MSGID: 1:317/3 6406bdfa   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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.   
      
      
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   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   
      
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