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More on Spintronics
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.'"
"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.'' "
"With lack of dissipation, spintronics may be the best mechanism for creating ever-smaller devices."
dawnlevy@stanford.edu
650-725-1944
Stanford University
'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).
''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
[Fuck Beta]
o0t!
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.
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?
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
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 concept of accomplishing something in a different way that is not possible on other ways. Like tryingto do advanced math using roman numerals instead of the decimal system that includes the zero place holder.
So does this spin thing make it possible to achieve antigravity or super conductivity in common use? If so, then aren't there other human resistance factors to deal with that may be more difficult and non-natural to have to deal with and overcome?
It took 300 years for the Hindu-Arabic decimal system to propogate thru the constraints of the roman numeral system supporters, regardless of the improvement in ease of math that was made possible, not to mention the technology that needed it, to be come a reality (computers).
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 going on.
Gentlemen! You can't fight in here, this is the War Room!
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.
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.
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.
Whenever the offence inspires less horror than the punishment, the rigour of penal law is obliged to give way...
I think the word your looking for is sketchy. I read the piece and wondered how this got to slashdot. This is so obviously a piece to get funding for further research from a couple of quacks you can't even explain the process.
-You know its like the earth orbits around the sun and then spins on its access that's how it works.-
Give me a break they are trying to lure in the gullible who know nothing about electronics to give them money. I think the idea of spintronics is great but what they propose is not worth anyone's time there are plenty of others who are doing valid research in this area. If the best they can explain is a planetary analogy or some sort of half assed flash animation then check someone else out.
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.
The real question is, what is 'spin current', and how does it relate to the conventional definition of electric current.
"Nothing exists except atoms and empty space; everything else is opinion." - Democritus
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.
If you're messing with electron spins, forget superconductivity and that stuff.
I want a Spindizzy.
(ref: James Blish, "Cities in Flight")
The living have better things to do than to continue hating the dead.
You think that a news release covering a article in Science isn't going to be dumbed down? Or that Dr.Shou-Cheng has managed to fool Stanford, Santa Barbara, and IBM with his slick descriptions of 'imagine a planet orbiting around the sun'. Or possibly you have a better explanation of quantum spin that will eludicate the masses in 30 words or less?
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
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.
Too lazy to create a sig...
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).
Sorry, no.
Entropy is not an absolute law, but a law based on extreme probabilities. In any reaction, certain quantities are completely conserved. One of these is energy.
The increase in entropy that occurs is due to energy being converted into less usable forms, such as from motion (kinetic energy) to heat (thermal energy).
It is not actually a decrease in total energy. Energy is perfectly conserved in any reaction.
In subatomic reactions, there is no place for energy to go, so to speak. In fact, the only thing energy really is is the motion (and mass, though those are remarkably interlinked) of subatomic particles.
When two subatomic particles collide, if neither of them splits or gives of any other particles, the energy remains entirely in the two particle system (that is, all that changes is kinetic energy; speed). Well, direction changes as well.
Mod parent down; he is incorrect. (or not, I'm actually in favor of the mod up only philosophy, but parent would be a good one to mod down if you believe in modding factually incorrect posts down).
For to end yet again.
I'll believe it when I can order one from Digi-Key. :-)
--- Ban humanity.
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.
No, no, he's right, that's why you always put the wings on upside-down.
I had to dig but eventually found it at the following location. http://www.sciencemag.org/cgi/data/1087128/DC1/1
Hard drives use dipole orientation to read data. Not electron spin.
UgaBuga!
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 rotationally invariant (ie, rotate all electrons by some angle and the system is indistinguishable from the original).
In the presence of interactions (ie. an E/M field), the alignment of the field specifies an axis, and the coupling to the spin means that up and down spins (with respect to this axis) have different energies. Thus there is no longer rotational symmetry and you can control the direction of spin.
This has nothing to do with the motion of the electrons themselves, but only the spin. One way to think about this is to think of each quantum number as corresponding to a different particle. An electron has spin 1/2 and charge 1 so you can consider an electron to be a bound state of a pure spin particle and a pure charge particle. In fact, in one-dimensional systems (and possibly sometimes in 2D) this is not even a mathematical trick, and it is possible to prove that the spin and charge components are no longer bound to each other! The system behaves as if it was composed of two separate species of particles, "spinons" (carrying the spin) and "holons" (carrying the charge). This is called "spin-charge separation", and it is a collective effect, it doesn't work in a few-body system.
This is not to say that Zhang's result has anything to do with spin-charge separation per se, just an example.
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:
And this is from 2003, or at least, last updated in 2003:
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...
Resistance is futile. Reactance buggers it up.
You are right; it is not possible to do computation without SOME losses even if we use completely reversible phenomena. The entropy increase comes when we "forget" information, .i.e., clearing a register.
That is different from what they are talking about in the article. Their goal is to move to essentially reversible reactions using spin rather than current-type electronic phenomena that contain Ohmic irreversibilities. The Ohmic losses dominate the heat generation in current ICs. The next on the list of energy loss for an IC is probably RF radiation. Entropy production from information loss is pretty far down the scale, but it is the one that cannot be "engineered away" so that is why it is always included in the "how big can a computer get" calculation.