Direct Observation of the Multisheet Fermi Surface in the Strongly Correlated Transition Metal CompoundZrZn2

Abstract

The existence of flat areas of a Fermi surface (FS), predicted by electronic structure calculations and used in models of both magnetically mediated and phonon-mediated Fulde-Ferrell-LarkinOvchinnikov superconducting states, is reported in the paramagnetic phase of the ferromagnetic superconductor ZrZn 2 using positron annihilation. The strongly mass-renormalized FS sheet, dominating the Fermi level density of states, is seen for the first time. The delocalization of the magnetization is studied using measured and calculated magnetic Compton profiles.

Probing the Fermi surface by positron annihilation and Compton scattering

“…24 and 25) caused great excitement, following so soon after the discovery of triplet superconductivity in UGe 2 . 26 The shape of the Fermi surface was the focus of much attention, 27,28 and measurements of de Haas-van Alphen oscillations in the ferromagnetic phase 29 and the paramagnetic Fermi surface by positron annihilation 24 revealed four separate sheets of Fermi surface (see Fig. 2) which were in excellent agreement with the predictions of band structure calculations.…”

“…Interestingly, the calculations which are performed within the mean-field coherent potential approximation, 35 while not able to perfectly predict the real Fermi surfaces (for example, in the calculations they predict that the necks, familiar from the pure Cu Fermi surface, along the h111i directions are still present), are able to accurately predict both qualitatively and quantitatively the trends under doping. A similar The band numbering refers to the original paper 24 and note that all four sheets are clearly revealed. conclusion was reached on the basis of a reconstruction from 28 directional Compton profiles in a Cu 0.75 Pd 0.25 measured by Matsumoto et al 36 …”

“…2) which were in excellent agreement with the predictions of band structure calculations. Although it was later found to be due to the spark erosion which led to superconductivity in a Zn-depleted surface layer, 30 the paper of Major et al 24 is an excellent example of the high quality information which can be extracted. That the Fermi surface of Cu 0.6 Pd 0.4 is much more nested than Cu 0.72 Pd 0.28 explains not only the location of the diffuse scattering peaks 32 but also their relative intensity.…”

Quantum Metamagnetic Transitions Induced by Changes in Fermi-Surface Topology: Applications to a Weak Itinerant-Electron Ferromagnet ZrZn2

“…Singh and Mazin 17) proposed the neck-free paramagnetic state, whereas electron-positron annihilation radiation measurements reveal the presence of the necks at ambient pressure. 18) A recent accurate ab initio electronic structure calculation by Harima shows that the necks around the L point in the band closest to the Fermi surface change their topology depending on the location of the Fermi level. 19) These results together suggest that ZrZn 2 is in a subtle proximity of the Lifshitz transition.…”

Non-Fermi Liquid State Bounded by a Possible Electronic Topological Transition in ZrZn2

“…This short-range ordering is presumably antiferromagnetic because ab initio calculations and positron annihilation measurements indicate that the Fermi surfaces of the paramagnetic phase are substantially nested. 22,23) As a result, it is likely that the antiferromagnetic short-range ordering develops over the low-field phase owing to the nesting effect of the Fermi surfaces. Remembering the fact that / T 3=2 is often observed in the vicinity of an antiferromagnetic QCP, 5) we propose the scenario that the NFL is caused by the antiferromagnetic fluctuations.…”