Phonon Modes of High-Tc YBa2Cu3O7-δ Films: Effects of Doping and Isotope Substitution
Bibliographic record
Abstract
The role of phonons in high-Tc superconductivity remains controversial [1]. Measuring phonon properties is central to the ongoing investigations on superconductivity. Standard methodologies for phonon characterization (e.g., inelastic neutron scattering) [2] offer mostly bulk phonon information but lack spatial sensitivity when probing phonons at/near nanoscale structural features, such as interfaces between superconductor films and substrates. Furthermore, high-Tc superconductor properties can be modified through the generation of interfaces [3], rare-earth elements or oxygen doping [4,5], and isotope substitution [6]. Understanding their potential effects on lattice vibrations requires information accessible by local probes such as those available in monochromated STEM microscopes [7]. Here, we present a study on phonon properties of YBa2Cu3O7-δ (YBCO) thin films supported on LSAT substrates using high-energy resolution monochromated STEM-EELS. The role of praseodymium doping and oxygen isotope substitution on YBCO lattice vibration properties is examined. YBCO thin films were epitaxially grown along the c-axis using pulsed laser deposition. Samples were annealed to optimize oxygen doping and induce isotope substitution. Pr doping of the film was achieved during growth. The structural and chemical analysis was conducted using aberration-corrected STEM imaging and EDXS analysis with atom-level sensitivity on a TF Spectra Ultra, operated at 200kV. The phonon behavior was studied using vibrational EELS on a Nion HERMES 100 operated at 60 kV, which delivered an atom-wide beam with 6-7 meV of energy resolution and a few pA of beam current. The atomically resolved HAADF-STEM image depicted in Figure 1 shows a typical YBCO/LSAT interface. The YBCO thin films contain regions with a 123 structure (Y:Ba:Cu ratio) and a 124 structure, distinguishably by double CuO2 chains. The interface forms between LSAT and Ba-terminated YBCO, a trend consistent across all films. On rare-earth doped samples, the EDXS analysis reveals that Pr tends to occupy mostly Y sites. We detected interface phonon modes with a long-range interaction within the undoped YBCO, evidenced by changes in the spectral response at different positions of the thin film (Figure 2). The EELS signal is primarily associated with O and Cu-O vibrations in the lattice. Pr-doping suggests a stiffening of Cu and O vibrational modes. EEL spectra on O-isotope-substituted doped and undoped samples reveal a small redshift (∼2 meV) on the higher energy loss modes at some probe positions. Our findings provide new insights into the phonon behavior of high-Tc YBCO thin films grown under different conditions. We uncovered a larger spectrum of phonon modes (e.g., interface phonon modes) that can extend our understanding of phonon properties of high-Tc superconductors [8]. STEM-HAADF image of the YBCO/LSAT interface. The LSAT substrate appears at the bottom. EELS spectra at different positions across an undoped YBCO/LSAT interface.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
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How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".