Welcome to the homepage of Emil Johansson Bergholtz. I am doing research in theoretical physics in the Quantum and Field theory group at Stockholm University.
I defend my PhD thesis "One-dimensional theory of the quantum Hall system" on May 28, 2008 (here is a picture, my introductory talk, and the document showing that I survived...). My thesis advisor was Anders Karlhede, and the faculty opponent was Nick Read form Yale. I also did my undergraduate studies at Fysikum, Stockholm University, where I started at the so called "forskargrenen" in 1999 and presented my Master's thesis in 2002. I defended my Licentiate thesis on September 28, 2005.
In september, I will move to Dresden, to join the condensed matter group lead by Roderich Moessner at the "Max Planck Institute for the Physics of Complex Systems".
The main topic of my thesis work has been a one-dimensional description of the quantum Hall (QH) system (2D cold electrons in a strong magnetic field). Although the QH system is two-dimensional it is in fact effectively one-dimensional when it is restricted to a single Landau level, within which most of the astonishing phenomena in the system occurs. We have exploited this fact to describe both abelian (hierarchical) and non-abelian QH states as well as gapless states (eg half filling) starting from the microscopic hamiltonian describing the system of strongly interacting electrons. In particular we have identified an exactly solvable limit of the QH problem (corresponding to electrons moving on the surface of a thin torus), which we claim to be of relevance for the experimentally accessible regime. For an introduction to this see our non-technical review article cond-mat/0611181, or the original publications Phys. Rev. Lett. 94, 026802 (2005) and J. Stat. Mech. (2006) L04001 (all with Anders Karlhede). If you would like an exhaustive discussion as well as proofs of our claims you should also have a look at Phys. Rev. B, 77, 155308 (2008).
How the 1D analysis shed some light on non-abelian pfaffian state is explained in Phys. Rev. B 74, 081308(R) (2006) (with Janik Kailasvuori, Emma Wikberg, Anders Karlhede and Hans Hansson). This state supposedly describes the \nu=5/2 quantum Hall state and has attracted great recent interest due to its supposedly non-abelian statistics of the quasiparticles and its possible application to topologically protected qbits (decoherence free quantum computational devices). A generalization of this analysis, to more general non-abelian states, is given in J. Stat. Mech. (2008) P04016 (with Eddy Ardonne, Janik Kailasvuori and Emma Wikberg)
Lately, we have also been interested in the role of conformal field theory (CFT) in the QH effect. We have used this connection to construct microscopic candidate wave functions for a large class of hierarchy states in terms of CFT correlators. These wave functions coincide with those due to Laughlin and Jain whenever these exsists, and reduces to the exact ground states in the solvable (thin torus) limit. Thus the CFT construction very nicely connects to our 1D construction as outlined in Phys. Rev. Lett. 99, 256803 (2007) (with Maria Hermanns, Hans Hansson and Anders Karlhede). This paper also contains a microscopic derivation of the hierarchy construction and the global phase diagram of the quantum Hall system. Further details of the CFT construction are given in Phys. Rev. B, 77, 165325 (2008) (with Maria Hermanns, Hans Hansson, Anders Karlhede and Susanne Viefers).
Recently we completed a technical project where we constructed hierarchy wave functions on the torus. Previously not even the form of Jain's wave functions were known in this geometry. This work is presented in Phys. Rev. B, 77, 125321 (2008) (with Maria Hermanns, Juha Suorsa, Hans Hansson and Anders Karlhede)
During my final year (2007/2008) I was teching on the course "Quantum Mechanics III" (advanced course). For more information (including my former teaching duties) see my teaching page.
There is quite a lot of summer schools, conferences and such things to attend im my area of physics. Here I list some of those that I have attended.
In December 2007 I gave a seminar at Max Planck Institute for the Physics of Complex Systems in Dresden.
In october 2007 gave a seminar at Freie Universität in Berlin.
I recently gave a talk on "The Quantum Hall system: solvable limit and beyond" on the Nordita program on quantum fluids .
In March 2007 I attended the APS March meeting in Denver, Colorado. I gave a talk titled "A simple view on the quantum Hall system".
In 2006 I was in France attending the Les Houches summer school on Quantum Magnetism .
I attended the 2006 APS March Meeting in Baltimore, where I presented our theory of the Half-filled lowest Landau level: "An Exact Solution for the Half-filled Lowest Landau Level".
I have participated at three summer schools (Master Class 2001, 2002 and Strongly Correlated Electrons 2003) at Nordita in Denmark (Nordita has now moved to Stockholm).
The network "Low-dimensional physics: The theoretical basis of nanotechnology", which I am a happy member of, arranges many nice conferences. In 2006 we met in Stockholm, at Lofoten and finally in Jyväskylä. In 2007 we will visit Lund and Göteborg.
In 2004 I went to Zuoz in eastern Switzerland for a nice summer school.
You can find out about current research in physics, mathematics and computer science etc here: http://xxx.lanl.gov/ .
My research group: www.kof.physto.se .
A new website (under construction) that provides numerical codes especially well suited for theoretical condensed matter research: http://alps.comp-phys.org/ .
Courses given at Fysikum: www.physto.se/studentexpedition/scheman/blockschema.html .
Visiting address: Roslagstullsbacken 21
Room: A5:1075
office: +46 8 5537 8742
mobile: +46 70 473 6063
