Superconductivity
Can stretching a cuprate vertically raise its superconducting temperature?
Open access · cc by · source: Europe PMC
Embedding a cuprate superconductor inside a stiffer partner material stretched its crystal layers vertically near their shared walls and raised the superconducting transition to about 50 K, above what ordinary films of this compound reach.
Study at a glance
- Design
- Other — Pulsed-laser-deposited vertically aligned nanocomposite films on SrTiO3, characterised by resistance and magnetisation versus temperature, XPS, low-temperature STM/STS and atomic-resolution STEM lattice mapping.
- N
- No participant sample; more than 10 films were grown, and the reported analysis focuses on five ~25 nm films (S1 to S5), with different films used for different measurements.
- Population
- Thin films of La2CuO4+δ (214) nanostructures embedded in a LaCuO3 (113) matrix on (001) SrTiO3 substrates
- Outcome
- Superconducting transition temperature, superconducting volume fraction, tunnelling gap, and local lattice parameters c and a near the 214/113 interfaces
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
The films showed a superconducting onset of about 50 K, compared with about 35 K for the best conventional 214 films grown on LSAO, and needed only mild oxygen annealing rather than ozone. Near the 214/113 walls, c reached 13.28 Å versus a bulk value of 13.165 Å, while a stayed close to bulk, matching a prediction from how 2 cells of 214 fit against 7 cells of 113. The strained regions extend roughly 10 nm from each interface, consistent with a broad transition and a superconducting volume fraction of only about 5%. Tunnelling showed gaps up to about 10 meV that varied from place to place.
Methodology
The authors grew films from a mixed target of superconducting La2CuO4 (214) and nonsuperconducting LaCuO3 (113) by pulsed laser deposition on SrTiO3, so the two phases self-assembled side by side with vertical interfaces. The idea was that the stiffer 113 would stretch the 214 lattice along c (raising the copper–apical oxygen distance) without squeezing the in-plane spacing a. They measured resistance top-to-bottom, magnetisation, electronic states by XPS and tunnelling spectroscopy, and mapped lattice parameters unit cell by unit cell with electron microscopy.
Limitations
Only a small fraction of each film superconducts at the higher temperature, the transition is broad, and films 50 nm or thicker did not reliably show the enhancement, so this is a proof of concept rather than a bulk material. The link between local c expansion and the 50 K phase is inferred by combining separate measurements, sometimes on different films, rather than mapping transition temperature directly at each location. Tunnelling spectra were degraded by surface quality and the 113 matrix, and elastic constants of both phases were assumed rather than measured.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Structure at the nanometre scale can change Tc a lot.
Thinning or straining a material can raise Tc sharply: aluminium films near four atomic layers reached Tc = 3.31 K versus 1.2 K in bulk, with a gap more than three times bulk, and strained regions near nanocomposite walls in La2CuO4 films gave an onset near 50 K versus about 35 K for conventional films.
Evidence for the claim as stated.
Structure at the nanometre scale can change Tc a lot.
Thinning or straining a material can raise Tc sharply: aluminium films near four atomic layers reached Tc = 3.31 K versus 1.2 K in bulk, with a gap more than three times bulk, and strained regions near nanocomposite walls in La2CuO4 films gave an onset near 50 K versus about 35 K for conventional films.
Scope note — Only about 5% of the film volume superconducts at the higher Tc; thick films did not reliably show it.
Limits the claim's scope: a different population, assay, or outcome.
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