Low Temperature Transport in Cuprate Superconductors and Microwave-Irradiated Two-Dimensional Electron Systems

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

The goal of this theoretical project is to extract the essential physics responsible for several measured transport phenomena by performing low temperature transport calculations relevant to the systems of interest and providing guidance for future experiments. The proposed research will focus on three objectives (outlined below), two of which concern the high-Tc cuprate superconductors and the third which concerns microwave-irradiated two-dimensional electron systems. Methods employed range from purely analytical to numerical and include equilibrium and non-equilibrium diagrammatic Kubo formula calculations, semi-classical approaches, electrodynamical stability analyses, solution of the Bogoliubov-de Gennes equation, and partial wave and Born approaches to scattering problems. The first part of the project is a study of the influence of coexisting charge order on quasiparticle transport in a d-wave (cuprate) superconductor. Charge order, recently shown via scanning tunneling microscopy (STM) experiments to coexist with the d-wave superconductivity, could significantly alter the quasiparticle spectrum, gapping out the nodes if sufficiently strong. The principle investigator (PI) and students will calculate the effect this will have on low temperature thermal conductivity, a probe frequently employed to measure the dynamics of quasiparticles in the cuprates. The second part of the project is a study of the contribution of Berry phase effects to the scattering of quasiparticles from magnetic vortices in the vortex state of a d-wave (cuprate) superconductor. The quasiparticle-vortex scattering problem reduces to that of a massless anisotropic Dirac fermion scattering from a non-central effective potential (due to the superflow circulating around the vortex) subject to the Berry phase of (-1) acquired upon circling the vortex. The contribution of Berry phase effects should make the scattering cross-section sensitive to the physics of the vortex core. The PI and students will explore ways to use this effect to probe vortex core physics via thermal transport measurements. The third part of the project concerns the zero-resistance states observed in high-mobility two-dimensional electron systems driven with microwave radiation in a weak magnetic field. Theory predicts that such states are characterized by an inhomogeneous distribution of current flow. The PI and students will study the kinetics of the non-equilibrium transition into this state, the structure of the resulting current distribution, and the nature of its fluctuations. Intellectual merit: The proposed research involves concepts of basic theoretical interest including coexisting charge and superconducting order, dynamics of massless Dirac quasi-particles, Berry phase contribution to quasiparticle-vortex scattering, and non-equilibrium electron dynamics driven by microwave radiation. Broader impact: All of the proposed calculations were inspired by recent experiments and are intended to explain measured transport phenomena and provide guidance for future experiments. Hence, there is potential for impact much larger than the scope of the calculations themselves. Work on quasiparticle transport in the cuprates is intended to provide clues to the larger issue of solving the cuprate problem itself. Work on the microwave problem touches on issues of non-equilibrium pattern formation which apply to a broad range of physical systems. Graduate, undergraduate, and high school students involved in this project will learn much physics and develop a wide range of broadly applicable skills. Non-Technical Abstract: The theoretical research proposed will study transport, the flow of matter or charge, in high temperature superconductors and related materials in hopes of gaining an understanding of their novel properties. Students ranging from high school to graduate school will be involved.