Friday, May 18, 2018

PRL accepted: Nanomechanical characterization of the Kondo charge dynamics in a carbon nanotube

Today's great news is that our manuscript "Nanomechanical characterization of the Kondo charge dynamics in a carbon nanotube" has been accepted for publication by Physical Review Letters.

The Kondo effect is a many-body phenomenon at low temperature that results from a quantum state degeneracy, as, e.g., the one of spin states in absence of a magnetic field. In its simplest case, it makes a quantum dot, in our case a carbon nanotube with some trapped electrons on it, behave very different for an even and an odd number of electrons. At an even number of trapped electrons, no current can flow through the nanotube, since temperature and applied bias voltage are too low to charge it with one more elementary charge; this phenomenon is called Coulomb blockade. Strikingly, at odd electron number, when two degenerate quantum states in the nanotube are available, Coulomb blockade seems not to matter, and a large current can flow. Theory explains this by assuming that a localized electron couples to electrons in the contacts, forming a combined, delocalized singlet quantum state.
What carries the Kondo-enhanced current, and how does the electric charge now accumulate in the carbon nanotube? We use the vibration of the macromolecule to measure this. As also in the case of, e.g., a guitar string, the resonance frequency of a nanotube changes when you pull on it; in the case of the carbon nanotube this is sensitive enough to resolve fractions of the force caused by a single elementary charge. From the vibration frequency, as function of the electrostatic potential, we calculate the average number of electrons on the nanotube, and can then compare the odd and even number cases.
A surprising result of our evaluation is that the charge trapped on the nanotube behaves the same way in the even and odd occupation case, even though the current through it is completely different. Sequential tunneling of electrons can model the charge accumulation, and with it the mechanical behaviour. The large Kondo current is carried by virtual occupation of the nanotube alone, i.e., electrons tunneling on and immediately off again so they do not contribute to the charge on it.

"Nanomechanical characterization of the Kondo charge dynamics in a carbon nanotube"
K. J. G. Götz, D. R. Schmid, F. J. Schupp, P. L. Stiller, Ch. Strunk, and A. K. Hüttel
accepted for publication by Physical Review Letters; arXiv:1802.00522 (PDF, HTML, supplementary information)

Wednesday, April 11, 2018

Manuscript on Lab::Measurement submitted for publication

Today's news is that we have submitted a manuscript for publication, describing Lab::Measurement and with it our approach towards fast, flexible, and platform-independent measuring with Perl! The manuscript mainly focuses on the new, Moose-based class hierarchy. We have uploaded it to arXiv as well; here is the (for now) full bibliographic information of the preprint:
 "Lab::Measurement - a portable and extensible framework for controlling lab equipment and conducting measurements"
S. Reinhardt, C. Butschkow, S. Geissler, A. Dirnaichner, F. Olbrich, C. Lane, D. Schröer, and A. K. Hüttel
submitted for publication; arXiv:1804.03321 (PDF, HTML, BibTeX entry)
If you're using Lab::Measurement in your lab, and this results in some nice publication, then we'd be very grateful for a citation of our work - for now the preprint, and later hopefully the accepted version.

Sunday, March 18, 2018

DPG 2018, the proof: Yes we've been in Berlin!
The 2018 spring meeting of the DPG condensed matter physics section in Berlin is over, and we've all listened to interesting talks and seen exciting physics. And we've also presented the Lab::Measurement poster! Here's the photo proof of Simon explaining our software... click on the image or the link for a larger version!

Monday, January 8, 2018

FOSDEM 2018 talk: Perl in the Physics Lab

FOSDEM 2018, the "Free and Open Source Developers' European Meeting", takes place 3-4 February at Universite Libre de Bruxelles, Campus Solbosch, Brussels - and our measurement control software Lab::Measurement will be presented there in the Perl devrooom! As all of FOSDEM, the talk will also be streamed live and archived; more details on this follow later. Here's the abstract:
Perl in the Physics Lab
Andreas K. Hüttel
    Track: Perl Programming Languages devroom
    Room: K.4.601
    Day: Sunday
    Start: 11:00
    End: 11:40 
Let's visit our university lab. We work on low-temperature nanophysics and transport spectroscopy, typically measuring current through experimental chip structures. That involves cooling and temperature control, dc voltage sources, multimeters, high-frequency sources, superconducting magnets, and a lot more fun equipment. A desktop computer controls the experiment and records and evaluates data.

Some people (like me) want to use Linux, some want to use Windows. Not everyone knows Perl, not everyone has equal programming skills, not everyone knows equally much about the measurement hardware. I'm going to present our solution for this, Lab::Measurement. We implement a layer structure of Perl modules, all the way from the hardware access and the implementation of device-specific command sets to high level measurement control with live plotting and metadata tracking. Current work focuses on a port of the entire stack to Moose, to simplify and improve the code.


Sunday, September 10, 2017

Fun with Hertz car rentals, part 3 (it ends well)

If you've read the last part, I had just arrived at my hotel in Kyparissia late in the night, slightly fuming. Well...

Next morning, saturday, around 10:15 somebody called my mobile phone. For some reason I didn't notice, but only got a text notification of a missed call an hour later. I called back; turns out this was the Kalamata airport Hertz office. "Your replacement car has arrived; you can pick it up anytime."

I arranged to come by around 16:00 in the afternoon, and from here on everything went smoothly. Now I'm driving a white BMW Mini convertible, and the roof and windows work just fine.

In the end, obviously I'm quite happy that a replacement car was driven from Athens to Kalamata and that I can now continue with my vacation as planned. The path that lead to that outcome, however, was not so great...

