• New thinnest mirrors on the planet use quantum ‘excitons’ to reflect light

    Date:24 January 2018 Author: Elise Kirsten Tags:, ,

    The thinnest mirrors in the world – sheets of molybdenum diselenide (MoSe2), each just one atom wide – have been built concurrently by two separate teams of scientists.

    Teams at Harvard University and the Institute for Quantum Electronics in Zurich developed these mirrors at the same time, and described in a pair of papers published Thursday, 18 January, in the journal Physical Review Letters.

    Despite being so absolutely minuscule, approaching the minimum thickness an object could possibly have while remaining reflective under the laws of physics – the mirrors reflected a great deal of the light shone on them. Mounted on a silicon base, the Harvard mirror reflected 85 percent of the light that struck it, according to the first paper. The other mirror, built in Zurich and mounted on silica (an oxidized form of silicon), reflected 41 percent, the Swiss research said. “Both mirrors reflected light in the 780-nanometer range, a deep red,” according to LiveScience.

    The researchers said that these engineering feats push the limits of what’s possible in this physical universe, but not only that, the researchers also say that the mirrors could be useful in the real world.

    Real-world application
    The potential of these ultra-thin mirrors could include application by optoelectronic engineers — people who make uses of photonics technology, working on tiny optical chips, fiber-optic networks, and other mechanisms that rely on controlling small beams of photons.

    According to the researchers, there is more to MoSe2 than just acting as a minute mirror. MoSe2’s reflectivity can be increased or decreased, the electrical charge applied to the substance. And the Zurich team wrote that this effect happens and can be altered quickly, so it could be useful in several high-speed computing applications.

    How it works
    The particular ways electrons behave as they surround the material’s nuclei allows MoSe2 to function as a mirror. This substance tends to form gaps in its electron fields (as described in a previous paper published in September 2017), these gaps are areas where no electron is present but an electron could orbit.

    When an atom absorbs a photon or particle of light, there’s a high probability that an electron will jump from a lower-energy orbit to a higher-energy orbit. This creates a gap called an “electron hole” in the electron field. Electrons surrounding MoSe2 hit with certain wavelengths of light, they are especially likely to behave this way.

    “Electrons are negatively charged quantum objects. And the protons in atomic nuclei are positively charged. So, and this is the tricky bit, those electron holes take on some of the positive charge from the protons in the nuclei. That allows the holes to behave a bit like particles, even though they’re really the absence of particles.

    Nearby, negatively charged electrons attract those fake particles, and under certain circumstances, pair up with them to form weird quantum-mechanical objects called excitons. Those excitons emit light of their own, interfering with incoming light and sending it back the way it came — just like the mirror in your bathroom,” reports LiveScience.

    Source: LiveScience

     

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