Self-Referenced XUV Transient Reflectivity Spectroscopy: Attosecond Electron Dynamics of 2D Layered Materials

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"The research and development of novel layered and 2D materials is at the center of a focused interest in the material sciences. The large photon coupling of their excitonic excitations and their varying degrees of localization, control over coupling to other degrees of freedom as well as novel spin- and momentum-dependent properties arising from symmetry and topology have made 2d materials a desirable platform for the development of new applications ranging from new photovoltaic and optoelectronical devices to spintronic and ""quantum"", i.e. coherent, data transport and storage devices. Since the coupling of electronic states to other material degrees of freedom, e.g. lattice, excitonic or spin-polarized states, might lead to desired or undesired behavior in these materials, powerful time-resolved experimental methods are needed to disentangle and understand their electron dynamics and achieve the implementation of the desired applications. The ultrashort timescales that govern electron dynamics warrant the application of novel methods such as XUV transient absorption (XTAS) or XUV transient reflectivity spectroscopy (XTRS), which achieve temporal resolutions on the natural timescale of electronic motion, i.e. attosecond timescales. Time-resolved core-level spectroscopy using attosecond pulses from high harmonic generation (HHG) offers intriguing opportunities to study the electron dynamics with high energy-resolution and unprecedented temporal-resolution with element-specific insight into the material's band-structure. The major goal of this proposed work is the advancement of XTRS and its application to study excitations in layered materials down to the few-layer limit. A novel interferometric and heterodyne approach to overcome existing limitations of XTRS will be developed and applied to a series of materials, where time resolved studies will lead to desirable insight into the ultrafast coupled dynamics of carriers, excitons, their spin and the lattice."