Electronic correlations are crucial in 2DEG based on STO

I have highlighted a number of studies on the 2DEG that were created about the interfaces based on SrTiO3 compounds. The 2DEG thus obtained have been shown with various interesting ground states including superconducting ones. Here comes a new work [Science, 331 (6019): 886-889] that demonstrates the importance of electronic correlations in determining the transport properties of this 2DEG. This time the 2DEG was introduced by inserting a RO layer, R=La, Pr,Nd,Sm and Y, in the SrTiO3 matrix. It turns out that, the electronic properties of this 2DEG are crucially hinging on the R element. For La, Pr and Nd, it is conducting while for the rest it is insulating.

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO₃) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO₃ matrix. Such correlation effects can lead to new functionalities in designed heterostructures.

Helical DNA filters spins

Spin filters might be salient devices in spintronics. One example of such filters is a ferromagnetic layer, which allows a spin in one direction to pass while blocks it in the other. The selectivity has been shown up to about 25%. Now a study using DNA makes a big difference, where the selectivity can be achieved of as high as 60%. In this case, periodic helice plays an essential role, but how this is so has not been understood yet [Science 18 February 2011: 894-897]. In general, it raises an interesting question on how an electron interacts with chiral supramolecules.

Göhler et al. (3) describe a surprisingly efficient method for electronic spin filtering. They have studied how electrons emitted by a gold substrate, upon absorption of light, pass through a self-assembled DNA monolayer on the gold surface. In particular, they have studied the spin of the electrons after their passage through the DNA layer and have found that one spin type passes through much more easily, meaning that this layer acts as a spin filter, strongly hindering the passage of the other spin type. This filter effect is observed only if the DNA is assembled on the gold surface as a closely packed ordered array of helices, and is stronger if the helices are longer, reaching selectivities of 60%. For chaotic assemblies of floppy DNA chains on the gold surface, the spin filter effect was not observed. [http://www.sciencemag.org/content/331/6019/864.full]

flaming tornado

It is always a pleasure to watch simple but 'wonder' provoking experiments like this one. It plays with flames. Places some fuel in a plate and ignite it and then trap it with a web cage. Now you spin the cage, and you'll see the flames grow tall and thin into a flame tornado. Ever wondered why ? It is actually easy to explain. Try it yourself. Cool !

A movie on Einstein

Hi, man, as a fans of him, I'm excited to read this ! I have never seem a film acting this big man's real life. So, it is really a wonderful thing to wait this thing to come. I read a lot of things about Einstein, and I would like to wipe eyes to test my memory.

HSI Films will handle worldwide sales on “Einstein” and immediately introduce the project to distributors in Berlin.

Said Eric Christenson, “Coming aboard a project that teams Wayne Wang and Ron Bass is tremendously exciting, and we have something special on our hands with ‘Einstein.’ People know the name and the theories, yet most people don't know the fascinating details of his life's story.”

Koldo Eguren added, “People don't know about his struggles with poverty, his dyslexia, his love for music, his relationships with the women in his life, his persecution by the Nazis and his battle to deal with living in the public eye and being under constant scrutiny. Ron's screenplay peels back the layers and allows us to see past Einstein the scientist and Einstein the celebrity, showing us Einstein the man.”

How do you get yourself less wet if you are caught in a rain ?

This is a daily problem and is funny enough and thus deserves a journal paper [Eur. J. Phys. v.32, p.355 (2011)] to deal with it. Unfortunately, I could not say more, as I'm not able to access it freely. Only the abstract is posted: "The question whether to walk slowly or to run when it starts raining in order to stay as dry as possible has been considered for many years—and with different results, depending on the assumptions made and the mathematical descriptions for the situation. Because of the practical meaning for real life and the inconsistent results depending on the chosen parameters, this problem is well suited to undergraduate students learning to decide which parameters are important and choosing reasonable values to describe a physical problem. Dealing with physical parameters is still useful at university level, as students do not always recognize the connection between pure numbers and their qualitative and quantitative influence on a physical problem. This paper presents an intuitive approach which offers the additional advantage of being more detailed, allowing for more parameters to be tested than the simple models proposed in most other publications."

Investigating into natural lighting

Lighting accompanies thunderstorms, during which large amounts of energy are released without being leased. Despite the ostensible familiarity, lighting is still enigmatic, as described in this interview:

We learn about lightning in school, I thought it was a closed case?
Well, we know lightning initiates up inside a thunderstorm but we're not sure how it initiates – how it gets started. In fact there are still three big questions. The first is the initiation. The second is how does it propagate, sometimes through miles of air? And the third is, when it reaches the ground – how does it choose to strike this object and not the other object?

But isn't it just an electrical discharge between thunderclouds and the ground?
In a sense, but the big problem is that to get a spark, air needs to break down. It needs to stop being an insulator and start being a conductor. We commonly experience this if you touch a doorknob and you get a spark between your finger and the doorknob. What happens is the charges get concentrated into your fingertip and you get a big electric field. Then, as your finger approaches, the conventional breakdown field is reached, which is about 3 million volts per metre – and then air sparks.

The problem is if you look up inside thunderclouds, the breakdown field that you need to make a spark is never found. People have been launching balloons for decades, they've been flying airplanes, they've been launching rockets...but the fields they record are not even close to this strength.

Back from vacation

Just came back from vacation. Time needed to catch up with what happened in the last two weeks. haha...