Nos últimos anos, os cientistas aplicaram conceitos de topologia a descoberta de materiais com propriedades eletra´nicas igualmente robustas. Em 2007, os pesquisadores previram os primeiros isolantes topola³gicos eletra´nicos - materiais nos...
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)
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O que seránecessa¡rio para tornar nossos eletra´nicos mais inteligentes, rápidos e resilientes? Uma ideia éconstrua-los a partir de materiais que são topola³gicos.
A topologia deriva de um ramo da matemática que estuda formas que podem ser manipuladas ou deformadas sem perder certas propriedades centrais. Um donut éum exemplo comum: se fosse feito de borracha, um donut poderia ser torcido e espremido em uma forma completamente nova, como uma caneca de cafanã, mantendo uma característica fundamental - ou seja, seu orifacio central, que assume a forma de a ala§a do copo. O furo, neste caso, éum traa§o topola³gico, robusto contra certas deformações.
Nos últimos anos, os cientistas aplicaram conceitos de topologia a descoberta de materiais com propriedades eletra´nicas igualmente robustas. Em 2007, os pesquisadores previram os primeiros isolantes topola³gicos eletra´nicos - materiais nos quais os elanãtrons se comportam de maneiras "topologicamente protegidas" ou persistentes diante de certas interrupções.
Desde então, os cientistas tem procurado mais materiais topola³gicos com o objetivo de construir dispositivos eletra´nicos melhores e mais robustos. Atérecentemente, apenas um punhado desses materiais foi identificado e, portanto, considerado uma raridade.
Agora, pesquisadores do MIT e de outros lugares descobriram que, de fato, os materiais topola³gicos estãopor toda parte, se vocêsouber como procura¡-los.
Em um artigo publicado na Science , a equipe, liderada por Nicolas Regnault, da Universidade de Princeton e da a‰cole Normale Supanãrieure Paris, relata o uso do poder de vários supercomputadores para mapear a estrutura eletra´nica de mais de 96.000 materiais cristalinos naturais e sintanãticos. Eles aplicaram filtros sofisticados para determinar se e que tipo de traa§os topola³gicos existem em cada estrutura.
No geral, eles descobriram que 90% de todas as estruturas cristalinas conhecidas contem pelo menos uma propriedade topola³gica, e mais de 50% de todos os materiais naturais exibem algum tipo de comportamento topola³gico.
“Descobrimos que háuma onipresença osa topologia estãoem toda parteâ€, diz Benjamin Wieder, colider do estudo e pa³s-doc no Departamento de Fasica do MIT.
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A equipe compilou os materiais recanãm-identificados em um novo banco de dados de materiais topola³gicos de acesso livre, semelhante a uma tabela peria³dica de topologia. Com esta nova biblioteca, os cientistas podem pesquisar rapidamente materiais de interesse para quaisquer propriedades topola³gicas que possam conter e aproveita¡-los para construir transistores de potaªncia ultrabaixa, novo armazenamento de memória magnanãtica e outros dispositivos com propriedades eletra´nicas robustas.
O artigo inclui o coautor principal Maia Vergniory do Vergniory do Donostia International Physics Center, Luis Elcoro da Universidade do Paas Basco, Stuart Parkin e Claudia Felser do Instituto Max Planck e Andrei Bernevig da Universidade de Princeton.
Além da intuição
O novo estudo foi motivado pelo desejo de acelerar a busca tradicional de materiais topola³gicos.
"A forma como os materiais originais foram encontrados foi atravanãs da intuição química", diz Wieder. "Essa abordagem teve muitos sucessos iniciais. Mas como teoricamente previmos mais tipos de fases topola³gicas, parecia que a intuição não estava nos levando muito longe."
Wieder e seus colegas utilizaram um manãtodo eficiente e sistema¡tico para erradicar sinais de topologia, ou comportamento eletra´nico robusto, em todas as estruturas cristalinas conhecidas, também conhecidas como materiais inorga¢nicos de estado sãolido.
Para seu estudo, os pesquisadores olharam para o Inorganic Crystal Structure Database, ou ICSD, um reposita³rio no qual os pesquisadores inserem as estruturas atômicas e químicas de materiais cristalinos que eles estudaram. O banco de dados inclui materiais encontrados na natureza, bem como aqueles que foram sintetizados e manipulados em laboratório. O ICSD éatualmente o maior banco de dados de materiais do mundo, contendo mais de 193.000 cristais cujas estruturas foram mapeadas e caracterizadas.
A equipe baixou todo o ICSD e, depois de realizar uma limpeza de dados para eliminar estruturas com arquivos corrompidos ou dados incompletos, os pesquisadores ficaram com pouco mais de 96.000 estruturas processa¡veis. Para cada uma dessas estruturas, eles realizaram um conjunto de ca¡lculos baseados no conhecimento fundamental da relação entre os constituintes quamicos, para produzir um mapa da estrutura eletra´nica do material, também conhecida como estrutura de banda de elanãtrons.
A equipe foi capaz de realizar com eficiência os ca¡lculos complicados para cada estrutura usando vários supercomputadores, que então empregaram para realizar um segundo conjunto de operações, desta vez para rastrear várias fases topola³gicas conhecidas ou comportamento elanãtrico persistente em cada material cristalino.
"Estamos procurando assinaturas na estrutura eletra´nica em que certos fena´menos robustos devem ocorrer neste material", explica Wieder, cujo trabalho anterior envolveu refinar e expandir a técnica de triagem, conhecida como química qua¢ntica topola³gica.
A partir de sua análise de alto rendimento, a equipe descobriu rapidamente um número surpreendentemente grande de materiais que são naturalmente topola³gicos, sem qualquer manipulação experimental, bem como materiais que podem ser manipulados, por exemplo, com dopagem de luz ou química, para exibir algum tipo de comportamento eletra´nico. Eles também descobriram um punhado de materiais que continham mais de um estado topola³gico quando expostos a certas condições.
"Fases topola³gicas da matéria em materiais de estado sãolido 3D foram propostas como locais para observar e manipular efeitos exa³ticos, incluindo a interconversão de corrente elanãtrica e spin de elanãtrons, a simulação de mesa de teorias exa³ticas da física de alta energia e atémesmo, sob o condições certas, o armazenamento e manipulação de informações qua¢nticas", observa Wieder.
Para os experimentalistas que estãoestudando esses efeitos, Wieder diz que o novo banco de dados da equipe agora revela uma variedade de novos materiais para explorar.