Title: "Momentum- and Energy-resolved Spectral Function of an Interacting 2D Electronic System"

Abstract: The single-particle spectral function measures the density of electronic states (DOS) in a material as a function of both momentum and energy, providing central insights into phenomena such as superconductivity and Mott insulators. While scanning tunneling microscopy (STM) and other tunneling methods have provided partial spectral information, until now only angle-resolved photoemission spectroscopy (ARPES) has permitted a comprehensive determination of the spectral function of materials in both momentum and energy. However, ARPES operates only on electronic systems at the material surface and cannot work in the presence of applied magnetic fields. To overcome these issues, we have developed unique approaches to tunneling spectroscopy.
    In this talk, first, I will introduce Time Domain Capacitance Spectroscopy, a method that allows accurate measurements of the density of states of 2D holes in GaAs at 20 mK and in a high magnetic field. We discovered filling factor dependent resonances that are antisymmetric in energy and density around filling factor nu=1 [1]. Analysis of the resonance structure gives evidence that holes are dressed by interactions with phonons of a long-range ordered electronic Wigner crystal. Building upon this technique, we developed a new method for determining the full momentum- and energy-resolved electronic spectral function of a 2D electronic system embedded in a semiconductor [2]. In contrast with ARPES, the technique remains operational in the presence of large externally applied magnetic fields and functions for electronic systems with zero electrical conductivity or with zero electron density. I will discuss how this technique provides a direct high-resolution and high-fidelity probe of the dispersion and many-body effects of an interacting electron system.

 [1] Joonho Jang, B. M. Hunt, L. N. Pfeiffer, K. W. West, and R. C. Ashoori., Nature Physics 13, 340–44 (2017)
 [2] Joonho Jang, H. M. Yoo, L. N. Pfeiffer, K. West, K. W. Baldwin, and R. C. Ashoori, Science 358, 901 (2017)