Finally I understand what my collaborators from Neel Institute are working on:
Btw, isn’t he the guy from the Daily Show?..
Finally I understand what my collaborators from Neel Institute are working on:
Btw, isn’t he the guy from the Daily Show?..
This is a sputtering machine. It is a high vacuum system inside of which argon plasma kicks atoms out of a target, after which the target atoms land onto a sample creating high quality thin films of metals or dielectrics.
This is the plasma:
The machine was made for us by AJA International in Massachusetts. It is a Pitt facility, but it is temporarily located in my lab since it is demanding as a flower (needs water and power), and there was no other place for it on campus.
The button has been pushed, and our two dilution fridges from Leiden Cryogenics are cooling down. Today they both reach 3 K and we start the condensation of He3/He4 mixture which is the first phase of the final cooldown to the base temperature of ~7 mK.
You can also here the pulse tubes humming, though from where I sit in the meeting room I almost don’t hear them, just see the fridges through the glass window.
This picture shows a semiconductor nanowire grown in Eindhoven that we contacted with gold leads. Because all of our measurements are “transport”, i.e. sending a current through a nanostructure, these contacts are absolutely necessary for us to go forward.
To make this sample, we spread nanowires on the surface of a silicon chip, then took pictures of them using an electron microscope. Based on the pictures we designed gold contacts are wrote them over the wire using electron beam lithography. The device in the picture was the first where we managed to send a current through a nanowire. A small step for mankind, a great step for a new lab.
This Spring semester I taught my first course, on the subject that is dear to my heart – Quantum Transport. I had fifteen students, counting also my entire group. All lectures are available on youtube, I hope they can help future group members and people from other labs.
A lot of the material was donated to me by colleagues in the field, for that I am greatful. However, the course was designed to my taste, with an emphasis on new experiments. I sacrificed a traditional historical approach and completely ditched all of the disordered stuff from the decades past. It has been fun to teach.
This is Allen Hall, a building of very interesting history, and home to our Department of Physics and Astronomy at Pitt.
But now and till September we are not living there, as it is undergoing a major upgrade on the inside. This is the second phase of physics renovation: our labs have already been finalized but they are located all over the mid-campus complex of buildings. In the renovated Allen Hall, the condensed matter group will occupy the entire 2nd floor (3rd from the ground). There will be offices there for faculty, students and postdocs, a new seminar room… Here is how it looks now:
This area will be our lounge, I mean discussion area, for which I am now trying to find a commercial grade espresso machine.
And my own office will be behind this door:
P.S. This post should calm down those who joined the blog early on and were thinking that it will be entirely devoted to half-finished construction projects. Stop sending me your nasty complaints!
We have an outstanding machine shop at Pitt. I am very impressed with the skill and creativity of the staff, and with how efficiently and timely they handle jobs.
Also important, the University supports the shop, we only pay for materials.
This is a very recent development, but I have decided to give everyone heads up. During a discussion last week we have uncovered a serious concern with our last year’s Science paper, that is likely to invalidate our conclusions regarding the observations of the signatures of Majorana fermions. There will most certainly be a retraction submitted to Science. Turns out, during our experiments we have overlooked a widely known reason for the observation of a zero-bias peak, which can be mistaken for Majorana. This same explanation will for sure apply for five other experiments that report zero-bias peaks. And the 200 theory papers that were published since will need to revise their optimistic statements. (Actually I am quite surprised that nobody pointed this out to us earlier).
The non-Majorana explanation, as reported by Uspensky in 1973 is Continue reading “Majorana update”
University of Pittsburgh has assembled an impressive and a fairly young cluster of researchers working on the fundamentals and applications of quantum mechanics. Pitt Quantum Initiative is a framework for increasing interactions within the cluster and for communicating with colleagues worldwide. In about a month we will have our first event to which we have invited a number of distinguished speakers.
Everyone is welcome to join! http://pqi.pitt.edu/events . I can already see this poster becoming a rare vintage item.
When I first entered my finished lab back in September I was brought to awe by the amazing piece of engineering stuck to the ceiling. It was a crane, that had a giant hook and moved in all three dimensions of space with a push of a button.
Despite its aesthetics, it was not quite right for the space. The thing was, the highest it could lift stuff was about half way between the floor and the ceiling, and it took so much space that if we moved it from one end to the other it would knock off equipment in its way. So unfortunately that wonderful beast had to go… Well this week we got a replacement – Crane 2.0 – a leaner, meaner younger brother with the same load capacity:
It is not electric, but it does conserve the most precious commodity we have in that lab – the vertical space. Thanks to everyone for a job well done. As for the old crane, I heard it went to a crane farm in northern Pennsylvania to play with his crane-friends. By the way it had enough cable to lower something down into the Earth’s mantle. Maybe we should have tried fracking with it…
With the help of Oxford Instruments and Levy group the Triton dilution fridge has been successfully cooled down. In this video you can see the test of the magnet as the field is swept through zero at a rate of few millitesla per second.
