Nanophotonic Optomechanical Devices for Torque Magnetometry

Torque magnetometry is a powerful and sensitive method for studying intricate mesoscopic magnetic events inside magnetic materials using nanomechanical resonators. Over the years, the field of cavity optomechanics has demonstrated ever increasing sensitivity, with measurements limited by the quantum motion of a device possible in state-of-the-art devices. In this thesis, a nanophotonic cavity is integrated into a nanomechanical resonator for optomechanical detection of torque driven by the interaction of a permalloy island with applied magnetic fields. This marks the first time were a nanocavity optomechanical sensor is applied to a nanoscale condensed matter system. This cavity optomechanics platform enabled torque magnetometry measurements to be performed with sufficient sensitivity for detection of Barkhausen features that were previously undetected in ambient conditions. The device was used to demonstrate a new form of nanomechanical radio-frequency susceptometry where enhanced magnetic susceptibility associated with single pinning and depinning events of a magnetic vortex core were observed. This optomechanical device increased torque magnetometer sensitivity by over an order of magnitude. The torque sensitivity of the device derives from the optimization of the optomechanical interactions in a photonic crystal split-beam cavity. Two types of dissipative optomechanical couplings were observed as a result of the mechanical motion modulating the intra-cavity photon lifetime and the cavity input-output coupling rate. Interference between dissipative and dispersive optomechanical mechanisms enhance detection sensitivity and generate mechanical-mode-dependent optomechanical wavelength response. Dissipative coupling of up to 500 MHz/nm and dispersive coupling of 2 GHz/nm, enables measurement of sub-pg torsional and cantilever-like mechanical resonances with a thermally-limited torque detection sensitivity of 1.2 ×10−20 Nm/sqrt(Hz) in ambient conditions. Tuning of both dissipative and dispersive optomechanical couplings is also demonstrated through renormalization of the cavity field mediated by its evanescent interaction with a fiber taper near-field probe. Strategic fiber taper placement allows for reconfiguration of the dominant optomechanical transduction mechanism and spatially selective optical readout of mechanical resonances such as out-of-plane cantilever modes suitable for sensing applications.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Physics and Astronomy

Grantor dc:publisher.institution

Graduate Studies

Year dc:date.issued

2016

Author dc:creator

• Wu, Marcelo

Advisor dc:contributor.advisor

• Barclay, Paul E.

Committee members dc:contributor.committeemember

• Simon, Christoph
• Tittel, Wolfgang
• Plume, René
• Kim, Seonghwan
• Fuchs, Greg

• Condensed Matter
• Optics

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

eng

DOI

http://dx.doi.org/10.11575/PRISM/27057

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:11023/3463