Reconstruction of Low Dimensional Electronic States by Altering the Chemical Arrangement at the SrTiO₃ Surface

Abstract

Developing reliable methods for modulating the electronic structure of the 2D electron gas (2DEG) in SrTiO 3 is crucial for utilizing its full potential and inducing novel properties. Herein, it is shown that relatively simple surface preparation reconstructs the 2DEG at the SrTiO 3 (STO) surface, leading to a Lifshitz-like transition. Combining experimental methods, such as angleresolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy with ab initio calculations, that the modulation of the surface band structures can be effectively achieved via transforming the chemical composition at the atomic scale is found. In addition, ARPES experiments demonstrate that vacuum ultraviolet light can be efficiently employed to alter the band renormalization of the 2DEG system and control the electronphonon interaction . This study provides a robust and straightforward route to stabilize and tune the low-dimensional electronic structure via the chemical degeneracy of the STO surface.

Transition Metal‐Oxide Nanomembranes Assembly by Direct Heteroepitaxial Growth

“…The in-plane FSs of the STOm (thicknesses of 10 and 30 nm) and the STOw show one circular Fermi pocket and two intersecting ellipsoidal pockets belonging to the light d xy orbital and heavy d xz /d yz orbitals, respectively (dashed pockets in Figure 2C i -E i ). [30][31][32][33][34] Figure 2C ii -E ii displays the electronic structures along Γ-X direction measured by linear vertical (LV) polarization, mainly probing the d xy and d yz orbitals (Figure 1B). The observed "waterfall-like" intensities extending to higher binding energy (E B ) of d xy bands (Figure 2C ii -E ii ) are attributed to the polaron formation, [33,34] which originates from electron-phonon interaction (EPI) between the electrons and breathing LO 3 phonon mode in the STO lattice.…”

“…[30][31][32][33][34] Figure 2C ii -E ii displays the electronic structures along Γ-X direction measured by linear vertical (LV) polarization, mainly probing the d xy and d yz orbitals (Figure 1B). The observed "waterfall-like" intensities extending to higher binding energy (E B ) of d xy bands (Figure 2C ii -E ii ) are attributed to the polaron formation, [33,34] which originates from electron-phonon interaction (EPI) between the electrons and breathing LO 3 phonon mode in the STO lattice. [33] When comparing the STOm and STOw, the d xy bands of the membranes shift to lower E B with the band bottoms around 200 meV resulting in an energy splitting of t 2g bands (inset panel in Figure 2E ii ).…”

“…Those findings suggest that for membrane down to thickness of 10 nm, the t 2g bands are still similar to the bulk material, showing a mixture of 2D and 3D characters. [32,34] However, it is crucial to highlight that the electronic response of STOm to irradiation is more akin to STO films grown on STOw (Figure S4, Supporting Information), [38] while the electronic structures are more waferlike. [30][31][32][33][34] We turn now to the study of coherent and incoherent nature of the 2D states in STOm by investigating the EPI, electron scattering, and quasiparticle lifetime, which play an important role in determining the physical properties of STO.…”

“…[32,34] However, it is crucial to highlight that the electronic response of STOm to irradiation is more akin to STO films grown on STOw (Figure S4, Supporting Information), [38] while the electronic structures are more waferlike. [30][31][32][33][34] We turn now to the study of coherent and incoherent nature of the 2D states in STOm by investigating the EPI, electron scattering, and quasiparticle lifetime, which play an important role in determining the physical properties of STO. [39] The peak-diphump line shape of the energy distribution curves (EDCs) at Fermi wavevector k F xy indicates the polarons induced by the interaction between phonons and electrons (Figure 2C iii -E iii ).…”

“…[ 33 ] When comparing the STOm and STOw, the d xy bands of the membranes shift to lower E B with the band bottoms around 200 meV resulting in an energy splitting of t 2 g bands (inset panel in Figure 2E). The origin of the t 2 g splitting is still debated in the literature, and it can be due to surface polarization, [ 35 ] electric field, [ 34 ] or tetragonal distortion. [ 36 ] The extracted value of Δ t 2 g (= d xz −d xy ) for the STOm (≈180 meV) (details are shown in Figure S3, Supporting Information) is found to be much larger than the STOw (≈60 meV) (Figure 2F), which is probably due to the strain relaxation of the freestanding membranes leading to a large splitting.…”