An array of passive metamaterial antennas fabricated on all protein-based silk substrates were conformally transferred and adhered to the surface of an apple. This process allows the opportunity for intimate contact of micro- and nanostructures that can probe, and accordingly monitor changes in, their surrounding environment. This provides in situ monitoring of food quality. It is to be noted that this type of sensor consists of all edible and biodegradable components, holding utility and potential relevance for healthcare and food/consumer products and markets.

These results reveal that strain engineering can tune emergent functionality towards proximal macroscopic states to enable dynamic ultrafast optical phase switching and control.Precision tuning of the local environment in complex materials provides a route to control macroscopic functionality thereby offering a glimpse into how microscopic interactions conspire toward emergent behavior. Figure 1ashows resistivity measurements for a strained 30 nm LCMO film. In zero applied magnetic field, the film remains insulating at all temperatures (due to strain-enhanced orthorombicity 22 23 as depicted in Fig. 1d). For fields above 3 T the insulating phase collapses becoming a ferromagnetic metal at low temperatures. Figure 1b details the phase diagram of strained LCMO as determined from the field-dependent transport measurements 22 23 . The FM and AFM phases coexist over the range from 0-3 T, depending on temperature. To characterize the time-integrated electrodynamic response of the strained films, the optical conductivity was measured from 100 meV to 5 eV using spectroscopic ellipsometry (Fig. 1c). With decreasing temperature, the film displays spectral weight transfer from a small polaron (~1.5 eV) peak to a sharp well- Fig. 3a).As we now show, photoexcitation recovers the hidden FM phase of the strain- The photoinduced THz conductivity (PTC) is stable as long as the temperature is maintained. Further, the maximum conductivity is the same value as obtained with a strong magnetic field. This is clear from the blue dots of Fig. 1a, where the PTC from pulses, the resistivity continues to decrease by an additional order of magnitude, reaching a minimum after ~20 pulses. Figure 3b plots the photoinduced conductivity versus shot number for different fluences. The 4 mJ/cm 2 (same data as Fig. 3a) saturates at 800 Ω -1 cm -1 , while at lower fluences the conductivity saturates at a lower value. This is important, showing that the conductivity change does not simply arise from the absorbed number of photons. If there were a simple dependence on the number of absorbed photons, the data at lower fluences would saturate to the same conductivity value as the higher fluence data after a sufficient number of pulses. This is clearly not the case and indicates a cooperative process with a photon-absorption threshold. Figure 3c plots the conductivity plateaus from Measuring the conductivity dynamics of the pristine AFI state following singlepulse excitation would provide insight into the photoinduced IMT but is not experimentally feasible on a shot-to-shot basis. Instead, we employed an all-optical single-shot ultrafast spectroscopic method 28 which faithfully represents the conductivity dynamics because of the aforementioned spectral weight transfer. Figure 3d shows the results of single-shot photoinduced reflectivity dynamics (R/R) probing at the peak of the intersite transition (1.7 eV) following 1.55 eV excitation. There is a decrease in R/R consistent with dynamic spectral weight transfer to THz frequencies and the IMT dy...

Advances in the synthesis, growth, and characterization of complex transition metal oxides coupled with new experimental techniques in ultrafast optical spectroscopy have ushered in an exciting era of dynamics and control in these materials. Experiments utilizing femtosecond optical pulses can initiate and probe dynamics of the spin, lattice, orbital, and charge degrees of freedom. Major goals include (a) determining how interaction and competition between the relevant degrees of freedom determine macroscopic functionality in transition metal oxides (TMOs) and (b) searching for hidden phases in TMOs by controlling dynamic trajectories in a complex and pliable energy landscape. Advances in creating intense pulses from the far-IR spectrum through the visible spectrum enable mode-selective excitation to facilitate exploration of these possibilities. This review covers recent developments in this emerging field and presents examples that include the cuprates, manganites, and vanadates.

Dynamic polarization control of light is essential for numerous applications ranging from enhanced imaging to materials characterization and identification. We present a reconfigurable terahertz metasurface quarter-waveplate consisting of electromechanically actuated micro-cantilever arrays. Our anisotropic metasurface enables tunable polarization conversion cantilever actuation. Specifically, voltage-based actuation provides mode selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metasurface has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We observe a ~230 GHz cantilever actuated frequency shift of the resonance mode, sufficient to modulate the transmitted wave from pure circular polarization to linear polarization. Our CMOS-compatible tunable quarterwaveplate enriches the library of terahertz optical components, thereby facilitating practical applications of terahertz technologies.