Heidelberg 2015 – scientific programme
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A: Fachverband Atomphysik
A 40: Ultracold Atoms and Molecules (with Q)
A 40.4: Talk
Friday, March 27, 2015, 11:45–12:00, B/SR
Role of excitation spectrum during a quantum phase transition: Semiclassical approach — •Manuel Gessner1, Victor Manuel Bastidas2, Tobias Brandes2, and Andreas Buchleitner1,3 — 1Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany — 2Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany — 3Freiburg Institute for Advanced Studies, Albert-Ludwig-Universität, Albertstr. 19, 79104 Freiburg
We develop a semiclassical method to reproduce spectral features of a family of spin chain models with variable range in a transverse magnetic field, which interpolates between the Lipkin-Meshkov-Glick and the Ising model. The semiclassical spectrum is exact in the limit of very strong or vanishing external magnetic fields. Each of the semiclassical energy landscapes shows a bifurcation when the external magnetic field drops below a threshold value. This reflects the quantum phase transition from the symmetric paramagnetic phase to the symmetry-breaking (anti-)ferromagnetic phase in the entire excitation spectrum - and not just in the ground state.