Unconventional Quantum Phases in Strongly Correlated Systems

Anwesha Chattopadhyay, H. R. Krishnamurthy, Arti Garg

We present a novel route for attaining unconventional superconductivity in a strongly correlated system without doping. In a simple model of a correlated band insulator at half-filling we demonstrate, based on a generalization of the projected wavefunctions method, that superconductivity emerges for a broad range of model parameters when e-e interactions and the bare band-gap are both much larger than the kinetic energy, provided the system has sufficient frustration against the magnetic order. As the interactions are tuned, the superconducting phase appears sandwiched between the correlated band insulator followed by a paramagnetic metal on one side, and a ferrimagnetic metal, antiferromagnetic half-metal, and Mott insulator phases on the other side.

Longhua Jiang

Hong Li, Siqi Zhang, Guo Ming +2 more

In this paper, we present a scheme to realize an unconventional photon blockade effect in a Fabry-Perot cavity and optical parametric amplifier (OPA) composite system. The system includes a tunable phase of complex driving strength, the second-order correlation function is used to describe the photon statistical properties. The numerical simulation of the photon blockade effect is conducted with different parameters. Our calculations show that the unconventional photon blockade effect can be controlled by the tunable phase of complex driving strength. Under the weak driving condition, the exact optimal conditions for strong photon anti-bunching are analytically derived (i.e. the optimal nonlinear gain of optical parametric amplifier and the phase of the field driving for the strong photon anti-bunching are obtained), and obtain the analytic calculations of the second-order correlation function. Under the optimal conditions, we perform a numerical simulation with different parameters. The optimal conditions for strong photon anti-bunching are found by analytic calculations, which are in good agreement with the numerical results. The results provide a platform for coherently operating the photon blockade and have potential applications in quantum information processing and quantum optical devices.

H. v. Löhneysen

Itamar Kimchi

In this doctoral dissertation, we consider the significance of spin-orbit coupling for the phases of matter which arise for strongly correlated electrons. We explore emergent behavior in quantum many-body systems, including symmetry-breaking orders, quantum spin liquids, and unconventional superconductivity. Our study is cemented by a particular class of Mott-insulating materials, centered around a family of two- and three-dimensional iridium oxides, whose honeycomb-like lattice structure admits peculiar magnetic interactions, the so-called Kitaev exchange. By analyzing recent experiments on these compounds, we show that this unconventional exchange is the key ingredient in describing their magnetism, and then use a combination of numerical and analytical techniques to investigate the implications for the phase diagram as well as the physics of the proximate three-dimensional quantum spin liquid phases. These long-ranged-entangled fractionalized phases should exhibit special features, including finite-temperature stability as well as unconventional high-Tc superconductivity upon charge-doping, which should aid future experimental searches for spin liquid physics. Our study explores the nature of frustration and fractionalization which can arise in quantum systems in the presence of strong spin-orbit coupling.

Fabien Alet, Aleksandra M. Walczak, Matthew P. A. Fisher