Spectroscopic signature of the Stark-shifted Tamm-type surface state of La(0001)

TL;DR

This study investigates how the Tamm-type surface state of La(0001) shifts under electric fields using tunneling spectroscopy, revealing a Stark shift and lifetime decrease, contrasting with noble metal surface states.

Contribution

It provides the first detailed experimental observation of Stark shifts in Tamm-type surface states of La(0001) under varying electric fields.

Findings

Significant Stark shift of the surface state toward Fermi energy.

Broadening of the resonance peak indicating reduced surface-state lifetime.

Results differ from previous observations on noble metal surfaces.

Abstract

We have studied the Tamm-type surface state of La(0001) by tunneling spectroscopy within a wide range of tunneling currents from 0.1 nA to 8000 nA, thereby tuning the electric-field strength in a tip-vacuum-sample tunnel junction. We observe a significant shift of the unoccupied Tamm-type surface state toward the Fermi energy with increasing electric-field strength, accompanied by a broadening of the width of the resonance peak indicating a decrease of the surface-state lifetime. Our experimental results are contrary to previous reports for Stark-shifted Shockley-type surface states of noble metal (111) surfaces.