Magnetic field tuning of crystal field levels and vibronic states in the spin ice compound Ho2Ti2O7 observed with far infrared reflectometry

Article

关键词: RE2TI2O7 RE;    PYROCHLORE;    PHONONS;    GD;    HO;    DY;    ER;   

DOI  :  10.1103/PhysRevB.105.165102

来源: SCIE

【 摘 要 】

Low-temperature optical spectroscopy in applied magnetic fields provides clear evidence of magnetoelastic coupling in the spin ice material Ho2Ti2O7. In far infrared (IR) reflectometry measurements, we observe fielddependent features around 30, 61, 72, and 78 meV, energies corresponding to crystal electronic field (CEF) doublets. The calculations of the crystal field Hamiltonian model confirm that the observed features in IR spectra are consistent with magnetic-dipole-allowed excitations from the ground state to higher 5I8 CEF levels. We present the CEF parameters that best describe our field-dependent IR reflectivity measurements. Additionally, we identify a weak field-dependent shoulder near one of the CEF doublets. This indicates that this level is split even in zero field, which we associate with a vibronic bound state. Modeling of the observed splitting shows that the phonon resides at slightly lower energy compared to the CEF level that it couples to, which is in contrast with previously published inelastic neutron measurements. The magnetic field dependence of the vibronic state shows a gradual decoupling of the phonon with the CEF level as it shifts. This approach should work in pyrochlores and other systems that have magnetic dipole transitions in the IR spectroscopic range, which can elucidate the presence and the ability to tune the nature of vibronic states in a wide variety of materials.

【 授权许可】

Free