Fermi-surface selective determination of the g -factor anisotropy in URu2Si2

Abstract

The g-factor anisotropy of the heavy quasiparticles in the hidden order state of URu2Si2 has been determined from the superconducting upper critical field and microscopically from Shubnikov-de Haas (SdH) oscillations. We present a detailed analysis of the g-factor for the α, β and γ Fermisurface pockets. Our results suggest a strong g-factor anisotropy between the c axis and the basal plane for all observed Fermi surface pockets. The observed anisotropy of the g-factor from the quantum oscillations is in good agreement with the anisotropy of the superconducting upper critical field at low temperatures, which is strongly limited by the paramagnetic pair breaking along the easy magnetization axis c. However, the anisotropy of the initial slope of the upper critical field near Tc cannot be explained by the anisotropy of the effective masses and Fermi velocities derived from quantum oscillations.

Comparison of two superconducting phases induced by a magnetic field in UTe2

“…23,31,35 ). A similar inverse relation between the magnetic anisotropy and the anisotropy of H c2 was observed in many other heavy-fermion superconductors, such as URu 2 Si 2 42,43 , CeCoIn 5 44,45 , UCoGe and URhGe 11,46 . Spectacularly, a second field-induced superconducting phase was reported in UTe 2 for a field tilted from b towards c by an angle 20 < θ < 40°3 3 .…”

Proximity to a critical point driven by electronic entropy in URu2Si2

“…Pauli paramagnetic limiting of this phase further implies that the electronic excitations retain their spin and charge quantum numbers throughout the HO phase and across the transition, both in weak and strong magnetic fields. Similarities in the magnitude and anisotropy of the quasiparticle g-factor to that previously observed suggest that these are the same quasiparticles that are responsible for the observed quantum oscillations 54,56 and that undergo pairing to produce a superconducting state at low temperatures 55,56,68 .…”

“…1), and an elliptical phase boundary that is usually the hallmark of valence transition systems [51][52][53] . The effective g-factor characterizing the ratio of the Pauli-limited critical magnetic field B o to the critical temperature T o is in quantitative agreement with prior measurements [54][55][56] . The near-degeneracy in the free energies of the HO and paramagnetic phase over a range of temperatures T ≥ T o further causes the hybridization gap in URu 2 Si 2 to become highly susceptible to the formation of a pseudogap 34,35 , should fluctuations or inhomogeneities be present.…”

Experimental evidence for Zeeman spin–orbit coupling in layered antiferromagnetic conductors

“…This dependence may happen to compensate that of the quasi-2D cyclotron mass, m 0 = cos θ, in the expression (2) for the spin-reduction factor R s , and render the latter nearly isotropic, with no spin zeros. Obviously, such a compensation requires a strong Ising anisotropy [g(θ = 0°) ≫ g(θ = 90°)]as found, for instance, in the heavy fermion compound URu 2 Si 2 , with the values g c = 2.65 ± 0.05 and g ab = 0.0 ± 0.1 for the field along and normal to the c axis, respectively 68,69 . However, this scenario is irrelevant to both materials of our interest: In κ-BETS, a nearly isotropic g-factor, close to the free-electron value 2.0, was revealed by a study of spin zeros in the PM state 46 .…”