3 research outputs found
All-optical seeding of a light-induced phase transition with correlated disorder
Ultrafast manipulation of vibrational coherence is an emergent route to
control the structure of solids. However, this strategy can only induce
long-range correlations and cannot modify atomic structure locally, which is
required in many technologically-relevant phase transitions. Here, we
demonstrate that ultrafast lasers can generate incoherent structural
fluctuations which are more efficient for material control than coherent
vibrations, extending optical control to a wider range of materials. We observe
that local, non-equilibrium lattice distortions generated by a weak laser pulse
reduce the energy barrier to switch between insulating and metallic states in
vanadium dioxide by 6%. Seeding inhomogeneous structural-fluctuations presents
an alternative, more energy efficient, route for controlling materials that may
be applicable to all solids, including those used in data and energy storage
devices
Giant ultra-broadband photoconductivity in twisted graphene heterostructures
The requirements for broadband photodetection are becoming exceedingly
demanding in hyperspectral imaging. Whilst intrinsic photoconductor arrays
based on mercury cadmium telluride represent the most sensitive and suitable
technology, their optical spectrum imposes a narrow spectral range with a sharp
absorption edge that cuts their operation to < 25 um. Here, we demonstrate a
giant ultra-broadband photoconductivity in twisted double bilayer graphene
heterostructures spanning a spectral range of 2 - 100 um with internal quantum
efficiencies ~ 40 % at speeds of 100 kHz. The giant response originates from
unique properties of twist-decoupled heterostructures including pristine,
crystal field induced terahertz band gaps, parallel photoactive channels, and
strong photoconductivity enhancements caused by interlayer screening of
electronic interactions by respective layers acting as sub-atomic spaced
proximity screening gates. Our work demonstrates a rare instance of an
intrinsic infrared-terahertz photoconductor that is complementary
metal-oxide-semiconductor compatible and array integratable, and introduces
twist-decoupled graphene heterostructures as a viable route for engineering
gapped graphene photodetectors with 3D scalability
Does VO_{2} Host a Transient Monoclinic Metallic Phase?
Ultrafast phase transitions induced by femtosecond light pulses present a new opportunity for manipulating the properties of materials. Understanding how these transient states are different from, or similar to, their thermal counterparts is key to determining how materials can exhibit properties that are not found in equilibrium. In this paper, we reexamine the case of the light-induced insulator-metal phase transition in the prototypical, strongly correlated material VO_{2}, for which a nonthermal Mott-Hubbard transition has been claimed. Here, we show that heat, even on the ultrafast timescale, plays a key role in the phase transition. When heating is properly accounted for, we find a single phase-transition threshold corresponding to the thermodynamic structural insulator-metal phase transition, and we find no evidence of a hidden transient Mott-Hubbard nonthermal phase. The interplay between the initial thermal state and the ultrafast transition may have implications for other transient states of matter