Relaxation and resonance ultrasound attenuation by Jahn–Teller centers in a GaAs:Cu crystal

The interaction of ultrasound with Cu$_{\rm Ga}$4As in a GaAs:Cu crystal has been experimentally studied. The temperature dependences of the attenuation of all normal ultrasonic modes propagating in the ${<}110{>}$ direction both in doped copper and in nominally pure gallium arsenide crystals have been measured. In the GaAs:Cu crystal, the attenuation peak has been revealed for a transverse wave polarized along the ${<}110{>}$ axis whose elastic shifts correspond to the symmetry of the tetragonal mode of the Jahn–Teller effect. The temperature dependence of the attenuation of this wave indicates that two types of attenuation—relaxation and resonance—occur. The constructed temperature dependence of the relaxation time indicates that tunneling through the potential barrier between the minima of the adiabatic potential energy is the main relaxation mechanism at temperatures below $10$ K. Tunneling splitting estimated from experimental data is in good agreement with the theoretical estimate.