Muon g-2 Results Signify New Physics? Maybe Not.

The big news of the week that got all the media coverage is the result that came out of Fermilab's Muon g-2 experiment that confirmed an earlier result from Brookhaven more than a dozen years ago. Fermilab even announced it like.

However, as with any scientific discovery or announcement, one has to take a deep breath and let the process works itself out before we put our stamp of validity to it. This is because there is a theoretical calculation that has also been published along with this result that basically recalculates what the Standard Model predicts as the magnetic moment of a muon, and they found that the new calculation produces a result consistent with the experiment. In other words, there is no new physics if this calculation is verified, because the old Standard Model does, in fact, predicted this new result.

One of the major difficulties in physics is that in many situations, we do not have a simple equation that we can plug-and-chug to get numbers out. In fact, this is why predicting the weather is difficult, because the non-linear differential equations that need to be solved to get the number out can only be done numerically, i.e. it has to be done via some numerical algorithm.

This is made worse when there are a gazillion interactions involved in a system. So one ends up making simplifying models or adopt calculational techniques to allow us to get to some numerical answers. We benchmark the technique to known values and known systems to make sure that it gives accurate and sensible answers, but as we push the boundary even more, there is no guarantee that that calculational technique will work all the time.

The author of the theoretical paper used a calculational technique called lattice QCD. This is a known calculational model that has been described in simple terms in the link I provided above. It appears that using this method, the Standard Model does provide a value for the muon magnetic moment that is consistent with the experiment. If this is true, then it means that the old calculation of the magnetic moment was incorrect in the first place, and that there is discrepancy between what the Standard model predicts, and what the experiment measures.

While this is good news for the Standard Model and is another evidences of why it is an amazing theory, those who are looking for new physics beyond the Standard Model will obviously not be jumping for joy. But that isn't the issue here and not what I want to highlight. Rather, it is the constant reminder that in science, and especially in such exotic areas of physics, every discovery or new ideas must not be overblown or overhyped, because those require multiple verification over a period of time. It is not a situation for instant gratification. A lot of hard work is still to come because we have seen way too many times where something that was touted turned out to not be valid.

This announcement received a lot of media coverage. I just hope that this is a valid "new physics" and not just something that turned out to be what the old theory did predict.

Zz.

Rebuilding Quantum Theory

Theorists and philosophers are trying to "rebuild" quantum theory's foundation and axioms. Good luck to them!

Still, this is a rather good article on some of the issues surrounding concepts that still do not sit well with many physicists. Those of us who are in the "Shut up and calculate" camp will leave it up to them to sort things out. We are busy with doing other things.

:)

Zz.

Arrow Of Time Due To Gravity?

I just got back from vacation and an unexpected trip out of the country, so I'm still catching up. But when I came across a news article on physics in Business Insider, I had to read it, and you should to. It is on another model to explain the nature of the arrow of time in our universe.

Tentative new work from Julian Barbour of the University of Oxford, Tim Koslowski of the University of New Brunswick and Flavio Mercati of the Perimeter Institute for Theoretical Physics suggests that perhaps the arrow of time doesn’t really require a fine-tuned, low-entropy initial state at all but is instead the inevitable product of the fundamental laws of physics. Barbour and his colleagues argue that it is gravity, rather than thermodynamics, that draws the bowstring to let time’s arrow fly. Their findings were published in October in Physical Review Letters.

The team’s conclusions come from studying an exceedingly simple proxy for our universe, a computer simulation of 1,000 pointlike particles interacting under the influence of Newtonian gravity. They investigated the dynamic behavior of the system using a measure of its "complexity," which corresponds to the ratio of the distance between the system’s closest pair of particles and the distance between the most widely separated particle pair. The system’s complexity is at its lowest when all the particles come together in a densely packed cloud, a state of minimum size and maximum uniformity roughly analogous to the big bang. The team’s analysis showed that essentially every configuration of particles, regardless of their number and scale, would evolve into this low-complexity state. Thus, the sheer force of gravity sets the stage for the system’s expansion and the origin of time’s arrow, all without any delicate fine-tuning to first establish a low-entropy initial condition.

Zz.

Particle Physics In A Superconductor

It has finally come full circle.

The Higgs mechanism, which came out of the phenomenon of superconductivity and were then used in elementary particle physics, has come back to superconductivity with the latest result published in Science. In this report, physicists see the similar Higgs boson signature in superconductors as those described in particle physics.

