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Reduced conductivity in the terahertz skin-depth layer of metals

Laman, N.
Grischkowsky, D.
The terahertz conductivities of plates of Cu and Al were measured to remain the same at 295 and 77 K using waveguide terahertz time domain spectroscopy (THz-TDS). This result was true for a variety of commercial alloys and surface preparations. Consequently, carrier scattering by lattice defects within the 100 nm THz skin depth is much larger than scattering by phonons at room temperature. However, an exception was found to be the THz skin-depth layer of an evaporated 300 nm Al film in contact with a polished Si surface. For this interface Al layer, the conductivity increased by a factor of 4 when cooled to 77 K.