Universiteit Leiden LION


Jan Zaanen

Universiteit Leiden
P.O. Box 9506
2300 RA Leiden
The Netherlands

Phone: +31-71-527 5506
Fax: +31-71-527 5511
Email: jan@lorentz.leidenuniv.nl

Jan Zaanen holds a chair of theoretical condensed matter physics at the Instituut-Lorentz. His core research interests are in the subject of quantum matter. Here are his CV and publication list.


*Quantum theory 2005

*Casimir Graduate School course on advanced condensed matter physics

On the light side

*Editorials in Nature & Science
It seems I could have become rich by having a career at the advertisement agency. I perceive it as a responsibility to use these peculiar skills to help out experimentalists with sophisticated PR. It is a matter of personal pride that the Nature editorship elected Pebbles as lead News and Views, despite the highly esoteric nature of the subject.

Nature Physics choose twenty years of high Tc superconductivity as the theme of their 'launch issue' aimed at the march meeting 2006. They did a wonderful job in collecting the opinions of the theoretical leadership. As related to the festivities surrounding the centennial of the discovery of superconductivity the dutch national science museum Boerhave arranged for a brochure with a piece by me describing the modern research in the subject. See also the chapter in the book "100 years of superconductivity" (Chapman and Hall, 2011) dealing with the history of the theory of high Tc superconductivity. After some earlier exposure In 2010 the New Scientist arranged for a theme issue on fifty ideas that might change science, with a contribution by my person advertising the recent flirtation between string theory and condensed matter physics. This also got attention in Nature . For the dutch reader, I wrote a hard selling piece on this subject matter for the Nederlands Tijdschrift voor de Natuurkunde, while the Volkskrant highlighted some human interest aspects.

*Oratie (inaugural lecture) december 2002 (in dutch).

*Popular piece in dutch, aimed at advertising the current excitement in high Tc superconductivity: Nederlands Tijdschrift voor de Natuurkunde 67, 270 (2001) -- "Hoge Tc's verleiding: quantum kritikaliteit en de verborgen orde" (originele, onverkorte versie)

*Popular piece in english, "Why high Tc is exciting", published in Annales Universitatis Mariae Curie-Sklodowska Lublin - Polonia 57, 9-22 (2002).

*Picture gallery

10 minute portrait of myself and my science made for TELEAC for dutch national TV (in dutch, broadcasted in 2001).

*Nationale Wetenschapsquiz
I am the proud winner of the VPRO - NWO Nationale Wetenschapsquiz 2004, after a lot of interesting hassles in 2003.

*Stanford Sabbatical
During the academic year 2004-2005 I was on the payroll of Stanford University as visiting professor and senior Fulbright fellow at the Physics Department. Among others, I acted like interim Bob Laughlin while he was making money and enemies in Korea, taking his office, his graduate quantum-physics course, and taking care of his junior coworkers Zaira Nazario and David Santiago. I had a wonderfully productive year, among others working with Shoucheng Zang et al. on spintronics, and Zhi-Xun Shen et al. on cuprates and manganites (News and Views) photoemission.

*Quantum bits
While at Stanford, the story on intrinsic decoherence together with Jasper van Wezel and Jeroen van den Brink triggered a remarkable amount of media attention.