To find it in a superconductor in its normal state, Shimano and colleagues violently shook the superconductor with a very brief pulse of light. Shimano says it is similar to how particle physicists create the real Higgs boson with energetic particle collisions. They first created the superconducting Higgs last year, and have now studied its properties to show that, mathematically speaking, it behaves almost exactly like the particle physics Higgs.

Again, this is similar to the discovery of magnetic monopole in spin-glass system and the discovery of Majorana fermions. A lot of particle physics can be done in condensed matter!

Many-Body Quantum Fluctuations In Residual Resistivity Of Metals

As a condensed matter physicist by training, the issue of charge transport in matter has always been a topic that I encounter often, especially when I was doing my postdoc many, many years ago. While the physics of charge transport in metals, under "ordinary" situations, can be adequately described by the Drude model, resulting in, for example, the beloved Ohm's Law, there are many other situations where such a simplistic model just doesn't work. And in those situations, that is where the physics gets very interesting and can be quite complicated.

The factors that influences charge transport in matter depends very much on how a charge carrier scatters. So the scattering rate determines the properties of resistivity/conductivity, etc. In a metal, there several types of scattering: electron-phonon scattering, electron-impurity scattering, and electron-electron scattering.[1] The dominant term that has a strong temperature dependence is the electron-phonon scattering, which is the primary mechanism that determines the resistivity of a metal. The electron-electron scattering has a weaker temperature dependence, while the electron-impurity scattering is mostly temperature independent.

What this means is that, as we lower the temperature, at some point, the electron-phonon scattering "freezes out", and no electron-phonon scattering contributes to the resistivity. The resistivity will then be a function of predominantly the electron-electron contribution. As the temperature approaches 0 K, one will notice indication that the resistivity will not be zero. This is the residual resistivity, whereby even at 0 K, there will still be a net resistivity of the material that is due to electron-impurity scattering. Note that this "impurity" need not be foreign atoms that are not part of the material. It can also be crystal defects and deformation that interrupts the long-range order of the crystal structure of the metals. The charge carriers can scatter off these defects as well.

That is how we were taught in solid state courses. we often deal with charge transport using the Boltzmann transport equation, and treating this within the Drude model The full quantum mechanical treatment, via the Kubo formulation, is a BEAST, and often unsolvable.

But now, along comes a new theoretical treatment of charge transport in metals, using DFT, that arrived at a rather unexpected result.[2] The new treatment showed that there is a strong contribution to the electron-impurity scattering due to the electron-electron many-body effects. The electron-impurity scattering is not as simple as we thought. They showed how well this new explanation matches the residual resistivity measured for aluminum.

This is another example where, something that we know very well and for a long time, can often reveal new physics and information when it is examined at the very edge of the boundary of our knowledge. We subject many of our ideas to the extreme case (in this case, very close to 0K) to see how well they work in those situations. It is one of the ways we expand the boundary of our knowledge.

Zz.

[1] see http://arxiv.org/abs/cond-mat/9904449
[2] http://physics.aps.org/articles/v7/70

You Can't Escape The Heisenberg Uncertainty Limit

A rather interesting treatment of redefining the Heisenberg uncertainty principle, in light of recent advancement in the so-called weak-measurement experiments.

The popular conception of the Heisenberg uncertainty principle is that measurement is unavoidably invasive. We disturb an object when we observe it, thus introducing error into subsequent measurements. However, recent experiments (see 6 September 2012 Synopsis) claim to have measurement errors below the Heisenberg limit. To address this apparent contradiction, a paper in Physical Review Letters reports a new formulation of the uncertainty principle in which measurement disturbance depends on the performance of the measuring device, which is quantified as the maximum possible change in the state of the object.
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Paul Busch of the University of York in the UK and his colleagues believe there is no contradiction here, but only a misunderstanding over how to characterize the effects of measurement. Previously, measurement-induced errors have been calculated on a state-by-state basis, by comparing the state of a system “before” and “after” a measurement. But Busch et al. show that defining measurement error in a state-independent way, through a kind of calibration process of the measuring device, leads to limits in line with the uncertainty principle.

 I expect more of something like this to occur as we probe the more minute detail of QM.

Zz.

Tunneling Experiment Proposed To Distinguish Superconducting Pairing Origin

It certainly was a nice coincidence that I mentioned about the paper on tunneling spectroscopy on superconductors earlier. It turns out that a new paper proposes an experiment using Josephson tunneling junction to distinguish between the pairing model proposed by 5 different theories.

