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More on Spintronics 202

Posted by michael from the round-and-round-she-goes dept.
segment writes "'We have discovered the equivalent of a new 'Ohm's Law' for spintronics - the emerging science of manipulating the spin of electrons for useful purposes,' says Shoucheng Zhang, a physics professor at Stanford. 'Unlike the Ohm's Law for electronics, the new 'Ohm's Law' that we've discovered says that the spin of the electron can be transported without any loss of energy, or dissipation. Furthermore, this effect occurs at room temperature in materials already widely used in the semiconductor industry, such as gallium arsenide.'"
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More on Spintronics

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  • arse.... (Score:2, Funny)

    by E1v!$ ( 267945 )
    materials already widely used in the semiconductor industry, such as gallium arsenide.'"

    Man it seems like that stuff NEVER goes away. Haven't we invented 10 technologies to get rid of that stuff already?

    • ...My physical electronics prof (who has over 80 patents in chip fab) told us that germanium had certain problems in collecting electrons. Which is why gallium hasn't gone away yet. But I'm not 100% sure (it was a while ago) so I could very well be wrong.

  • The Article (Score:3, Informative)

    by TubeSteak ( 669689 ) on Saturday August 09, 2003 @08:26PM (#6657301) Journal
    Contact: Dawn Levy
    dawnlevy@stanford.edu [mailto]
    650-725-1944
    Stanford University [stanford.edu]
    'Spintronics' could enable a new generation of electronic devices, physicists say Moore's Law - a dictum of the electronics industry that says the number of transistors that fit on a computer chip will double every 18 months - may soon face some fundamental roadblocks. Most researchers think there'll eventually be a limit to how many transistors they can cram on a chip. But even if Moore's Law could continue to spawn ever-tinier chips, small electronic devices are plagued by a big problem: energy loss, or dissipation, as signals pass from one transistor to the next. Line up all the tiny wires that connect the transistors in a Pentium chip, and the total length would stretch almost a mile. A lot of useful energy is lost as heat as electrons travel that distance.

    Theoretical physicists at Stanford and the University of Tokyo think they've found a way to solve the dissipation problem by manipulating a neglected property of the electron - its ''spin,'' or orientation, typically described by its quantum state as ''up'' or ''down.'' They report their findings in the Aug. 7 issue of Science Express, an online version of Science magazine. Electronics relies on Ohm's Law, which says application of a voltage to many materials results in the creation of a current. That's because electrons transmit their charge through the materials. But Ohm's Law also describes the inevitable conversion of electric energy into heat when electrons encounter resistance as they pass through materials.

    ''We have discovered the equivalent of a new 'Ohm's Law' for spintronics - the emerging science of manipulating the spin of electrons for useful purposes,'' says Shoucheng Zhang, a physics professor at Stanford. Professor Naoto Nagaosa of the University of Tokyo and his research assistant, Shuichi Murakami, are Zhang's co-authors. ''Unlike the Ohm's Law for electronics, the new 'Ohm's Law' that we've discovered says that the spin of the electron can be transported without any loss of energy, or dissipation. Furthermore, this effect occurs at room temperature in materials already widely used in the semiconductor industry, such as gallium arsenide. That's important because it could enable a new generation of computing devices.''

    Zhang uses a celestial analogy to explain two important properties of electrons - their center of mass and their spin: ''The Earth has two kinds of motion. One is that its center of mass moves around the Sun. But the other is that it also spins by itself, or rotates. The way it moves around the Sun gives us the year, but the way it rotates around by itself gives us the day. The electron has similar properties.'' While electronics uses voltage to move an electron's center of mass, spintronics uses voltage to manipulate its spin.

    The authors predict that application of an electric field will cause electrons' spins to flow together collectively in a current. The applied electric force, the spins and the spin current align in three different directions that are all perpendicular to each other (see film of the effect at http://news-service.stanford.edu/news/2003/august2 0/zhang-video-820.html [stanford.edu]).

    ''This is a remarkable thing,'' explains Zhang. ''I push you forward and you move sideways - not in the direction that I'm pushing you.''

