Electron–Phonon Coupling and Electron–Phonon Scattering in SrVO3

Abstract Understanding the physics of strongly correlated electronic systems has been a central issue in condensed matter physics for decades. In transition metal oxides, strong correlations characteristic of narrow d bands are at the origin of remarkable properties such as the opening of Mott gap, enhanced effective mass, and anomalous vibronic coupling, to mention a few. SrVO3 with V4+ in a 3d1 electronic configuration is the simplest example of a 3D correlated metallic electronic system. Here, the authors' focus on the observation of a (roughly) quadratic temperature dependence of the inverse electron mobility of this seemingly simple system, which is an intriguing property shared by other metallic oxides. The systematic analysis of electronic transport in SrVO3 thin films discloses the limitations of the simplest picture of e–e correlations in a Fermi liquid (FL); instead, it is shown show that the quasi‐2D topology of the Fermi surface (FS) and a strong electron–phonon coupling, contributing to dress carriers with a phonon cloud, play a pivotal role on the reported electron spectroscopic, optical, thermodynamic, and transport data. The picture that emerges is not restricted to SrVO3 but can be shared with other 3d and 4d metallic oxides.

NGO, LSAT and STO (tensile strain) were fully strained (aSVO = aS). Thick SVO films (70 nm) deposited on LAO (compressive strain) show strain relaxation, while thinner ones (10-20 nm) are nearly fully strained. (g-i) Corresponding tetragonal distortion (c/a ratio). Supporting Information S2: Carrier density, carrier mobility, and residual resistivity ratio. Figure S2: Transport data for most SVO films of this study. From left to right column: strain series (different substrates), P(Ar) series on LSAT and NGO, and thickness series (10, 20 and 70 nm) on various substrates. Upper panels show the room-temperature carrier density n and mobility μ. Lower panels show residual resistivity ratio (RRR) of the corresponding samples.
Supporting Information S3: Illustrative Hall effect measurements. Figure S3: Illustrative Hall effect measurements at 300 K and 5 K of a 70 nm thick SVO film deposited on NGO substrate, at P(Ar) = 0.2 mbar.
Supporting Information S4: Fits of resistivity data to a quadratic temperature dependence and polaronic models.   represent digitized data of 45 and 20 nm thick films, respectively, from Zhang et al. [2] Data in (c) are taken from Moyer et al. [3] (50 nm thick). Insets are zooms of the low temperature region where the Fermi liquid fits show highest discrepancy.

Fitting parameters:
Table S4-I: Fitting parameters for Fermi liquid (constrained and unconstrained) and polaronic fits, for some illustrative SVO films: SVO films (10 nm) on STO, NGO and LAO (data are shown in Figure 5). Notice the errors of parameters are < 6 %.

Sample
Fit  Figure S5a: Experimental details of the Seebeck measurements: a) Steps of temperature difference between the Pt resistances and corresponding longitudinal thermoelectric voltages, at a base temperature of 250 K, for one of the SVO films of this study. b) Linear fit of the longitudinal voltage vs temperature difference. The accuracy of the method allows a good measurement of the Seebeck coefficient without increasing much the temperature difference (always lower than 1.5 K), ensuring the reversibility of the process. In this example a Seebeck coefficient of S = -5.42 μV K -1 at T = 250 K was extracted. The whole temperature dependence of the Seebeck coefficient for this sample can be seen in Figure S5b (SVO//LSAT, blue curve). Preliminary data for phonons displaying the strongest e-phonon coupling are shown. The (7-12) indexes refer to optical modes of increasing energy. As the modes 7, 8 and 9, as well as the modes 10, 11 and 12, are split due to the tetragonal distortion, here we plot the averaged values for each group of modes.
Supporting Information S7: Ellipsometric data. Figure S7: a) Ellipsometric data (FIR + MIR) of a SVO film (72 nm thick) deposited on LSAT substrate. The measured (Ψ, Δ) spectra are fitted with a substrate/film/ambient model, where only the film response is varied. Substrate response was determined from ellipsometric measurements on a bare substrate. [4] The far-infrared response of the film is dominated by a Drude component. The extracted unscreened plasma frequency is ωp = 19500 cm -1 (≈ 2.42 eV) and broadening γ = 680 cm -1 , which corresponds to a screened plasma energy * = 1.21 eV (considering = 4, as reported by Makino et al. [5] ). The corresponding effective mass * ≈ 4.1 me. Notice that we reported similar values in our previous studies, [1,6] and that similar values were encountered in literature. [2] Features in the Ψ/Δ spectra below 1000 cm -1 originate from the substrate phonons. b) Optical conductivity σ1 of the SVO film up to UV (6.2 eV, 50000 cm -1 ) resulting from point-by-point fit to ellipsometry data.