Ultrafast response of photoexcited carriers in VO₂ at high-pressure

Abstract

We utilize near-infrared pump-mid-infrared probe spectroscopy to investigate the ultrafast electronic response of pressurized VO 2 . A clear anomaly in the linear mid-infrared response as well as in the fluence dependence of the pump-probe signal is observed around 8 GPa indicating a pressureinduced phase transition. Distinct pump-probe signals and a pumping threshold behavior typical for the insulating VO 2 phase persist also in the high-pressure phase. Thus, in contrast to the temperatureinduced rutile metallic state of VO 2 , the pressure-induced monoclinic phase preserves the energy gap. However, our results indicate the appearance and a gradual growth of additional intragap states upon increasing pressure above 8 GPa. These observations can be interpreted in terms of a bandwidthcontrolled Mott-Hubbard transition.

Misuse of the minimal coupling to the electromagnetic field in quantum many-body systems

“…Furthermore, properly tailoring the pump pulse allows ultrafast photoinducing phase transitions into states that may not even exist in thermal equilibrium [1,2]. Strongly correlated materials appeared as ideal candidates for such kind of experiments [3][4][5][6][7][8][9][10][11], because of their rich phase diagrams that include different insulating and conducting states, often displaying notable properties, such as high-T c superconductivity [12][13][14].…”

Optical Limiting Based on Huygens’ Metasurfaces

“…First, the metasurface design relies on the spectral overlap of the Huygens’ point of the resonator and the ENZ point of the metallic-state VO 2 , and even small fabrication errors can result in spectral misalignment. Second, the permittivity function of VO 2 is sensitive to stress in the film, and its switching behavior is highly dependent on its environment . At 35 nm thickness, the VO 2 is not a completely continuous film, and only certain regions of VO 2 may be completely switching.…”

A Strategy to Identify Materials Exhibiting a Large Nonlinear Phononics Response: Tuning the Ultrafast Structural Response of LaAlO$_3$ with Pressure

“…For LaAlO 3 in particular we predict a large (compared to ambient pressure) structural change around 12 GPa due to displacements of the Γ + 1 and Γ + 3 Ramanactive modes following excitation of a Γ − 3 IR-active mode. Based on recent high pressure ultrafast studies, [45] we believe pressure will be a useful tool for the study and enhancement of the nonlinear phononics effect in materials like LaAlO 3 . We elucidated the origin of these responses by defining a figure of merit based on intrinsic materials properties.…”