    So far, only superconductors are known to carry current without any dissipation. However, extremely low temperatures, typically -150 degree Celsius, are required for the dissipationless current to flow inside a superconductor. Unlike electronic superconductors being investigated in advanced laboratories throughout the world, whose operating temperatures are too low to be practical in commercial devices, Zhang, Nagaosa and Murakami theorize that the dissipationless spin cur

  • Ohms = 0 (Score:2, Interesting)

    by E1v!$ ( 267945 )
    Superconductors anyone? If we could figure out a way to transfer some of the spin to linear motion at the end of a wire..

    YEA BABY!

  • Not so remarkable (Score:5, Funny)

    by Anonymous Coward on Saturday August 09, 2003 @08:28PM (#6657310)
    The applied electric force, the spins and the spin current align in three different directions that are all perpendicular to each other ''This is a remarkable thing,'' explains Zhang. ''I push you forward and you move sideways - not in the direction that I'm pushing you.''

    Same thing happens with me after about a six pack.

  • entanglement? (Score:3, Interesting)

    by andrewl6097 ( 633663 ) * on Saturday August 09, 2003 @08:33PM (#6657323)
    OK, I RTFA, and it wasn't what I was expecting.

    Isn't it a property of these kinds of things that you can seperate two electrons (or some subatomic particle, can't remember) and change one's spin, and the other, no matter how far away, will instantly change? I recall an experiment in which this worked over a distance of six miles. Wouldn't this be the perfect interconnect? No wires at all?

    • Re:entanglement? (Score:3, Informative)

      by MrLint ( 519792 )
      I think you are referring to spooky action at a distance [arstechnica.com]

    • Re:entanglement? (Score:5, Informative)

      by fiartruck ( 578161 ) on Saturday August 09, 2003 @09:10PM (#6657416)
      If I recall correctly there are a few problems with this method of transmission:

      1. Once you transmit using a particular electron pair you can't use that pair again, so you have to pre-prepair as many electron pairs as you think you will need for a transmission.
      2. Creating perfectly isolated pairs is difficult. The basic problem is making sure the pairs you create aren't entangled with any other qubits (and using extra bits to do error correction because its next to impossible produce pure states) People are working on efficient ways to do this, but although it won't be prohibitive for, say, prearranged data transmission it really wouldn't be economical for circuits.

      This article is talking about something else aparently: some kind of wave of spin -- like a current.
      (BTW in the method you're talking about one doesn't exactly "change the spin" ... its a bit more complicated than that.)
      • If I recall correctly there are a few problems with this method of transmission:

        You can't actually use it to transmit anything. When either person makes a measurement on their own they always get a random result. It's just that one person's random results will always match up in certain patterns when you compare them with the other person's results.

        It does allow something really weird though. If you make a measurement and transmit a single bit in a normal sub-light way and THEN the other person makes a m

    • Re:entanglement? (Score:5, Informative)

      by Angry Black Man ( 533969 ) <`vverysmartman' `at' `hotmail.com'> on Saturday August 09, 2003 @09:15PM (#6657433) Homepage
      your reffering to the Alan Aspect [google.com] experiment, which was built on top of the EPR thought experiment(Einstein-podolsky-rosen [google.com].

    • Re:entanglement? (Score:4, Informative)

      by backdoorstudent ( 663553 ) on Saturday August 09, 2003 @11:22PM (#6657883)
      Yes, but the receiver would get nothing but noise since you cannot control the direction of spin. You'll have only a probability of the spin being in a specific direction. So you cannot modulate the signal to send information. The receiver will only have corresponding results if you compare notes later. That is, sender and receiver will always have corresponding states of their entangled particles, but because the states are random they cannot carry information. It's presently a metaphysical question about how entangled particles always match states over long distances. This "quantum nonlocality" is one of the greatest scientific mysteries of the world.

  • What does this have to do with ohm's law? (Score:4, Insightful)

    by Jason1729 ( 561790 ) on Saturday August 09, 2003 @08:35PM (#6657335)
    Ohm's law is "voltage dropped across a load is directly proportional to the current through the load, for a constant load". What does this have to do with the law the article talks about?

