Yidi Liu

All Publications

• Structural modifications in strain-engineered bilayer nickelate thin films. Nature Bhatt, L., Abarca Morales, E., Jiang, A. Y., Ko, E. K., Zhao, Y. F., Schnitzer, N., Pan, G. A., Ferenc Segedin, D., Liu, Y., Yu, Y., Brooks, C. M., Botana, A. S., Hwang, H. Y., Mundy, J. A., Muller, D. A., Goodge, B. H. 2026

  Abstract

  The discovery of high-temperature superconductivity in bulk La3Ni2O7 under high hydrostatic pressure1-4 and biaxial compression in epitaxial thin films5-8 has ignited significant interest in understanding the interplay between atomic and electronic structure in these compounds. Subtle changes in the nickel-oxygen bonding environment are thought to be key drivers for stabilizing superconductivity, but specific details of which bonds and which modifications are most relevant remains so far unresolved. While direct, atomic-scale structural characterization under hydrostatic pressure is beyond current experimental capabilities, static stabilization of strained La3Ni2O7 films provides a platform well-suited to investigation with new picometer-resolution electron microscopy methods. Here, we use multislice electron ptychography (MEP)9,10 to directly measure the atomic-scale structural evolution of La3Ni2O7 thin films across a wide range of biaxial strains tuned via substrate choice. By resolving both the cation and oxygen sublattices, we study the strain-dependent evolution of atomic bonds, providing the opportunity to isolate and disentangle the effects of specific structural motifs for stabilizing superconductivity. We identify the lifting of crystalline symmetry through modification of the nickel-oxygen octahedral distortions under compressive strain as a key structural ingredient for superconductivity and identify in-plane lattice compression as a common attribute between bulk and thin film superconductivity. Building upon the detailed structures obtained by MEP, we introduce a theoretical framework to disentangle coupled structural distortions in corner-sharing octahedra11, which suggest that both known superconducting geometries of La3Ni2O7 (hydrostatic pressure and compressive strain) suppress local t2g orbital mixing in the low-energy Ni bands by raising the octahedral symmetry.

  View details for DOI 10.1038/s41586-026-10446-2

  View details for PubMedID 41922777

• Author Correction: Signatures of ambient pressure superconductivity in thin film La3Ni2O7. Nature Ko, E. K., Yu, Y., Liu, Y., Bhatt, L., Li, J., Thampy, V., Kuo, C. T., Wang, B. Y., Lee, Y., Lee, K., Lee, J. S., Goodge, B. H., Muller, D. A., Hwang, H. Y. 2026

  View details for DOI 10.1038/s41586-026-10335-8

  View details for PubMedID 41917275

• Fermi-liquid transport beyond the upper critical field in superconducting La2PrNi2O7 thin films. Nature communications Hsu, Y. T., Liu, Y., Kohama, Y., Kotte, T., Sharma, V., Tarn, Y., Wang, B. Y., Shen, Z. X., Yu, Y., Hwang, H. Y. 2026

  Abstract

  Unconventional superconductivity typically emerges out of a strongly correlated normal state, manifesting as a highly renormalised Fermi liquid or a strange metal with T-linear resistivity. In Ruddlesden-Popper bilayer nickelates, superconductivity with a critical temperature Tc exceeding 80 and 40 K has been respectively realised in pressurised bulk crystals and epitaxially strained thin films. These advancements call for the characterisation of fundamental normal-state and superconducting parameters in these new materials platforms of high-Tc superconductivity. Here we report detailed magnetotransport experiments on superconducting La2PrNi2O7 (LPNO) thin films under pulsed magnetic fields up to 64 T and access the normal-state behaviour over a wide temperature range between 1.5 and 300 K. We find that the normal state of thin-film LPNO exhibits the hallmarks of Fermi-liquid transport, including T2 temperature dependence of resistivity and Hall angle, and H2 magnetoresistance obeying Kohler scaling. Using the empirical Kadowaki-Woods ratio, we estimate a quasiparticle effective mass m*/me ≃ 10, thereby revealing the highly renormalised Fermi liquid state therein. Our results demonstrate that thin-film LPNO follows the same Tc/TF scaling observed across a myriad of strongly correlated superconductors and establish key normal-state characteristics of strained bilayer superconducting nickelates.

