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Orientador: Pascoal José Giglio Pagliuso / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T07:35:54Z (GMT). No. of bitstreams: 1 HolandaJunior_LinoMartinsde_D.pdf: 3936724 bytes, checksum: 5a1e9e5453184dac769d35041c7414d0 (MD5) Previous issue date: 2014 / Resumo: Nesta Tese de Doutorado desenvolvemos estudos de Ressonância de Spin Eletrônico (ESR) em compostos intermetálicos, incluindo os férmions pesados ?-YbAlB4, ?-YbAlB4 and ? -YbAlxFe1-xB4, os metais ?-LuAlB4, AlB2 e o isolante Kondo, FeSi. Nossas medidas foram feitas em um espectrômetro modelo ELEXSYS-CW Bruker usando uma cavidade ressonante do tipo TE102 para a faixa de frequência em banda X (?~ 9.4GHz). A técnica de Ressonância de Spin Eletrônico aplicada aos compostos Férmions pesados foi sempre um desafio devido a presença de fortes correlações eletrônicas que tendem a alargar as linhas de ESR. Porem, nos últimos anos essa técnica ganhou renovado interesse após a descoberta do sinal de ESR na rede Kondo YbRh2Si2. Após esse trabalho, ESR voltou a ser considerada uma técnica importante para explorar os elétrons 4f e suas interações microscópicas em compostos de terras raras, uma vez que ela sonda diretamente o íon no sitio da rede. A motivação desse trabalho e, portanto, usar a técnica de ESR para entender a dinâmica dos elétrons 4f pesados em uma rede de Kondo, para os novos compostos férmions pesados ?-YbAlB4, -YbAlB4 and ?-YbAlxFe1-xB4. Neste trabalho buscou-se utilizar a técnica de ESR nesses compostos para alcançar o entendimento microscópio dos critérios que permitem a observação de um sinal de ESR em férmios pesados. Alem do mais, quando o sinal e observado, a sonda de ESR e propícia para acompanhar a evolução dos elétrons 4f em altas temperaturas para quase-partículas pesadas em baixas temperaturas. Nossas observações nos permitiram propor um cenário qualitativo baseado na existência de um modo ressonante acoplado entre ons Kondo e os elétrons de condução. Nos discutimos as características físicas gerais para que compostos férmios pesados sejam candidatos a apresentarem tal sinal de ESR. Ainda neste trabalho, estudamos os compostos intermetálicos ?-LuAlB4, AlB2 e FeSi com propriedades estruturais ou eletrônicas similares as dos compostos ?-YbAlB4, ?-YbAlB4 and ?-YbAlxFe1-xB4 em busca de uma generalizac~ao mais abrangente do cenário proposto neste trabalho / Abstract: In this work, we have performed an Electron Spin Resonance (ESR) study in intermetallic compounds including the heavy fermions ?-YbAlB4, ?-YbAlB4 and ? -YbAlxFe1-xB4, the Fermi liquid metals ?-LuAlB4, AlB2 and the Kondo insulator, FeSi. Our measurements were made on a spectrometer Bruker CW-model ELEXSYS using a resonant cavity TE102 in X Band ( ?~ 9.4GHz). The Electron Spin Resonance technique applied to heavy fermions compounds was little explored due to difficulty in finding ESR signal of Kondo ions due to the large coupling between the resonating spins and conduction electrons. However, in recent years this technique has become focus of great attention especially after the discovery of the ESR signal in a Kondo lattice YbRh2Si2. In this context, ESR was brought to the scene as one of the main techniques to bring insights to this problem since it could probe directly the f electrons of Kondo ions and their interaction with the conduction electrons. The motivation of this work is to use the ESR technique to investigate new heavy fermions compounds and to understand when these systems can present an ESR signal. In these cases ESR can help to understand more deeply how localized f electrons at high-T evolve to itinerant heavy quasi-particles in a low-T metallic state. Our observations for ?-YbAlB4, -YbAlB4 and ?-YbAlxFe1-xB4, allowed us to make some qualitative speculations about this phenomenon and within this scenario, we propose some general characteristics for heavy fermions compounds to become candidates to present ESR signal. In this work we have also measured ?-LuAlB4, AlB2 and the Kondo insulator, FeSi, in an attempt to generalize the ESR results found for ?-YbAlB4, ?-YbAlB4 and ?-YbAlxFe1-xB4 to a more broad family of compounds / Doutorado / Física / Doutor em Ciências

