Monday, May 8, 2023

Update to: Evidence of near-ambient superconductivity in a N-doped lutetium hydride


Given the questions, several scientists say Dias should make his data public. “I am unhappy that Dias is supposedly not cooperating with researchers who are questioning his data,” says Marvin Cohen, a theoretical physicist at UC Berkeley. Schilling is blunt: “I told Dias to give [Hirsch] the raw data, for heaven’s sake.”

In his email [responding to Hirsch's request for the raw data], Dias wrote, “Given that you have an active comment on our work, we consider such a request would not be reasonable.” Frustrated, Hirsch requested the data from Nature and the National Science Foundation (NSF), which funded the work. On 30 August, Nature appended an editor’s note to Dias’s paper saying: “The editors of Nature have been alerted to undeclared access restrictions relating to the data behind this paper. We are working with the authors to correct the data availability statement.” NSF and the University of Rochester both tell Science they cannot comment on possible investigative matters.

A theoretical analysis on the theoretical feasibility of superconductivity in lutetium hydride was published. The results add an interesting dimension to the controversy.


Recently, room-temperature superconductivity has been reported in a nitrogen-doped lutetium hydride at near-ambient pressure [Dasenbrock-Gammon et al., Nature 615, 244 (2023)]. 

Here, we systematically study the phase diagram of Lu–N–H at 1 GPa using first-principles calculations, and we do not find any thermodynamically stable ternary compounds.

Our theoretical results show that the Tc values of N-doped LuH3 estimated using the Allen–Dynes-modified McMillan equation are much lower than room temperature.

The conclusion seems to be that, based on existing theory, it is not possible to form a stable combination of lutetium, nitrogen, and hydrogen. 

Notably, all predicted potential ternary compounds lie above the convex hull at 1 GPa. Thus, no ternary Lu–N–H compounds can remain thermodynamically stable at this pressure, which is consistent with the main results of Xie et al.26

And even if it were, it seems it would superconduct at far lower than room temperature, in line with existing experiments. 

Our simulations show that the lowest T_c is 4 K for LuH3 without doping. In addition, T_c increases with increasing N-doping concentration; thus, doping N atoms into LuH3 will increase T_c. However, the highest T_c in this VCA calculation is 22 K, obtained with 1% N-doping at 30 GPa, which is much lower than room temperature.

It's worth noting that 30 GPa is about 300 kbar, which is 30 times higher than the pressures reported in Dias et al. (2023). Further investigation is needed, but it seems theoretically unlikely to produce a material like the doped LuNH3 at the reported temperatures and pressures. Certainly even less likely for it to superconduct at room temperatures. This is based on existing theory, so the possibility remains that Dias et al. have discovered an exciting new effect that will require more advanced models to explain.  

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