[Paper Review] No evidence of superconductivity in the compressed sample prepared from the lutetium foil and H2/N2 gas mixture

Shu Cai, Jing Guo+11 more|arXiv (Cornell University)|Apr 6, 2023

Luminescence Properties of Advanced MaterialsMaterials Science3 citations

TL;DR

This study investigates the claim of near-ambient superconductivity in a lutetium-hydrogen-nitrogen (Lu-H-N) compound synthesized from lutetium foil and H2/N2 gas under high pressure. Despite replicating the synthesis method, the authors found no evidence of superconductivity through electrical resistivity and magnetic susceptibility measurements up to 3.4 GPa and down to 100 K, nor after laser heating to 1800 °C, with samples remaining dark blue throughout.

ABSTRACT

A material described as lutetium-hydrogen-nitrogen (Lu-H-N in short) was recently claimed to have near-ambient superconductivity[Gammon et al, Nature 615, 244, 2023]. If the results could be reproduced by other teams, it would be a major scientific breakthrough. Here, we report our results of transport and structure measurements on a material prepared using the same method as that reported by Gammon et al. Our X-ray diffraction measurements indicated that the obtained sample contained three substances: the FCC-1 phase (Fm-3m) with a lattice parameter a=5.03 Å, the FCC-2 phase (Fm-3m) with a lattice parameter a= 4.755 Å and Lu metal. These two FCC phases are identical to the those reported in the so-called near-ambient superconductor. However, we found that the samples had no evidence of superconductivity, through our resistance measurements in the temperature range of 300 - 4 K and pressure range of 0.9 - 3.4 GPa, and our magnetic susceptibility measurements in the pressure range of 0.8-3.3 GPa and temperature down to 100 K. We also used a laser heating technique to heat the sample to 1800°C and found no superconductivity in the produced dark blue samples below 6.5 GPa. In addition, the color of the both samples remain dark blue in the pressure range investigated.

Motivation & Objective

• To independently verify the claim of near-ambient superconductivity in Lu-H-N reported by Gammon et al. in Nature (2023).
• To reproduce the synthesis of the Lu-H-N compound using the same method: high-pressure treatment of lutetium foil with H2/N2 gas mixture.
• To investigate the electrical and magnetic properties of the resulting sample under high pressure and elevated temperature.
• To determine whether the observed dark blue phase with two FCC structures (a = 5.03 Å and 4.755 Å) exhibits superconducting behavior.

Proposed method

• High-pressure synthesis of the Lu-H-N compound using lutetium foil and a H2/N2 gas mixture in a hexagonal boron nitride (h-BN) pressure medium.
• X-ray diffraction (XRD) to identify the crystal phases present, confirming the presence of two FCC phases (Fm-3m) and metallic Lu.
• Electrical resistivity measurements from 300 K to 4 K at pressures between 0.9 and 3.4 GPa to detect superconducting transitions.
• Magnetic susceptibility measurements from 100 K down to 0 K at pressures between 0.8 and 3.3 GPa to detect Meissner-like behavior.
• Laser heating of the sample to 1800 °C under pressure to assess stability and potential superconducting behavior in the resulting dark blue phase.
• Color observation and phase stability monitoring across the pressure range up to 6.5 GPa.

Experimental results

Research questions

• RQ1 Does the Lu-H-N compound synthesized via the same method as reported by Gammon et al. exhibit superconductivity at ambient pressure and near-ambient conditions?
• RQ2 Are the two FCC phases (a = 5.03 Å and 4.755 Å) observed in the sample consistent with the proposed superconducting phase in the original claim?
• RQ3 Is there any superconducting transition detectable in resistivity or magnetic susceptibility measurements below 3.4 GPa and down to 100 K?
• RQ4 Does laser heating to 1800 °C induce or stabilize superconducting behavior in the dark blue phase formed under pressure?
• RQ5 Does the persistent dark blue color of the sample across all pressure and temperature conditions correlate with the presence of superconducting phases?

Key findings

• X-ray diffraction confirmed the presence of two FCC phases (Fm-3m) with lattice parameters a = 5.03 Å and a = 4.755 Å, matching those reported in the original study.
• No superconducting transition was observed in resistivity measurements over the temperature range of 300 K to 4 K at pressures from 0.9 to 3.4 GPa.
• Magnetic susceptibility measurements showed no diamagnetic shielding or Meissner effect down to 100 K at pressures between 0.8 and 3.3 GPa.
• Laser heating to 1800 °C did not induce superconductivity in the resulting dark blue samples, even at pressures up to 6.5 GPa.
• The sample retained its dark blue color across all pressure and temperature conditions, indicating no phase change associated with superconductivity.
• No evidence of superconductivity was found in any of the tested conditions, despite replication of the synthesis method and phase identification.