Is a mean transverse energy below the thermal value achievable and usable?
In plain words
The sideways energy of emitted electrons was thought to bottom out at the temperature of the cathode. Some proposals and data suggest it can go lower, but this is not established.
Precise statement
For near-threshold photoemission the mean transverse energy is usually bounded below by $\mathrm{MTE} \sim k_{\mathrm{B}} T$ of the electron distribution. Determine whether mechanisms such as refraction at an effective-mass discontinuity at the surface or band-structure selection give $\mathrm{MTE} < k_{\mathrm{B}} T$ at useful quantum efficiency ($\mathrm{QE} > 10^{-5}$), and the minimum attainable MTE for a given material at $T = 300\,\mathrm{K}$.
What would settle it
Direct MTE measurements below $k_B T$ at room temperature with a calculation reproducing them from the material band structure.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
A 2026 Physical Review Letters report attributed subthermal MTE to electron refraction in multialkali cathodes; independent confirmation is pending.
Parent problems
- Special case of Lowest mean transverse energy obtainable from a photocathode · open · from revision 1 Sub-thermal MTE is a sharper version of the minimum photocathode MTE The parent was revised since revision 1: it now states another question.
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