Specifically, if one sees quantum oscillations, such as Shubnikov de Haas, or maps out the Fermi surface using Angle Dependent MagnetoResistance, has one "seen" the Fermi surface?
The secondary point is an unfortunate one. It provides another concrete example of the perverse influence of luxury journals, particularly the Nature Publishing Group, on science.
People make silly unjustified claims to get published.
At first I was excited when I saw the Nature Communications paper
Quasiparticles and Fermi liquid behaviour in an organic metal
T. Kiss, A. Chainani, H.M. Yamamoto, T. Miyazaki, T. Akimoto, T. Shimojima, K. Ishizaka, S. Watanabe, C.-T. Chen, A. Fukaya, R. Kato, S. Shin
It reports Angle Resolved PhotoEmission Spectroscopy (ARPES) measurements on an organic metal. For the last 20 years ARPES has been a workhorse for studying cuprate superconductors. However, organics seem to have been beyond its reach, partly because the crystals can be easily damaged by the high intensity X-rays used. When I give talks about organics people often ask about ARPES measurements. So, I thought perhaps finally the time had come.
The authors of the paper are to be commended for taking on this challenging task.
The abstract of the paper states
Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results.
Then I looked at the actual data in the paper. Some is shown below.
It is rather noisy!
The lower figure shows the deduced Fermi surface on top of an ARPES intensity map.
The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface".
What do you think?
Prior to this paper there were Shubnikov de Haas measurements on the same material and Angle-Dependent MagnetoResistance, reported here. The data is shown below.
From the ADMR one can map out the intra-layer Fermi surface, using some theory, which assumes Fermi liquid quasi-particles. The result is below. The area is consistent with the frequency of SdH oscillations.
The authors neglect to mention this, even though they reference the paper that contains this figure. Furthermore, they make the extraordinary claim,
the present result constitutes the only case of an experimentally measured k-resolved Fermi surface of an organic metal.
I am gobsmacked because in 1996 a book was published
Fermi Surfaces of Low-Dimensional Organic Metals and Superconductors by Joachim Wosnitza.
It contains multiple pictures of "experimentally measured k-resolved Fermi surfaces".
If you asked me "Does this material have a Fermi surface?" I would say, purely based on the ADMR that I was pretty confident it did.
Putting aside all the noisy data and hype, there is an important philosophical and scientific question,
"Is ARPES really a more fundamental measurement of or robust evidence for a Fermi surface than ADMR and SdH?"
There are some subtle issues here, as discussed here. For example, with a marginal Fermi liquid one can still get SdH.