Introduction to Solid State Physics

Last semester I recorded 23 lectures on Solid State Physics for Undergraduate students. The first 15 lectures are following the wonderful texbook by Steven Simon “Oxford Solid State Basics”, and the last lectures cover superconductivity and advanced topics from Quantum Transport. This class can be a prequel to my Quantum Transport course and I hope it will be useful for students thinking of going into condensed matter research.

Because this is so great for binge watching, I am releasing the whole season at once.

Back to the Future

So there is this great movie that you should totally go see, it is about an eccentric scientist who befriends a simple-minded neighborhood teenager and sends him backwards in time in a car converted into a time machine…

Something like this just happened in our lab. We started out a couple of years ago as a cryogen-free operation. Instead of relying of liquid helium, we used closed-cycle cryostats where helium circulates between a compressor and a cryostat and extracts heat from a vacuum-shielded volume. There are two reasons why cryogen-free systems are great – they save money on (pricey) liquid helium and they are easy to operate at a push of a button.

But in the meantime our generous university set up a helium liquefier, which supplies nearly-free liquid helium to us. And so now we built our first liquid helium setup – a dunker stick! It derives its name from a concept of dunking your specimen into liquid helium in order to reach a low temperature of 4.2 Kelvin, at which helium is stored in liquid form.

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From the technological point of view, it is a step back compared to our cryofree setups. But we can use it for many quick measurements and tests, which is great.

Rashba Effect at 35

Last year was the 35th anniversary of the seminal paper by Bychkov and Rashba which introduced a spin-orbit coupling which is now known as “the Rashba effect“. It is a beautiful piece of physics that brings a bit of relativity into condensed matter world. Turns out, in an electric field (or under a broken symmetry) electron spins in a solid can behave as if they are in a magnetic field.

Anyhow, 35 years later the Rashba effect lives on and find itself at the frontiers of some of the hottest research of the 21-st century, as you can convince yourself by arxiving it (it is like googling but with arxiv.org).

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So a few months ago Aurelien Manchon approached me and several other folks to be part of a review of what is the face of Rashba effect 35 years later. As with all manuscripts, preparation took forever, so we are celebrating the 35th birthday of Rashba effect one year later. But finally the paper it out there and we are hoping it can serve those who want to know how Rashba spin-orbit physics beats along with spintronics, quantum computing, topological physics and cold atomic research.

I learned a lot about spin-orbit interaction myself from working on this review, I also learned the difference between stirring and steering, as in ‘steering wheel’ not ‘stirring wheel’ (thank you, anonymous referee!).

Helium Liquefier

Our University has sacrificed a parking lot to realize this project:

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It is an expansion to the machine shop which among other things now hosts this helium liquefier:

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Our lab is now connected to the helium recovery system, and we are building our first “wet” cryostat in which liquefied helium is used to cool a sample to 4.2 degrees Kelvin (-269 degrees centigrade). We are also now officially shopping for a used wet dilution refrigerator.

Quantum Triangles

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A friend once told me that all that physicists ever measure is either a sine wave or a straight line. Nothing proves him wrong better than this piece of data we obtained by measuring on a semiconductor nanowire device (Ge/Si nanowires). These double-triangles represent a charge stability diagram of a double quantum dot. Charge stability actually happens in between the triangles, where current is zero (blue), and the number of charges on each of the two quantum dots is fixed. We don’t know how many charges are there on each dot but it is few tens. In the triangular regions, charges move because they have enough energy to jump from one quantum dot into the other and out into the lead that takes them to our ammeter. Inside the triangles, we get a glimpse of quantum energy levels, orbital and spin, of the particles trapped in quantum dots – those energy levels are the stripes of the triangles. The axes of the graphs are voltages on remote electrodes located 10 nanometers away from the nanowire, voltages on these electrodes (gates) are used to change the capacitive energy of the quantum dots.

Pittsburgh Nano Jobs

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Our university’s Nanoscience Institute (PINSE) is looking for a Technical Director to run the nanofabrication and characterization facility. The job is part of a major reinvestment effort, and the new Director will play a central role in how the facility will look and operate going forward. We want to attract a truly outstanding candidate, so we are trying to spread the word as far and wide as we can.

The job ad is here: PINSE Technical Director

http://nano.pitt.edu/