  View details for DOI 10.1038/s41467-026-70250-4

  View details for PubMedID 41807407

• Reducing the Strain Required for Ambient-Pressure Superconductivity in Ruddlesden-Popper Bilayer Nickelates. Advanced materials (Deerfield Beach, Fla.) Tarn, Y., Liu, Y., Theuss, F., Li, J., Wang, B. Y., Bhatt, L., Wang, J., Song, J., Thampy, V., Goodge, B. H., Muller, D. A., Shen, Z. X., Yu, Y., Hwang, H. Y. 2026: e20724

  Abstract

  The discovery of high-temperature superconductivity in pressurized bulk Ruddlesden-Popper (RP) bilayer nickelates has prompted the conjecture that epitaxial compressive strain might mimic essential aspects of hydrostatic pressure. The realization of superconductivity in films on SrLaAlO4 (001) (SLAO) supports this correspondence, yet it remains unclear whether the pressure-temperature phase diagram of RP bilayer nickelates can be systematically mapped (and studied at ambient pressure) as a function of epitaxial strain. To this end, experimental access near the elusive edge of the superconducting phase boundary would provide invaluable insight into the nature of the superconducting state and the ground state from which it emerges. Here we report superconducting RP bilayer nickelates grown on LaAlO3 (001) (LAO), where the compressive strain required for ambient-pressure superconductivity is nearly halved to -1.2%. These films exhibit a superconducting onset above 10 K and reach zero resistance at 3 K, with normal-state transport properties differing from those of films grown on SLAO. Our comparative study shows that strain-rather than interfacial structure is the primary factor governing the superconductivity and normal-state properties. This work offers a new opportunity to probe emergent phenomena near the superconducting phase boundary in the strain-temperature phase diagram of RP bilayer nickelates.

  View details for DOI 10.1002/adma.202520724

  View details for PubMedID 41677074

• Author Correction: Superconductivity and normal-state transport in compressively strained La2PrNi2O7 thin films. Nature materials Liu, Y., Ko, E. K., Tarn, Y., Bhatt, L., Li, J., Thampy, V., Goodge, B. H., Muller, D. A., Raghu, S., Yu, Y., Hwang, H. Y. 2025

  View details for DOI 10.1038/s41563-025-02394-5

  View details for PubMedID 41073659

• Superconductivity and normal-state transport in compressively strained La2PrNi2O7 thin films. Nature materials Liu, Y., Ko, E. K., Tarn, Y., Bhatt, L., Li, J., Thampy, V., Goodge, B. H., Muller, D. A., Raghu, S., Yu, Y., Hwang, H. Y. 2025

  Abstract

  The discovery of superconductivity under high pressure in Ruddlesden-Popper phases of bulk nickelates has sparked great interest in stabilizing ambient-pressure superconductivity in the thin-film form using epitaxial strain. Recently, signs of superconductivity have been observed in compressively strained bilayer nickelate thin films with an onset temperature exceeding 40 K, although with broad, two-step-like transitions. Here we report the intrinsic superconductivity and normal-state transport properties in compressively strained La2PrNi2O7 thin films, achieved through a combination of isovalent Pr substitution, growth optimization and precision ozone annealing. The superconducting onset occurs above 48 K, with zero resistance reached above 30 K, and the critical current density at 1.4 K is 100-fold larger than previous reports. The normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour, and other phenomenological similarities to transport in overdoped cuprates suggest parallels in their emergent properties.

  View details for DOI 10.1038/s41563-025-02258-y

  View details for PubMedID 40442446

  View details for PubMedCentralID 10951943

• Signatures of ambient pressure superconductivity in thin film La3Ni2O7. Nature Ko, E. K., Yu, Y., Liu, Y., Bhatt, L., Li, J., Thampy, V., Kuo, C. T., Wang, B. Y., Lee, Y., Lee, K., Lee, J. S., Goodge, B. H., Muller, D. A., Hwang, H. Y. 2024

  Abstract

  Recently, the bilayer nickelate La3Ni2O7 has been discovered as a new superconductor with transition temperature Tc near 80 K under high pressure1-3. Despite extensive theoretical and experimental work to understand the nature of its superconductivity4-29, the requirement of extreme pressure restricts the use of many experimental probes and limits its application potential. Here, we present signatures of superconductivity in La3Ni2O7 thin films at ambient pressure, facilitated by the application of epitaxial compressive strain. The onset Tc varies approximately from 26 K to 42 K, with higher Tc values correlating with smaller in-plane lattice constants. We observed the co-existence of other Ruddlesden-Popper phases within the films and dependence of transport behavior with ozone annealing, suggesting that the observed low zero resistance Tc of around 2 K can be attributed to stacking defects, grain boundaries, and oxygen stoichiometry. This finding initiates numerous opportunities to stabilize and study superconductivity in bilayer nickelates at ambient pressure, and to facilitate the broad understanding of the ever-growing number of high temperature and unconventional superconductors in the transition metal oxides.

  View details for DOI 10.1038/s41586-024-08525-3

  View details for PubMedID 39701131