Drexel

Transient optical reflectivity in CuTiSe2

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Published on Tuesday, 18 December 2018 14:10

In this work we have performed an ultrafast optical pump-probe experiments in which we have varied laser fluence, copper doping, and temperature to explore the phase diagram of Cu_xTiSe₂ single crystals. Copper doping was found to weaken the excitonic condensate and decouple it from the L₁ − phonon mode, leading to fluctuations that are indicative of a quantum phase transition near x=0.04. This, along with a loss of coherence in the A_1g response at Cu_0.04TiSe₂ , supports the picture of a commensurate CDW in intrinsic TiSe₂ which, upon Cu intercalation, transitions into a state with a different symmetry characterized by an incommensurate CDW that coexists with superconductivity.

By varying the pump fluence we were able to non-thermally melt the CDW order. At pump pulse fluences  higher than 0.9 mJ/cm² we show that non-thermal melting of the CDW yields the normal phase A_1g response at 6.2 THz shown in the figure while the lattice temperature (T=3K) is well below the CDW phase transition. 

The details about the experiment and the findings can be found in the manuscript.