Electric Control of 2D Van Hove Singularity in Oxide Ultra‐Thin Films

Abstract

Divergent density of states (DOS) can induce extraordinary phenomena such as significant enhancement of superconductivity and unexpected phase transitions. Moreover, van Hove singularities (VHSs) are known to lead to divergent DOS in two-dimensional (2D) systems. Despite the recent interest in VHSs, only a few controllable cases have been reported to date. In this work, we investigate the electronic band structures of a 2D VHS with angle-resolved photoemission spectroscopy and control transport properties by utilizing an atomically ultrathin SrRuO3 film. By applying electric fields with alkali metal deposition and ionic-liquid gating methods, we precisely control the 2D VHS, and the sign of the charge carrier. Use of a tunable 2D VHS in an atomically flat oxide film could serve as a new strategy to realize infinite DOS near the Fermi level, thereby allowing efficient tuning of electric properties.

The discovery of three-dimensional Van Hove singularity

“…For the previously reported systems with VHS, much effort has been devoted to shifting the Fermi level position by applying an electric field or chemical doping 15,18,90 . Meanwhile, it remains a substantial challenge to tune the VHS itself.…”

“…For two-dimensional (2D) systems or quasi-2D bands in the bulk systems, the DOS of 2D VHS exhibits logarithmic divergence at the saddle points while the band extrema becomes non-divergent. For instance, the 2D VHS is found at the saddle points in the strontium ruthenium oxide 18,19 and layered vanadium antimonides AV 3 Sb 5 (A = K, Rb, Cs) 20,21 . The 2D VHS in…”

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“…After film growth, the samples are transferred in-situ to the preparation chamber and post-annealed at 500 • C for 10 min. The samples are then transferred in-situ into the angle-resolved photoemission spectroscopy (ARPES) chamber [60,61]. Measurements are perfromed with He-Iα (hλ = 21.2 eV) at 10 K using a DA30 analyzer (Scienta Omicron) and a He discharge lamp (Fermi Instruments).…”