🔬 physics

Enhanced and robust superconductivity in La0.8Sr0.2NiO2 membranes compressed up to 210 GPa

This study demonstrates that superconductivity in freestanding La0.8Sr0.2NiO2 membranes remains robust under ultrahigh pressures up to 210 GPa, exhibiting a dome-like transition temperature evolution that peaks at 74.5 K, a phenomenon unprecedented in high-Tc oxide superconductors.

Original authors: Liling Sun, Shu Cai, Yuqing Tian, Shengjun Yan, Jinyu Zhao, Bo Hao, Jianfeng Zhang, Shuaihang Sun, Yang Ding, Qi Wu, Ho-Kwang Mao, Ivan Božović, Yuefeng Nie

Published 2026-08-06

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Liling Sun, Shu Cai, Yuqing Tian, Shengjun Yan, Jinyu Zhao, Bo Hao, Jianfeng Zhang, Shuaihang Sun, Yang Ding, Qi Wu, Ho-Kwang Mao, Ivan Božović, Yuefeng Nie

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where electricity flows without any resistance at all, like a ghost gliding through a wall without ever bumping into anything. This magical state is called superconductivity, and it's the holy grail for scientists trying to build faster computers, powerful magnets, and energy grids that don't waste power. For decades, the champions of this world have been materials made of copper and oxygen (called cuprates). But recently, a new contender has entered the ring: a family of materials made with nickel instead of copper. These "nickelates" look and act a lot like their copper cousins, offering a fresh clue to solve the mystery of how superconductivity works.

However, there's a catch. To really test these materials, scientists need to squeeze them with incredible force, mimicking the crushing pressure found deep inside planets. Usually, these materials are glued to a thick, rigid backing (a substrate) that breaks or gets in the way when you try to squeeze them that hard. It's like trying to test the strength of a rubber band while it's still taped to a heavy wooden block. To get around this, researchers recently learned how to peel these materials off their backing, creating tiny, freestanding "membranes" that can be squeezed freely. The big question was: if you keep squeezing these nickel membranes harder and harder, will they keep getting better at superconducting, or will they eventually snap and give up?

This paper tells the story of what happens when scientists took a freestanding membrane made of a specific nickel material (La0.8Sr0.2NiO2) and squeezed it with the most powerful pressure machines available. They pushed the pressure up to a staggering 210 GPa (that's 2.1 million times the pressure of the Earth's atmosphere!). The results were surprising and robust. Instead of giving up, the material's ability to superconduct actually got stronger as the pressure increased.

Here is what they found:

The Rise: At normal air pressure, the material started superconducting at about 16 K (a very cold -257°C). As they squeezed it, this temperature kept climbing. By the time they reached 146 GPa, the material was superconducting at a peak temperature of 74.5 K.
The Peak and the Fall: After hitting that peak, the temperature started to slowly drift downward as they squeezed even harder. But even at the extreme pressure of 210 GPa, the material was still superconducting at a very impressive 57.4 K.
The Comparison: This is a record-breaking level of toughness. Most other high-temperature superconductors (like the famous copper-based ones) stop working or lose their superconducting power once the pressure gets too high (often around 20 to 40 GPa). This nickel membrane, however, kept going strong all the way to 210 GPa.

The researchers also checked to make sure this wasn't just an artifact of the measurement. They confirmed that the "onset" of superconductivity wasn't just getting blurry or wider; the actual temperature where the magic happened was genuinely rising. They compared their results to a similar nickel material made with a different element (neodymium), and while that one peaked earlier and stopped rising, both materials showed that the nickel layers are the true heroes of the show, not the other atoms surrounding them.

In short, this study shows that superconductivity in these nickel membranes is incredibly tough. It doesn't just survive extreme pressure; it thrives under it, reaching higher temperatures than ever seen before in this type of material. It suggests that the secret to making these materials work better might be found in how we squeeze them, opening up a new frontier for understanding how these quantum materials behave under the most extreme conditions imaginable.

Technical Summary: Enhanced and Robust Superconductivity in La0.8Sr0.2NiO2 Membranes Compressed up to 210 GPa

Problem Statement
The discovery of superconductivity in infinite-layer nickelate thin films has established a new frontier for investigating unconventional oxide superconductors, drawing significant parallels to cuprate systems. However, a critical experimental limitation has hindered the exploration of these materials under extreme conditions: the presence of thick substrates (typically ~500 µm) prevents measurements in diamond anvil cells (DACs), where sample hole heights are generally restricted to less than 50 µm. While recent studies on freestanding Nd0.85Sr0.15NiO2 membranes successfully circumvented this issue, revealing a linear increase in superconducting transition temperature ( $T_{c,onset}$ ) up to 91.5 GPa without saturation, fundamental questions remained regarding the behavior of nickelates at even higher pressures. Specifically, it was unknown whether superconductivity could persist beyond 100 GPa, if $T_{c,onset}$ would continue to rise, and how the pressure response of freestanding infinite-layer nickelates compares to other high- $T_c$ oxide superconductors, which typically exhibit suppressed superconductivity under high pressure.

