## Physics@FOM Veldhoven 2010 / Lorentz Workshop April 2011 Poster

At the Physics@FOM Veldhoven 2010 (January 19, 2010) conference I presented a poster with the title “How a Neutral and Massless Superfluid can still exhibit Flux Quantization” (pdf, 2.8 MB).

Image: In concentric bilayers a supercurrent of excitons will exhibit a quantization of the flux in between the two cylinders. The magnetic field lines are shown in red. (Figure made by Jeroen Huijben.)

Update, March 12, 2010: Recently we found that the results, as presented in Veldhoven, were not completely correct. Flux quantization does appear in exciton double layers, however, the trapped flux must be a multiple of $latex \frac{h}{e} \chi_m$ where $latex \chi_m$ is the diamagnetic susceptibility of the exciton double layer.

Update, April 4, 2011: At the Lorentz workshop ‘100th Anniversary of Superconductivity’ I presented a corrected version of the poster. The results have by now been peer-reviewed and published in PRB. On this website I replaced the incorrect old version with the new correct version!

## Presentation at the DRSTP Spring School 2011

This year at the Dutch Research School for Theoretical Physics AIO/OIO School for Statistical Physics and Theory of Condensed Matter (aka the DRSTP SPTCM School 2011) I gave some introduction to the idea of linear spin-wave theory and how it can be applied to interlayer excitons. More information on the school itself can be found here, the presentation itself can be downloaded below.

Title: Excitons and spins in strongly correlated systems (pdf, 741 kB)

## Publication: Prediction of quantization of magnetic flux in double-layer exciton superfluids

My work on flux quantization in exciton superfluids finally culminated into a paper published in PRB. A preprint version (which is slightly different) can be found on the arXiv.

Title: Prediction of quantization of magnetic flux in double-layer exciton superfluids

Abstract: Currently, there is no way to detect unambiguously the possible phase coherence of an exciton condensate in an electron-hole double layer. Here, we show that, despite the fact that excitons are charge neutral, the double-layer exciton superfluid exhibits a diamagnetic response. In devices with specific circular geometry, the magnetic-flux threading between the layers must be quantized in units of h/e χm, where χm is the diamagnetic susceptibility of the device. We discuss possible experimental realizations of the predicted unconventional flux quantization.

## Physics@FOM Veldhoven poster on exciton motion

This years contribution to the annual FOM meeting in Veldhoven is a poster entitled “Exciton motion in strongly correlated heterostructures” (PDF, 700 kB). It was a combined poster with my collaborators from Twente (Marcel Hoek, Francesco Coneri and Hans Hilgenkamp), who were responsible for the experimental part; and with Kai Wu and Jan Zaanen, my theoretical colleagues in Leiden.

## Presentation at Stripe Club, january 2011

Today Kai Wu and I gave a presentation at Jan Zaanen’s group meeting called the “Stripe Club”. Our presentation was named “The motion of a single exciton in a bilayer quantum antiferromagnet” (PDF, 1.9 MB). In summary: we developed a spin wave theory for the bilayer Heisenberg model in order to describe the motion of an exciton through such a bilayer, which we solved using the self-consistent Born approximation. Recently, we obtained numerical results for the exciton spectral function. It appears to be that the Ising-type ladder spectrum reappears even though quantum fluctuations are taken into account, as you can see in the following ‘teaser’ result for alpha=0.2.

## arXiv preprint: Prediction of the quantization of magnetic flux in double layer exciton superfluids

I just posted a preprint paper on the arXiv, with the following abstract.

Currently a way is lacking to detect unambiguously the possible phase coherence of an exciton condensate in an electron-hole double layer. Here we show that despite the fact that excitons are charge-neutral, the double layer exciton superfluid exhibits a diamagnetic response. In devices with specific circular geometry the magnetic flux threading between the layers must be quantized in units of $latex \frac{h}{e} \chi_m$ where $latex \chi_m$ is the diamagnetic susceptibility of the device. We discuss possible experimental realizations of the predicted unconventional flux quantization.

See the whole article at arXiv:1009.1793.

## Presentation at Casimir Spring School 2010

Last week at the Casimir Spring School 2010 I was invited to give a talk on my work on ‘Flux Quantization in Double Layer Exciton Superfluids’. With this talk I was awarded the prize for best oral presentation! 🙂 You can download the presentation here in Powerpoint-format. Note that this talk is intended for general physics PhD-audiences. A more theoretical talk can be found here.

TitleFlux Quantization in Double Layer Exciton Superfluids (pptx, 7.5 MB)
Abstract: We predict an unconventional magnetic flux quantization effect to occur in double layer exciton superfluids and we discuss designs for a device to measure this universal electromagnetic signature of the exciton superfluid. This would provide an unambiguous test for the macroscopic phase coherence associated with an exciton Bose-Einstein Condensate.

## Hilgenkamp appointed as professor Experimental Physics in Leiden

Today my supervisor Hans Hilgenkamp got appointed as professor in Experimental Physics at Leiden University. In the corresponding press release (in Dutch) I’m mentioned in the third paragraph, as I’m his only PhD-student in Leiden. The press release describes briefly the main focus of our research: electron correlations at interfaces.