About

I am a postdoctoral researcher at Oak Ridge National Lab. I worked with Jeremy Levy at University of Pittsburgh for my PhD. I majorly worked on mesoscopic devices (quantum dot, electron waveguides), superconducting nanowires at LaAlO3/SrTiO3. I first-authored 2 reviews for this field (Google Scholar, My CV)

Selected Works

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.

Physics of SrTiO3-based heterostructures and nanostructures: a review

This review provides a summary of the rich physics expressed within SrTiO3-based heterostructures and nanostructures. The intended audience is researchers who are working in the field of oxides, but also those with different backgrounds (eg, semiconductor nanostructures). After reviewing the relevant properties of SrTiO3 itself, we will then discuss the basics of SrTiO3-based heterostructures, how they can be grown, and how devices are typically fabricated. Next, we will cover the physics of these heterostructures, including their phase diagram and coupling between the various degrees of freedom. Finally, we will review the rich landscape of quantum transport phenomena, as well as the devices that elicit them.

Yun-Yi Pai, Anthony Tylan-Tyler, Patrick Irvin, Jeremy Levy, Reports on Progress in Physics 81 (3), 036503 (2018).


One-Dimensional Nature of Superconductivity at the LaAlO3/SrTiO3 Interface

We examine superconductivity in LaAlO3/SrTiO3 channels with widths that transition from the 1D to the 2D regime. The superconducting critical current is independent of the channel width and increases approximately linearly with the number of parallel channels. Signatures of electron pairing outside of the superconducting regime are also found to be independent of the channel width. Collectively, these results indicate that superconductivity exists at the boundary of these channels and is absent within the interior region of the channels. The intrinsic 1D nature of superconductivity at the LaAlO3/SrTiO3 interface imposes strong physical constraints on possible electron pairing mechanisms.

Yun-Yi Pai, Hyungwoo Lee, Jung-Woo Lee, Anil Annadi, Guanglei Cheng, Shicheng Lu, Michelle Tomczyk, Mengchen Huang, Chang-Beom Eom, Patrick Irvin, Jeremy Levy, Physical review letters 120 (14), 147001 (2018).

Superconductivity in 1D Zigzag Nanowires

We investigate the effects of the geometrical shapes of the 1D nanowires created at LaAlO3/SrTiO3 in order to study the origin of superconductivity of SrTiO3, which has puzzled researchers for more than 50 years. It was recently suggested that electron pairing in SrTiO3 may be related to ferroelastic domain walls. By using conductive-AFM lithography to create 1D superconducting nanowires at the LaAlO3/SrTiO3 interface, we can investigate the influence of nanowire shape, and in particular the effect of sharp turns in the nanowire, on superconducting behavior in the nanowires. We find a significant stabilization of the superconducting state in “zigzag” wires compared with straight control wires, both created at the same time and located only a few micrometers apart. We discuss possible origins for this behavior within the context of ferroelastic domain structure that surrounds the nanowires.

Yun-Yi Pai, Megan Briggeman, Hyungwoo Lee, Jung-Woo Lee, Mengchen Huang, Jianan Li, Chang-Beom Eom, Patrick Irvin, Jeremy Levy, Bulletin of the American Physical Society APS 2019 P09.00014.

LaAlO3/SrTiO3: a tale of two magnetisms

This book chapter reviews the experimental evidence for magnetic phenomena at the LaAlO3/SrTiO3 interface. We argue that essentially all of the signatures of magnetism can be sorted into two distinct categories: (1) magnetic phases (e.g., ferromagnetic or Kondo) involving local magnetic moments and their coupling to itinerant electrons; (2) metamagnetic effects that are mediated by attractive electron-electron interactions that do not involve local moments. We review possible candidates for the local moments that give rise to the ferromagnetic phases and focus on arguments for one potential source: oxygen vacancies. For the metamagnetic transport signatures, band-structure effects (e.g., Lifshitz transition) and strong attractive electron-electron interaction can help consolidate disparate experimental findings.

Yun-Yi Pai, Anthony Tylan-Tyler, Patrick Irvin, Jeremy Levy, Vol. 2, Ch.12, in Spintronics Handbook, Second Edition: Spin Transport and Magnetism, 2nd ed., CRC Press 2019.

Conference Talks

Honor

Visiting

Teaching

Teaching Assistant, University of Pittsburgh, Pittsburgh, PA

Lab Assistant Cornell University, Ithaca, NY

Outreach