Regensburg 1998 – wissenschaftliches Programm

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SYD: Symposium Phasenübergänge in Elektronensystemen mit Wechselwirkung

SYD 1: Phasenübergänge in Elektronensystemen mit Wechselwirkung I

SYD 1.2: Fachvortrag

Mittwoch, 25. März 1998, 15:10–15:30, H3

Magnetic quantum phase transition of clean and disordered itinerant electrons — •Thomas Vojta^1,2, Dietrich Belitz², and Theodore R. Kirkpatrick³ — ¹Institut für Physik, Technische Universität, D-09107 Chemnitz — ²Department of Physics, University of Oregon, Eugene, OR 97403 — ³Department of Physics, University of Maryland, College Park, MD 20742

Itinerant electrons at zero temperature can show a phase transition from paramagnetic to ferromagnetic behavior as a function of the exchange interaction. We develop an order parameter field theory for this transition for clean as well as for disordered electrons. We find that the order parameter couples to additional soft modes in the electron system which leads to singular coupling constants in the Landau-Ginzburg-Wilson functional. These couplings generate an effective long-range interaction between the spin fluctuations. The resulting scaling behavior at the quantum critical point is unusual but can nonetheless be determined exactly. The quantum-to-classical crossover at small but finite temperatures is characterized by the appearance of multiple temperature scales. We also discuss consequences of the long-range effective coupling between the spin fluctuations for the properties of the magnetic phase.