Switching polarization in FE in a continuous way

Due to symmetry, domains usually occur in any ferroics. Each domain represents one episode of possible low energy configurations that are allowed by symmetry. Domains are separated by domain walls. Every wall has a definite thickness, across which the order parameter changes continuously but rather steeply. By applying an external field, the polarization of a domain can be switched, either continuously or abruptly. In this experiment [PRL 105, 167601 (2010)] on a PbTiO3 thin film, the switching takes place in a continuous way: the original polarization gradually diminishes to zero as the field increases and grows up in the other direction from zero. There is no threshold value required. It might be a very interesting question to study the general conditions for continuous and abrupt switching.

Magnetic oscillations observed in Cuprates and their implications

There have been the very prolonged debate on the nature of the fermi surface measured of cuprate superconductors. Magnetic oscillations are the conventional probe in mapping out the surface. Here is an overview [Physics 3, 86 (2010)] of what has been learned in this field, with a useful list of resource references.

CO2 as the climate control knob

Ample physical evidence shows that carbon dioxide (CO₂) is the single most important climate-relevant greenhouse gas in Earth’s atmosphere. This is because CO₂, like ozone, N₂O, CH₄, and chlorofluorocarbons, does not condense and precipitate from the atmosphere at current climate temperatures, whereas water vapor can and does. Noncondensing greenhouse gases, which account for 25% of the total terrestrial greenhouse effect, thus serve to provide the stable temperature structure that sustains the current levels of atmospheric water vapor and clouds via feedback processes that account for the remaining 75% of the greenhouse effect. Without the radiative forcing supplied by CO₂ and the other noncondensing greenhouse gases, the terrestrial greenhouse would collapse, plunging the global climate into an icebound Earth state.

http://www.sciencemag.org/cgi/content/full/330/6002/356

Topological Insulators used to determine fundamental constants

Topological phenomena (TP) play crucial role in determining the precise values of fundamental constants such as elementary charge, Planck constant and speed of light. This is so because of the robustness of topological phenomena against local variation in samples and also weak disorder and interactions between particles. Some famous TP have already been in use to this end: the quanta of magnetic flux has been measured with circular superconducting devices; the electrical conductance has been measured with the help of quantum Hall effect. Recently, a new TP was discovered in materials now known as topological insulators (TI). These materials are characterized by their bulky band gap and gapless surface states that are topologically robust. Examples include Te-Bi type compounds. It is expected that, such TP may also be employed to improve the precision of measurement. This came to realization in a latest publication [PRL 105, 166803 (2010)]:

Fundamental topological phenomena in condensed matter physics are associated with a quantized electromagnetic response in units of fundamental constants. Recently, it has been predicted theoretically that the time-reversal invariant topological insulator in three dimensions exhibits a topological magnetoelectric effect quantized in units of the fine structure constant ¼ e2=@c. In this Letter, we propose an optical experiment to directly measure this topological quantization phenomenon, independent of material details. Our proposal also provides a way to measure the half-quantized Hall conductances on the two surfaces of the topological insulator independently of each other.

Friction not so simple

Friction is certainly a standard part of middle school physics courses. It is observed that, to move an object in contact with another one, a force must be applied larger than the static friction, which is supposed to be uniform across the interface. However, this picture is inadequate. Actually, it was perceived that non-uniformity occurs at least locally. Understanding the nature of friction and how to model it better is not only theoretically interesting but practically imperative, because friction is relevant to a plenty of phenomena, such as rampant earthquakes and snow ruptures. Friction is the force that holds those events from bursting out. On the hand, it is also desirable to gain insight into how slip occurs locally when friction fails. This is key to modeling. This latest publication investigated this problem.

The way in which a frictional interface fails is critical to our fundamental understanding of failure processes in fields ranging from engineering to the study of earthquakes. Frictional motion is initiated by rupture fronts that propagate within the thin interface that separates two sheared bodies. By measuring the shear and normal stresses along the interface, together with the subsequent rapid real-contact-area dynamics, we find that the ratio of shear stress to normal stress can locally far exceed the static-friction coefficient without precipitating slip.
Moreover, different modes of rupture selected by the system correspond to distinct regimes of the local stress ratio. These results indicate the key role of nonuniformity to frictional stability and dynamics with implications for the prediction, selection, and arrest of different modes of earthquakes.

Molecules filtering spins

Using STM with a magnetic tip can be used to probe the magnetic feature of a surface. The tunneling current shall be sensitive to the alignment (collimation) between the spin orientation of the surface and that of the tip. If the tunneling, as is usually the case, is non-magnetic, then parallel alignment yield a bigger current. A very valuable aspect of STM is that this device probes the local properties of a material. This makes it especially useful in investigating defects or impurities of a surface. Now these authors [Phys. Rev. Lett. 105, 066601 (2010)] came to examine what will happen to the signal if the electrons tunnel from the Fe surface into the tip through a single organic molecule with Beneze rings. The result is this: this molecule allows more spin-up electrons to pass. So, it works as a selective valve, which may be tailored to specific applications that needs manipulate spin current. This phenomenon was predicted 3 years ago in Ref.[3], where the computation was implemented in the aid of DFT. However, it may prove more elucidating if a simple model description is prescribed.
For convenience, some references are attested on this subject:

1. Atodiresei, N. et al. Phys. Rev. Lett. 105, 066601 (2010).
2. Brede, J. et al. Phys. Rev. Lett. 105, 047204 (2010).
3. Rocha, A. R. & Sanvito, S. J. Appl. Phys. 101, 09B102 (2007).
4. Barraud, C. et al. Nature Phys. 6, 615–620 (2010).
5. Sanvito, S. Nature Phys. 6, 562–564 (2010).
6. Cinchetti, M. et al. Nature Mater. 8, 115–119 (2009).
7. Drew, A. J. et al. Nature Mater. 8, 109–114 (2009).
8. Szulczewski, G., Sanvito, S. & Coey, J. M. D. Nature Mater. 8, 693–695 (2009)

Pioneering papers on Graphene

1. Novoselov, K. S. et al. Science 306, 666-669 (2004). | Article | PubMed | ISI | OpenURL | | ChemPort |
2. Zhang, Y. et al. Nature 438, 201-204 (2005). | Article | PubMed | ISI | OpenURL | | ChemPort |
3. Novoselov, K. S. et al. Nature 438, 197-200 (2005). | Article | PubMed | ISI | OpenURL | | ChemPort |
4. Kim, K. S. et al. Nature 457, 706-710 (2009). | Article | PubMed | OpenURL | | ChemPort |