Now, She et al. lay out in parallel the theoretical expectations for the pair susceptibility of 5 different theories of superconductivity in quantum critical metals. These scenarios include the orthodox BCS theory with a simple Einstein-oscillator pairing function, BCS with a Hertz-Millis-type criticality of the bosonic spectrum, BCS with a simple pairing function and quantum critical electrons, and two limits of the recently developed holographic superconductivity that borrow mathematical concepts from string theory [anti–de Sitter/conformal field theory (AdS/CFT) correspondence] in order to handle scaling near a quantum critical point.

It will be interesting to see which group gets to do this test first, and whether the results can actually distinguish one versus the others. Still, this is a prime example of the tunneling phenomenon being used to study other things.

Zz.

Cuprates - An Overview

This is a very good review article on the theoretical aspects of the high-Tc cuprate superconductors, and why it is such a complex system that a single accepted theoretical description still evades us after 20 years of its discovery. I actually had a chuckle when I read the end passage of the article:

Regardless, magnetic correlations definitely play a prominent role in the entire doping range superconductivity is observed . Whether this means RVB, spin fluctuations, orbital currents, or some combination thereof, such magnetic correlations are the likely source of d-wave pairing. But building a rigorous strong coupling theory has certainly proven to be a challenge. Perhaps ideas from string theory and black hole physics will help in this regard. But then again, perhaps not!

Ooooh boy! :)

Zz.

High-Tc Superconductors Are Very Kinky - Update 10

A new preprint on arXiv today analyzes the low-energy kink in the dispersion curve on Bi-2212 high-Tc superconductor. They concluded that this low energy kink (smaller than the gap) is due to an in-plane acousting phonon branch.

So this adds more intrigue to the picture. The cuprate superconductors seems to have a lot of "kinks" in the band structure. Last count, we now have 3. To catch up on all the issues surrounding this, read my first entry on the kink structure that we have seen from ARPES measurement. That entry will be continually updated as more papers and new stuff are published.

Zz.

Your Vehicle Starts Due To Relativity!

Thanks to "Cthugha" at the Physics Forums for bringing this paper to my attention (this is what happens when one is trying to catch up with work after the holidays - one forgets to troll the various physics journals sites).

A new paper in PRL has a very interesting theoretical calculation for lead-acid battery used in motor vehicles. Supposedly, there are no ab initio calculations for such battery works, i.e. no theoretical calculation for the energies of the reactants - till now[1]!

Abstract: The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7–1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

But what made it stood out is the end of of the paper, where the authors wrote "Finally, we note that cars start due to relativity"! :)

Well, there ya go! If anyone questions you on the use of relativity, you point to their car batteries!

I love it!

Zz.

Edit: Don't miss the Physical Review Focus coverage of this work.

[1] R. Ahuja et al., Phys. Rev. Lett. v.106, p.018301 (2011).

Inflationary Versus Cyclic Universe

I'm guessing that most of you have heard of the battle being done on arXiv between Penrose/Gurzadyan and a number of groups disputing their conclusion. This is being reported on Nature News (which has a limited amount of time for free access).

Simply put, Penrose/Gurzadyan examined the cosmic microwave background data from WMAP and showed that there are these concentric rings of uniform temperature in the CMB. This is not in dispute. What is in dispute is that they concluded that that these are signatures of "... black holes colliding in a previous cosmic 'aeon' that existed before our Universe....", thus, giving an evidence towards a cyclic universe[1].

That led to a flurry of activities, and 3 groups have independently challenged that view[2,3,4].

To gauge this significance, Gurzadyan compared the observed circles with a simulation of the cosmic microwave background in which temperature fluctuations were completely scale invariant, meaning that their abundance was independent of their size. In doing so, he found that there ought not to be any patterns. But the groups who are critical of his work say that this is not what the cosmic microwave background is like.

They point out that the WMAP data clearly show that there are far more hot and cold spots at smaller angular scales, and that it is therefore wrong to assume that the microwave sky is isotropic. All three groups searched for circular variance patterns in simulations of the cosmic microwave background that assume the basic properties of the inflationary Universe, and all found circles that are very similar to the ones in the WMAP data.

Moss and his colleagues even carried out a slight variation of the exercise and found that both the observational data and the inflationary simulations also contain concentric regions of low variance in the shape of equilateral triangles. "The result obtained by Gurzadyan and Penrose does not in any way provide evidence for Penrose's cyclical model of the Universe over standard inflation," says Zibin.

