back to article Ames boffins mix metals to boost electron velocity

A platinum-tin “topological metal” discovered by the Department of Energy's Ames Laboratory could cut energy needed in computing applications, by moving electrons around faster. A topological quantum material – a class of stuff that includes superconductors – has a characteristic that's handy for electronics: electrons travel …

  1. frank ly

    Interesting

    "The electrons in topological quantum materials can travel close to speed of light ..."

    What does that do to the mass of the electrons? Is it the electrons themselves that move at close to the speed of light or some phenomenon, supported by electron movement, that propogates at close to the speed of light?

    1. Flocke Kroes Silver badge

      Re: Interesting

      M(v)=M(0)/sqrt(1-v^2/c^2)

      M(99% c) is about 7 times M(0). A big difference for the few electrons going fast. Electrons contribute less than 1 part in 4000 to the mass of metals, so you are not going to notice the wire putting on weight until you have most of them going at 99.99999%c. (If real life about 98% of the electrons in platinum are not going anywhere).

      1. Anonymous Coward
        Anonymous Coward

        Re: Interesting

        @"M(99% c) is about 7 times M(0)."

        Except they don't actually move at the speed of light do they? It's not like some super-heavy electron travels at near light speed through the material without hitting anything.

        A Dirac material has bound electrons and holes, in a nice regular pattern, with an energy gap such that if you filled a hole with an electron, its enough to kick the next electron into the next hole.

        It's not *a* single electron that moves from A to B its the effect of holes and electrons that does it.

        vs Copper which can free outer electrons given enough energy, which then creates a hole that can be filled. You're making the holes as you go along, and the electron #1 has to move away to create the hole before that hole can be filled by electron #2.

  2. Pascal Monett Silver badge

    A topological quantum material

    Yikes. Tried looking into that and now I feel a headache coming on.

    Nevertheless,it is fascinating to see how our global available knowledge is bubbling every which way. It is even more fascinating to see how we are capable of describing in excruciating detail how matter is defined by the way its atoms are structured, yet we still don't have room-temperature superconductors. So there are still things we don't know, even though what we do know already fills entire collections of books.

    1. willi0000000

      Re: A topological quantum material

      @Pascal Monet, according to that wiki you cited

      topological order is defined/described by robust ground state degeneracy

      i don't mind my computer getting heavier but i do mind if it starts downloading kiddie-porn as it's ground state!

  3. allthecoolshortnamesweretaken

    Find codes to enable God mode, tweak universe's parameters to increase speed of c - there, fixed it.

    BTW, very good Q & A re the electron mass - for a minute I was worried about portable computers getting heavier again in the future.

  4. Unep Eurobats
    Trollface

    I c what u did there

    But never mind that - when can I buy this tech in an obscenely expensive hi-fi connector?

  5. John Smith 19 Gold badge
    Go

    Obvious question

    Could you make an alloy where the speed of electrons exceeds the speed of light?

    1. Dave 126 Silver badge

      Re: Obvious question

      You can make an alloy where the electrons exceed the speed of light in the alloy*, but you can't make an alloy where the electrons exceed the speed of light in a vacuum.

      https://en.wikipedia.org/wiki/Cherenkov_radiation

  6. Tom 7

    Many moons ago

    ( a habit I must get out of) someone made 'thermionic' valves on silicon. Not thermionic as it was purely electrostatic fields around pointy bits that freed the electrons. I can see the above technology leading to some slightly faster (but not as fast as electrons in vacuum) technology but platinum isn't going to get any cheaper so maybe we need to wonder about freeing the little buggers from lattices and crappy crystal structures.

    1. Jan 0 Silver badge

      Re: Many moons ago

      > 'thermionic' valves on silicon.

      Errm, aren't they called "FETs"? (Field Effect Transistors). I can't see the relevance here.

  7. DocJD

    Getting technical about electron velocity

    There is a property of solids, called "mobility," used to describe the relationship between the velocity of the moving electrons and the applied electric field. (Most electrons are not moving, they are bound to their host atoms. The electrons which are free to carry electricity are called the "conduction electrons.")

    In a vacuum the force on the electron would be qE (where q is the electron charge and E is the electric field--should be a script E with a vector bar on top to differentiate from Energy, but I don't know how to format text on this site) and there is ballistic acceleration just like in a particle accelerator.

    In a solid, the electrons do not accelerate ballistically for very long because the they are continually scattering off crystal defects or other things and so they bounce around, moving in the general direction of the E field.

    In a superconductor, because of some quantum effects, electrons can pair together (Cooper Pairs) and avoid scattering.

    In non-superconducting solids the relationship is

    v = µ x E

    {That should be the Greek letter "mu" right after the = in case your display font handles optional characters differently than mine} µ stands for "mobility."

    There is a limiting AVERAGE electron velocity for a given electric field because the electrons accelerate, then scatter, then accelerate etc. That average velocity in the equation above is called the "drift velocity" because it is just an average net velocity after taking all the scattering into account.

    As E increases, the drift velocity increases. However, there is a "saturation velocity" (different for each material) beyond which increasing E doesn't help and mobility doesn't apply. That's one reason why gallium arsenide devices can be faster than silicon devices--GaAs has a higher saturation velocity. Digital GaAs has mostly fallen by the wayside because they haven't been able to shrink device dimensions as well as the silicon industry has. GaAs is still used for some high frequency analog applications. If you shrink a transistor small enough you start to get ballistic effects where some electrons cross the device without scattering, but the new material of this article is meant for the wiring interconnects, not the transistors themselves.

    So this new material basically, through quantum effects called "Dirac dispersion," just has a longer mean free path before the electrons scatter. That means a higher drift velocity for the same E field and a higher saturation velocity. (That's why the article says you can use less voltage. Electric field is voltage divided by the distance across which it is applied.) Also important is the fact that this material has a large number of conduction electrons. Total current "I" through a small metal wire on a chip is

    I = qnµEA

    where q is the charge on an electron

    n is the number of conduction electrons per cubic meter

    µ is the electron mobility

    E is the electric field (given a fixed distance d between ends of the wire, E = V/d)

    A is the cross sectional area of the wire

    So this material has a large "n" and a large "µ" which leads to a larger current for the same voltage and wire area. But the goal isn't a larger current, which would mean higher power. However, it gives the SAME current at a smaller voltage (lower power) and smaller wire area (higher density of circuits).

    I hope this clears things up.

  8. Conundrum1885

    Interesting stuff

    A while back I read that stanene (one dimensional tin) was the next wonder material and also that an iridium/silver alloy *might* be a candidate for a better conductor than copper.

    Certainly plain silver is slightly better due to the higher conductivity but this could be ideal for at least the signal lines in a chip with plain copper used for just the power.

    I've also read that the conductivity of some heavy metal alloys are better than pure metals, perhaps this is due to relativistic effects of the outer electrons in much the same way as mercury is liquid at room temperature.

  9. mi1400

    Let the nm (nanometer) race end and vnm (velocity per nanometers) race begin!!! so whose gonna trademark/patent this terminology. vnm?, VeNM?, VeNoM? VeNoMOUS? (Velocity per NanoMeter over Old µ Silicon), or VeNoMOUS? (Velocity per NanoMeter Over µ-ed Silicon)

    µ is the electron mobility

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