My research addresses the macroscopic quantum physics of emergent quantum matter at low temperatures. Active research interests include studies of superconductors, superfluids, supersolids, spin liquids, monopole liquids and heavy-fermion systems. Virtually all of these projects have involved the development of specialized scientific instruments, including scanning tunneling microscopes, quantum interferometers, quantum mechanical oscillators and spin noise spectrometers. For instance, we introduced the Scanned Josephson Tunneling Microscope (SJTM), featuring a superconducting scanning probe, for atomic-scale visualization of electron-pair condensates. This instrument allowed my team to discover, in a cuprate superconductor, the elusive ‘Cooper-pair density wave’ state which was theoretically predicted in 1960s.
We are currently expanding the capability of SJTM to lower temperatures and high magnetic fields, which will allow us to determine the phase diagram of the pair density wave state and search for this state in other superconductors. Additionally, we have developed and introduced the capability to measure the momentum-space symmetry of the superconducting order parameters and thus of their Cooper pair wavefunction. This information is key to complete theoretical understanding of all complex superconductors.Now, we are expanding and generalizing this powerful technique for use with topological, heavy fermion and high-temperature superconductors. We are also developing and employing spin noise spectroscopy, which has recently allowed us to detect the magnetic noise signature generated by a fluid of emergent magnetic monopoles in the magnetic insulator Dy2Ti2O7. Further developments of this method may allow us to establish the spin noise ‘fingerprints’ of other exotic magnetic states, including the elusive quantum spin liquid, characterized by long-range quantum entanglement.
My group uses artificial intelligence approaches for accelerated discovery in the field of quantum materials. In collaboration with our Cornell colleague Prof. Eun-Ah Kim, we are developing artificial neural network techniques for analysis of quantum materials data archives, with the goal of developing automated identification of distinct quantum phases of matter in large volumes of data.
Emergent Phenomena in Quantum Systems