We are pleased to share our recent publication:
👉 https://journals.iucr.org/s/issues/2026/03/00/rv5203/index.html
published in the J. Synchrotron Rad. (2026). 33, 693–697
A fundamental mismatch
ARPES is commonly interpreted as a direct measurement of electronic structure in energy–momentum space.
In practice, experimental data are almost always presented as
intensity vs binding energy and momentum along a high-symmetry direction.
However, this representation does not correspond to a direct observable of the experiment.
What ARPES actually measures
As shown in this work, ARPES data are inherently defined in a space of emission angles and kinetic energies, while the conventional representation corresponds to a projection of this space.
As a result, using single photon energy:
- no high-symmetry directions of the Brillouin zone are directly accessible
- the commonly used representation of ARPES data cannot be regarded as intensity vs energy and momentum along any line
- an energy distribution at a single k-point cannot be measured
These are not technical limitations — they are intrinsic to the kinematics of ARPES.
Why conventional analyzers fall short
Conventional hemispherical analyzers are designed around the idea of acquiring data along predefined line in angular space.
This design implicitly enforces the projected representation and limits access to the full information content of the experiment.
From limitation to design principle
At Fermiologics, we take a different approach.
Instead of optimizing data acquisition within a projected space, we design instrumentation that is aligned with the native variables of ARPES.
The FeSuMa analyzer is built around this principle:
- acquisition in the 2D angular space
- direct access to a higher-dimensional dataset
- reduced reliance on reconstruction from projections
Towards a more complete ARPES measurement
The ideas presented in this work are not only conceptual — they directly inform the design of next-generation ARPES instrumentation.
They point towards a shift:
from measuring cuts in angular space
to accessing the full information content of the experiment.
A note from Fermiologics
FeSuMa is not an incremental improvement of existing analyzers.
It is a response to a more fundamental question:
What is the natural unit of information in ARPES — and how should it be measured?
This publication reflects the conceptual foundation behind FeSuMa.