Of course, that's not the end of it. Gurzadyan/Penrose has posted a rebuttal (also on arXiv)[5]. I'm sure there will be more forthcoming to rebut that one as well. People don't even wait anymore for such a thing to be published.

This, btw, is what happens when we try to deduce something using only a set of data and not in possession of other types of data. Often, in such a case, the conclusion isn't unique. You say the data is consistent with A, someone else can also say it is consistent with B. That is why we seldom accept anything to be valid until this non-uniqueness has been sufficiently removed, and Mother Nature clearly points to a single, clear description of such-and-such phenomenon. It is why science can take a very long time to come up with a valid theory of something.

Z.

1. Gurzadyan, V. G. and Penrose, R. Preprint at http://arxiv.org/abs/1011.3706 (2010).

2. Wehus, I. K. and Eriksen, H. K. Preprint at http://arxiv.org/abs/1012.1268 (2010).

3. Moss, A., Scott, D. and Zibin, J. P. Preprint at http://arxiv.org/abs/1012.1305 (2010).

4. Hajian, A. Preprint at http://arxiv.org/abs/1012.1656 (2010).

5. Gurzadyan, V. and Penrose, R Preprint at http://arxiv.org/abs/1012.1486 (2010).

High-Tc Superconductors Are Very Kinky - Update 9

More theoretical analysis of the "kink" in the band structure of the cuprate superconductors. This time the analysis of the low and high energy kink in the ARPES spectrum can be reproduced using phonons via the extended Eliasberg theory[1].

Abstract: Eliashberg theory generalized for the account of the electron-hole nonequivalence and electron correlations in the vertex function is used. The phonon contribution to the nodal electron Green function in cuprates is viewed. At non- zero temperatures the singularities (kinks) in the frequency behavior of a real and imaginary part of an electron nodal Green function, and also in the nodal part of the density of the electron states modified by an electron-phonon interaction are studied. It is shown that near the optimal doping both the low-energy and high-energy nodal Green function kinks and also the abnormal broadening of a band in cuprates are reproduced with the electron-phonon interaction in the extended Eliashberg theory.

So here's another argument in favor of phonons for the origin of these kinks. The original blog entry that lists all of these development has been updated.

Zz.

[1] E.A. Mazur http://arxiv.org/abs/1005.3930

A Search for the Mpemba Effect: When Hot Water Freezes Faster Than Cold Water

I've mentioned before that when I got into physics, I didn't have some grandiose idea about solving the problems of the universe. I got into physics because I was curious about some of the apparently simplest observations around me. This is why I continue to be fascinated by this Mpemba effect.

I reported this a while back regarding both the theoretical and experimental observation of this effect. It appears that this effect is still being studied and remains a curiosity for others as well. A preprint appeared today on ArXiv detailing a "search" for this effect.

Abstract: An explanation for why hot water will sometime freeze more rapidly than cold water is offered. Two specimens of water from the same source will often have different spontaneous freezing temperatures; that is, the temperature at which freezing begins. When both specimens supercool and the spontaneous freezing temperature of the hot water is higher than that of the cold water, then the hot water will usually freeze first, if all other conditions are equal and remain so during cooling. The probability that the hot water will freeze first if it has the higher spontaneous freezing temperature will be larger for a larger difference in spontaneous freezing temperature. Heating the water may lower, raise or not change the spontaneous freezing temperature. The keys to observing hot water freezing before cold water are supercooling the water and having a significant difference in the spontaneous freezing temperature of the two water specimens. We observed hot water freezing before cold water 28 times in 28 attempts under the conditions described here.

There ya go! This effect certainly has a lot of legs!

Zz.

Edit 12/20/2010: This article has been published in AJP. The exact reference is:
J.D. Brownridge Am. J. Phys. v.79, p.78 (2011).

Dark Matter Claims Face Challenge

Recent claims of possible dark matter origin for excess high energy electrons and positrons from Fermi, HESS, ATIC, and PAMELA may be down the tubes. It seems that a new model has shown a more conventional explanation for these excesses and thus, causing more doubt that these were signatures from the presence of dark matter {link available for free only for a limited time}.

Galactic electrons are thought to originate in the explosion of supernovae, and conventional models predict that they lose energy as they pass through the Milky Way's magnetic field. The annihilation of proposed dark-matter particles would also create electrons, and some theorists had interpreted the recent experimental detections of surplus high-energy electrons as evidence for this process.

