Photoemission investigations of URu₂Si₂

Abstract

A brief review of selected experimental photoemission works on URu 2 Si 2 spanning almost 25 years is presented. We focus on the areas of importance for both the paramagnetic (PM) and hidden-order (HO) phases, where photoemission provides direct and strong evidence for: (i) f-d hybridization, (ii) presence of hybridization gap, (iii) details of the massive reconstruction of FS upon transition and (iv) a non-integer valence likely close to 2.6. While most of the FS reconstruction details have been mapped and are now known, the most recent high resolution and low temperature ARPES studies reveal novel electronic structure features related to HO. No single ARPES experiment so far captures all of the phases appearing in this system as temperature is lowered.

Electronic structure ofThRu2Si2studied by angle-resolved photoelectron spectroscopy: Elucidating the contribution of U5fstates inFujimori1, Kobata2, Takeda3 et al. 2017Phys. Rev. B141150View full textAdd to dashboardCite

“…Band γ has relatively simple hole-like dispersion in ThRu 2 Si 2 , while the corresponding band γ exhibits more complex behavior just below E F in URu 2 Si 2 , suggesting that the hybridization is anisotropic in the momentum space. The strongly hybridized nature is consistent with the result of previous ARPES studies [12][13][14].…”

“…A number of angle-resolved photoelectron spectroscopy (ARPES) studies on URu 2 Si 2 have been also performed, particularly after the discovery of the spectral change at the HO transition observed by Santander-Syro et al [11]. Although a few common perceptions are shared among those studies, there remains unresolved issues [12][13][14]. In particular, the role of U 5f electrons in URu 2 Si 2 remains under extensive debate.…”

Probing5f-state configurations inURu2Si2with ULIII-edge reso

“…We therefore tentatively conclude that this feature is primarily due to f /d hybridization, consistent with several photoemission studies. 26 An interesting issue in these calculations is that the calculated E F is about 3 eV lower in UO 2 than the other calculations. This difference exists in both the small cluster and the 6.58Å radius calculations.…”

“…Photoemission (both angle-integrated and angle-resolved) results generally favor delocalized 5f states and paint a very interesting picture of the details of the Fermi surface. 26 In particular, the larger features in the band structure and Fermi surface of URu 2 Si 2 measured by soft x-ray photoemission in the paramagnetic (PM) state above the HO transition are well explained by treating all of the U 5f electrons as itinerant with n f ≈ 2.6.…”

“…26 One technique that is less sensitive to the exact electronic details is electron energy-loss spectroscopy (EELS). EELS experiments suggest that URu 2 Si 2 has 5f states which are more localized than α-U (even at room temperature), but still not completely localized, with a 5f electron count n f = 2.7 ± 0.1 suggesting a mixed valence ground state and/or some 5f -electron itinerancy.…”