Optical and Terahertz Measurements of Spintronic Materials

Terahertz time-domain spectroscopy (THz-TDS) is a versatile method to determine lattice, electronic charge and spin dynamics. This dissertation employs THz-TDS to study the spin and charge dynamics in topological insulator and antiferromagnetic systems. Observing time-domain effects on the scale of picoseconds gives unprecedented control over optoelectronic properties. Methods and challenges of THz generation, detection, and transmission are outlined. The wealth of light-matter interactions present in all nonlinear optical experiments are discussed, including primarily optical rectification, shift currents, and injection currents. Each of these gives valuable insight into the carrier dynamics of a material type.;Conventional electronics can be improved in their speed and efficiency by taking advantage of an additional degree of freedom- electron spin. Therefore, we consider material types which exhibit great potential to replace common electronic materials while simultaneously employing electron spin for information storage or transport.;Antiferromagnets show a type of spin-order that has the ability to store bits without unwanted interactions between neighboring particles. In antiferromagnetic MnF2 which has a Neel temperature of TN = 67 K, THz-TDS is performed on one-magnon and two-magnon resonances in the 0.1-2.3 THz range while varying the temperature from 6 to 295 K. The behavior of the one-magnon resonance is modeled by modified molecular field theory with an additional coupling term j set as a free parameter to fit the data. The resulting best fit value j = 1.1 provides the first experimental evidence indicating that neighboring spins in MnF 2 are only weakly coupled, closely approximating mean-field theory. Time-of-flight analysis was performed on the transmitted THz pulses to measure the temperature-dependent THz refractive index, which was modeled by phonon energy in the T \u3e TN regime and magnetic energy in the T \u3c TN regime. In the range T \u3c 10 K, measured data deviates from this theory, and can be modeled by internal energy from hyperfine interactions, providing the first direct observation of hyperfine interactions in THz spectroscopy.;Topological insulators exhibit the ability to transport spin-polarized currents along their surfaces with high mobilities. Phase-related pulses at photon energies 0.8 and 1.6 eV are used to simultaneously inject shift and injection currents into thin-films of the prototypical topological insulator Bi2Se3, and the foundation is laid out for an extensive study of the novel carrier properties in topological surface states. A method of symmetry analysis based on the crystal lattice is developed for isolation and individual study of the surfaceonly shift currents, which are threefold symmetric with equal components parallel and perpendicular to the pump polarization, and bulk/surface injection currents, which are isotropic parallel to the pump polarization and vanishing perpendicular to it. Pump energies can be tuned through the Dirac point, a capability which holds promise for the search of smoking gun evidence for the novel topological insulator surface state behavior that has been theorized

Terahertz Waveguiding in Silicon-Core Fibers

We propose the use of a silicon-core optical fiber for terahertz (THz) waveguide applications. Finite-difference time-domain simulations have been performed based on a cylindrical waveguide with a silicon core and silica cladding. High-resistivity silicon has a flat dispersion over a 0.1 - 3 THz range, making it viable for propagation of tunable narrowband CW THz and possibly broadband picosecond pules of THz radiation. Simulations show the propagation dynamics and the integrated intensity, from which transverse mode profiles and absorption lengths are extraced. It is found that for 140 - 250 micron core diameters the mode is primarily confined to the core, such that the overall absorbance is only slightly less than in bulk polycrystalline silicon.Comment: 6 pages, 3 figures, journal submissio

The birds of Tinjil and Deli Islands, West Java

Pulau Tinjil and Pulau Deli are islands of 600 ha and 950 ha respectively lying 14 km off the south coast of West Java. The authors made six visits to one or other of the islands between 1988 and 1995. Both are covered with primary forest, but a large population of Long-tailed Macaque monkeys has recently been introduced on both islands as a free-range monkey-breeding facility. The islands have an depauperate avifauna with probably just 20 resident landbird species, common to both islands. These include one near-threatened species, the Nicobar Pigeon, which was formerly very common but which may have suffered as a result of the introduction of monkeys. Other small island/coastal specialists include the Beach Thick-knee, Pied Imperial Pigeon and Chestnut-capped Thrush. Except along the beaches, there are few forest-edge habitats, and most of the landbirds, including those normally occupying open habitats on the mainland such as White-breasted Waterhen, Yellow-vented Bulbul and Brown-throated Sunbird, have expanded their range to occupy the forest nich

Identification of photocurrents in topological insulators

Optical injection and detection of charge currents is an alternative to conventional transport and photoemission measurements, avoiding the necessity of invasive contact that may disturb the system being examined. This is a particular concern for analyzing the surface states of topological insulators. In this work one- and two-color sources of photocurrents are isolated and examined in epitaxial thin films of Bi2Se3. We demonstrate that optical excitation and terahertz detection simultaneously captures one- and two-color photocurrent contributions, which has not been required for other material systems. A method is devised to extract the two components, and in doing so each can be related to surface or bulk excitations through symmetry. The separation of such photocurrents in topological insulators opens a new avenue for studying these materials by all-optical methods