But starlight also scatters the electrons. Petrosian says that starlight suppresses the energy of most electrons in a way that makes it seem as if there is an excess of certain high-energy electrons. The Stanford group's models show an excess that is similar to that reported by NASA's Fermi Gamma-ray Space Telescope; the High Energy Stereoscopic System (HESS), a ground-based detector in Namibia; and the Advanced Thin Ionization Calorimeter (ATIC), a balloon-borne detector that flew over Antarctica.
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But by tweaking parameters in their model, the Stanford group can also mimic the PAMELA results. Like the electrons, the positrons are also thought to originate near supernovae — although through secondary collisions of protons. By increasing the density of gas and the number of photons near these supernovae — both possible scenarios given that supernovae occur in gas-rich star-forming regions near lots of stars — the model predicts high-energy positrons similar to those reported by PAMELA.

The exact reference to the paper is:

L.Stawarz et al., Astrophys. J. v.710, p.236 (2010).

This certainly throws a huge damper on those theorists who think they've seen tantalizing evidence of dark matter beyond just astronomical observations.

Zz.

High-Tc Superconductors Are Very Kinky - Update 5

The origin of the energy energy kink in the cuprates' ARPES data continue to be debated. This is while the low-energy kink remains a mystery after all these years. One of the issue that has been brought up is that the high energy kink could be nothing more than an artifact of the photoemission matrix element and thus, has nothing to do with superconductivity.

This issue has been tackled in the latest manuscript appearing on arXiv. Basak et al.[1] have performed a calculation to see to what extent the matrix element effects come into play in shaping the band dispersion. Their conclusion is that the high energy kink isn't due to the matrix element and is more of a signature of the coupling of the quasiparticle to the electronic mode.

I've updated my original essay on the kinks in the high-Tc superconductors to include this manuscript.

Zz.

[1] Basak et al. http://arxiv.org/abs/0904.1749

String Theory Predicts an Experimental Result?

A rather fascinating item that came out of the 2009 AAAS Meeting in Chicago. A panel discussion during one of the session presented a possible explanation out of String Theory that could describe two very widely separated experimental observations from 2 very different field of study.

First came out of condensed mater from the observation of the behavior of supercooled lithium 6, producing a strongly interacting Fermi gas that behaves like a superliquid. The second came from nuclear physics with the observation of the quark-gluon "liquid" from collisions at RHIC.

It appears that a claim has been made that the holographic principle of String Theory can produce a description that mimic these two phenomena. So in essence, you have the convergence of condensed matter, nuclear physics, and string theory.

So does that mean that string theory finally has an experimental verification? Hardly.

Not to say that string theory has been proved. Clifford Johnson of the University of Southern California, the string theorist on the panel, was very clear about that. All the arguments about whether nature is composed of unimaginably tiny vibrating strings and multiple dimensions, and whether this will eventually explain the basic workings of the universe, are still unresolved.

Furthermore, we also do not know if there aren't any other better explanations, i.e. is the string approach really unique? After all, condensed matter theory already has a well-established line of formulation for the Fermionic gas. If string theory claims to have a more fundamental theory, then it will have to reproduce all of those other observations as well, and not just this.

Zz.

High-Tc Superconductors Are Very Kinky - Update 3

Another update of my compilation of papers on the nature of the "kink" in the band dispersion observed in ARPES measurement on high-Tc superconductors. This time it comes from a theoretical analysis with parameters extracted from the inelastic neutron scattering (INS) experiment and applied to the ARPES results[1].

What they found out was that the scattering mediated by the incommensurate spin excitation seen in the INS measurement could account for practically all of the ARPES observations on the YBCO compound. This includes the observation of the kinks and their temperature "evolution" (or non-evolution) with temperature across the doping range. The previous models that depended on the magnetic resonance that disappeared above Tc and strongly dependent on temperature is a red herring.

This paper has been accepted on Nature Physics. A complete citation to it will be added once it is published.

Zz.

[1] T. Dahm et al., http://arxiv.org/abs/0812.3860.

QCD - The Source of Everyday Mass

Reported in this week's issue of Science, a new ab initio theoretical calculation using lattice QCD has produced a good agreement between the mass of various nucleons and other hadrons. This work was done by Durr et al.[1]

As reviewed in the Perspective by Andreas S. Kronfeld in the same issue of Science, this means that the source of our everyday mass lies in QCD.

