Interlayer coupling enhanced superconductivity near 100 K in La$_{3-x}$Nd$_x$Ni$_2$O$_7$

Abstract

Systematically controlling the superconducting transition temperature ($T_\text{c}$) in the bilayer Ruddlesden-Popper nickelate La$_3$Ni$_2$O$_7$ remains a significant challenge. Here, we address this by synthesizing high-quality polycrystalline La$_{3-x}$Nd$_x$Ni$_2$O$_7$ ($0 \leq x \leq 2.4$) with record-level rare-earth substitution. Nd doping compresses the lattice, particularly along the $c$ axis, enhances the spin density wave transition temperature, and elevates the pressure required for the orthorhombic-to-tetragonal structural transition. Superconductivity is observed across all doping levels under high pressures, with the onset $T_\text{c}$ rising to $\sim$93~K for $x = 2.1$ and $2.4$ from the electronic transport measurement. Using the radio-frequency transmission technique, newly applied to nickelate superconductors, we detect signatures of superconductivity at $98 \pm 2$~K in the $x=2.4$ compound, pushing the $T_\text{c}$ frontier further. We identify a universal linear relationship where $T_\text{c}$ decreases with the $c$-axis lattice parameter at a rate of approximately $-28$~K/Å, demonstrating that enhanced interlayer magnetic exchange coupling is the dominant mechanism for superconducting pairing. Our work establishes the critical role of magnetism and provides a unified structural descriptor for elevating $T_\text{c}$ in bilayer nickelates.

Figures (10)

• Figure 1: Structural characterizations of La$_{3-x}$Nd$_x$Ni$_2$O$_7$ under pressure.a,b, Ambient-pressure lattice parameters of La$_{3-x}$Nd$_x$Ni$_2$O$_7$ as a function of doping level $x$, showing the $c$-axis parameter (a) and the $a$- and $b$-axis parameters (b) obtained from XRD refinements. For comparison, lattice parameters of La$_{3-x}$Sm$_x$Ni$_2$O$_7$ are included, adopted from Ref.Zhong2025e. c, Doping dependence of the spin density wave transition. d, Pressure evolution of the lattice parameters $a$, $b$, and $c$ for La$_{0.9}$Nd$_{2.1}$Ni$_2$O$_7$ refined from synchrotron XRD data. Solid symbols represent the orthorhombic $Amam$ phase, while hollow symbols correspond to the tetragonal $I4/mmm$ phase.
• Figure 2: High-pressure transport properties of La$_{3-x}$Nd$_x$Ni$_2$O$_7$.a, Temperature dependence of the normalized resistance $R/R_{150\text{K}}$ for La$_{3-x}$Nd$_x$Ni$_2$O$_7$ ($0 \leq x \leq 2.4$). The blue and dark orange arrows indicate the superconducting onset temperatures $T_\text{c}^{\text{onset}}$ for the $x = 0$ and $x = 2.4$ compositions, respectively. b, Normalized resistance $R/R_{150\text{K}}$ versus temperature for La$_{0.9}$Nd$_{2.1}$Ni$_2$O$_7$ at pressures from 27.0 GPa to 34.9 GPa (Run 1). The purple arrow marks the $T_\text{c}^{\text{onset}}$ of 93 K at 34.9 GPa. c, Magnetic field dependence of the normalized resistance $R/R_{150\text{K}}$ for La$_{0.9}$Nd$_{2.1}$Ni$_2$O$_7$ at 34.9 GPa. d, Temperature-dependent resistance of La$_{0.6}$Nd$_{2.4}$Ni$_2$O$_7$ under pressures ranging from 30.0 GPa to 45.0 GPa (Run 2). The steel blue arrow indicates the $T_\text{c}^{\text{onset}}$ of 92 K at 33.8 GPa. e, Magnetic field dependence of the resistance for La$_{0.6}$Nd$_{2.4}$Ni$_2$O$_7$ at 40.3 GPa. f, Upper critical fields for La$_{0.9}$Nd$_{2.1}$Ni$_2$O$_7$ at 34.9 GPa and La$_{0.6}$Nd$_{2.4}$Ni$_2$O$_7$ at 40.3 GPa. The hollow circles represent experimental $T_\text{c}^{\text{onset}}$ data, and the solid lines show fits using the Ginzburg-Landau model.
• Figure 3: Radio-frequency measurements of La$_{3-x}$Nd$_x$Ni$_2$O$_7$ ($x = 2.1$ and $2.4$).a, b, Optical image and front-view schematic of the RF DAC culets. c, Experimental setup for RF transmission measurements in a DAC. An external solenoid (L) generates a low-frequency modulating magnetic field, which interacts with the sample (S). d, Temperature dependence of the transmitted RF signal for the $x=2.1$ sample at $36 \pm 4$ GPa during warming cycles, showing the real (20 MHz) and imaginary (25 and 60 MHz) components. e, Real component of the transmitted signal versus temperature for two $x=2.4$ samples (S1 and S2) at 41 GPa. For S1, data were collected at 5 MHz (cooling) and 25 MHz (warming); for S2, data were taken at 40 MHz during both cooling and warming cycles.
• Figure 4: A phase diagram of La$_{3-x}$Nd$_x$Ni$_2$O$_7$. The carmine circle, blue-gray pentacle, and purple-gray triangle represent the onset $T_\text{c}$ of the resistance curves for the $x$ = 1.5, 2.1, 2.4 compounds. Those points depict a cyan area representing the superconducting region of $x=2.1$. The saffron yellow area symbolizing superconductivity of $x=0$, which was cited from RefLi2025i. The dashed lines represent structural transitions of the $x=0$ and $x=2.1$ compounds, respectively.
• Figure 5: Relationship between $T_\text{c}^{\text{onset}}$ and lattice parameters.a,$T_\text{c}^{\text{onset}}$ as a function of the in-plane lattice parameter $a_\text{p}$. b,$T_\text{c}^{\text{onset}}$ as a function of the out-of-plane lattice parameter $c$. Solid symbols represent data for bulk La$_{3-x}$Nd$_x$Ni$_2$O$_7$ ($x = 0.9, 1.5, 2.1$) from this work. For comparison, open symbols show literature data for bulk La$_3$Ni$_2$O$_7$, La$_2$PrNi$_2$O$_7$, and La$_{1.5}$Sm$_{1.5}$Ni$_2$O$_7$, as well as for thin films of La$_3$Ni$_2$O$_7$ and related doped compounds under high pressure or at ambient conditions. A pink dashed box highlights data points corresponding to thin-film samples. Part of the data are adoped from Ref.Li2025iWang2024bKo2025Hao2025Zhou2025aLiu2025sOsada2025.