Highlights from the past

  • My thesis work, often quoted as 'Zaanen-Sawatzky-Allen', is about the demonstration that Hubbards models in sufficiently generalized form have to do with the electronic structure of transition metal salts. It attracted an obscene number of citations at the height of the high Tc superconductivity hype, and it earned my advisor Sawatzky a lot of fame, which he surely fully deserves.
  • LDA+U, a density functional method taylored to incorporate Mott-physics in bandstructure theory. I can claim to have invented the functional (around 1990) but it would never have acquired its present status in the band structure world were it not for the hard work of Vladimir Anisimov.
  • The stripes of the high Tc superconductors. This started out as an accidental friday late-afternoon discovery in october 1987: the 'Zaanen-Gunnarsson' paper took 1.5 years to get published (for the connaisseurs of the refereeal system, I kept the files, these reports are very funny indeed!). I ran around with these stripes for some time in the late 1980's but in the process I got increasingly demoralized. I took it up again in 1992, and Vic Emery gets the credit for re-moralizing me. After my seminar in Brookhaven in 1992, Tranquada decided to look for them in Nickelates and this eventually triggered a mini-hype which peaked around 1999. Upon my return to Leiden in 1993 I went full force trying to develop the quantum theory of stripe liquids. A first attempt is the work with Horbach and van Saarloos, where you already find the basic ideas, although in hindsight the major claims made in this paper are wrong (again delayed for the wrong reasons by the refereeal proces for 1.5 years!). I abandoned this line of research by the discovery of the order-out-of-disorder physics, and you find a detailed exposition of this research in a quasi-review, and in the Handbook article. In the mean time I got seriously bored with stripe matters although it still excerts indirect influences on my present research.
  • Superconductivity in buckyballs. I co-authored a paper with Varma as first author claiming that this is the most classic example of all BCS superconductors [Science 254, 989 (1991)]. Although very influential, I am still quite sceptical, if not only because of the weird transport properties Palstra discovered very early on.
  • Spin-orbital-lattice systems. Alerted by Sawatzky about the existence of orbital degeneracies in real life 3d oxides I started to worry in 1988, based on flawed data by an italian group, about a possible mechanism for high Tc superconductivity based on triplet holes. It had the effect that I rediscovered the famous Kugel-Khomskii models, spurring my interest in this general subject. When this became fashionable with the arrival of the manganites I had basically lost interest, but it had the beneficial side effect that Feiner, Oles and myself discovered the dynamical frustration point in the classical limit of the KK model. This points at the possible existence of genuine spin-orbital quantum liquids, inspiring Keimer and coworkers to attempt to put this on the real axis.

Recent research interests (excluding AdS/CMT)

