westurner
14 hours ago
"Universality in quantum critical flow of charge and heat in ultraclean graphene" (2025) https://www.nature.com/articles/s41567-025-02972-z :
> Abstract: [...] Here we have discerned the quantum critical universality in graphene transport by combining the electrical and thermal conductivities in very high-quality devices close to the Dirac point. We find that they are inversely related, as expected from relativistic hydrodynamics, and the characteristic conductivity converges to a quantized value. We also observe a giant violation of the Wiedemann–Franz law, where the Lorentz number exceeds the semiclassical value by more than 200 times close to the Dirac point at low temperatures. At high temperatures, the effective dynamic viscosity to entropy density ratio close to the Dirac point in the cleanest devices approaches that of a minimally viscous quantum fluid within a factor of four.
magicalhippo
12 hours ago
Wikipedia lists some limitations of the Wiedemann–Franz law[1], and also some previous violations in other materials.
Reading the Wikipedia page I don't get the sense the law is quite as fundamental as the headline and summary make it sound like.
Here's one of the previous violations:
In 2011, N. Wakeham et al. found that the ratio of the thermal and electrical Hall conductivities in the metallic phase of quasi-one-dimensional lithium molybdenum purple bronze Li0.9Mo6O17 diverges with decreasing temperature, reaching a value five orders of magnitude larger than that found in conventional metals obeying the Wiedemann–Franz law. This due to spin-charge separation and it behaving as a Luttinger liquid.
Still, graphene is cool and seems to be the gift that keeps on giving in terms of surprising results in solid state physics.
[1]: https://en.wikipedia.org/wiki/Wiedemann%E2%80%93Franz_law#Li...
westurner
an hour ago
That twisted SWCNT store energy basically without heat loss is incredibly under capitalized.
/?hnlog graphene (345 references), vortices (70 references) .. westurner.github.io/hnlog/
That's it, I'm writing a tool to parse this for citations
From "Single atom defect in 2D material can hold quantum information at room temp" (2024) https://news.ycombinator.com/item?id=40478219 :
> - "Observation of current whirlpools in graphene at room temperature" (2024) https://www.science.org/doi/10.1126/science.adj2167 .. "Electron Vortices in Graphene Detected" https://news.ycombinator.com/item?id=40360691
>> re: the fractional quantum hall effect, and decoherence: How are spin currents and vorticity in electron vortices related?
> [...] But the Standard Model Lagrangian doesn't describe n-body gravity, n-body quantum gravity, photons in Bose-Einstein Condensates; liquid light in superfluids and superconductors, black hole thermodynamics and external or internal topology, unreversibility or not, or even fluids with vortices or curl that certainly affect particles interacting in multiple fields.
This is probably wrong if these are also true:
This says that the standard model actually does describe the n-body orbits of the planets:
"Perihelion precession of planetary orbits solved from quantum field theory" (2025) https://arxiv.org/abs/2506.14447 .. https://news.ycombinator.com/item?id=45220460
There's also this:
"Fluid vacuum yields exact solutions to Pioneer anomaly and Mercury's perihelion (2019)" https://news.ycombinator.com/item?id=45220585