Magnetic field induced tunneling and relaxation between orthogonal configurations in solids and molecular systems

Magnetoacoustic Relaxation by Cr2+ Jahn–Teller Centers Revealed from Elastic Moduli

“…In ref. , the increase of with B from 0 to 0.1 T was interpreted as due to a new channel of relaxation via tunneling from one distorted configuration of the JTE center to another one, made possible by the magnetic field‐induced coupling between their otherwise orthogonal orbital states. The decrease from 0.1 to 2 T was explained as due to the change of the attenuation mechanism with the relaxation replaced by quasi‐resonance transitions between greatly broadened energy levels, so that only decaying tail‐resonance dependence is seen.…”

“…We assume that the magnetic field induces a new channel of relaxation (similar to ref. ). It means that the relaxation rate should be written as follows where τ B is the part of relaxation time induced by the magnetic field only, and τ T is the temperature‐dependent relaxation time defined at B = 0.…”

Interplay Between Relaxation and Resonance in Ultrasound Attenuation by the Cubic Crystal ZnSe:Cr

“…Cr atoms substitute Zn atoms in the cubic ZnSe crystal resulting in its ground electronic 5 T 2 state, which can be characterized by the effective orbital momentum L = 1 and total spin S = 2. The orbital states of the center couple with local doubly degenerated e ‐symmetry displacements of the four near‐neighbor Se atoms of the tetrahedral environment, resulting in the T⊗e JT problem . The adiabatic potential energy surface (APES) of the CrSe 4 center in the space of normal coordinates Q 2 , Q 3 of the nuclear displacements in this case has three equivalent minima in which the system is distorted along one of the three axes x, y, z , respectively; they correspond to distortions along the [100], [010], and [001] directions of the crystal.…”

“…The matrix in Equation shows that there is a splitting of the orbital states and , while the ultrasound wave does not affect the state . The diagonal character of the Hamiltonian (Equation ) means that the interaction of the ultrasonic wave propagating along [110] is not affected by the vibronic reduction factors, which are proportional to the overlap of the vibrational functions of two minima of the APES, , .…”

“…It takes place as an ultrasonic power dissipation due to the changes in the energy level populations produced by the ultrasound deformation wave followed by restoration of thermal equilibrium (note that the size of the impurity complex is much smaller than the ultrasound wavelength). An additional channel of relaxation which increases the ultrasound attenuation was also revealed in applying external magnetic fields, which was shown to remove the orthogonality of the electronic orbital wavefunctions in the minima, thus allowing for tunneling transitions between them . But to reveal the origin of the frequency dependent resonance mechanisms of ultrasound attenuation (with and without external fields) the fine structure of JT impurity energy levels should be considered in more detail.…”