    Jason
    ProfQuotes [profquotes.com]

    • Re:What does this have to do with ohm's law? (Score:5, Informative)

      by Daetrin ( 576516 ) on Saturday August 09, 2003 @09:43PM (#6657518)
      Ohm's law is "voltage dropped across a load is directly proportional to the current through the load, for a constant load". What does this have to do with the law the article talks about?

      Ohm's law describes the creation of a current by the application of a voltege. This new law seems to describe the creation of a, um, whatever you want to call the "movement" of the spin of an electron, by the application of an electric field. Or more accuratly, it probably describes the movement of a group of spins.

      They're describing generally the same kind of action, at least viewed in a certain way, in two different kind of "substances."

    • Re:What does this have to do with ohm's law? (Score:5, Informative)

      by wass ( 72082 ) on Sunday August 10, 2003 @11:49AM (#6659952)
      Ohm's law, in the form you've most likely heard it, relates the Voltage across a device to the current flowing through it. Microscopically, a more popular version of Ohm's Law relates the applied electric field to the local current density, which allows for spatial variations.

      Not all devices are linear and follow Ohm's law over wide ranges of voltages/currents. Sometimes there's an exponential relation, or others. For example, in a superconducting filament, one has bizarre quantum effects kicking in for the effectively 1-D system, and the effective Ohm's law has the voltage proportional to exp[I]. Only linear (and hence Ohmic) at small currents.

      Then there's the Hall Effect where a current flowing through a wire (can be a thin foil) with a perpendicular magnetic field will cause the current carriers (either electrons or holes) to drift to one side or the other of the foil [F=q(v x B)] where the F is the force, v is the carrier velocity, and B is the magnetic field. x is a cross-product (v and B are vectors, so is F). In other words, the force acting on the carriers is perpendicular to the B-field and the current velocity, and creates a transverse voltage, often called the "Hall Voltage". So you now have a current creating a transverse voltage, which lets you apply a variant of Ohm's Law to define a Hall Resistance, sometimes called Rxy, where Rxy=Vhall/I (could be a non-linear relation too).

      So in this case of spintronics, they define another variant of Ohm's Law to relate the current of the spins in relation to an applied electric field. Note that the transfer of spins across the device probably doesn't correspond to the actual transfer of electrons, but a signal propagation of spins instead.

      Finally, there are other cases where one can have current flow without resistance. One case is superconductors. Another is the so-called Quantum Hall Effect. However, both of these occur at cryogenic temperatures.

  • Communication faster than teh speed of light that is very slow.

    In theory you take a rod that goes from one galaxy to a distant galaxy many many lighyt years away. With a slight movement on one end of the rod, ina back and forth movement, the other end moves, effectively allowing communication based upon movement. Movement that is far slower than the speed of light but able to communicate to distances beyond the limitation of the speed of light.

    Of course that is a simple theory only to communicate the con
    • The problem: no object is truly "solid." You might push on one end of the rod -- how long it takes the force to propogate across the galaxy is another question.
    • Won't happen. The rod doesn't move as a rigid whole.

      Nick Herbert describes this fallacy in Faster Than Light: Superluminal Loopholes in Physics [amazon.com].
      • :) I think there are even more obvious issues as to why the rod would not work, like the fact as galaxies spin the location of the end of the rod would as well be moving through galaxies it would exist in and passing thru... bound to be hit by something...

        But the point I was making was in regards to aproaching a problem or situation from a different perspecitve and finding a much easier solution.

        If two objects are traveling at near the speed of light, but in opposite directions and you were on one of them
        • If two objects are traveling at near the speed of light, but in opposite directions and you were on one of them as the other was approaching in on a collision course, would you see it comming? Or would it look like a black hole?

          Could they collide if they were traveling in opposite directions? I guess they could, but that would it might make it clearer if you said they were traveling towards each other at the start.

          Ok, so I poked a little fun of the question, but really, unless the object travelling towar
          • The space suit and flashlight would interfer with the perfectly reflective nature of the sphere where size (relative to the sphere), position and movement of the space suit and flashlight beam factors would result in any number of variations. Even the color of the space suit and flashlight will have an influence on the effect and affect.

