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Full momentum- and energy-resolved spectral function of a 2D electronic system

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Science  17 Nov 2017:
Vol. 358, Issue 6365, pp. 901-906
DOI: 10.1126/science.aam7073

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Delving deep into electronic properties

The spectral function of a material, which reflects the distribution of its electronic states as a function of momentum and energy, carries a wealth of information on its properties. However, measuring the spectral function directly is tricky, particularly in systems inaccessible to surface probes or in insulators. Jang et al. introduce a method dubbed momentum- and energy-resolved tunneling spectroscopy, in which electrons tunnel from a probe layer to unoccupied states in a target layer deep in a heterostructure. Because the momentum and energy of the electrons are tightly controlled, the measured tunneling probability is proportional to the spectral function of the target system.

Science, this issue p. 901

Abstract

The single-particle spectral function measures the density of electronic states in a material as a function of both momentum and energy, providing central insights into strongly correlated electron phenomena. Here we demonstrate a high-resolution method for measuring the full momentum- and energy-resolved electronic spectral function of a two-dimensional (2D) electronic system embedded in a semiconductor. The technique remains operational in the presence of large externally applied magnetic fields and functions even for electronic systems with zero electrical conductivity or with zero electron density. Using the technique on a prototypical 2D system, a GaAs quantum well, we uncover signatures of many-body effects involving electron-phonon interactions, plasmons, polarons, and a phonon analog of the vacuum Rabi splitting in atomic systems.

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