Search

Detecting electromagnetic radiation scattered from a tip-sample junction has enabled overcoming the diffraction limit and started the flourishing field of polariton nanoimaging. However, most techniques only resolve amplitude and relative phase of the scattered radiation. Here, we utilize field-resolved detection of ultrashort scattered pulses to map the dynamics of surface polaritons in both space and time. Plasmon polaritons in graphene serve as an ideal model system for the study, demonstrating how propagating modes can be visualized and modeled in the time domain by a straightforward mathematical equation and normalization method. This novel approach enables a direct assessment of the polaritons' group and phase velocities, as well as the damping. Additionally, it is particularly powerful in combination with a pump-probe scheme to trace subcycle changes in the polariton propagation upon photoexcitation. Our method readily applies to other quantum materials, providing a versatile tool to study ultrafast nonequilibrium spatiotemporal dynamics of polaritons.

Uncooled terahertz photodetectors (PDs) showing fast (ps) response and high sensitivity (noise equivalent power (NEP) < nW/Hz 1/2 ) over a broad (0.5-10 THz) frequency range are needed for applications in high-resolution spectroscopy (relative accuracy ∼10 -11 ), metrology, quantum information, security, imaging, optical communications. However, present terahertz receivers cannot provide the required balance between sensitivity, speed, operation temperature, and frequency range. Here, we demonstrate uncooled terahertz PDs combining the low (∼2000 k B μm -2 ) electronic specific heat of high mobility (>50 000 cm 2 s -1 s -1 ) hexagonal boron nitride-encapsulated graphene, with asymmetric field enhancement produced by a bow-tie antenna, resonating at 3 THz. This produces a strong photo-thermoelectric conversion, which simultaneously leads to a combination of high sensitivity (NEP ≤ 160 pW Hz -1/2 ), fast response time (≤3.3 ns), and a 4 orders of magnitude dynamic range, making our devices the fastest, broad-band, low-noise, room-temperature terahertz PD, to date.

The growth of semiconductor nanowires (NWs) has recently opened new paths to silicon integration of device families such as light-emitting diodes, high-efficiency photovoltaics, or high-responsivity photodetectors. It is also offering a wealth of new approaches for the development of a future generation of nanoelectronic devices. Here we demonstrate that semiconductor nanowires can also be used as building blocks for the realization of high-sensitivity terahertz detectors based on a 1D field-effect transistor configuration. In order to take advantage of the low effective mass and high mobilities achievable in III-V compounds, we have used InAs nanowires, grown by vapor-phase epitaxy, and properly doped with selenium to control the charge density and to optimize source-drain and contact resistance. The detection mechanism exploits the nonlinearity of the transfer characteristics: the terahertz radiation field is fed at the gate-source electrodes with wide band antennas, and the rectified signal is then read at the output in the form of a DC drain voltage. Significant responsivity values (>1 V/W) at 0.3 THz have been obtained with noise equivalent powers (NEP) < 2 × 10(-9) W/(Hz)(1/2) at room temperature. The large existing margins for technology improvements, the scalability to higher frequencies, and the possibility of realizing multipixel arrays, make these devices highly competitive as a future solution for terahertz detection., (© 2011 American Chemical Society)