Two weeks ago I went back to Urbana, the place where I did my PhD, after 7 years of absence. It was good to be back, it felt like being at home. I met many new bright people, and people that I know and love for a long time. One of them is Celia Elliot who is the department’s keeper, at least when it comes to the spirit and the rich culture of Physics at Illinois. She showed me a box full of old strange stamps, like these:
They are graphs from somebody’s paper, flipped backwards. The story was that Professor Gordon Baym had this box in the trunk of his car for years, and one day he decided that Celia should have it. The side of the box said ‘1940’. Armed with that clue, Celia found the paper that these figures belonged to:
In the picture above you see Figures 1 and 20 from Bardeen’s paper. The drawings were prepared by an artist, then etched into these plates, and used to print the journal pages – in a way similar to Gutenberg’s printing press. “How silly and hard was the life of a scientist back then” was my first thought. But wait a minute – are we now doing anything profoundly different from what Bardeen had to do 70 years ago? We are taking a picture of our data and sending it to a journal, where they put it into a .pdf file. So the .eps format replaced the etched plates, and paper is replaced with a computer screen.
But the data, live raw scientific data, is not a picture – it is a bunch of numbers. We have everything at our fingertips to start sharing the bits and bytes of our data, for our colleagues to fit, analyze, and play with. We just need to start doing it.
ALso last week we received a much awaited delivery from Leiden – our own first fridge. Now sitting safely and neatly in the lab waiting for the installation.
The delivery had a few intense moments. Risking life in traffic. Thankfully Pittsburgh drivers are very polite when it comes to ‘Extremely fragile scientific equipment’.
Not every box fit through the doors. Our lab is separated from the outside world by a rabbit-hole type corridor. This is maybe good for Alice in Wonderland, but this is one thing I’d change if I could.
“I am going to count till three, and if you don’t come out I am gonna start drilling”.
One brave student was abandoned outside for a good half hour. We literally forgot about him. He did not leave his important post protecting the box.
Last week I went out with the group. We celebrated Chinese New Year. And what better place to do it than a local French restaurant?
The lab is very lively now, everyone is busy with fridge installation, nanowire positioning, sample design, eating, sleeping… Yesterday the first item broke down, which is a good indication that work is being done.
In parallel, I am very lucky to be able to teach a Special Topics course this semester. I chose ‘Quantum Transport’. I hope it will benefit my group and a couple other groups in Pittsburgh. Helps us get on the same page in terms of background for research. The lectures are recorded by CIDDE, and I post them on youtube: https://sergeyfrolov.wordpress.com/teaching/
Last semester was lab building, this one will be group building.
This nice coffee machine was donated to us by Levy group today. Yay! Now we are awaiting gifts from other groups.
This setup can be viewed as temporary arrangement to get us through the tough period of setting up the lab, and as support on the way to our final goal:
In other kitchen news, several days ago I bought dried majoram (origanum majorana). For cooking. But when I wanted to use it I could not find it in my house… Until I looked inside the fridge! This must be a powerful habit I developed to always put majorana in the fridge.
This Oxford Instruments cryo-free dilution system is a campus facility. But we have adopted it since the University has set up our lab space so nicely just for this kind of equipment. Coincidentally, the first fridge from Leiden has been shipped today after thorough testing, and work on the second Leiden system is well under way.
We make devices out of semiconductor nanowires which are filamentary crystals that grow like a forest on flat substrates. One challenge that we face is to cut down the forest, isolate a single nanowire and build it into a multilayer structure of a transistor-like device. For years we used to rely on a ‘random’ method: grab thousands of wires and spread them on a chip where we wish to fabricate a transistor. But now we have this neat setup:
It is an optical microscope just powerful enough to barely make out a single nanowire. Next to it is a micromanipulator featuring three grey knobs for moving in X-Y and Z. In this setup we are able to break off a single nanowire from the forest, carry it over to another chip and place it in a desired location.
Here is an example where my student picked up a couple of nanowires (this sometimes can happen) and dropped them in between markers that will help us find back the location later. The idea of this setup came to me from Aachen, where students in the group of Prof. Morgenstern showed me a similar setup. I am greatful to them, as it makes our life much easier. They have published a very nice paper reviewing this instrument.
Isotope He-3 is a very rare and interesting substance. For example, it becomes a fermionic superfluid when cooled below a few milliKelvin. Along with its slightly heavier brother He-4, it is one of the two quantum liquids, meaning it remains liquid (in theory) down to absolute zero temperature. By circulating it in a closed loop one can produce cryogenic temperatures below 1 degree Kelvin, where all other substances turn solid. So most low temperature experiments rely on He-3.
Here are two stories about He-3, one of them mostly true, the other mostly false. I will not tell you which is which. But I will tell you that one of them is a plot of a recent movie.
Story #1. United States government stockpiled all He-3 available on the planet. After the generals find out that He-3 can be used to detect radioactive isotopes, a plan emerges to build a wall around the U.S. borders with designated gates equipped with neutron detectors that run on He-3. As a first stage of the program, all He-3 is made unavailable and declared a national security resource. Research in low tempearture physics, medical imaging and fusion comes to the brink of a halt. A black market emerges with overpriced He-3 from shady sources like Russia and possibly Canada. Students who loose He-3 in their labs are never seen again.
Story #2. In 1945 Nazis manage to send a space ship to the dark side of the Moon. The primary mission was to harvest He-3, abundant on the Moon, which they were going to use for world domination. They have established a base and built a refinery. They also built a space fleet capable of destroying Earth. Now all they need to launch an invasion is an iPad to navigate the ship.