            To some extent this can be calculated by using ray tracing animation software. But it should be noted that additional calculations would need to be taken into account as va
        • If two objects are traveling at near the speed of light, but in opposite directions and you were on one of them as the other was approaching in on a collision course, would you see it comming? Or would it look like a black hole?

          The speed of light is not absolute. Its relative to the movement of the observer. When you say "near the speed of light," you must always specify whose reference point are you referring to? An observer at rest, or the objects reference point? Either way, there is no fallacy.

          anyway
    • Reading the article make me recall how I believe that the cooling of some elements to achieve superconductivity is in reality just the syncing of the relative atomic speed of the elements involved.

      This spin issue seems to suggest syncing as well, but without the concerns of tempature constraints below room tempature.
    • effectively allowing communication based upon movement.

      The rod would move at the speed of sound through its medium (the speed of sound varies largely depending on its medium). IN any case, it would be MUCH slower than the speed of light.

      Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons. Two elextrons in a pair alwats spin in reverse directions. Even if the two electrons are 1000 miles apart, if you polarize one (change the spin), then the other spin will reverse itself instaneously.

      This was tested by alan aspect (who built upon the EPR thought experiment), who subjected two electrons traveling in opposite directions to a polarizer and found that the correspondency between the two electrons meant that there HAD to be some osrt of faster than light communication (it violated "bells theorum" if you want to do more googling). That is, it wasnt a coincidence, or due to 'hidden variables' as einstien thought. It truly was faster than light communication, somehow, between the electrons.

      This is the main discrepancy between Einstein's relativity and Bohr's quanutm theory (Einstein's theories actually pushed quantum theory, ironically). Einstien's relativity theory states that should anything move faster than the speed of light in the spatial dimensions (x,y,z), it must move backwards in the fourth dimension (time). Basically, he argues that everything moves through the four dimensions (x,y,z,t) at the speed of light. Photons move through the spatial dimensions (x,y,z) at the speed of light, and thus do not mvoe through time at all. The photons that exist now have not aged at all since the big bang. This is how einstien explains "Time dilation." This has been confirmed a number of ways, most easily by clocks on airplanes. Clocks put on airplanes, which move through the spatial dimensions(x,y,z) through high speeds (high being relative to normal human movement) have been found to register less time than their "at-rest" counterparts. Of course, quantum theory somehow defies this concept. String theory explains this by offering multiple dimensions past the 4th (I beleive steven hawking's count is at 14 right now)...

      Not so sure about quantum computers, but i belive this is the idea behind them. Transistors used now read either High or low, +5v or 0v, which correspond to binary terms of 0 or 1. Thus we can gather data by reading the charges on the transistors. If we could use electrons, a up-spin meaning 0 and a down-spin 1 (not really up or down, but thats how we denote them), then we could use a 100% efficient replacement for transistors.

      If anyone wants to correct me, please do. I havent taken a physics course in my life (yet) and am probably wrong about some (most) of what i just said.
      • If anyone wants to correct me, please do.

        Not so sure about quantum computers, but i belive this is the idea behind them. Transistors used now read either High or low, +5v or 0v, which correspond to binary terms of 0 or 1. Thus we can gather data by reading the charges on the transistors. If we could use electrons, a up-spin meaning 0 and a down-spin 1 (not really up or down, but thats how we denote them), then we could use a 100% efficient replacement for transistors.

        No, quantum computers aren't about eff

      • Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons.

        Not even close. There are TONS of things faster than light. The focal point on a pair of fast-closing scissors, shadows across the moon, etc. Here, imagine this, you are point a super powerful laser at the moon and you move your laser in an arc. Now, from your perspective, the laser dot on the moon moves from one side to
        • Not even close. There are TONS of things faster than light. The focal point on a pair of fast-closing scissors, shadows across the moon, etc.

          If the focal point on a pair of scissors is the point at which the two blades meet, the for the focal point to move, would not each of the blades have to be traveling at > 1/2 C to have that point move faster than C? The focal point really isn't an object, just a point that appears to move as the blades cross.


          Here, imagine this, you are point a super powerf
          • would not each of the blades have to be traveling at > 1/2 C to have that point move faster than C?

            Nope, they can move a fraction of an inch per year.