Friday, September 8, 2017

Fun with Hertz car rentals, part 2 (or how to waste more vacation time!)

If you're reading this, the last act in this drama (see the previous blog post) was that in Patras a friendly employee from Hertz picked up the rental car to bring it to a repair workshop. A bit later than planned, but nevertheless. Now the story continues.

  • About 20:00 the same day I get a phone call from the same lady that my car was ready, and we could meet in about 20min next to my hotel so I can pick it up again. That sounded great to me. Some minutes later I saw the car coming.
  • Of course I wanted to try out the repaired roof / window immediately, so we did that. Opened the roof, closed the roof. The passenger side window did not close; precisely the same phenomenon. Oops.
  • I tried a few more times on instruction by the Hertz employee, with the result that the window got stuck at half height and did not move anymore even after shutting down and restarting the ignition. Since it was stuck on the wrong side of its rubber seal, also the passenger door did not open anymore.
  • The visibly nervous Hertz employee calls her manager on the mobile, who arrives after a few minutes. The manager opens the passenger door with application of force. Afterwards, and after restarting the engine, the window slides up again.
  • We have some discussion about a replacement car, where I point out that I paid a lot of money for having a convertible, and really want one. I agree to come to the office thursday morning to sort things out.
  • Next morning, Thursday, at the Hertz office, I'm glad to learn that a replacement car will be sent. Of course, I'm now leaving Patras, so the car will have to be sent to a station near my next stops.
  • We discuss this and agree that I will pick the car up tomorrow (Friday) afternoon in Kalamata (which is only about 80km from my Friday evening hotel in Kyparissia).
Oh well. Glad that things are somehow sorted out. I spend the rest of the day visiting a Mycenaean castle (1200 BC), a Frankish castle (1200 AD), and re-visiting Olympia, spend the night near Olympia, and then start towards Kalamata through the mountains via, e.g. the excavations of ancient Messene. Sometime on the way I realize that the Kalamata Hertz offices (according to the website) are closed 14:00 to 17:00, so I plan with arriving there around 18:00. That's ample time since they should be open 17:00 - 21:00 (search for Kalamata here).
  • Arrive 18:10 at the Kalamata city office. Nobody there, and there's a sign on the door saying "We are at Kalamata Airport."
  • Drive back the ~10km to the airport (which I passed on the way before). Arrive there around 18:30. The entire airport is already closed for the day. No Hertz employees in sight.
  • Call the Kalamata office. First response, "We closed half an hour ago." When I start explaining my problem, the lady on the phone says "But your car has not arrived from Athens yet!" I point out that I have to go back to Kyparissia, quite some way, today. She doesnt know when it will arrive, but says something about late evening. 
  • I tell her I will now get dinner here in Kalamata, and afterwards call her again.
That's where we are now. Just as a reminder, it's now Friday evening, and the problem has essentially been known to Hertz since last Sunday.

  • Tried calling the Hertz Kalamata office again around 20:45. No response, after a while some mailbox text in Greek. 
  • Drove back the 60km to Kyparissia, arrived at the hotel 22:00. Will call Hertz again tomorrow.
Update 2: Yes, Hertz knows my mobile phone number. It's big and fat on my contract, and I also gave it again and reconfirmed it to the employee at Patras. So, one could assume if something goes wrong they phone me...

Update 3: It ends well. See the next post.

Wednesday, September 6, 2017

Fun with Hertz car rentals (or how to waste vacation time)

So, I decided to get myself a rather expensive treat this summer. For travelling the Peloponnes I rented a Mini Cooper convertible. These are really cute, and driving around in the sun with the roof open felt like a very nice idea. I'm a Hertz Gold Club customer, so why not go for Hertz again.

I picked up the car in Athens, all looked fine. The first day I had some longer driving to do, and also the manual was only in Greek, so I decided to drive to my first stop and check out the convertible roof there. OK, with some fiddling I found and read a German manual on the BMW website (now I know where to find the VIN number, if anyone asks :), opened the roof, enjoyed half a day in the mountains near Kalavrita.

Afterwards the passenger side window didn't close anymore.

It turns out something was already bent or damaged inside the door, so the window was sliding up on the wrong side of its rubber seal. At some point it can't move any further, so the electronics stops and disables the window. The effect is perfectly reproducible, and scratch marks on the rubber seal and door frame indicate it's been doing that already for a while. Oh well.

  • Phoned the nearest Hertz office in Patras. After some complicated discussion in English they advised me to contact the office in Athens.
  • Phoned the Hertz office in Athens. I managed to explain the problem there. They said I should contact their central technical service office, since maybe they know something easy to do. 
  • Phoned the central technical service office. There the problem was quickly understood; a very helpful lady explained to me that most likely the car would have to be exchanged. Since it was Sunday afternoon, they couldn't do it now, but somebody would call me back on Monday morning 9-10.
  • Waited Monday morning for the call. Nothing happened. 
  • Phoned the central technical service office, Monday around 13:00. They asked me where I was. After telling them I'm going to Patras the next day, they told me I should come by their office there.
  • Arrived at the Patras office tuesday around 17:30. I demonstrated the problem to the lady there. She acknowledged that something's broken, and told me she'd come to my hotel the next day between 11:00 and 12:00 to pick up the car and bring it to the BMW service for repair. 
  • Now I'm sitting in the bar of the hotel, it's 12:30, no one has called or come by, and slowly I'm getting seriously annoyed.
Let's see how the story continues...
  • Update: 13:00, friendly lady from Hertz picked up the car. Fingers crossed. Made clear it's a long rental, so delaying makes no sense. Wants to phone me either in the afternoon or tomorrow morning.
  • Update 2: The drama continues in the next blog post.