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Title: High-spin impurities and surface acoustic waves in piezoelectric crystals for spin-lattice coupling
Author: Magnusson, Einar B.
ISNI:       0000 0004 6496 7333
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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In this thesis we investigate various aspects of SAW devices and strain sensitive spin species in ZnO and LiNbO3 for coupling surface acoustic waves to spin ensembles. Firstly, we performed a series of ESR experiments exploring the potential of Fe3+ impurities in ZnO for spin-lattice coupling. This spin system has already been identified as a high potential quantum technology component due to its long coherence time. We show that the system also has good properties for spin-lattice coupling experiments, with a strain-coupling parameter G33 = 280 ± 5GHz/strain, which is about 16 times larger than the largest reported for NV centres in diamond. We found that the LEFE effect as well as the spin Hamiltonian parameter D have a linear temperature dependence. As the relative change in each coincide, this strongly supports the notion that the modification of D by an electric field is a multiplicative effect rather than an additive one, D = D0(1 + κΕ). The LEFE coefficient we measured is several times larger for Fe3+:ZnO than for Mn2+:ZnO. Secondly, we have fabricated and characterised SAW devices on bulk ZnO crystals and Fe doped lithium niobate. We found that the nominally pure ZnO was conductive at room temperature due to n-type intrinsic doping, and electrical losses inhibited any transmission through a SAW delay line above T = 200K. The one-port resonator measured down to milli-Kelvin temperatures showed excellent quality factors of up to Q ≃ 1.5 x 105 in its superconducting state. Finally, we performed a surface acoustic wave spin resonance (SAWSR) experiment using a one-port SAW resonator fabricated on Fe2+:LN. We observed a clear signal at T ≃ 25 K, at a field near the expected one for a Δms = 2 transition between the |−1⟩ and |+1⟩ states. We concluded it to be a transition induced by acoustic coupling since the signal intensity did not tend to zero when the magnetic field was parallel to the crystal anisotropy axis. Furthermore, this tells us that the coupling is due to a modulation of the E zero-field splitting parameter rather than D. We investigated the dependence on microwave power and found the saturation limit. We performed a measurement of Fe3+:LN as well to reassure ourselves that the resonance is not magnetically excited by the field around the IDT.
Supervisor: Ardavan, Arzhang ; Leek, Peter J. Sponsor: Clarendon Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Physics ; Surface acoustic wave ; Spin