Engineering topics
Taylor, Antoinette
Publications and source records attributed to Taylor, Antoinette.
Quasiparticle dynamics across the full Brillouin zone of Bi 2 Sr 2 CaCu 2 O 8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy
A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy which significantly limits the accessible momentum space. Using 20.15eV, 12 fs pulses we show for the first time the evolution of quasiparticles in the antinodal region of Bi 2 Sr 2 CaCu 2 O 8+δ and demonstrate that nonmonotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in severe contrast to the monotonic relaxation in the nodal and off-nodal regions.
Ultrafast optical microscopy on single semiconductor nanowires
Abstract Not Provided
Innovation in Materials Science: Electromagnetic Metamaterials Summary
Electromagnetic metamaterials have been developed over the past ten years in the form of composites of ordered subwavelength constituents. They are man-made effective media that exhibit unusual electromagnetic properties not normally found in nature. The idea was inspired by the pioneering works of John Pendry in reducing electrical plasma frequency in metal wires and creating an artificial magnetic response via metal split-ring resonators (SRRs).
Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials
The outline of this presentation are: (1) Motivation - Non-tunability of metal metamaterials; (2) Superconductors for temperature tunable metamaterials; (3) Ultrafast optical switching in superconductor metamaterials; (4) Controlling the conductivity with infrared pump beam; (5) Complex metal oxides as active substrates - Strontium Titanate; and (6) Conclusion. Conclusions are: (1) High Tc superconductors good for tunable and ultrafast metamaterials; (2) Large frequency and amplitude tunability in ultrathin superconductor films; (3) Such tunable properties cannot be accessed using metals; (4) Complex metal oxides can be used as active substrates - large tunability; (5) Complex oxides fail to address the issue of radiation losses in THz metamaterials.
Ultrafast optical pump-probe spectroscopy is used to reveal the coexistence of coupled antiferromagnetic (AFM)/ferroelectric (FE) and ferromagnetic (FM) orders in multiferroic TbMnO3 films, which can guide researchers in creating new kinds of multiferroic materials.
Multiferroic materials have attracted much interest in the past decade, due not only to their novel device applications, but also their manifestations of coupling and interactions between different order parameters (particularly electric polarization and magnetic order). Recently, much attention has been focused on perovskite manganites, RMnO{sub 3} (R = rare earth ions), due to the discovery of a large magnetoelectric effect in these materials. The first member of this family to be discovered was TbMnO{sub 3} (TMO), which is now well established as a typical magnetoelectric multiferroic. Extensive experimental and theoretical studies have already been done on single crystal TMO (SC-TMO). In brief, SC-TMO, with a distorted orthorhombic perovskite structure, has an antiferromagnetic (AFM) phase transition at T{sub N} {approx}40 K with sinusoidally ordered Mn moments. Below T{sub FE} {approx} 28 K, ferroelectric (FE) order develops owing to the appearance of cycloidal spiral spin structure. In contrast, there are relatively few reports describing the properties of TMO thin films (typically grown on SrTiO{sub 3} (STO) substrates). In general, thin films can enable new functionality in materials, as their physical parameters can be changed by modifying their structure via strain imposed by the substrate. Strain in particular has the potential to directly couple FE and FM orders, which is very rare. This could benefit electronic device applications by providing low power consumption, high speed operation, and greater electric/magnetic field controllability. Previous investigations of magnetic properties in TMO films revealed an unexpected ferromagnetic (FM) order, in contrast to SC-TMO. However, several important questions regarding these films are still unanswered for instance: (1) What mechanism induces FM order? (2) Can FM, sinusoidal AFM and spiral AFM (or FE) orders coexist? (3) Can FM order be coupled to FE order? To fully understand these unique materials, experimental techniques capable of dynamically unraveling the interplay between these degrees of freedom on an ultrafast timescale are needed. Here, we use ultrafast optical pump-probe spectroscopy to reveal coexisting coupled magnetic orders in epitaxial TMO thin films grown on (001)-STO, which were not observed in previous work. Our temperature (T)-dependent transient differential reflectivity ({Delta}R/R) measurements show clear signatures of sinusoidal AFM, spiral AFM (FE) and FM phases developing as the film thickness changes. We carry out first-principle density functional theory (DFT) calculations to explain the coupling between AFM/FE and FM orders. These results reveal that the coupling between different magnetic orders observed in our multiferroic TMO thin films may offer greater control of functionality as compared to bulk single crystal multiferroics.
Tunnel-dioxide loaded split-ring resonators as a function for nonlinear metamaterials
Abstract Not Provided
Polarization anisotropy of transient carrier dynamics in single Si nanowires
Abstract Not Provided
Polarization dependence of ultrafast dynamics in single Si nanowires
Abstract Not Provided
Ultrafast optical control of terahertz surface plasmons in subwavelength hole-arrays at room temperature
Extraordinary optical transmission through subwavelength metallic hole-arrays has been an active research area since its first demonstration. The frequency selective resonance properties of subwavelength metallic hole arrays, generally known as surface plasmon polaritons, have potential use in functional plasmonic devices such as filters, modulators, switches, etc. Such plasmonic devices are also very promising for future terahertz applications. Ultrafast switching or modulation of the resonant behavior of the 2-D metallic arrays in terahertz frequencies is of particular interest for high speed communication and sensing applications. In this paper, we demonstrate optical control of surface plasmon enhanced resonant terahertz transmission in two-dimensional subwavelength metallic hole arrays fabricated on gallium arsenide based substrates. Optically pumping the arrays creates a conductive layer in the substrate reducing the terahertz transmission amplitude of both the resonant mode and the direct transmission. Under low optical fluence, the terahertz transmission is more greatly affected by resonance damping than by propagation loss in the substrate. An ErAs:GaAs nanoisland superlattice substrate is shown to allow ultrafast control with a switching recovery time of {approx}10 ps. We also present resonant terahertz transmission in a hybrid plasmonic film comprised of an integrated array of subwavelength metallic islands and semiconductor holes. A large dynamic transition between a dipolar localized surface plasmon mode and a surface plasmon resonance near 0.8 THz is observed under near infrared optical excitation. The reversal in transmission amplitude from a stopband to a passband and up to {pi}/2 phase shift achieved in the hybrid plasmonic film make it promising in large dynamic phase modulation, optical changeover switching, and active terahertz plasmonics.