You are here : Home > The Imapec team > Fermi-surface instabilities in the topological superconductor UTe2

highlight / actuality

Fermi-surface instabilities in the topological superconductor UTe2

Researchers in our laboratory, collaborating with the high magnetic field facility LNCMI-Grenoble, (CNRS-EMFL), present transport measurements up to 29T on the newly discovered topological superconductor UTe2. When the field is swept along the easy magnetisation axis, the thermopower exhibits successive anomalies at low temperatures, signalling Fermi surface instabilities; one of them could be clearly be identified as a field-induced Lifshitz transition.

Published on 19 March 2020
The recently discovered heavy-fermion superconductor UTe2 with TSC=1.6K is one of the rare examples of heavy fermion materials with TSC > 1K. In contrast to the ferromagnetic heavy-fermion superconductors UCoGe and URhGe, UTe2 is paramagnetic and nevertheless it exhibits re-entrant superconductivity up to unrivalled magnetic field strengths (65T) among this class of materials. For H II b, the upper critical field Hc2b is strongly enhanced and equals the first-order meta-magnetic transition occurring at Hm= Hc2b = 35T at low temperatures, highly exceeding the Pauli limit. Recent studies on the U-based ferromagnetic superconductors have highlighted the importance of the interplay between magnetic fluctuations and Fermi surface instabilities when crossing the ferro- to paramagnetic quantum phase transition, which raises the question of the precise role of Fermi surface instabilities in the reinforcement of superconductivity.

Here we present transport measurements up to 29T with magnetic field applied along the easy magnetization an axis of the body-centered orthorhombic structure (Hc2a = 6T). As a function of field, thermopower exhibits successive anomalies (see fig. 1a) at low temperatures, signalling Fermi surface instabilities; one of them (H1, green squares fig. 1b) could clearly be identified as a Lifshitz transition. Such a behaviour is reminiscent of what we have already observed in UCoGe, i.e. the appearance of Fermi surface instabilities for H // to the easy magnetization axis (direction with a high magnetic susceptibility). Another striking feature is that the instability at H1 occurs at exactly the same critical value of magnetization (0.4µB) than Hm =35T for H // b. Finally, recent measurements [1] under pressure for H II a reveal a peculiar feature in Hc2(T) around the critical field H1.

Figure 1 a) Field-dependence of thermopower at different temperatures exhibiting anomalies at the superconducting transition (black arrows) and at 3 successive electronic instabilities (critical fields) for H II a.
Figure 1 b) Magnetic field - temperature phase diagram with the superconducting phase and the critical fields, which correspond to specific values of the magnetization. Figures from PRL. 124, 086601 (2020).

Contact: Alexandre Pourret

Top page