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1. Topological Hall Effect in a Topological Insulator Interfaced with a Magnetic Insulator

   https://doi.org/10.1021/acs.nanolett.0c03195  

   Li, Peng; Ding, Jinjun; Zhang, Steven S.-L.; Kally, James; Pillsbury, Timothy; Heinonen, Olle G.; Rimal, Gaurab; Bi, Chong; DeMann, August; Field, Stuart B.; et al (December 2020, Nano Letters)

   null (Ed.)
2. Transition to an excitonic insulator from a two-dimensional conventional insulator

   https://doi.org/10.1103/PhysRevB.107.075105  

   Manousakis, Efstratios (February 2023, Physical Review B)
3. Quantum Sensing of Insulator‐to‐Metal Transitions in a Mott Insulator

   https://doi.org/10.1002/qute.202000142  

   McLaughlin, Nathan_J; Kalcheim, Yoav; Suceava, Albert; Wang, Hailong; Schuller, Ivan_K; Du, Chunhui_Rita (March 2021, Advanced Quantum Technologies)

   Abstract Nitrogen vacancy (NV) centers, optically active atomic defects in diamond, have attracted tremendous interest for quantum sensing, network, and computing applications due to their excellent quantum coherence and remarkable versatility in a real, ambient environment. Taking advantage of these strengths, this paper reports on NV‐based local sensing of the electrically driven insulator‐to‐metal transition (IMT) in a proximal Mott insulator. The resistive switching properties of both pristine and ion‐irradiated VO₂thin film devices are studied by performing optically detected NV electron spin resonance measurements. These measurements probe thelocaltemperature and magnetic field in electrically biased VO₂devices, which are in agreement with theglobaltransport measurement results. In pristine devices, the electrically driven IMT proceeds through Joule heating up to the transition temperature while in ion‐irradiated devices, the transition occurs nonthermally, well below the transition temperature. The results provide direct evidence for nonthermal electrically induced IMT in a Mott insulator, highlighting the significant opportunities offered by NV quantum sensors in exploring nanoscale thermal and electrical behaviors in Mott materials. 

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4. Changes of Magnetism in a Magnetic Insulator due to Proximity to a Topological Insulator

   https://doi.org/10.1103/PhysRevLett.125.017204  

   Liu, Tao; Kally, James; Pillsbury, Timothy; Liu, Chuanpu; Chang, Houchen; Ding, Jinjun; Cheng, Yang; Hilse, Maria; Engel-Herbert, Roman; Richardella, Anthony; et al (July 2020, Physical Review Letters)
5. Evidence for a monolayer excitonic insulator

   Jia, Y. (January 2020, ArXivorg)

   null (Ed.)

   The interplay between topology and correlations can generate a variety of unusual quantum phases, many of which remain to be explored. Recent advances have identified monolayer WTe2 as a promising material for exploring such interplay in a highly tunable fashion. The ground state of this two-dimensional (2D) crystal can be electrostatically tuned from a quantum spin Hall insulator (QSHI) to a superconductor. However, much remains unknown about the nature of these ground states, including the gap-opening mechanism of the insulating state. Here we report systematic studies of the insulating phase in WTe2 monolayer and uncover evidence supporting that the QSHI is also an excitonic insulator (EI). An EI, arising from the spontaneous formation of electron-hole bound states (excitons), is a largely unexplored quantum phase to date, especially when it is topological. Our experiments on high-quality transport devices reveal the presence of an intrinsic insulating state at the charge neutrality point (CNP) in clean samples. The state exhibits both a strong sensitivity to the electric displacement field and a Hall anomaly that are consistent with the excitonic pairing. We further confirm the correlated nature of this charge-neutral insulator by tunneling spectroscopy. Our results support the existence of an EI phase in the clean limit and rule out alternative scenarios of a band insulator or a localized insulator. These observations lay the foundation for understanding a new class of correlated insulators with nontrivial topology and identify monolayer WTe2 as a promising candidate for exploring quantum phases of ground-state excitons. 

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