Valley Susceptibility of an Interacting 2D Electron System

Manipulating different degrees of freedom for electrons in semiconductors offers the promise of new and different kinds of electronic devices. For example, controlling carrier spin is the foundation for the emerging area of "spintronics", and could also impact the more futuristic area of quantum computing, since many of the current proposals envision spin as the quantum bit (qubit) of information. PCCM researchers have recently explored another such degree of freedom in a semiconductor where electrons occupy multiple conduction band minima (valleys). They developed a novel technique to measure the "valley susceptibility", χ_V, i.e., how the relative numbers of electrons shift in a two-valley, two-dimensional (2D) AlAs quantum well when symmetry-breaking mechanical deformation is applied. This quantity is directly analogous to the spin susceptibility, χ_S, which specifies how the spin populations are shifted by an applied magnetic field. The measured χ_V and χ_S are strikingly similar, both exhibiting an interaction-induced enhancement at low electron densities. The results establish the general analogy between the spin and valley degrees of freedom, implying the potential use of valleys in applications such as quantum computing.