Dror Orgad

Office: Danciger B 214
Phone: (972-2) 6586980
Fax: (972-2) 6586168
Email: orgad@phys.huji.ac.il
Research Interests:

A comparison between (a) the measured spectral function of a cuprate (LNSCO) and (b) the spectral function of an interacting one-dimensional electronic system. From 'Evidence for Electron Fractionalization From Photoemission Spectra in the High Temperature Superconductors', D. Orgad et.al, Phys. Rev. Lett. 86, 4362 (2001).

In the conventional quantum theory of the electronic structure of solids the interacting and the free spectra are adiabatically connected, the strong bare couplings are significantly renormalized and the resulting state is that of a weakly interacting gas of excitations.
This approach, known as the "Fermi-liquid theory'', has been extraordinarily successful at describing the properties of metals and semiconductors.
However, in the last two decades a large number of materials has been discovered in which the Fermi-liquid paradigm breaks down. Among the systems in question one finds the fractional quantum Hall effect, high mobility semiconducting devices which appear to show metal-insulator transition in two dimensions, the cuprate high-temperature superconductors, and other oxides, including the ruthenates, the nickelates and the colossal magnetoresistance materials - the manganites. There is a clear need for new theoretical principles and techniques to deal with the wealth of novel behaviors that these systems exhibit. I take part in the search for such principles.

In my work I have focused my attention on two problems in particular. The first is the interacting two-dimensional electron gas in a strong magnetic field. This system exhibits a plethora of exotic phenomena such as the fractional quantum Hall effect and the existence of excitations with fractional charge and statistics. In addition to that, the edges of such samples offer a realization of a peculiar state of matter, the "Luttinger liquid", made out of interacting electrons moving in one dimension. I have been interested in its properties and the way it is born out of the physics that governs the bulk of the sample.

I have carried my interest in low-dimensional interacting systems to the field of high temperature superconductivity which currently constitutes my prime field of study. One concept that has emerged in this context is the electronic stripe phase in which the charge carriers spontaneously segregate into one-dimensional "rivers of charge". There is a growing body of experimental evidence supporting the existance of such phases in the cuprate high temperature superconductors and other systems, most recently in quantum Hall samples.
Stripes occur commonly in systems with short range attractive interactions and long range repulsive forces. In the cuprates, which become superconductors upon doping of holes into an antiferromagnet, the holes tend to phase separate in order to reduce the energetic penalty associated with their motion through the antiferromagnetic background. However, owing to the presence of long range Coulomb forces complete phase separation is averted and stripes emerge as the best compromise. I am pursuing an understanding of the electronic properties of stripe phases and their relation to the phenomenology of the high temperature superconductors.

Selected Publications:

"From the Chern-Simons Theory for the Fractional Quantum Hall Effect to the Tomonaga-Luttinger Model of Its Edges'', D. Orgad, Phys. Rev. Lett. 79, 475 (1997).

"Dimensional Crossover in Quasi-One-Dimensional and High T_c Superconductors'', E. W. Carlson, D. Orgad, S. A. Kivelson and V. J. Emery, Phys. Rev. B 62, 3422 (2000).

"Evidence for Electron Fractionalization From Photoemission Spectra in the High Temperature Superconductors'', D. Orgad, S. A. Kivelson, E. W. Carlson, V. J. Emery, X. J. Zhou and Z. X. Shen, Phys. Rev. Lett. 86, 4362 (2001).

"Concepts in High Temperature Superconductivity", E. W. Carlson, V. J. Emery, S. A. Kivelson and D. Orgad, review chapter in "The Physics of Superconductors: Superconductivity in Nanostructures, High-Tc and Nivel Superconductors", Vol 2, p. 275-452, edited by K. H. Bennemann and J. B. Ketterson (Springer-Verlag 2004).

Present Graduate Students:

  • Shirit Baruch

  • Uri London

Collaborators Outside of the Hebrew University:

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