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Ku, Mark Jen-Hao

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Ku

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Mark Jen-Hao

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Ku, Mark Jen-Hao

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2020 - 20212

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Author's Publications: search.filters.isAuthorOfPublication.16547314-a080-47c6-bdab-02b8d8082158

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    Imaging viscous flow of the Dirac fluid in graphene
    (Springer Science and Business Media LLC, 2020-07-22) Ku, Mark Jen-Hao; Zhou, Tony X.; Li, Qing; Shin, Young J.; Shi, Jing K.; Burch, Claire; Anderson, Laurel E.; Pierce, Andrew T.; Xie, Yonglong; Hamo, Assaf; Vool, Uri; Zhang, Huiliang; Casola, Francesco; Taniguchi, Takashi; Watanabe, Kenji; Fogler, Michael M.; Kim, Philip; Yacoby, Amir; Walsworth, Ronald L.
    The electron-hole plasma in charge-neutral graphene is predicted to realize a quantum critical system whose transport features a universal hydrodynamic description, even at room temperature. This quantum critical “Dirac fluid” is expected to have a shear viscosity close to a minimum bound, with an inter-particle scattering rate saturating at the Planckian time ℏ/(kB T). While electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene, a clear demonstration of viscous behavior at the charge neutrality point remains elusive. In this work, we directly image viscous Dirac fluid flow in graphene at room temperature via measurement of the associated stray magnetic field. Nanoscale magnetic imaging is performed using quantum spin magnetometers realized with nitrogen vacancy (NV) centers in diamond. Scanning single-spin and wide-field magnetometry reveals a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge neutrality point, establishing the viscous transport of the Dirac fluid. This measurement is in contrast to the conventional uniform flow profile imaged in a metallic conductor and also in a low-mobility graphene channel. Via combined imaging-transport measurements, we obtain viscosity and scattering rates, and observe that these quantities are comparable to the universal values expected at quantum criticality. This finding establishes a nearly-ideal electron fluid in charge-neutral, high-mobility graphene at room temperature. Our results pave the way to study hydrodynamic transport in quantum critical fluids relevant to strongly-correlated electrons in high-Tc superconductors. This work also highlights the capability of quantum spin magnetometers to probe correlated-electronic phenomena at the nanoscale.
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    Directional Detection of Dark Matter With Diamond
    (IOP Publishing, 2021-03-10) Marshall, Mason; Turner, Matthew; Ku, Mark Jen-Hao; Phillips, David; Walsworth, Ronald
    Searches for WIMP dark matter will in the near future be sensitive to solar neutrinos. Directional detection offers a method to reject solar neutrinos and improve WIMP searches, but reaching that sensitivity with existing directional detectors poses challenges. We propose a combined atomic/particle physics approach using a large-volume diamond detector. WIMP candidate events trigger a particle detector, after which spectroscopy of nitrogen vacancy centers reads out the direction of the incoming particle. We discuss the current state of technologies required to realize directional detection in diamond and present a path towards a detector with sensitivity below the neutrino floor.