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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!

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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)

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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.

Reference: Louk Rademaker, Jan Zaanen and Hans Hilgenkamp, Phys. Rev. B 83, pp. 012504 (2011)

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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.

Exciton spectral function for alpha=0.2.

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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.

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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.

Title: Flux 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.