            Imagine a pair of scissors 10 light years long with the tip only open 1/10th of an inch. Move the blades that 1/10th of an inch over the course of an entire year and the intersection point moves 10 times the speed of light.

            This is not a violation of the speed of light because the intersection point is not really a "thing". No object is exceeding the spe

      • Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons. Two elextrons in a pair alwats spin in reverse directions. Even if the two electrons are 1000 miles apart, if you polarize one (change the spin), then the other spin will reverse itself instaneously.

        Are you sure about this?

        As I remember the initial thought experiment, the two photons have opposite spins and so when you mea

      • Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons. Two elextrons in a pair alwats spin in reverse directions. Even if the two electrons are 1000 miles apart, if you polarize one (change the spin), then the other spin will reverse itself instaneously.

        Close, but not exactly. You are not changing the polarization. This is a really bizzare part of quantum mechanics, but neither
      • Short response:
        • The electron does not "reverse" spin. It didn't HAVE a definite spin beforehand. When you gave the other one (electron A) a definite spin, you gave the entangled one (electron B) a definite spin. (*)
        • Nothing travels faster than the speed of light. Yes, quantum phase information travels faster than the speed of light, but that's because quantum phase information is nothing.
        • It's not "faster than light communication". It's instantaneous collapse of the quantum state. This isn't communicated.
    • "In theory you take a rod that goes from one galaxy to a distant galaxy many many lighyt years away."

      You mean that stuff they sell in e-mails really works?
  • that with Spintronics they can make James Blish Cities in Flight type Spindizzies yet?
    • I've re-read Cities in Flight at least three or four times and see this spintronics stuff would make the spindizzy engine work. All we need now is a way to break New York City free from it's base of bed rock, and send it on it's way. Then Washington, D.C. whilst Congress is in session, and I see a Win-Win situation here. Hell, let's just spin off the whole Northeast corridor from The Beltway to Boston and be done with it.

  • A decade isn't that much time... (Score:5, Funny)

    by mkweise ( 629582 ) on Saturday August 09, 2003 @08:48PM (#6657365)
    In maybe a 10-year timeframe, spintronics will be on par with electronics

    If the actually manage to go from idea to commerically competitive "spintronic" circuitry in only a decace, I'll consider that proof of some sort of space-alien technology transfer deal [dreamlandresort.com] going on.

  • Ohm's law (Score:5, Funny)

    by Anonymous Coward on Saturday August 09, 2003 @08:54PM (#6657383)
    I had a prof in college who loved to tell the tale of finishing his bsee at mit, and didn't know what to do next. Being young and stupid (his words) he went down to the army recruiting office and inquired about electronics. The guy behind the desk says he has to come back the next week to take a test.

    So, he shows up with a bunch of other hopefuls (again, his words), and takes the test. One of the questions is 'state the 3 forms of Ohm's law." As a good ee, he immediately writes down 'V = IR', no problem. Thinking (!!), he remembers there is a form involving current density, and sets about to derive it (in class this included the steps he took). Now, a third form. He drew a blank, so went and finished other parts of the test.

    Coming back to this question, he's suddenly inspired by remembering something based on magnetic density in a coil or transformer. Again, he sets out to derive the equation, but the guy giving the test says 'times up' before he can finish.

    The next day, he heads back to the recruiting office, and asks how he did. "Great," says the sargeant, "but, what was up with the Ohm's law question?"

    "Oh, the standard form, and then experessed in current density, and...."

    "Nah, all we wanted was V = IR, I = V/R, and R = V/I."

    Proof of, once again, that engineers, like musicians should not try to be funny.

  • IANAL nor am I involved in post doctoral study of Physics, but I wonder at the notion of being able to transfer energy (or motion) with 100% efficiency. Is it too good to be true?

    • Re:Does Anyone Remember Cold Fusion? (Score:5, Interesting)

      by kenthorvath ( 225950 ) on Saturday August 09, 2003 @09:02PM (#6657397)
      At subatomic levels, every process is 100% efficient. The basic principles that you learn in mechanics which warn you that there is no such thing as a perpetual motion machine, etc... are results of statistics and macroscopic effects. Microscopic is not miniaturized macroscopic.

