arXiv subjects

J. A. Haigh

Publications and source records attributed to J. A. Haigh.

14 recordsLinked to original sources

arXiv2021

Polarization dependent scattering in cavity optomagnonics

The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Due to the short cavity length, the mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one side-band is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-film geometry. A co-polarized scattering due to Cotton-Mouton effect is also observed. In addition, the magnon modes involved are identified as Damon-Eshbach surface modes, whose non-reciprocal propagation could be exploited in devices applications. This work experimentally demonstrates the important role of second order Cotton-Mouton effect for optomagnonic devices.

cond-mat.mes-hall↗

arXiv2020

Sub-pico-liter magneto-optical cavities

Microwave-to-optical conversion via ferromagnetic magnons has so-far been limited by the optical coupling rates achieved in mm-scale whispering gallery mode resonators. Towards overcoming this limitation, we propose and demonstrate an open magneto-optical cavity containing a thin-film of yttrium iron garnet (YIG). We achieve a 0.1 pL (100 $μ$m$^{3}$) optical mode volume, $\sim$50 times smaller than previous devices. From this, we estimate the magnon single-photon coupling rate is $G\approx50$ Hz. This open cavity design offers the prospect of wavelength scale mode volumes, small polarization splittings, and good magneto-optical mode overlap. With achievable further improvements and optimization, efficient microwave-optical conversion and magnon cooling devices become a realistic possibility.

cond-mat.mes-hall↗

arXiv2019

Fast gate-based readout of silicon quantum dots using Josephson parametric amplification

Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers compact and scalable readout with high fidelity, however further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast-feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622 MHz with a Josephson parametric amplifier (JPA), that operates in the 500-800 MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio (SNR), we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 $μ$s, well-below the requirements for fault-tolerant readout and 30 times faster than without the JPA. Additionally, the JPA allows operation at a lower RF power while maintaining identical SNR. We determine a noise temperature of 200 mK with a contribution from the JPA (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the read-out speed.

cond-mat.mes-hall↗

arXiv2018

Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes

We experimentally identify the magnetostatic modes active for Brillouin light scattering in the optical whispering gallery modes of a yttrium iron garnet sphere. Each mode is identified by magnetic field dispersion of ferromagnetic-resonance spectroscopy and coupling strength to the known field distribution of the microwave drive antenna. Our optical measurements confirm recent predictions that higher-order magnetostatic modes can also generate optical scattering, according to the selection rules derived from the axial symmetry. From this we summarize the selection rules for Brillouin light scattering. We give experimental evidence that the optomagnonic coupling to non-uniform magnons can be higher than that of the uniform Kittel mode.

cond-mat.mes-hall↗

arXiv2016

Triple-resonant Brillouin light scattering in magneto-optical cavities

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance (FMR) frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wavevector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

physics.optics↗

arXiv2016

Efficient conversion of light to charge and spin in Hall-bar microdevice

We report an experimental demonstration of a local amplification of the spin Hall voltage using an expanding depletion zone at a pn-junction in GaAs/AlGaAs Hall-bar microdevices. It is demonstrated that the depletion zone can be spatially expanded by applying reverse bias by at least 10~$μ$m at low temperature. In the depleted regime, the spin Hall signals reached more than one order of magnitude higher values than in the normal regime at the same electrical current flowing through the micro-device. It is shown that the pn-bias has two distinct effects on the detected spin Hall signal. It controls the local drift field at the Hall cross which is highly non-linear in the pn-bias due to the shift of the depletion front. Simultaneously, it produces a change in the spin-transport parameters due to the non-linear change in the carrier density at the Hall cross with the pn-bias.

cond-mat.mes-hall↗

arXiv2015

Magneto-optical coupling in whispering gallery mode resonators

We demonstrate that yttrium iron garnet microspheres support optical whispering gallery modes similar to those in non-magnetic dielectric materials. The direction of the ferromagnetic moment tunes both the resonant frequency via the Voigt effect as well as the degree of polarization rotation via the Faraday effect. An understanding of the magneto-optical coupling in whispering gallery modes, where the propagation direction rotates with respect to the magnetization, is fundamental to the emerging field of cavity optomagnonics.

