Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.

The mobility and carrier concentration of a number of InSb-based modulation-doped quantum well heterostructures are examined over a range of temperatures between 4.5 and 300 K. Wide well ͑30 nm͒ and narrow well ͑15 nm͒ structures are measured. The temperature dependent mobilities are considered within a scattering model that incorporates polar optical and acoustic phonon scatterings, interface roughness scattering, and scattering from charged impurities both in the three-dimensional background and within a distributed "quasitwo-dimensional" doping layer. Room temperature mobilities as high as 51 000 cm 2 / V s are reported for heterostructures with a carrier concentration of 5.8ϫ 10 11 cm −2 , while low-temperature mobility ͑below 40 K͒ reaches 248 000 cm 2 / V s for a carrier concentration of 3.9ϫ 10 11 cm −2. A Schrödinger-Poisson model is used to calculate band structures in the material and is shown to accurately predict carrier concentrations over the whole temperature range. Low-temperature mobility is shown to be dominated by remote ionized impurity scattering in wide well samples and by a combination of ionized impurity and interface roughness scattering in narrow well samples.

Hybrid plasmonic metal-graphene systems are emerging as a class of optical metamaterials that facilitate strong light-matter interactions and are of potential importance for hot carrier graphene-based light harvesting and active plasmonic applications. Here we use femtosecond pump-probe measurements to study the near-field interaction between graphene and plasmonic gold nanodisk resonators. By selectively probing the plasmon-induced hot carrier dynamics in samples with tailored graphene-gold interfaces, we show that plasmon-induced hot carrier generation in the graphene is dominated by direct photoexcitation with minimal contribution from charge transfer from the gold. The strong near-field interaction manifests as an unexpected and long-lived extrinsic optical anisotropy. The observations are explained by the action of highly localized plasmon-induced hot carriers in the graphene on the subresonant polarizability of the disk resonator. Because localized hot carrier generation in graphene can be exploited to drive electrical currents, plasmonic metal-graphene nanostructures present opportunities for novel hot carrier device concepts.

We report measurements of the electron g-factor in InSb quantum wells using the coincidence technique, polarization transition, and temperature-dependent resistivity. All three methods show that there is a giant enhancement of the spin slitting which is proportional to the spin polarization. Electron Zeeman energies as high as 51 meV are measured leading to the conclusion that the additional contribution to the spin splitting is of order 30 meV, more than ten times larger than expected from conventional theories.

We measure transverse magnetically focused photocurrent signals in an InSb/InAlSb quantum well device. Using optical spin orientation by modulated circularly polarized light an electron spin dependent signal is observed due to the spin-orbit interaction. Simulations of the focusing signal are performed using a classical billiard ball model which includes both spin precession and a spin dependent electron energy. The simulated data suggests that a signal dependent on the helicity of the incident light is expected for a Rashba parameter α > 0.1 eVÅ and that a splitting of the focusing signal is not expected to be observed in linear polarised photocurrent and purely electrical measurements.

Abstract.We report the optical measurement of the spin dynamics at elevated temperatures and in zero magnetic field, for two types of degenerately doped n-InSb quantum wells (QWs), one asymmetric (sample A) and one symmetric (sample B) with regards to the electrostatic potential across the QW. Making use of three directly determined experimental parameters: the spin lifetime, τ s , the sheet carrier concentration, n, and the electron mobility, , we directly extract the zero field spin splitting. For the asymmetric sample where the Rashba interaction is the dominant source of spin splitting, we deduce a room temperature Rashba parameter of  = 0.09 ± 0.1 eVÅ which is in good agreement with calculations and we estimate the Rashba coefficient α 0 (a figure of merit for the ease with which electron spins can be modulated via an electric field). We review the merits/limitations of this approach and the implications of our finding for spintronic devices.

We present high-field magnetotransport data from a range of 30-nm-wide InSb/InAlSb quantum wells with room-temperature mobilities in excess of 6 m 2 V −1 s −1 . Samples with the narrowest Landau level broadening exhibit beating patterns in the magnetoresistance attributed to zero-field spin splitting. Rashba parameters are extracted from a range of samples and gate biases using the difference in spin populations inferred from fast Fourier transforms of the data. The influence of Landau level broadening and spin-dependent scattering rates are investigated by magnetoconductance simulations, which provide key signatures that we were able to verify by experimental observation. These results demonstrate that in addition to the large Zeeman splitting, the combination of large and spin-dependent broadening is the significant parameter in controlling the appearance of beating in these structures.

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