Methodology
To address these questions, the authors synthesized freestanding single-crystal La0.8Sr0.2NiO2 membranes using a topotactic reduction process on SrTiO3-buffered substrates. The synthesis involved growing La0.8Sr0.2NiO3 perovskite films with a water-soluble Sr4Al2O7 sacrificial layer, followed by reduction with CaH2 to form the infinite-layer phase. The membranes were chemically released by etching the sacrificial layer and transferred onto diamond anvils using a flexible polymer support and a high-precision micromanipulator.

High-pressure electrical resistance measurements were conducted on three distinct membrane samples (S#1, S#2, S#3) within diamond anvil cells equipped with culets ranging from 50 µm to 110 µm. Pressure was applied up to a maximum of 210 GPa. The study employed four-probe resistance measurements with gold electrodes patterned directly onto the membrane surface. To distinguish genuine superconductivity enhancement from transition broadening, the authors analyzed the temperature-dependent resistance ( $R(T)$ ) using two criteria for $T_{c,onset}$ : the 0.5% resistance drop ( $T_{c,99.5\% R}$ ) and the two-line intersection method ( $T_{c,2 line}$ ). Additionally, the derivative of resistance ($dR/dT$) was used to determine the midpoint transition temperature ( $T_{cm}$ ). Magnetic field sweeps up to 7 T were performed on the compressed sample at 80 GPa to characterize the suppression of superconductivity and determine the upper critical field ( $H_{c2}$ ).

Key Results
The study demonstrates that superconductivity in freestanding La0.8Sr0.2NiO2 membranes persists under ultrahigh pressures up to 210 GPa, a regime previously unexplored for this class of materials. The evolution of the superconducting transition onset temperature ( $T_{c,onset}$ ) with pressure exhibits a distinct "dome-like" behavior:

Pressure Range 0–146 GPa: $T_{c,onset}$ increases continuously from approximately 16 K at ambient pressure to a peak of 74.5 K at 146 GPa. The initial increase (below 60 GPa) is nearly linear with a slope of 0.62 K/GPa.
Pressure Range 146–210 GPa: Beyond the peak, $T_{c,onset}$ gradually decreases but remains remarkably robust. At 210 GPa, the transition onset is still observed at 57.4 K.
Verification: Analysis of the $dR/dT$ curves confirmed that the increase in $T_{c,onset}$ reflects a genuine enhancement of superconductivity, as the midpoint temperature ( $T_{cm}$ ) also increased significantly (from 13 K at 15 GPa to 57 K at 147 GPa). Magnetic field measurements at 80 GPa confirmed the systematic suppression of superconductivity, consistent with a true superconducting state.

Comparative analysis with freestanding Nd0.85Sr0.15NiO2 membranes reveals that while both materials show linear $T_c$ enhancement below 60 GPa, their behaviors diverge at higher pressures. Nd0.85Sr0.15NiO2 reached a peak of ~~74 K at 91.5 GPa, whereas La0.8Sr0.2NiO2 reached a similar peak (~~74.5 K) at a much higher pressure (146 GPa) and maintained superconductivity up to 210 GPa. In contrast, other high- $T_c$ oxide systems, including cuprates (Bi-2212, PLCCO) and other nickelates (RP-phase La3Ni2O7), typically show monotonic suppression of superconductivity or disappearance at pressures well below 100 GPa.

Significance and Claims
The authors claim that this work demonstrates an unprecedented robustness of superconductivity against ultrahigh pressure in an oxide superconducting system. The persistence of superconductivity up to 210 GPa (2 Mbar) challenges the typical fragility observed in high- $T_c$ ceramic superconductors. The results suggest that the superconducting pairing strength in infinite-layer nickelates remains robust across this extreme pressure range, likely governed by the NiO2 planes rather than f-orbital magnetic moments, given the similarity in peak $T_c$ between La- and Nd-based variants despite their different lattice constants.

The study establishes that the pressure response of freestanding infinite-layer nickelates is distinct from other high- $T_c$ oxide families, which generally exhibit suppressed superconductivity under similar conditions. By extending the pressure window to 210 GPa, the research provides critical data on the limits of superconductivity in nickelates, indicating that the enhancement of kinetic energy and orbital overlap (Ni 3d and O 2p) does not immediately destroy the superconducting state, even as the effective Coulomb repulsion is reduced. This work underscores the potential of freestanding membrane techniques to unlock new quantum phenomena in complex oxides under extreme conditions.

Technical Summary: Enhanced and Robust Superconductivity in La0.8Sr0.2NiO2 Membranes Compressed up to 210 GPa

More like this