Theoretical Condensed Matter Physics
In January 2013 I managed to be at two places at the same time: in FOM Veldhoven and at the Winter School in the National High Magnetic Field Laboratory in Tallahassee, FL, USA. Okay, to be honest: I was physically in Florida, whilst Robert-Jan and Kai made sure my poster was presented in Veldhoven. Thanks guys!
The poster, entitled “Exciton condensation in strongly correlated electron bilayers“, can de downloaded here (PDF, 4.4 MB).
The extended paper on the properties of a single exciton, following up on my earlier Europhys Lett, is accepted and published in the New Journal of Physics.
Title: Dynamics of a single exciton in strongly correlated bilayers
Abstract: We formulated an effective theory for a single interlayer exciton in a bilayer quantum antiferromagnet, in the limit when the holon and doublon are strongly bound onto one interlayer rung by the Coulomb force. Upon using a rung linear spin-wave approximation of the bilayer Heisenberg model, we calculated the spectral function of the exciton for a wide range of the interlayer Heisenberg coupling α = J⊥/Jz. In the disordered phase at large α, a coherent quasi-particle peak appears, representing free motion of the exciton in a spin singlet background. In the Néel phase, which applies to more realistic model parameters, a ladder spectrum arises due to Ising confinement of the exciton. The exciton spectrum is visible in measurements of the dielectric function, such as c-axis optical conductivity measurements.
Reference: Louk Rademaker, Kai Wu and Jan Zaanen, New J. Phys. 14, 083040 (2012).
At the EXCON 2012 conference in Groningen and at the `Innovations in Strongly Correlated Electron Systems’ Summer School and Workshop at the ICTP (Trieste, Italy) I presented this poster about the most recent developments in the exciton business. You can download the poster here (PDF, 1.6 MB).
As a quasi-member of the Interfaces and Correlated Electron systems (ICE) group from Hans Hilgenkamp I joined the ICE2UK-tour. Together with Marcel Hoek, who is also on the VICI project, I gave a talk in Bristol – the hometown of Nevill F. Mott! We couldn’t resist, the talk is called ‘Mott insulator bilayers’, and can be downloaded here (PDF, 10 MB).
Title: Dynamics of a single exciton in strongly correlated bilayers
Abstract: We formulated an effective theory for a single interlayer exciton in a bilayer quantum antiferromagnet, in the limit that the holon and doublon are strongly bound onto one interlayer rung by the Coulomb force. Upon using a rung linear spin wave approximation of the bilayer Heisenberg model, we calculated the spectral function of the exciton for a wide range of the interlayer Heisenberg coupling \alpha=J_{\perp}/Jz. In the disordered phase at large \alpha, a coherent quasiparticle peak appears representing free motion of the exciton in a spin singlet background. In the N\'{e}el phase, which applies to more realistic model parameters, a ladder spectrum arises due to Ising confinement of the exciton. The exciton spectrum is visible in measurements of the dielectric function, such as c-axis optical conductivity measurements.
Reference: Louk Rademaker, Kai Wu and Jan Zaanen, arXiv:1202.3616
At this years edition of the annual Dutch Physics@FOM conference in Veldhoven I will present a poster entitled “Exciton condensation in strongly correlated electron bilayers“. Actually, for the first time the poster will actually be about exciton condensation, the initial goal of my PhD research.
In the picture here you see an excerpt from the poster, explaining the exciton t-J model Hamiltonian. The poster itself can be downloaded here (pdf, 1.3 MB).
The paper on the properties of a single exciton is accepted and published in the January issue of Europhysics Letters! (See the completely different arXiv version here.)
Title: The dynamical frustration of interlayer excitons delocalizing in bilayer quantum antiferromagnet
Abstract: Using the self-consistent Born approximation we study the delocalization of interlayer excitons in the bilayer Heisenberg quantum antiferromagnet. Under realistic conditions we find that the coupling between the exciton motion and the spin system is strongly enhanced as compared to the case of a single carrier, to a degree that it mimics the confinement physics of carriers in Ising spin systems. We predict that the “ladder spectrum” associated with this confinement physics should be visible in the c-axis exciton spectra of insulating bilayer cuprates such as YBa2Cu3O6. Our discovery indicates that finite density systems of such excitons should show very rich physical behavior.
Reference: Louk Rademaker, Kai Wu, Hans Hilgenkamp and Jan Zaanen, EPL 97, 27004 (2012).
On 9 September 2011 I was presenting my work on interlayer excitons (see this preprint) at the University of Utrecht in the so-called ‘BEC group meeting’ (that is: the groups of Henk Stoof, Rembert Duine and Cristiane de Morais Smith combined).
Title: Frustrated interlayer excitons in antiferromagnets (click to download the presentation in PDF, 3.6 MB)
In Erice (a beautiful place in Sicily, Italy) both a summer school and a workshop was held about “Quantum Phenomena in Graphene, other Low-Dimensional Materials, and Optical Lattices“. Needless to say I was there for the “other low-dimensional materials”, with lectures on bilayer exciton condensation (by Allan MacDonald) and oxide heterostructures. At the workshop part I presented a poster on my latest work on excitons in bilayer quantum antiferromagnets, which you of course can download here.
Poster title: Dynamical frustration of interlayer excitons in bilayer quantum antiferromagnets (PDF, 397 kB)
In addition, I discovered that Shou-Cheng Zhang used the picture Jeroen Huijben made for me in his presentation of topological insulators. Zhang’s presentation (amongst others) can be downloaded here.
Update: I presented this very same poster at the international conference on Optics of Excitons in Confined Systems (OECS12) in Paris, 12-16 September 2011.
Last week I put my work on exciton dynamics in strongly correlated bilayers onto the arXiv!
Title: The dynamical frustration of interlayer excitons delocalizing in bilayer quantum antiferromagnets
Abstract: Using the self-consistent Born approximation we study the delocalization of interlayer excitons in the bilayer Heisenberg quantum antiferromagnet (see figure above). Under realistic conditions we find that the coupling between the exciton motion and the spin system is strongly enhanced as compared to the case of a single carrier, to a degree that it mimics the confinement physics of carriers in Ising spin systems. We predict that the ‘ladder spectrum’ associated with this confinement physics should be visible in the c-axis exciton spectra of insulating bilayer cuprates such as YBa2Cu3O6. Our discovery indicates that finite density systems of such excitons should show very rich physical behavior.
Reference: Louk Rademaker, Kai Wu, Hans Hilgenkamp and Jan Zaanen, arXiv:1106.5347
