Perpustakaan Digital ITB

The observation of metallic ground states in a variety of two-dimensional electronic systems poses a fundamental challenge for the theory of electron fluids. Here evidence is analyzed for the existence of a regime, called the “anomalous metal regime,” in diverse 2D superconducting systems driven through a quantumsuperconductor to metal transition by tuning physical parameters such as themagnetic field, the gate voltage in the case of systems with a metal-oxide semiconductor field-effect transistor (MOSFET) geometry, or the degree of disorder. The principal phenomenological observation is that in the anomalous metal, as a function of decreasing temperature, the resistivity first drops as if the systemwere approaching a superconducting ground state, but then saturates at low temperatures to a value that can be orders of magnitude smaller than the Drude value. The anomalous metal also shows a giant positive magnetoresistance. Thus, itbehaves as if itwere a “failedsuperconductor.” This behavior is observedina broad range of parameters. It will be moreover exhibited, by theoretical solution of a model of superconducting grains embedded in ametallicmatrix, that as amatter of principle such anomalousmetallic behavior can occur in the neighborhood of a quantumsuperconductor to metal transition. However, it will be also argued that the robustness and ubiquitous nature of the observed phenomena are difficult to reconcile with any existing theoretical treatment and speculate about the character of a more fundamental theoretical framework.