Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L11: Dopants and Defects in Semiconductors - Complex Oxides and Oxide Interfaces
11:15 AM–2:03 PM,
Wednesday, March 7, 2018
LACC Room: 303A
Sponsoring Units: DMP DCOMP FIAP
Chair: C Stephen Hellberg, Naval Research Lab
Abstract: L11.00012 : Optically-pumped 75As NMR Reveals an Electric Field Gradient at an Al2O3-GaAs Interface and Very Low Nuclear Spin Temperatures*
1:51 PM–2:03 PM
We have investigated the interface between bulk GaAs and an 11nm thick layer of atomic layer deposition (ALD) Al2O3. Comparing GaAs with a native oxide and that with alumina results in different spectra. Using optical pumping of conduction electrons, nuclear spins enhancements localized near the interface is achieved by tuning the laser to bandedge states that result in a shallow penetration depth.
The 75As OPNMR spectra that are recorded in this regime show evidence of unusual quadrupolar splitting for GaAs. The splitting arises in part from biaxial strain, introduced by the different thermal expansion coefficients of the two materials (OPNMR is conducted at temperatures of 6 -10 K). However, strain alone does not account for the quadrupolar satellite shapes. We will discuss contributions to the electric field gradient at the interface that lead to the quadrupolar satellites.
In addition, the satellites themselves are asymmetric and reveal that these depend strongly on the photon energy used for optical pumping. Our models of spin temperature suggest a surprising cooling of the spin system to between 1.5 to 3 mK.
*Support from the NSF, DMR-1206447, and Prof. John Conley, Oregon State Univ for ALD sample growths.
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