Knowledge

Superconductivity in pressurized trilayer La₄Ni₃O₁₀−δ single crystals

In recent years, significant breakthroughs have been achieved in the study of Ruddlesden-Popper (RP) nickel oxide superconductors. This article systematically reviews the experimental and theoretical progress in this field, with a particular focus on thin-film systems. Key findings include the emergence of superconductivity in bilayer La₃Ni₂O₇ (T_c ~ 80 K) and trilayer La₄Ni₃O₁₀ under high pressure, and, critically, the realization of ambient-pressure superconductivity in ultra-thin films of La₃Ni₂O₇ grown on substrates providing compressive strain—a breakthrough that overcomes the high-pressure limitation and enables the use of experimental techniques previously inaccessible in the superconducting state, such as angle-resolved photoemission spectroscopy (ARPES). On the theoretical side, the system requires simultaneous consideration of both the Ni e_g and a_{1g} orbitals, as well as the strong interlayer coupling within bilayers that gives rise to a “dimer” picture, and exhibits strange metal behavior and strong correlation features reminiscent of cuprates. By comparing the similarities and differences among various RP nickel oxides, this article offers a new perspective on understanding the mechanism of high-temperature superconductivity in correlated electron systems and outlines future research directions.

This study employed the enormous oxidation atomic layer epitaxy method to grow (La,Pr)3Ni2O7 thin films on SrLaAlO4 substrates under extreme non-equilibrium conditions, achieving a superconducting onset transition temperature of approximately 63 K at ambient pressure, with zero-resistance temperature reaching about 37 K and diamagnetic signal onset at around 23 K. This method overcomes the structural instability of the metastable superconducting phase through high-temperature and in-situ sufficient oxidation; X-ray diffraction and scanning transmission electron microscopy confirmed that the films possess large-scale crystalline purity. Transport measurements reveal a systematic evolution of the normal-state resistivity temperature power-law exponent α from Fermi liquid behavior (α≈2) in samples with low onset transition temperatures to strange metal behavior (α≈1) in samples with high onset transition temperatures, directly correlating enhanced superconductivity with non-Fermi liquid behavior. The vortex melting phase diagram constructed via mutual inductance technique indicates that the two-dimensional melting limit is suppressed to near zero, with interlayer coupling strength significantly stronger than that of bismuth-based cuprates. These results demonstrate that nickelates are strange metal high-temperature superconductors with strong interlayer coupling at ambient pressure.

3 linked papers

By developing an in situ monitoring reduction (OMR) method, this study achieved continuous modulation of the Ni 3d orbital electron occupancy in infinite-layer nickelate superconductors over an ultra-wide range from approximately 3d⁷ to 3d⁹, thereby controllably driving the superconductor-insulator transition (SIT). Combining synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy analysis of oxygen atoms, the electron occupancy states were precisely calibrated, and the SIT was further modulated using ionic liquid gating and magnetic fields. Nernst effect measurements reveal that, unlike in cuprates, pairing initiates as soon as the resistance starts to drop, while the Meissner effect only appears in the zero-resistance state, marking the establishment of global phase coherence. Angle-dependent magnetotransport studies show that within the transition temperature range, superconductivity exhibits a mixture of two-dimensional and three-dimensional characteristics, indicating that the observed SIT deviates from the classical 2D model. These results provide a unique perspective for understanding the interplay between structural and electronic phase transitions in infinite-layer nickelates within the oxygen content–magnetic field–temperature parameter space.

4 linked papers

The suppression of density wave in bilayer nickelate La3⁢Ni2⁢O7 under pressure has been identified as a critical factor enabling pressure-induced high-temperature superconductivity. However, this density wave state exhibits remarkable stability against most alternative tuning methods except the high-pressure technique. Herein through systematic investigations of Tb doping effects on electrical transport and magnetic properties, we observe a gradual suppression of density wave transition temperature with the increasing Tb concentration, accompanied by the emergence of negative magnetoresistance persisting up to 14 T. Magnetic susceptibility measurements further reveal the formation of a doping-induced spin-glass state, which likely accounts for the observed negative magnetoresistance phenomenon. This work establishes an effective chemical doping approach to manipulate the density wave state and correlated quantum state in La3⁢Ni2⁢O7, offering new insights into the mechanism of high-temperature superconductivity and potential pathways toward achieving ambient-pressure superconductivity in bulk nickelate crystals.

1 linked paper

This study systematically investigates the low-temperature physics and unconventional pairing mechanism of the hybrid nickelate La₅Ni₃O₁₁ using a symmetry-based phenomenological approach combined with charge self-consistent density functional theory and dynamical mean-field theory. The monolayer subsystem is found to be in a Mott insulating state, and superconductivity primarily originates from the Ni-e_g orbitals in the bilayer subsystem. The system exhibits a two-gap superconducting feature, with the dominant pairing arising from interlayer coupling between d_{z²} orbitals and the secondary pairing from intralayer coupling within d_{x²-y²} orbitals. Compared with high-pressure La₃Ni₂O₇, the reduction of the superconducting transition temperature T_c in La₅Ni₃O₁₁ can be attributed to the weakening of interlayer pairing contributions, which is directly reflected in the decreased magnitude of the hopping parameter ratio |t_{\perp}^z/t_{\parallel}^{x}|. This unified picture provides a microscopic theoretical framework for understanding the superconducting pairing mechanism within bilayer NiO₂ planes and the role of the γ pocket.

8 linked papers