Nuclear Magnetic Resonance in Semiconductors. II. Quadrupole Broadening of Nuclear Magnetic Resonance Lines by Elastic Axial Deformation

Nuclear electric-quadrupole moments interact with electric-field gradients at the nucleus. In a perfect cubic crystal, the average gradients vanish and there are no quadrupolar interactions. Nuclear magnetic resonance studies of the semiconductors InSb and GaSb have revealed no quadrupolar interactions in our samples, indicating a high degree of crystalline perfection. By applying stresses to these crystals, we have been able to destroy the crystalline symmetry reversibly, thereby producing quadrupole broadening of the nuclear magnetic resonance lines. Strains of less than 10^-4 have been detected and the resulting field gradients measured. The "gradient-elastic" proportionality constants connecting stress and field gradient are discussed in relation to crystal symmetry and have been deduced from the measurements.