Seminar By Rong Cong, Brown University and Center for Intergrated Nanotechnology (CINT)

Title: Orbital glass induced unconventional magnetic order in a correlated insulator

Host: Arneil Reyes

Abstract:Intertwined electronic and orbital degrees of freedom in strongly correlated materials with strong spin-orbit-coupling has shown to give rise to many exotic quantum phenomena, especially to emergent quantum phases and transitions [1]. Coupling between the spin and orbit degrees of freedom can lead to two different viable order parameters: magnetic (spin) order and multi-polar (orbital) order. In this talk, I will present our recent direct observation of an orbital glass state caused by such a coupling in the 5d¹ relativistic Mott insulator Ba₂NaOsO₆ by implementing a technique that is able to independently probe interactions of different symmetries [2]. I will talk about simultaneous measurements of the fluctuations in the spin and orbital order using a Hahn echo sequence, giving an unprecedented view into the nature of a complex spin-orbit phase transition. We observe short-range quadrupolar order up to room temperature and a dramatic increase of orbital fluctuations near the phase transition. The presence of quadrupolar fluctuations well above the phase transition solves a long-standing puzzle of missing entropy in this material. In the end of the talk, I will transition the focus and discuss our most recent progress in using resistive detected magnetic resonance techniques to probe spin properties in 2D quantum materials and phases.

[1] Witczak-Krempa, William, et al. "Correlated quantum phenomena in the strong spin-orbit regime." Annu. Rev. Condens. Matter Phys. 5.1 (2014): 57-82.

[2] Carr, Stephen, et al. "Multi-modal spectroscopy of phase transitions." Phys. Rev. B 108, 054421 (2023)