Almost all of the mass (or weight) of the world we live in comes from atomic nuclei, which are composed of neutrons and protons (collectively called "nucleons"). Nucleons, in turn, are composed of particles called quarks and gluons, and physicists have long believed that the nucleon's mass comes from the complicated way in which gluons bind the quarks to each other, according to the laws of quantum chromodynamics (QCD). A challenge since the introduction of QCD has been to carry out an ab initio calculation of the nucleon's mass. On page 1224 of this issue, Dürr et al. (4) report the first such calculation that incorporates all of the needed physics, controls the numerical approximations, and presents a thorough error budget. Because these accurate calculations agree with laboratory measurements, we now know, rather than just believe, that the source of mass of everyday matter is QCD.

It is now up to the LHC to show that this premise is correct.

Dürr et al. start with QCD's defining equations and present a persuasive, complete, and direct demonstration that QCD generates the mass of the nucleon and of several other hadrons. These calculations teach us that even if the quark masses vanished, the nucleon mass would not change much, a phenomenon sometimes called "mass without mass" (19, 20). It then raises the question of the origin of the tiny up and down quark masses. The way nature generates these masses, and the even tinier electron mass, is the subject of the LHC, where physicists will explore whether the responsible mechanism is the Higgs boson or something more spectacular.

Edit: there's a coverage of this on Nature's daily news. {the link is open for free only for a limited time}

Zz.

[1] S. Dürr et al., Science v.322, p.1224 (2008).

Physicists Quantify the 'Coefficient of Inefficiency'

One of the skill one learns as a physicist is to tackle a problem systematically, and to quantify it, if possible, by making an effective, accurate model of the system. This problem doesn't have to be in physics. It can be anything. I mentioned earlier of someone who tried to find the most optimum way to load an airplane, simply because he became curious after observing how an airplane is typically boarded. Well, this is a similar problem.

Three physicists from the University of Vienna examines the efficiency of committees in making a decision in terms of the number of people that makes up the committee.

To understand why, Thurner and fellow physicists Peter Klimek and Rudolf Hanel turned to the British historian C Northcote Parkinson, who studied how the British Navy was once administered. Parkinson, who died in 1993, discovered a strong correlation between a committee’s ability to make a good decision, and its size. In particular, Parkinson found that committees with more than about 20 members are much more ineffectual at making decisions than smaller groups — something he dubbed the “coefficient of inefficiency”.

You can read the preprint of the paper from a link given in that article. It is a clever way to quantify and model this problem. Now if only people who form such committees would pay attention to it.

Zz.

Death For Phonons In High-Tc Superconductors?

This is a highly interesting and certainly provocative result.

Remember I posted a while back on the "kink" observed in the angle-resolved photoemission spectra (ARPES) on high-Tc superconductors? There have been a continuing debate since the kink was observed on the origin of this observation. Two leading candidates are the coupling of the charge carrier to a spin fluctuation mode, and a coupling to the phonons.

Now two separate theoretical papers have calculated the coupling to the phonon modes and have arrived at the conclusion that such coupling cannot account for the strength of the kink observed in ARPES spectra.

In recent years, despite mounting experimental evidence against it, some physicists have clung on to this interpretation. But now teams from Germany and the US have performed calculations to suggest that lattice vibrations in cuprates can at best account for just a small fraction of the materials’ superconducting behaviour.
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Manske’s team found that the theoretical energy–momentum relationship produced by these calculations did contain a kink — but about a three to five times smaller than the 2001 observations (Phys. Rev. Lett. 100 137001). This is bad news for physicists who have been hoping phonons can account for all of the behaviour of high-temperature superconductors. “It is embarrassing for people to admit they have worked on something for 20 years if it is not true,” jokes Manske.

Meanwhile, Steven Louie and colleagues at the Univerisity of California in Berkeley have come to a similar conclusion with the cuprate LaSrCuO4. From their calculations, the phonon contribution is almost an order of magnitude too small for the observed kink (Nature 452 975).

This could be rather devastating to the phonon picture. If this is true, the two new results still cannot account for the origin of superconductivity, but at least they have eliminated a red herring. Still, all this could be moot if an earlier report is true about the absence of any kind of "glue" in the mechanism for high-Tc superconductors.

So stay tune. The story is by no means over, and the fat lady hasn't even warmed her vocal cords yet.