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

Abstract

Thermoelectric power (S) and Hall effect (R H) measurements on the paramagnetic superconductor UTe 2 with the magnetic field applied along the hard magnetization b axis are reported. The first-order nature of the metamagnetic transition at H m = H b c2 = 35 T leads to drastic consequences on S and R H. In contrast to the field dependence of the specific heat in the normal state through H m , S(H) is not symmetric with respect to H m. This implies a strong interplay between ferromagnetic fluctuations and a Fermi-surface reconstruction at H m. R H is very well described by incoherent skew scattering above the coherence temperature T m corresponding roughly to the temperature of the maximum in the susceptibility T χmax and coherent skew scattering at lower temperatures. The discontinuous field dependence of both S(H) and the ordinary Hall coefficient R 0 , at H m and at low temperature, provides evidence of a change in the band structure at the Fermi level.

Magnetic Properties under Pressure in Novel Spin-Triplet Superconductor UTe2

“…5,6) Superconductivity is cutoff above H m probably due to a drastic change of the electronic state. 7) It is pointed out that the huge H c2 displaying the reentrant behavior resembles those observed in ferromagnetic superconductors, URhGe 8) and UCoGe, 9) where field-reentrant (-reinforced) superconductivity is induced due to the development of ferromagnetic fluctuations associated with the collapse of the Curie temperature T Curie . 2,[10][11][12] However, UTe 2 is a paramagnet and the values of H c2 are large in all field directions.…”

Unconventional Superconductivity in UTe2

“…This is a clear indication that the majority heat carriers change at the metamagnetic transition and gives a strong hint to a Fermi surface instability. Additional support for this is given by Hall effect measurements which also indicate a decrease of the charge carrier number by a factor of nine, which presents a clear hint to a Fermi surface instability occurring at H m [53].…”

“…It is obvious that under a magnetic field the Zeeman splitting of the heavy bands drives an eletronic instability for a critical value of the magnetization M * b ∼ 0.4µ B at H m . At the opposite to the behavior of γ and the A coefficient on crossing the metamagnetic transition, the thermoelectric power changes steplike at H m and a sign change from negative to positive occurs at low temperature [53]. This is a clear indication that the majority heat carriers change at the metamagnetic transition and gives a strong hint to a Fermi surface instability.…”

“…17. Increasing temperature above 7 K the first order nature gets lost and the maximum in the magnetoresistivity and the Hall effect indicates a crossover which seems to be connected to the maximum in the magnetic susceptibility χ b [32,53].…”

“…28(b) and Refs. [101,53]). To the best of our knowledge, no bulk measurement has confirmed this field reinforcement of superconductivity for H baxis.…”