Yun-Yi Pai

Postdoctoral Research Associate


Mesoscale Interplay Between Phonons and Crystal Electric Field Excitations in Quantum Spin Liquid Candidate CsYbSe2

CsYbSe2, a recently identified quantum spin liquid (QSL) candidate, exhibits strong crystal electric field (CEF) excitations. Here, we identify phonon and CEF modes with Raman spectroscopy and observe strong CEF-phonon coupling resulting in a vibronic bound state. Complex, mesoscale interplay between phonon modes and CEF modes is observed in real space. Additionally, unexpected resonant Raman excitation condition is satisfied, yielding up to third-order combination modes, with a total of 17 modes identified in the spectra. This study paves the way to coherent control of possible QSL ground states with optically accessible CEF-phonon manifolds and mesoscale engineering of CEF-phonon interactions.

Yun-Yi Pai, Claire E Marvinney, Liangbo Liang, Jie Xing, Allen Scheie, Alexander A Puretzky, Gábor B Halász, Xun Li, Rinkle Juneja, Athena S Sefat, David Parker, Lucas Lindsay, Benjamin J Lawrie, J. Mater. Chem. C, 2022, 10, 4148.

Magneto Optical Sensing beyond the Shot Noise Limit

Magneto-optical sensors including spin noise spectroscopies and magneto-optical Kerr effect microscopies are now ubiquitous tools for materials characterization that can provide new understanding of spin dynamics, hyperfine interactions, spin-orbit interactions, and charge-carrier g-factors. Both interferometric and intensity-difference measurements can provide photon shot-noise limited sensitivity, but further improvements in sensitivity with classical resources require either increased laser power that can induce unwanted heating and electronic perturbations or increased measurement times that can obscure out-of-equilibrium dynamics and radically slow experimental throughput. Proof-of-principle measurements have already demonstrated quantum enhanced spin noise measurements with a squeezed readout field that are likely to be critical to the non-perturbative characterization of spin excitations in quantum materials that emerge at low temperatures. Here, we propose a truncated nonlinear interferometric readout for low-temperature magneto-optical Kerr effect measurements that is accessible with today's quantum optical resources. We show that 10 nrad/√Hz sensitivity is achievable with optical power as small as 1 μW such that a realistic T = 83 mK can be maintained in commercially available dilution refrigerators. The quantum advantage for the proposed measurements persists even in the limit of large loss and small squeezing parameters.

Yun-Yi Pai, Claire E. Marvinney, Chengyun Hua, Raphael C. Pooser, Benjamin J. Lawrie, Adv. Quantum Technol. 2022, 5, 2100107.

Magnetostriction of α-RuCl3 Flakes in the Zigzag Phase

Motivated by the possibility of enhanced magnetic fluctuations in exfoliated α-RuCl3 flakes, we study magneto-Raman spectra of exfoliated multilayer α-RuCl3 in out-of-plane magnetic fields of −6 to 6 T at temperatures of 670 mK to 4 K. While the literature currently suggests that bulk α-RuCl3 is in an antiferromagnetic zigzag phase with R3̅ symmetry at low temperatures, we do not observe R3̅ symmetry in exfoliated α-RuCl3 at low temperatures. While we saw no magnetic field-driven transitions, the Raman modes exhibit unexpected stochastic shifts in response to the applied magnetic field that are above the uncertainties inferred from Bayesian analysis. These stochastic shifts are consistent with the emergence of magnetostrictive interactions in exfoliated α-RuCl3.

Yun-Yi Pai, Claire E. Marvinney, Matthew A. Feldman, Brian Lerner, Yoong Sheng Phang, Kai Xiao, Jiaqiang Yan, Liangbo Liang, Matthew Brahlek, Benjamin J. Lawrie, Magnetostriction of α-RuCl3 flakes in the zigzag phaseJ. Phys. Chem. C 2021, 125, 25687.

Specialized Equipment

Optical microscopy and spectroscopy at milliKelvins
Quantum transport