Condensed Matter Seminar Series

Title: Jump Instantons and Spin Tunneling in Magnetic Molecules

Ersin Kececioglu

Northwestern University

Thursday August 21, 1h30 pm, Room 234, Physics Building

Abstract: Coherent state path integrals for spin, with jumps at the boundaries, i.e., with discontinuous semiclassical paths are investigated. For the magnetic molecule Fe_8, it is shown that such paths are crucial in understanding the quenching of the tunnel splitting. In Fe_8, such paths are shown to arise when fourth order anisotropy term in the energy is turned on . Fourth order anisotropy term, which is very small compared to second order terms, are making the contribution singular from the semiclassical point of view. For external magnetic fields beyond a certain value, these singular paths are shown to dominate and the quenching is shunted. The instanton approximation is shown to have a quantitative agreement with the observed structure and magnetic field dependence of the tunnel splitting.