    • Re:Does Anyone Remember Cold Fusion? (Score:5, Interesting)

      by Compuser ( 14899 ) on Saturday August 09, 2003 @10:26PM (#6657651)
      If you read the abstract for the actual paper you'll
      see that they are basically talking about a more
      sophisticated version of a quantum-hall effect,
      i.e. they are talking about the evolution of a
      correlated state, a different one from superconducting
      condensate or bose condensate but another type
      of correlated state. Correlated states can result
      in negligible dissipation (e.g. superconductivity
      or superfluidity). They will not be immune from
      thermal fluctuations esp. at room temperature nor
      will they be immune from dissipation at impurities
      and such. But other than that having spin supercurrent
      seems quite possible.
      And I am a graduate student doing physics research
      in the are of high-temperature superconductivity.
      Mr. Zhang is quite well known in this area since
      he proposed a so called SO5 theory which aimed to
      explain everything about high-Tc in one elegant
      formalism (his theory is oversimplified at best).
      He has worked with Bob Laughlin a lot lately (Laughlin
      got a Nobel prize for his theoretical work on, you
      guessed it, quantum-hall effect). So these people
      are legit, they know what they are talking about
      but Zhang has been known to throw wild ideas out
      there (and more often than not even those have
      at least a grain of truth in them).
    • It is not a transfer of energy, but a transfer of spin. Its essentially a transfer of information.

      In general, electons exist in a superposition of two states, "up" and "down", with oppositely directed "spin" (which obeys almost the same mathematical formalism as angular momentum, with some interesting twists). For a free system of electrons, the up and down states occur with equal measure so that the resulting wavefunction is spinless (sum of spin over all electrons is zero) which implies it is rotation

  • Spins (Score:2, Informative)

    by heli0 ( 659560 )
    Spin is an intrinsic, unchangeable quantity for an elementary particle. Particles with half-integer spins are called fermions, while particles with integer spins are called bosons. Fermions can only be created or destroyed in particle-antiparticle pairs, whereas bosons can be created or destroyed singly.

  • makes me think of... (Score:3, Funny)

    by 1nv4d3r ( 642775 ) on Saturday August 09, 2003 @09:11PM (#6657423)
    Maybe now O'Reilly can finally deliver on his 'no spin zone' promise.

    Of course, if all his electrons stopped spinning it would probably be the most interesting televised farewell I've ever seen.

  • Ampere's Law (Score:3, Interesting)

    by Dr. Mojura ( 584120 ) on Saturday August 09, 2003 @09:19PM (#6657445)
    The authors predict that application of an electric field will cause electrons' spins to flow together collectively in a current. The applied electric force, the spins and the spin current align in three different directions that are all perpendicular to each other
    It seems they should be making more comparisons to Ampere's Law [wikipedia.org] than Ohm's Law, as they are suggesting an applied electric field will create a spin current, similar to how Ampere's Law states how an applied magnetic field will create conventional current flow.

    The real question is, what is 'spin current', and how does it relate to the conventional definition of electric current.
    • If they explained any of this I would have given more credibility to it. But then again it's Stanford so we all know they are credible. *wink* *wink*

  • Spintronics is NOT the next thing (Score:4, Interesting)

    by Anonymous Coward on Saturday August 09, 2003 @09:32PM (#6657484)
    Spintronics is promising, but I doubt that it will be the NBT. Quantum-dot Cellular Automata (QCA), which encodes binary information based on electron orientation, seems to hold more promise. It is highly scalable, small, can hybridize with CMOS, and can already be fabricated at low temperatures. With the addition of clocking regions to lower inter-dot tunneling barriers, even pseudo-pipelining is realizable. Perhaps the best thing about this is that it all cells are coplanar! I just attended a conference (IWQDQC) on Quantum Computing, and believe me, spintronics faces its share of problems.

  • Spindizzy (Score:3, Funny)

    by dpilot ( 134227 ) on Saturday August 09, 2003 @09:43PM (#6657515) Homepage Journal
    If you're messing with electron spins, forget superconductivity and that stuff.

    I want a Spindizzy.

    (ref: James Blish, "Cities in Flight")
  • "materials already widely used in the semiconductor industry, such as gallium arsenide.'""