Patient perceptions after the operative and nonoperative treatment of shoulder instability:A qualitative focus group study

Background: Little evidence is available regarding patient perceptions of the treatment of shoulder instability. The aim of this study is to investigate patient perceptions regarding the operative and nonoperative treatment of anterior shoulder instability. Methods: Patients who presented to the emergency department or outpatient clinic between 2016 and 2020 were retrospectively selected using diagnosis and procedure codes. Online focus groups and semistructured interviews were conducted, systematically recorded and subsequently transcribed to MaxQDA 2007 for qualitative analysis. Coded transcripts of all focus groups were subjected to a grounded theory–based analysis. Results: Six focus groups and two semistructured interviews were hosted with 35 included patients. The mean age of included patients was 34.1 years (±11.5). Eight patients were female (23%), and 27 patients were male (77%). Fear of (recurrent) dislocation, preoperative counseling, communication between surgeon and physiotherapists and need for a consistent postoperative rehab protocol turned out to be important patient perceptions. The most crucial factor for discontent was a lack of communication from the surgeon. Discussion: This patient-centered focus group study revealed that fear of (recurrent) dislocation, preoperative counseling, communication between surgeons and physiotherapists and the need for a consistent postoperative rehabilitation protocol was the most frequently discussed themes.</p

Establishing a Core Domain Set for early-phase clinical trials of electrical stimulation interventions for tinnitus in adults: protocol for an online Delphi study

Background: Tinnitus is the awareness of a sound in the ear or head in the absence of an external source. It affects around 10–15% of people and current treatment options are limited. Experimental treatments include various forms of electrical stimulation of the brain. Currently, there is no consensus on the outcomes that should be measured when investigating the efficacy of this type of intervention for tinnitus. This study seeks to address this by establishing a Core Domain Set: a common standard of what specific tinnitus-related complaints are critical and important to assess in all clinical trials of electrical stimulation-based interventions for tinnitus. Methods: A two-round online survey will be conducted, followed by a stakeholder consensus meeting to identify a Core Domain Set. Participants will belong to one of two stakeholder groups: healthcare users with lived experience of tinnitus, and professionals with relevant clinical, commercial, or research experience. Discussion: This study will establish a Core Domain Set for the evaluation of electrical stimulation-based interventions for tinnitus via an e-Delphi study. The resulting Core Domain Set will act as a minimum standard for reporting in future clinical trials of electrical stimulation interventions for tinnitus. Standardisation will facilitate comparability of research findings

The impact of tinnitus on adult cochlear implant recipients: A mixed-method approach

BackgroundTinnitus is a common problem in patients with a cochlear implant (CI). Between 4% and 25% of CI recipients experience a moderate to severe tinnitus handicap. However, apart from handicap scores, little is known about the real-life impact tinnitus has on those with CIs. We aimed to explore the impact of tinnitus on adult CI recipients, situations impacting tinnitus, tinnitus-related difficulties and their management strategies, using an exploratory sequential mixed-method approach. MethodsA 2-week web-based forum was conducted using Cochlear Ltd.’s online platform, Cochlear Conversation. A thematic analysis was conducted on the data from the forum discussion to develop key themes and sub-themes. To quantify themes and sub-themes identified, a survey was developed in English with face validity using cognitive interviews, then translated into French, German and Dutch and disseminated on the Cochlear Conversation platform, in six countries (Australia, France, Germany, New Zealand, the Netherlands and United Kingdom). Participants were adult CI recipients experiencing tinnitus who received a Cochlear Ltd. CI after 18 years of age. ResultsFour key themes were identified using thematic analysis of the discussion forum: tinnitus experience, situations impacting tinnitus, difficulties associated with tinnitus and tinnitus management. Among the 414 participants of the survey, tinnitus burden on average was a moderate problem without their sound processor and not a problem with the sound processor on. Fatigue, stress, concentration, group conversation and hearing difficulties were the most frequently reported difficulties and was reported to intensify when not wearing the sound processor. For most CI recipients, tinnitus seemed to increase when performing a hearing test, during a CI programming session, or when tired, stressed, or sick. To manage their tinnitus, participants reported turning on their sound processor and avoiding noisy environments. ConclusionThe qualitative analysis showed that tinnitus can affect everyday life of CI recipients in various ways and highlighted the heterogeneity in their tinnitus experiences. The survey findings extended this to show that tinnitus impact, related difficulties, and management strategies often depend on sound processor use. This exploratory sequential mixed-method study provided a better understanding of the potential benefits of sound processor use, and thus of intracochlear electrical stimulation, on the impact of tinnitus