The complex interplay between the quantum degrees of freedom in oxides is known to cause a rich variety of intriguing emergent phenomena. While model Hamiltonians are often used to capture the underlying physics, they could be difficult to solve theoretically. This challenge calls for model-based designs for materials synthesis and measurement controls to experimentally simulate the corresponding behaviors. In this talk, I will review examples from our recent work that exploited this strategy to investigate the correlation-topology interplay in the Hubbard Hamiltonian, metallization of the dipolar spin ice Hamiltonian, and competition between orthogonal magnetic anisotropy. The results showcase the use of symmetry as the guide to implement the key ingredients of the targeted model in the experiment designs, which synergistically combine atomic layering synthesis, single-crystal growth, ultralow-temperature high-field transport measurements, and/or synchrotron x-ray scattering with multi-modal controls. New opportunities enabled by most recent capability advances will be discussed as well.

Symmetry is central to our understanding of natural phenomena. And a Sagnac interferometer, first invented by George Sagnac for the detection of the hypothetical “ether” in the Michelson–Gale experiment [1] a century ago, is intrinsically sensitive to broken time-reversal symmetry (TRS). In this talk, I will first describe a loop-less version of the Sagnac interferometer and microscope that has achieved unprecedented nanoradian level Kerr and Faraday sensitivity even at DC. With this Sagnac technique, I will discuss a few examples of our Sagnac studies of 2D magnetism and superconductivity. In exfoliated Cr2Ge2Te6 (CGT), we report [2] the discovery of intrinsic ferromagnetism in 2D van der Walls crystals, defying the well-known Mermin-Wagner theorem. In epitaxial Bi/Ni bilayer samples, we report [3] the observation of 2D superconductivity that spontaneously breaks TRS, which might have an order parameter with a nonzero phase winding number around the Fermi surface, making it a rare example of a 2D topological superconductor. In the Fe-Chalcogenide superconductor FeTe1−xSex, we found intertwined magnetism and superconductivity in its topological surface state [4]. Additionally, our study on exfoliated FeTe1−xSex flakes indicates the existence of a chiral edge state that may be useful for robust quantum computing (unpublished).

1. “The Effect of the Earth’s Rotation on the Velocity of Light, II” Michelson, A. A.; Gale, Henry G. (1925). Astrophysical Journal. 61: 140.
2. “Discovery of intrinsic ferromagnetism in 2D van der Waals crystals”, Nature, 546, 265-269 (2017).
3. “Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel Bilayers”, Science Advances, 3, 3, e1602579 (2017).
4. “Revealing the Origin of Time-Reversal Symmetry Breaking in Fe-Chalcogenide Superconductor FeTe1−xSex”. Physical Review Letters, 130(4):046702 (2023)

In the study of quantum matter, measurements have traditionally been viewed as a means of learning about a system. Measurements can, nevertheless, play a more active role—generating novel quantum phenomena that may be difficult or impossible to realize in measurement-free settings. As an interesting example, I will discuss how measurements can dramatically alter universal properties of quantum systems tuned to a phase transition. I will also highlight a path to experimental realization in analog quantum simulators based on Rydberg atom arrays. Finally, I will describe how these ideas inform optimization of quantum teleportation protocols against imperfections—establishing a long-term quantum science application of ‘measurement-altered quantum criticality’.