    Kirk: Warp Factor Ten Scotty!

    Scotty: I'm giving her all the gallium arsenide we've got Captain but she's suckin' mud!
    • Kirk: I don't need any resistance from you, Mr. Scott!

      Scotty: We haven't go the power capt'n, the electrons are spinning out of control!!!

  • I'll apply my general rule... (Score:3, Insightful)

    by HarveyBirdman ( 627248 ) on Saturday August 09, 2003 @11:15PM (#6657854) Journal
    I'll believe it when I can order one from Digi-Key. :-)

  • The article is misleading on key points (Score:5, Insightful)

    by Iainuki ( 537456 ) on Sunday August 10, 2003 @12:02AM (#6658010)
    The paper is blocked behind a pay wall, so this is what I got from the article.

    The discussion on spin is wrong. Spin has nothing to do with the rotation of macroscopic objects like the Earth, it's an intrinsic quantum property of particles like the electronic with no macroscopic analog. The best explanation I've heard of spin that doesn't involve explaining the details goes like this: spin is a measurement of the number of rotations required to bring a particle back to its initial state. One-half spin particles, like the electron, require, counterintuitively, two full rotations to go back to their initial state.

    The physical situation seems to have very little to do with Ohm's Law except in the loosest sense. They're describing a current consisting of electron spins under an external electric field. This has some interesting properties (I'd like to poke at the math, if I could read the paper), one of which seems to be that it is predicted to persist at much higher temperatures than the best superconductors. If so, because this spin current seems to be dissipationless, this would allow information to be transmitted without generating heat.

    Interesting stuff; a pity the article was so poor.

  • For what it's worth, spintronics is already in use for disk drives.

    From what I understand, the read/write heads of just about every modern disk drive are spintronics devices. Without them, we'd probably still be stuck with 1 GB disk drives.
    • Hard drives use dipole orientation to read data. Not electron spin.

      • With a quick google search, you can find a number of references to the use of spintronics for disk drive heads. Here are just a couple.

        Here is something from 1999: [aip.org]

        MAGNETOELECTRONICS, SPIN ELECTRONICS, AND SPINTRONICS are different names for the same thing: the use of electrons' spins (not just their electrical charge) in information circuits. One magnetoelectronic device is the magnetic hard drive based on the giant magnetoresistance (GMR) effect. In a GMR material, consisting of a stack of alternatin

  • A link to the paper (Score:3, Informative)

    by pauldy ( 100083 ) on Sunday August 10, 2003 @02:46AM (#6658493) Homepage
    I had to dig but eventually found it at the following location. http://www.sciencemag.org/cgi/data/1087128/DC1/1 [sciencemag.org]

  • Say goodbye to your fans... (Score:4, Interesting)

    by Epsillon ( 608775 ) on Sunday August 10, 2003 @08:55AM (#6659243) Journal
    Perhaps more relevant to us is the fact that zero dissipation means, in effect, zero heat. It also means zero loss so power requirements, so important in the portable market, would lessen exponentially. Spintronics based devices would therefore not need the elaborate cooling solutions current semiconductors do. A truly silent computer may be just over the horizon, folks...
    • This isn't actually an "exponential" decrease. Your new power requirements would be whatever you need to manipulate the state of the electrons (spin current may have no dissipation, but creating pulses of spin current for signalling will need some energy). You'd probably use less power, but "exponential" refers to a way that two variables relate to each other, not just a "really big" decrease in power consumption, which is what you'd really get. Also, unless there's a breakthrough in non-volatile solid-s

      • This isn't actually an "exponential" decrease.

        Yes, I know, I was using the vernacular. Your point is well made, though, so thank you for elucidating.

        The hard drive problem isn't likely to go away until we overcome the problem of the read/write lifespan of flash RAM and similar technology, not to mention price, as you say.

  • If you're mystified by spin and quantum physics in general, This entry on ElectronOrbitals [wolfram.com] is a good place to start.

    This is a new part of (or companion to?) Eric Weisstein's Mathworld [wolfram.com]. It's expanded now into Science World [wolfram.com]. Some of the references to electrons and spin are not yet complete, but there's enough here to get started.

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