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キーワード:
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要旨:
This thesis explores the electronic structure and ultrafast dynamics of quasi- one dimensional (1D) materials by means of high resolution angle-resolved photoemission spectroscopy (ARPES) and femtosecond time-resolved ARPES (trARPES) respectively. Confining electrons to quasi-1D environments induces a range of broken symmetry ground states and emergent properties that result from the increased inter-particle couplings and reduced phase space that such a confinement enforces. Investigating the energy relaxation and transfer between electrons and other degrees of freedom enables fundamental insights into the microscopic mechanisms behind these novel behaviours; for example by reference to characteristic time scales. Furthermore, since quasi-1D objects always interact with a higher dimensional environment, it is also of fundamental interest to investigate the influence that these interactions have on such phases, and whether they play a role in stabilising them. In this work, a number of model quasi-1D systems have been analysed to explore the coupling of 1D objects to a 3D environment, as well as the ultrafast dynamics of photoexcited broken symmetry phases. The bulk 1D compound NbSe3 is found to show behaviour consistent with a dimensional crossover from 1D to 3D as a function of decreasing energy and temperature, resulting from the coupling between individual 1D chains. Intriguingly, residual 1D behaviour is found to persist even in the 3D regime. Additionally, charge density wave gaps in the electronic structure are observed at low temperatures. The candidate 1D system Ag/Si(557) is investigated to reveal its electronic dimensionality. While the doped Fermi surface reveals predominantly two-dimensional behaviour, the influence of the stepped Si substrate anisotropically induces replica states. The atomic nanowire system In/Si(111) is well known to undergo concomitant structural and metal-to-insulator transitions. By resolving the dynamics of multiple individual electronic states following photoexcitation, a detailed picture of the electronic structure evolution is obtained. An impressive agreement between theory and experiment is obtained, allowing important microscopic insights into this system. Finally the spin density wave phase transition in thin films of Cr is driven by photoexcitation, highlighting the role of electron-electron scattering as the mechanism behind this phase. The applicability of an equilibrium-like order parameter is found to be appropriate in this ultrafast transition.
