Definitive determination of superconducting electrostatic screening

Determine whether electrostatic screening at a superconducting surface changes upon entering the superconducting state, specifically whether the screening length for static longitudinal electric fields remains the Thomas–Fermi length or instead becomes governed by the London penetration depth.

Background

Conventional superconducting electrodynamics predicts that static longitudinal electric fields are screened over the short Thomas–Fermi length, whereas Hirsch’s alternative theory predicts that both electric and magnetic fields are screened over the much larger London penetration depth. This difference provides an experimental test distinguishing the two descriptions of superconductivity.

Earlier local-probe measurements using a qPlus atomic force microscope investigated the electrostatic interaction between a probe-tip dipole and a superconducting surface, but their force sensitivity was insufficient to establish whether the screening response changed across the superconducting transition. The present paper addresses this unresolved issue using more sensitive force-gradient and field-emission-resonance measurements.

References

While their experiments established an important benchmark, the achievable force sensitivity prevented a definitive determination of the screening response, leaving the question unresolved.

— Thomas-Fermi screening of electrostatic fields in a type-I superconductor  (2609.08516 - Sivakumar et al., 8 Sep 2026) in Introduction, paragraph discussing prior local-probe experiments