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Science Forum

  1. Standard member sonhouse
    Fast and Curious
    09 Mar '11 18:31 / 1 edit
    Here is an article about transferring spin angular momentum of electrons to perhaps engender a new kind of computer memory, which is great.

    My question is, suppose an electron does give up some of it's angular momentum, what happens to the electron? What happens if you somehow can totally stop the angular momentum of electrons? What does that mean, and do electrons naturally come with a spectrum of angular momentum energies or are they all spinning with the same momentum?
  2. Subscriber AThousandYoung
    Do ya think?
    10 Mar '11 07:17
    Is it the angular momentum of the electron's spin or it's orbit?

    Where is the article?
  3. Standard member sonhouse
    Fast and Curious
    10 Mar '11 17:42
    Originally posted by AThousandYoung
    Is it the angular momentum of the electron's spin or it's orbit?

    Where is the article?
    Well, picky picky Here it is:
    http://www.physorg.com/news/2011-03-physicists-current-induced-torque-nonvolatile-magnetic.html

    Thought I had already done that, sorry.
  4. Standard member DeepThought
    Losing the Thread
    15 Mar '11 05:13
    Originally posted by sonhouse
    Here is an article about transferring spin angular momentum of electrons to perhaps engender a new kind of computer memory, which is great.

    My question is, suppose an electron does give up some of it's angular momentum, what happens to the electron? What happens if you somehow can totally stop the angular momentum of electrons? What does that mean, and ...[text shortened]... e with a spectrum of angular momentum energies or are they all spinning with the same momentum?
    I had a quick look at the article. They skim over that a little. Electrons can have 2 possible spins, since they are charged this means they have a magnetic moment which can have 2 states, so they are ideal for computer memory if you can manipulate them. The two spin states for the electron are normally labeled by the spin component in some reference direction (+1/2 or -1/2) - in this case there's a preferred axis provided by the applied field. They differ in which way round the electron is spinning, not the overall rate. The spectrum consists of only those 2 states, if an elementary particle has more or fewer than 2 possible spin states available it means it is not an electron. You cannot stop them spinning altogether as their spin is one of the quantum numbers that makes them an electron.

    The Wikipedia page on "spin (physics)" gives a reasonable qualitative explanation given it was probably written by an undergraduate, but the mathematical explanation in the second half of the page seems to assume that you already know what you're reading.
  5. Standard member sonhouse
    Fast and Curious
    15 Mar '11 15:04
    Originally posted by DeepThought
    I had a quick look at the article. They skim over that a little. Electrons can have 2 possible spins, since they are charged this means they have a magnetic moment which can have 2 states, so they are ideal for computer memory if you can manipulate them. The two spin states for the electron are normally labeled by the spin component in some reference ...[text shortened]... on in the second half of the page seems to assume that you already know what you're reading.
    So the article was wrong when it said 'transfered SOME of its angular momentum'?
    I gather you can't transfer SOME momentum that way. So what is really happening?
  6. Standard member DeepThought
    Losing the Thread
    15 Mar '11 17:43
    Originally posted by sonhouse
    So the article was wrong when it said 'transfered SOME of its angular momentum'?
    I gather you can't transfer SOME momentum that way. So what is really happening?
    Scientific journalists often oversimplify to the point where they say something like that and end up making things more confusing, it's a little difficult to see what they mean - they may not have a science background, but a general journalism one.

    The problem is that this is all happening in a semi-conductor and the presence of a lattice changes things, the fundamental spin rules don't change, but angular momentum can also be transferred to the lattice, so on average only some of the angular momentum is transferred to the applied field - I assume that is what they mean.
  7. Standard member sonhouse
    Fast and Curious
    19 Mar '11 10:08
    Originally posted by DeepThought
    Scientific journalists often oversimplify to the point where they say something like that and end up making things more confusing, it's a little difficult to see what they mean - they may not have a science background, but a general journalism one.

    The problem is that this is all happening in a semi-conductor and the presence of a lattice changes thin ...[text shortened]... of the angular momentum is transferred to the applied field - I assume that is what they mean.
    Here is some new work on just this subject:

    Engineers trying to develop next gen transistors and such made a realization that space may be quantized, something like on a chess board or Hex board:

    http://www.physorg.com/news/2011-03-space-chessboard.html
  8. 19 Mar '11 10:56
    Originally posted by sonhouse
    Here is some new work on just this subject:

    Engineers trying to develop next gen transistors and such made a realization that space may be quantized, something like on a chess board or Hex board:

    http://www.physorg.com/news/2011-03-space-chessboard.html
    This is not really a new idea (though it appears it does increase experimental evidence for it) - for example in the second quantization formalism of quantum mechanics space is already assumed to be discrete.
  9. Standard member DeepThought
    Losing the Thread
    20 Mar '11 00:42
    Originally posted by KazetNagorra
    for example in the second quantization formalism of quantum mechanics space is already assumed to be discrete.
    No it's not. Quantum field theory takes place in the same space time as classical field theory. In deriving the path integrals you might initially have a discrete lattice, but you take the continuum limit. Discrete space-times are thought to be a consequence of string theory by some researchers, but there is no requirement for a discrete space-time in the standard model.
  10. 20 Mar '11 09:33
    Originally posted by DeepThought
    No it's not. Quantum field theory takes place in the same space time as classical field theory. In deriving the path integrals you might initially have a discrete lattice, but you take the continuum limit. Discrete space-times are thought to be a consequence of string theory by some researchers, but there is no requirement for a discrete space-time in the standard model.
    Depends on how you look at it, I guess. It's at least not a far leap in logic from discretized operators in space to discrete spacetime.