In the present work three different proteins were investigated, namely IGPS, the SRII/HtrII complex and ChR2. EPR spectroscopy combined with SDSL were applied to investigate the relation of the respective protein dynamics and their functions. In case of IGPS spin label side chain dynamics were recorded and allow a classification of loop dynamics during catalysis. For SRII/HtrII an equilibrium of spin label side chain dynamics was found to reflect the equilibrium of the activated and deactivated states, which are responsible for signal transfer through the complex. Time-resolved analyses of side chain dynamics and trapping of intermediates of the light-triggered channel ChR2 identified conformational changes to occur during channel function. Thereby, the EPR spectroscopy proves to be a powerful tool to investigate proteins in context of structural changes during their protein function.

No description available.

The spins of phosphorus doped in silicon are potential candidates for a quantum computing device, with models based on the use of nuclear and/or electron spins suggested. For a quantum computing device, several essential criteria must be demonstrated before any physical implementation, and these include qubit control gates, long decoherence time and scalability. Scalability and compatibility with existing fabrication technologies are strong points in favour of a silicon based system. For spin based schemes, silicon has the potential to provide a host with zero nuclear spin (isotopically purifed 28Si) and also the phosphorus donor provides both nuclear and electron half integer spins (ideal case). In this work, a magnetic resonance method (electron spin resonance) was utilised to investigate these critical issues (controllable quantum gates and decoherence time) for the electron spins of phosphorus donors in silicon. Electron spin resonance (ESR) studies of an ensemble of phosphorus electron spins in silicon were conducted via both continuous wave and pulsed methods. For pulsed ESR operations, two low temperature (4 K and millikelvin) X-band pulsed ESR systems were built. They were designed especially to suit Si:P decoherence time measurements. The design, modelling, construction and evaluation of the probe heads are described. With the aid of computer simulations, the performance of the probe heads was optimised and a rectangular loop gap resonator was found to be the most suitable for wafer type samples. The resonant frequency, quality factor, and coupling coeffcient were calculated via simulation and are in reasonable agreement with experimental results. This demonstrates the effectiveness of such simulations as a tool for optimising the probe head performance. A millikelvin pulsed ESR system was set up through the combination of a dilution refrigerator, superconducting magnet and the in-house construction of a pulsed ESR spectrometer. This novel system allows pulsed ESR experiments on an ensemble system to be realised down to the millikelvin temperature range, hence providing conditions considered most favourable for quantum computing studies. The use of light in combination with the pulsed ESR systems was also explored in an endeavour to overcome the problem of very long spin-lattice relaxation time, T1, allowing the decoherence time to be measured more effciently. With these novel low temperature pulsed ESR units, two-pulse electron spin echo experiments were conducted on phosphorus donors in silicon (both natural silicon (natSi) and 28Si) with the phosphorus concentration in the range of 1015- 1016 P/cm3 and to lower temperatures than previously investigated. Decoherence times measured for both natSi:P and 28Si:P (with similar donor concentrations) were longer than previously reported. Discussions on several effective ways to obtain even longer Si:P decoherence times including variations to sample configurations and experimental conditions are presented. In addition to the pulsed ESR studies, the Si:P controllable quantum gate functions, A gate and J gate, were examined by the continuous wave technique via Stark shift and exchange interaction experiments respectively. Stark shift experiments on bulk samples were carried out to investigate possible manipulation of the spins by the applied electric field. Continuous wave ESR was also used to examine low energy ion implanted Si:P devices, both by single (P+) and dimer (P+2 ) implanted donors. The outcomes from these studies provide materials information useful in formulating a strategy toward the Si:P device fabrication via the top down approach.