Novel phases and phenomena in quantum materials

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The progression of human civilization is intertwined with its ability to make and use materials. The ages of humanity are distinguished by the materials innovations of their time - from the Stone Age, the Bronze Age, the Iron Age, to what can be called the Silicon Age. The most important invention of the 20th century is the transistor, a device built from silicon that underlies all information technology today - the culmination of several decades of work by physicists worldwide to understand how electrons behave in solids. Our civilization is now at the dawn of the Quantum Age, which will be based on new materials that manifest the full richness of the quantum world. The new ideas that permeate the field of quantum materials today are emergence, entanglement and topology. They have both fundamental and technological implications. The research I propose explores all three. My first objective is to elucidate the nature of the pseudogap phase, a mysterious electronic phase present in cuprate superconductors, widely considered one of the major puzzles in physics. Recent ideas suggest we are dealing with a new state of matter, with topological order and an emergent Higgs field reminiscent of the Higgs boson recently discovered at CERN. To explore this possibility, I will probe the pseudogap phase of several cuprate materials with new measurements in high magnetic fields. Success here could enable the design of new high-temperature superconductors. My second objective is to understand Planckian dissipation, a remarkable phenomenon whereby the flow of electrons in some metals is limited by a scattering time set by Planck's constant. It is now clear that the highly entangled electrons involved here are deeply connected to the highest entropy objects in the cosmos: black holes. I will explore this Planckian dissipation in a number of materials, using various measurements at very low temperature. The knowledge gained by studying strange metals in my lab may advance our understanding of quantum gravity and chaos. It is well established theoretically that under certain conditions the tendency of certain magnetic insulators to form magnetic order at low temperature is frustrated, and the low-temperature state is instead a quantum spin liquid, without order. This new state of matter has not yet been solidly confirmed by experiment. However, the very recent observation of a quantized thermal Hall conductivity in one material provides tantalizing evidence of a quantum spin liquid, with topological excitations called Majorana fermions. My third major objective is to confirm this revolutionary observation and explore this bright new frontier. The definitive observation of Majorana fermions could usher in an era of topological quantum computing, a possibility that is already being explored by some corporations.