• Graphene quantum dots show promise as no

    From ScienceDaily@1:317/3 to All on Mon Mar 6 21:30:30 2023
    Graphene quantum dots show promise as novel magnetic field sensors
    Physicists found that speeding electrons trapped in circular loops in
    graphene quantum dots are highly sensitive to external magnetic fields

    Date:
    March 6, 2023
    Source:
    University of California - Santa Cruz
    Summary:
    Trapped electrons traveling in circular loops at extreme speeds
    inside graphene quantum dots are highly sensitive to external
    magnetic fields and could be used as novel magnetic field sensors
    with unique capabilities, according to a new study.


    Facebook Twitter Pinterest LinkedIN Email
    FULL STORY ========================================================================== Trapped electrons traveling in circular loops at extreme speeds inside
    graphene quantum dots are highly sensitive to external magnetic fields and could be used as novel magnetic field sensors with unique capabilities, according to a new study.


    ========================================================================== Electrons in graphene (an atomically thin form of carbon) behave as
    if they were massless, like photons, which are massless particles of
    light. Although graphene electrons do not move at the speed of light,
    they exhibit the same energy-momentum relationship as photons and can
    be described as "ultra- relativistic." When these electrons are confined
    in a quantum dot, they travel at high velocity in circular loops around
    the edge of the dot.

    "These current loops create magnetic moments that are very sensitive
    to external magnetic fields," explained Jairo Velasco Jr., associate
    professor of physics at UC Santa Cruz. "The sensitivity of these current
    loops stems from the fact that graphene electrons are ultra-relativistic
    and travel at high velocity." Velasco is a corresponding author of a
    paper on the new findings, published March 6 in Nature Nanotechnology. His group at UC Santa Cruz used a scanning tunneling microscope (STM) to
    create the quantum dots in graphene and study their properties. His collaborators on the project include scientists at the University of Manchester, U.K., and the National Institute for Materials Science
    in Japan.

    "This was highly collaborative work," Velasco said. "We did the
    measurements in my lab at UCSC, and then we worked very closely with theoretical physicists at the University of Manchester to understand
    and interpret our data." The unique optical and electrical properties
    of quantum dots -- which are often made of semiconductor nanocrystals --
    are due to electrons being confined within a nanoscale structure such that their behavior is governed by quantum mechanics. Because the resulting electronic structure is like that of atoms, quantum dots are often called "artificial atoms." Velasco's approach creates quantum dots in different
    forms of graphene using an electrostatic "corral" to confine graphene's speeding electrons.

    "Part of what makes this interesting is the fundamental physics
    of this system and the opportunity to study atomic physics in the ultra-relativistic regime," he said. "At the same time, there are
    interesting potential applications for this as a new type of quantum
    sensor that can detect magnetic fields at the nano scale with high
    spatial resolution." Additional applications are also possible,
    according to co-first author Zhehao Ge, a UCSC graduate student in
    physics. "The findings in our work also indicate that graphene quantum
    dots can potentially host a giant persistent current (a perpetual
    electric current without the need of an external power source) in a
    small magnetic field," Ge said. "Such current can potentially be used
    for quantum simulation and quantum computation." The study looked at
    quantum dots in both monolayer graphene and twisted bilayer graphene. The graphene rests on an insulating layer of hexagonal boron nitride, and
    a voltage applied with the STM tip creates charges in the boron nitride
    that serve to electrostatically confine electrons in the graphene.

    Although Velasco's lab uses STM to create and study graphene quantum dots,
    a simpler system using metal electrodes in a cross-bar array could be
    used in a magnetic sensor device. Because graphene is highly flexible,
    the sensor could be integrated with flexible substrates to enable magnetic field sensing of curved objects.

    "You could have many quantum dots in an array, and this could be used
    to measure magnetic fields in living organisms, or to understand how the magnetic field is distributed in a material or a device," Velasco said.

    The co-first authors of the paper are Zhehao Ge, a graduate student
    in Velasco's lab at UCSC, and Sergey Slizovskiy at the University of Manchester.

    Vladimir Fal'ko at the University of Manchester is a corresponding author,
    and the other coauthors include Peter Polizogopoulos, Toyanath Joshi,
    and David Lederman at UC Santa Cruz, and Takashi Taniguchi and Kenji
    Watanabe at the National Institute for Materials Science in Japan. This
    work was supported in part by the National Science Foundation and the
    Army Research Office.

    * RELATED_TOPICS
    o Matter_&_Energy
    # Spintronics # Graphene # Physics # Quantum_Physics #
    Quantum_Computing # Materials_Science # Medical_Technology
    # Engineering_and_Construction
    * RELATED_TERMS
    o Particle_accelerator o Quantum_dot o
    Magnetic_resonance_imaging o Magnetic_field o Radiant_energy
    o Transformer o Quantum_number o Lewis_structure_in_chemistry

    ========================================================================== Story Source: Materials provided by
    University_of_California_-_Santa_Cruz. Original written by Tim
    Stephens. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Zhehao Ge, Sergey Slizovskiy, Peter Polizogopoulos, Toyanath Joshi,
    Takashi Taniguchi, Kenji Watanabe, David Lederman,
    Vladimir I. Fal'ko, Jairo Velasco. Giant orbital magnetic
    moments and paramagnetic shift in artificial relativistic
    atoms and molecules. Nature Nanotechnology, 2023; DOI:
    10.1038/s41565-023-01327-0 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2023/03/230306143430.htm

    --- up 1 year, 1 week, 10 hours, 50 minutes
    * Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)