confirmed by other calculations in the framework of a density functional theory (DFT), then DFT+U calculations have been performed [13,14]. Both calculations show metallic band structures with increasing effective U, then the cylindrical Fermi surfaces like Fig.…”

“…4 are obtained with U = 2.0 eV by Ishizuka et al (Fig. 2 (d) [13]) and with U = 7 eV by Xu et al (Fig. 4 (a) [14]).…”

“…Even with smaller U, the DFT+U calculations have obtained a metallic band structure [13,14]. But, another possibility to obtain a metallic state is considered here.…”

Evidence of Fermi surface reconstruction at the metamagnetic transition of the strongly correlated superconductor UTe2

“…The recent discovery of unconventional superconductivity (SC) in the uranium chalcogenide paramagnet UTe 2 with a superconducting transition temperature of T SC ∼ 1.6 K [1][2][3] opens new perspectives on superconducting topological properties including emergent Majorana quasiparticles at the verge of magnetic and electronic instability. Transport and thermodynamic measurements demonstrated that correlations play an important role in this system, requiring theoretical treatment beyond the local-density approximation approach [2,[4][5][6][7][8]. The closeness of UTe 2 to ferromagnetic quantum criticality [9] induces astonishing superconducting properties.…”

Theory of Spin-polarized Superconductors —An Analogue of Superfluid 3He A-phase—

“…Recently a new member of a superconductor UTe 2 with T c =1.6K 2,3 is discovered, which is almost ferromagnetic, and attracts much excitement. Many researchers start devoting to UTe 2 experimentally 4-16 and theoretically [17][18][19] and show renewed interest on the former three compounds too. Those heavy Fermion materials belong to a strongly correlated system where 5f electrons responsible for it is believed to form a coherent narrow band with the large mass enhancement below a Kondo temperature.…”