cond-mat.mes-hall↗

arXiv2015

Cavity mediated coherent coupling of magnetic moments

We demonstrate the long range strong coupling of magnetostatic modes in spatially separated ferromagnets mediated by a microwave frequency cavity. Two spheres of yttrium iron garnet are embedded in the cavity and their magnetostatic modes probed using a dispersive measurement technique. We find they are strongly coupled to each other even when detuned from the cavity modes. We investigate the dependence of the magnet-magnet coupling on the cavity detuning $Δ$, and find a $1/Δ$ dependence also characteristic of cavity-coupled superconducting qubits. Dark states of the coupled magnetostatic modes of the system are observed, and ascribed to mismatches between the symmetries of the modes and the drive field.

cond-mat.mtrl-sci↗

arXiv2015

Dispersive read-out of ferromagnetic resonance for strongly coupled magnons and microwave photons

We demonstrate the dispersive measurement of ferromagnetic resonance in a yttrium iron garnet sphere embedded within a microwave cavity. The reduction in the longitudinal magnetization at resonance is measured as a frequency shift in the cavity mode coupled to the sphere. This measurement is a result of the intrinsic non-linearity in magnetization dynamics, indicating a promising route towards experiments in magnon cavity quantum electro-dynamics.

cond-mat.mtrl-sci↗

arXiv2015

Identification of spin wave modes strongly coupled to a co-axial cavity

We demonstrate, at room temperature, the strong coupling of the fundamental and non-uniform magnetostatic modes of an yttrium iron garnet (YIG) ferrimagnetic sphere to the electromagnetic modes of a co-axial cavity. The well-defined field profile within the cavity yields a specific coupling strength for each magnetostatic mode. We experimentally measure the coupling strength for the different magnetostatic modes and, by calculating the expected coupling strengths, are able to identify the modes themselves.

cond-mat.mtrl-sci↗

arXiv2015

Anisotropic magneto-capacitance in ferromagnetic-plate capacitors

The capacitance of a parallel plate capacitor can depend on applied magnetic field. Previous studies have identified capacitance changes induced via classical Lorentz force or spin-dependent Zeeman effects. Here we measure a magnetization direction dependent capacitance in parallel-plate capacitors where one plate is a ferromagnetic semiconductor, gallium manganese arsenide. This anisotropic magneto-capacitance is due to the anisotropy in the density of states dependent on the magnetization through the strong spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2015

Optical spin transfer torque driven domain wall motion in ferromagnetic semiconductor

We demonstrate optical manipulation of the position of a domain wall in a dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified. Firstly, photocarrier spin exerts a spin transfer torque on the magnetization via the exchange interaction. The direction of the domain wall motion can be controlled using the helicity of the laser. Secondly, the domain wall is attracted to the hot-spot generated by the focused laser. Unlike magnetic field driven domain wall depinning, these mechanisms directly drive domain wall motion, providing an optical tweezer like ability to position and locally probe domain walls.

cond-mat.mes-hall↗

arXiv2012

Piezoelectric strain induced variation of the magnetic anisotropy in a high Curie temperature (Ga,Mn)As sample

We show that effective electrical control of the magnetic properties in the ferromagnetic semiconductor (Ga,Mn)As is possible using the strain induced by a piezoelectric actuator even in the limit of high doping levels and high Curie temperatures, where direct electric gating is not possible. We demonstrate very large and reversible rotations of the magnetic easy axis. We compare the results obtained from magneto-transport and SQUID magnetometry measurements, extracting the dependence of the piezo-induced uniaxial magnetic anisotropy constant upon strain in both cases and detailing the limitations encountered in the latter approach.

cond-mat.mtrl-sci↗

arXiv2009

Manipulation of the magnetic configuration of (Ga,Mn)As nanostructures

We have studied the magnetic reversal of L-shaped nanostructures fabricated from (Ga,Mn)As. The strain relaxation due to the lithographic patterning results in each arm having a uniaxial magnetic anisotropy. Our analysis confirms that the magnetic reversal takes place via a combination of coherent rotation and domain wall propagation with the domain wall positioned at the corner of the device at intermediate stages of the magnetic hysteresis loops. The domain wall energy can be extracted from our analysis. Such devices have found implementation in studies of current induced domain wall motion and have the potential for application as non-volatile memory elements.

cond-mat.mtrl-sci↗