Quantum phases driven by strong correlations

Abstract

It has long been thought that strongly correlated systems are adiabatically connected to their noninteracting counterpart. Recent developments have highlighted the fallacy of this traditional notion in a variety of settings. Here we use a class of strongly correlated electron systems as a platform to illustrate the kind of quantum phases and fluctuations that are created by strong correlations. Examples are quantum critical states that violate the Fermi liquid paradigm, unconventional superconductivity that goes beyond the BCS framework, and topological semimetals induced by the Kondo interaction. We assess the prospect of designing other exotic phases of matter, by utilizing alternative degrees of freedom or alternative interactions, and point to the potential of these correlated states for quantum technology.

Quantum criticality in a layered iridate

“…Actually, according to very general scaling considerations, a power-law behavior σ(T) ∝ T x signals a metal-insulator quantum phase transition 22 . The positive exponent contrasts with the negative values found in metallic materials where the quantum criticality is not due to the proximity of a metal-insulator transition but interfaces two different conducting states, such as in a magnetic/heavy fermion quantum phase transition 51,52 . The specific value x~+1 for SICO must be captured by an appropriate microscopic model (see below).…”

The many faces (phases) of strong correlations

“…Experimentally, the change of the Fermi surface across such a Kondo destruction QCP was evidenced by Hall effect measurements [3]. Associated with this transition is the strange metal linear-in-temperature electrical resistivity referred to above.…”

“…They form spin singlets among themselves, which destabilizes the inter-species Kondo singlets. With this Kondo destruction [3], the Fermi surface is formed by the conduction electrons alone and is called small (subscript S in Fig. 2).…”

Origin of the different electronic structure of Rh- and Ru-doped Sr2IrO4

“…Inducing a metal-insulator transition (MIT) in correlated systems is a major way to reveal new and exotic electronic states [1]. After a decade of study of the spin-orbit Mott insulator Sr 2 IrO 4 , it has proved difficult to reach good metallic states, either by doping, beyond the first attempts [2], or by pressure [3].…”