Time Domain Capacitance Spectroscopy

TDCS is a high resolution spectroscopic technique that opens a new dimension, energy from the Fermi surface, to systematic measurement and exploration. We gain unique insight into the contribution of interactions to the physics of 2D systems by starting with an empty quantum well and examining how the quasiparticle spectrum changes as a continuous function of carrier density.

Tunneling measurements provide remarkable insight in many body physics; the relatively simple quantity dI/dV provides access to the single particle density of states (SPDOS), a quantity integral to our theoretical understanding of many-body systems. Two-dimensional systems, host to remarkable correlated phenomena such as the fractional and integer quantum Hall effects, have proven difficult to probe using tunneling spectroscopy because of difficulties including ohmic heating and low in-plane conductivities. We have developed an improved version of time domain capacitance spectroscopy (TDCS) that overcomes all of these difficulties. Using it, we probe the integer quantum Hall effect in a GaAs 2DES, directly observing exchange splittings and quasiparticle lifetimes. These measurements reveal the difficult to reach and beautiful structure present in this highly correlated system far from the Fermi surface.