Physics and Physicists: High-Tc Superconductors Are Very Kinky - Update 10

Physics and Physicists: High-Tc Superconductors Are Very Kinky - Update 10

Relativity and the Lead-Acid Battery

This relation may seem at first glance quite unusual. For most, relativity needs be concerned only when the considered speed becomes comparable to that of light. The Lead -acid battery seems having no attachment to this speed. However, if you look into the electrons that are busy inside the substance, you may change your mind. Lead is a heavy element, and relativity effects, as you can derive from Dirac's equation, scale as the quartic power of the atomic numbers. That is how relativity plays a role, which proves crucial for your cars to start, in Lead-Acid Battery [http://prl.aps.org/pdf/PRL/v106/i1/e018301].

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.

Kinks cannot be ascribed to phonons

In cuprate superconductors, the dispersion of energy with wave vectors features some kinks. As regards the cause of such kinks, suppliers with phonons has appeared. However, this paper [http://www.fkf.mpg.de/metzner/manske/Pub/PRL100_137001.pdf] disfavors such choice.

Using the local density approximation and a realistic phonon spectrum we determine the momentum and frequency dependence of 2F k;! in YBa2Cu3O7 for the bonding, antibonding, and chain band. The resulting self-energy is rather small near the Fermi surface. For instance, for the antibonding band the maximum of Re as a function of frequency is about 7 meVat the nodal point in the normal state and the ratio of bare and renormalized Fermi velocities is 1.18. These values are a factor of 3–5 too small compared to the experiment showing that only a small part of can be attributed to phonons. Furthermore, the frequency dependence of the renormalization factor Z k;! is smooth and has no anomalies at the observed kink frequencies which means that phonons cannot produce well-pronounced kinks in stoichiometric YBa2Cu3O7, at least, within the local density approximation.

Physics and Physicists: More Evidence The Public Can't Tell The Difference Between Scientific and Anecdotal Evidence

Physics and Physicists: More Evidence The Public Can't Tell The Difference Between Scientific and Anecdotal Evidence

Ferromagetism demises SC in overdoped LSCO ?

The phase diagram of cuprate superconductors is as perplexing as one can imagine. It is like winning a holy grail to theoretically explicate this diagram. One feature in it is the SC dome: the SC phase survives only a segment between x1 and x2. Much attention has been paid to the regime around x1, while little to that around x2. A basic question is, what destroys SC in the course of overdoping ? Experiments actually have found no traces of what can be seen in the vicinity of x1, the Mottness behaviors showing significant AFM fluctuations. Some claimed that, the compound becomes a normal Fermi liquid beyond x2, which is however questioned for several reasons [http://www.pnas.org/content/104/15/6123.full.pdf]. A novel proposal surmised that, there is a new order, a ferromagnetic order, that competes with SC [http://www.pnas.org/content/104/15/6123.full.pdf]. Their proposal finds advocate from an upturn in the uniform magnetic susceptibility that is usually associated with FM correlations. More interestingly, a recent experiment claimed a direct observation of this FM phase [http://www.pnas.org/content/107/40/17131.full.pdf]. This makes the x2-region very fashionable.

Cloak enough to cover visible objects

A team in UK recently fabricated a cloak that works under green light to make optical delusions [http://arxiv.org/ftp/arxiv/papers/1012/1012.2783.pdf]. This cloak is large and able to cover an object as large as 10mm^3. The physics is governed by Maxwell's equations. The substance is calcite, which has anisotropic optical properties.

Varma's Current

The short review [http://arxiv.org/PS_cache/arxiv/pdf/1012/1012.5461v1.pdf] of the history of High Tc superconductivity by J.Zannen has mentioned the work by C. M.Varma, who proposed the so-called circulating current phase as a candidate explanation of the observed pseudogap phase [http://prl.aps.org/pdf/PRL/v83/i17/p3538_1]. As beautiful as it seems, one should take caution with this: such current is incompatible with the formation of Zhang-Rice singlets. The only claimed experimental support of this phase comes from Neutron scattering and optical experiments which detected a time-reversal symmetry breaking state. However, it might be too hasty to identify this phase with the Varma's phase. Let's wait and see how the holy grail will be won !