The presence of active orbital degrees of freedom in open electronic shells leads to an extremely rich phenomenology which has been explored and understood only partially. In particular, multipolar moments may play a key role in determining static and dynamical properties and may even be order parameters in phase transitions. In this case, elementary excitations around the broken symmetry state include multipolar waves, but none of these exotic dispersive excitation branches has ever been identified. This has hampered to reach a satisfactory understanding of the microscopic mechanisms governing this rich physics. We show that quadrupolar waves constitute a major component of the dynamics of uranium dioxide and that many unexplained features in existing data, including a whole excitation branch, are associated with propagating quadrupolar fluctuations driven jointly by magnetoelastic and superexchange multipolar interactions. These results enable a remarkable insight into the physics of orbital degrees of freedom.

CARRETTA S.;  SANTINI P.;  CACIUFFO Roberto;  AMORETTI G.; 

2010-10-20

AMER PHYSICAL SOC

JRC57443

0031-9007,   

http://prl.aps.org/abstract/PRL/v105/i16/e167201,    https://publications.jrc.ec.europa.eu/repository/handle/JRC57443,   

10.1103/PhysRevLett.105.167201,