### Session U12: Strongly Correlated Electron Systems: Quantum Phase Transitions

8:00 AM–11:00 AM, Thursday, March 13, 2008
Morial Convention Center Room: 203

Chair: Andrew Millis, Columbia University

Abstract ID: BAPS.2008.MAR.U12.14

### Abstract: U12.00014 : Criticality in Inhomogeneous magnetic systems: Applications to Quantum Ferromagnets

10:36 AM–10:48 AM

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#### Authors:

R. Saha
(Dept. of Physics, Univ. of Oregon, Eugene, OR 97403 \& Dept. of Physics, Univ. of Maryland, College Park, MD 20742)

T.R. Kirkpatrick
(Dept. of Physics, Univ. of Maryland, College Park, MD 20742)

D. Belitz
(Dept. of Physics, Univ. of Oregon, Eugene, OR 97403)

In standard phase transitions such as the liquid-gas transition, a homogeneous order parameter (OP) vanishes as one crosses from the ordered phase to the disordered one. An external field may preclude a homogeneous OP. This happens for a fluid in a gravitational field, where the transition becomes smeared[1] in the sense that the OP is nonzero everywhere, albeit very small in some regions of the phase diagram. A ferromagnet (FM) subject to mechanical stress is another realization of a system in an external field that has an inhomogeneous OP. We first investigate a classical Heisenberg FM, which is modeled by a $\phi^{4}$ theory with a spatially dependent mass $r(x)$. In contrast to the fluids case, we find a sharp phase transition where the envelope of the local magnetization vanishes uniformly, and mean-field critical exponents. The first order transition in quantum itinerant FMs also remains sharp and the fluctuation effects leading to a tricritical point are suppressed, and one recovers a quantum critical point with mean field exponents[2]. [1] J.V. Sengers and J.M.J. van Leeuwen, Physica A, 116, 345 (1982). [2] D. Belitz, T.R. Kirkpatrick, and R. Saha, Phys. Rev. Lett., 99, 147203(2007).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.MAR.U12.14