ARPES data conventions

ERLabPy’s ARPES-specific tools use the coordinate and attribute names below. Supported data loader plugins map source-specific names and metadata to these conventions. Source-specific information can remain as additional coordinates or attributes.

These conventions let momentum conversion, Fermi edge fitting, and ARPES-aware plotting find the required physical quantities. General xarray operations do not depend on these names.

Coordinates and metadata

• A dimension coordinate gives the physical values along an array axis.

• A scalar coordinate records a measurement condition that does not vary along any axis.

• A non-scalar coordinate that is not a dimension coordinate represents a physical quantity that varies along one or more axes but is not used for indexing (for example, temperature recorded during a scan along the time axis).

• Everything else can be stored as an attribute.

Name	Storage	Unit	Role
eV	Coordinate	eV	Binding or kinetic energy
alpha, beta, delta,xi, chi	Coordinate	deg	See Experimental geometry
hv	Coordinate	eV	Photon energy
sample_temp	Coordinate or attribute	K	Sample temperature
configuration	Attribute	—	Experimental geometry, stored as 1–4
sample_workfunction	Attribute	eV	System work function used to convert binding energy to kinetic energy
angle_resolution	Attribute	deg	Angular resolution for the default momentum step estimate
inner_potential	Attribute	eV	Inner potential for out-of-plane momentum conversion
alpha_scale, beta_scale	Attributes	—	Optional compensation for known angle coordinate scale errors

Energy coordinates

ERLabPy uses one name, eV, for both binding and kinetic energy. Momentum conversion applies these rules:

eV and hv coordinates	Interpretation
eV contains zero or negative values	Binding energy; occupied states use negative values
Nonscalar eV is all positive and hv is fixed	Kinetic energy; ERLabPy converts it to binding energy
Multiple values for hv	eV must already be in binding energy

Incorrect values can produce a wrong momentum scale or a nonphysical kinetic energy.

Experimental geometry

Momentum conversion follows the four configurations defined in Ishida and Shin [2018]. alpha is always the analyzer angle. delta is always the sample azimuth. The roles of the other angles depend on configuration.

The following table summarizes angle conventions for commonly encountered configurations with a vertical cryostat.

Configuration	Analyzer slit orientation	Mapping angle	Polar	Tilt	Deflector	Azimuth	Analyzer
1 (Type 1)	Vertical	Polar	beta	xi	–	delta	alpha
2 (Type 2)	Horizontal	Tilt	xi	beta	–
3 (Type 1 + DA)	Vertical	Deflector	chi	xi	beta
4 (Type 2 + DA)	Horizontal

For instance, imagine a typical Type 1 setup with a vertical analyzer slit that acquires maps by rotating about the z axis in the lab frame. In this case, the polar angle (rotation about z) is \(\beta\), and the tilt angle becomes \(\xi\).

Note

Analyzers that measure two-dimensional angular information, such as time-of-flight analyzers, can be treated as hemispherical analyzers with a deflector.

Related procedures

• Use Data loading and saving to load supported data and inspect coordinates and metadata that use the ERLabPy names.

• Use Data loading and saving to load data and edit acquisition metadata in ImageTool Manager.

• Use Data formats and loader plugins to find loader and file-format interfaces.

• Use Momentum conversion to select a variable experimental configuration, set normal emission, and convert data.

• Read Momentum conversion for the distinction between the momentum conversion functions and grid interpolation.

• Use erlab.constants.AxesConfiguration and xarray.DataArray.kspace for exact values and accessor behavior.