Decoupling Carrier Concentration and Electron-Phonon Coupling in Oxide Heterostructures Observed with Resonant Inelastic X-Ray Scattering

Abstract

We report the observation of multiple phonon satellite features in ultra thin superlattices of form nSrIrO3/mSrTiO3 using resonant inelastic x-ray scattering. As the values of n and m vary the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electronphonon coupling strength as a function of n and m. Combined with the negligible carrier doping into the SrTiO3 layers, these results indicate that tuning of the electron-phonon coupling can be effectively decoupled from doping. This work showcases both a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling which is often associated with superconductivity in SrTiO3-based systems.Despite the discovery of several new classes of superconductors, a comprehensive understanding of superconductivity continues to evade the community, preventing attempts to systamtically control its behavior. The discovery of superconductivity at the interface of two insulating compounds, SrTiO 3 (STO) and LaAlO 3 , is particularly promising for expanding our understanding of superconductivity due to the myriad of control parameters introduced by the heterostructure morphology [1][2][3][4]. Furthermore, superconductivity in monolayer FeSe was recently found to be remarkably enhanced by an order of magnitude when interfaced with STO [5-7]. These findings point to heterostructuring as a promising route towards the rational engineering of the superconducting ground state.While debate remains, the coupling of the conduction electrons to the longitudinal optical (LO 4 ) phonon branch is routinely regarded as an essential ingredient in STO-based superconductors [8][9][10][11][12][13]. Recent angleresolved photoemission spectroscopy (ARPES) experiments observed the systematic tuning of the electron- * dmeyers@bnl.gov † tberlijn@gmail.com ‡

High-resolution resonant inelastic x-ray scattering study of the electron-phonon coupling in honeycomb α−Li2IrO3

“…However, a single Lorentzian did not give a satisfactory fit to the data; two Lorentzians of equal width separated by 0.25 eV were required. From the fit, we find that Γ = 0.235(4) eV, which is in good agreement with previous experimental estimates at the oxygen Kedge [10]. We note, however, that it is significantly larger than theoretical values [45,[47][48][49].…”

Magnetism in iridate heterostructures leveraged by structural distortions

“…Reflectively measurements and SL peaks confirm the B -site ordering and lack of stacking faults. Previous measurements of the heterostructures studied here have shown no appreciable deviation of the Ti valance from its 4 + state in bulk STO 40,44,45 . The STO layers in n SIO/1STO are consequently expected to have a negligible contribution to the magnetism studied here, although such effects have been discussed in other heterostructures 46–48 .…”

Role of Dopants on the Local Electronic Structure of Polymeric Carbon Nitride Photocatalysts

“…Electron–phonon coupling has been estimated from experimental RIXS data on strongly correlated materials using the Ament model when the time scale of the phonon mode is much shorter than the core‐hole lifetime. [ 19–21 ] In our case, the CN stretching mode (190 meV, corresponding to ≈22 fs) is slightly larger than the core‐hole lifetime broadening at the N 1s (100–130 meV, ≈30–40 fs) [ 36,37 ] therefore this procedure cannot be applied. [ 22 ] Furthermore, Geondzhian and Gilmore recently suggested that RIXS may rather be probing exciton–phonon coupling when the core‐hole is not well screened, [ 38 ] which is likely to be the case for PCN.…”

“…Over the last years, the development of high‐resolution RIXS has enabled the observation of vibrational structures in the quasi‐elastic part of RIXS spectra opening new insights into ultrafast molecular dynamics [ 18 ] and vibronic coupling in solid materials. [ 19–22 ] Nevertheless, RIXS has not been applied to PCN so far to our knowledge.…”