Optical pumping NMR in the compensated semiconductor InP:Fe

TL;DR

This study investigates optical pumping NMR effects in InP:Fe, revealing photon energy-dependent oscillations, asymmetries, and buildup times for nuclear polarization, linked to donor-acceptor pairs and dipolar interactions.

Contribution

It provides new insights into the energy-dependent dynamics of optical pumping NMR in compensated semiconductors, highlighting the role of DAPs and dipolar interactions.

Findings

Oscillation period is similar for 31P and 115In and nearly field-independent.

Buildup time for 31P polarization strongly depends on photon energy.

Buildup times for 31P and 115In are comparable despite different T1 relaxation times.

Abstract

The optical pumping NMR effect in the compensated semiconductor InP:Fe has been investigated in terms of the dependences of photon energy (E_p), helicity (sigma+-), and exposure time (tau_L) of infrared lights. The {31}P and {115}In signal enhancements show large sigma+- asymmetries and anomalous oscillations as a function of E_p. We find that (i) the oscillation period as a function of E_p is similar for {31}P and {115}In and almost field independent in spite of significant reduction of the enhancement in higher fields. (ii) A characteristic time for buildup of the {31}P polarization under the light exposure shows strong E_p-dependence, but is almost independent of sigma+-. (iii) The buildup times for {31}P and {115}In are of the same order (10^3 s), although the spin-lattice relaxation times (T_1) are different by more than three orders of magnitude between them. The results are discussed in terms of (1) discrete energy spectra due to donor-acceptor pairs (DAPs) in compensated semiconductors, and (2) interplay between {31}P and dipolar ordered indium nuclei, which are optically induced.