Realizing Low-Temperature Charge-Transfer-Type Insulating Ground State in Strained V₂O₃ Thin Film

Abstract

Controlling the electronic properties of strongly correlated systems, observing electron–electron correlation-driven metal to insulator transition (MIT) is a key point for the next-generation solid-state Mottronic devices. Thus, the knowledge of the exact nature of the insulating state is an essential need to enhance the functionality of the material. Therefore, we have investigated the electronic nature of the insulating state of a classical Mott insulator V2O3 thin film (epitaxial) using low-temperature (LT) (120 K) resonant photoemission spectroscopy and X-ray absorption near-edge spectroscopy measurements. Temperature-dependent valence band spectra (VBS) reflect the transfer of spectral weight from the metallic coherent band (AM) near the Fermi level (E F) to the insulating Mott–Hubbard screened band (CI) at a binding energy of around 2.4 eV. Such a transfer of spectral weight upon MIT leads to vanishing of the density of states at E F and opens a band gap. The strong presence of the 3d n L final state is observed near the E F of LT VBS, confirming the presence of an O 2p band participating in low-energy charge fluctuation. This study further endorses the charge-transfer (CT)-type (U > Δ) insulating nature of a strained V2O3 thin film at LT, unlike its bulk counterpart, which is placed intermediate (U–Δ) between the CT and the Mott–Hubbard regime. Modifying the electronic ground state of V2O3 to the CT nature via the epitaxial strain in thin films provides a way to tailor the electronic energetics, with its implications to next-generation correlation-derived switching devices.

Reactive Oxidation Induced Stoichiometric Modulation of Multivalent Vanadium Oxides

“…Moreover, the peak positions of the substrate and the film match together, suggesting the epitaxial growth of the V 2 O 3 film on the Al 2 O 3 (0001) substrate. [ 39 ] On the other hand, the sixfold peaks of monoclinic VO 2 (011) rotated by 30° relative to the Al 2 O 3 (012) peaks must be shown for the VO 2 film deposited on c‐plane Al 2 O 3 . Furthermore, the sixfold peaks arise from the three equivalent domains of VO 2 matched with the surface hexagonal plane of c‐plane Al 2 O 3 , indicating the following epitaxial relationship: VO 2 (010)//Al 2 O 3 (0001) and VO 2 [100]//Al 2 O 3 [100].…”

“…The peak positions have no noticeable variation, indicating that all films are M1 phase. [38] With further increases in ROA time to 20 [39] On the other hand, the sixfold peaks of monoclinic VO 2 (011) rotated by 30°relative to the . [32] However, we could not observe the VO 2 (011) plane associated with data from the ϕ-scan (Figure S5b, Supporting Information).…”

“…It is worth noting that the resistance (not shown) was too large to be measured for the 20 min-treated film. [39,40] VO 2 , [27] and V 2 O 5 [41] for comparison. The inset shows the expanded region of VB.…”

“…Figure 4. a) VB spectra of the vanadium oxide films with various ROA times and b) energy-level schematics of bulk V 2 O 3 ,[39,40] VO 2 ,[27] and V 2 O 5[41] for comparison. The inset shows the expanded region of VB.…”

Electronic correlations in epitaxial CrN thin film

“…In case of CrN thin film, feature A shows a dip in the CIS spectra and fitted well using lower q value (= 0.9) indicating their strong hybridized N-2 and Cr-3 (3 final-state) band character while the higher value of q (1.36) for feature B confirming its pure Cr-3 (3 final state) band character. To the best of our knowledge, no such reports are available in the literature for CrN or other similar nitride compounds in which RPES is used to differentiate the final electronic states of the specific feature though it is thoroughly used for strongly correlated TM oxide materials 49 – 51 .…”