  • General description.
    In a broad sense, my interest has been, and continues to be primairily in the search for novel forms of collective quantum phenomena realized in systems build from mundaine constituents like electrons, spins, atoms, etcetera. Humanity got used already a long time ago to gasses, fluids, solids and magnets. The conventional quantum fluids (Fermi-liquids, superfluids and superconductors) are a much more recent discovery, and the topological states underlying the fractional quantum Hall effect are the latest. What comes next? In order to keep myself from wishful mathematical thinking I insist that nature should be around the corner. I am regarded by the world in first instance as a high Tc superconductivity expert, but I also keep a close track of the developments in quantum Hall, BEC's, manganites, quantum spin systems, heavy fermions, quantum computing, while I cannot resist to be fascinated by the stunning developments in cosmology. On the theoretical side, I am undoubtedly viewing this universe from the perspective of a quantum field theorist. To give a feeling, let me list the two fundamental problems which I perceive as most pressing:
    • General relativity and string theory are rooted in concepts involving geometry. Can such geometrical structures emerge as effective descriptions of collective quantum phenomena involving infinities of simple building blocks? The reasons to put this up first: (a) if true, a whole class of weird stuff should be around, and this stuff could possibly make some of us even rich. (b) The real reason is of course that it would resolve in one blow item 1 up to 10 on the mystery list of the high energy physicists. Gravity would be an emergent phenomenon, and general relativity no more than another effective theory which should not be mindlessly extrapolated to the Planck scale, while the cosmological constant, dark energy and whatever else is found important would surely find some trivial resolution.
    • The solution of the fermion minus sign problem. This problem is often misconcieved as a technical detail frustrating the careers of numerical simulators. It is much more. It is the nightmare of modern physics. At the moment one is dealing with an infinity of interacting fermions, it is a tragic fact that no methodology is available to handle the problem in a systematic, controlled fashion. The standard escapes are to either declare the non-interacting fermion gas to be the universal truth, or to suppose that fermions are completely eaten by collective bosonic fields. The devastating influences of the minus signs are most clearly felt in high Tc superconductivity, the subject of heavy fermions, and adjacent areas like the 2d metal-insulator transition. However, it permeates all of fundamental physics, from the nature of the core of neutron stars up to string theory. When you still think it is a non-existent problem, I am interested to hear your answer to the following simple question: can a state of matter exist, characterized by an irreducible sign problem in the scaling limit (i.e. it cannot be absorbed by an appropriate transformation) which cannot be adiabatically continued to the Fermi-gas?
  • Stripe review.
    For a recent exposition about my understanding of the stripe microscopy see the Handbook article I wrote recently together with Hans Brom: Handbook of magnetism and magnetic materials.
  • Stripe fractionalization.
    The sleep of many in the community is taken by the question: can the gauge principle be emergent so that in a condensed matter context the highlights of interacting quantum gauge-field theory can come alive? Is there (de)confinement in matter under earthly circumstances? This obsession emerged in the late 1980's when Anderson, Baskaran and others observed that the local constraints forming the fabric of strongly correlated electron problems can be turned into gauge fields. Up to the present day this is a very controversial subject, due to the absence of rigorous arguments demonstrating that anything of this kind is of relevance to nature. Zohar Nussinov was the first to see it and I rediscovered it independently, followed later by Eugene Demler and Subir Sachdev, dealing with quantum stripe liquids, or if you wish quantum disordered incommensurate colinear spin density waves (it is symmetry wise the same thing), a perfectly straightforward argument shows that its long wavelength dynamics is governed by Ising local symmetry. The construction rests on the geometrical side of gauge theory (the gauge fields as connections) and a most reasonable 'material' interpretation (i.e. a recipy how to make them from electrons, litterally) of the gauge fields and the physics they cause follows.
  • Geometrical order in Luttinger liquids.
    Started as a byproduct of stripe fractionalization, the hard work by the postdoc Ian McCulloch and the student Herman Kruis turned this in a story by itself. The bottomline is that 'squeezed spaces', simple geometrical constructions which are also at the heart of stripe fractionalization, 'rule the waves' in one dimensional physics. Although discovered quite some time ago by Ogata and Shiba in Bethe Ansatz solutions, and in a sense identified even earlier by den Nijs and Rommelse in spin one 'Haldane' chains, the squeezed spaces were percieved as excentricities occurring in special limits. We make the case that squeezed spaces are generic, that they dictate the structure of bosonization, and that they can even be identified in the non-interacting fermion gas. These insights help us to identify several new states of 1+1D quantum matter.
  • Duality in quantum elasticity: quantum liquid crystals and cosmology.
    I perceive this as our most substantive contribution in recent years. It has taken us (Sergei Mukhin, Zohar Nussinov, myself) some five years to sort this out. This excercise should have been done some twenty (or even fifty) years ago because it is so basic. Originally inspired on the ideas of Steve Kivelson and friends regarding the potential existence of quantum versions of the liquid crystals familiar from flat screen displays, this got lifted to a higher level when we discovered the brillaint ground work laid down by Hagen Kleinert. This allowed us to seek for a dynamical generalization of Hagen's dual descriptions of elasticity to the quantum regime. The outcome is that the superfluid or superconductor in 2+1D can be viewed as the dual of the bosonic elastic state where the Bose condensate of dislocations eats the shear stress by a Higgs mechanism. As a byproduct we come up with various novel quantum nematics. Upon telling this story to Hagen Kleinert he got in no time quite excited because it removed some severe problems in his earlier attempts to link the theory of elasticity to the Einstein theory of gravity. This work has close links to Zhang's four dimensional fractional quantum Hall state and Laughlin's quantum critical black hole horizon's.
  • Quantum criticality. This subject is really owned by Subir Sachdev, but I cannot resist to pay attention and to highlight it in colloquium style talks (popular accounts in dutch and english and original contributions (1, 2, 3). I also contributed some very simple thoughts to the latest experimental news on the 'quantum critical' state of the high Tc superconductors. The quotation marks are added because this work shows that actually the standard understanding of quantum criticality is not so subtly flawed when confronted with the real thing in the high Tc superconductors.