Increasing performance demands on photodetectors and solar cells require the development of entirely new materials and technological approaches. We report on the fabrication and optoelectronic characterization of a photodetector based on optically-thick films of dense, aligned, and macroscopically long single-wall carbon nanotubes. The photodetector exhibits broadband response from the visible to the mid-infrared under global illumination, with a response time less than 32 μs. Scanning photocurrent microscopy indicates that the signal originates at the contact edges, with an amplitude and width that can be tailored by choosing different contact metals. A theoretical model demonstrates the photothermoelectric origin of the photoresponse due to gradients in the nanotube Seebeck coefficient near the contacts. The experimental and theoretical results open a new path for the realization of optoelectronic devices based on three-dimensionally organized nanotubes.

In contrast to a free-electron system, a Tomonaga-Luttinger (TL) liquid in a one-dimensional (1D) electron system hosts charge and spin excitations as independent entities 1-4 . When an electron is injected into a TL liquid, it transforms into chargeand spin-density wavepackets that propagate at di erent group velocities and move away from each other. This process, known as spin-charge separation, is the hallmark of TL physics. While spin-charge separation has been probed in momentumor frequency-domain measurements in various 1D systems 5-9 , waveforms of separated excitations, which are a direct manifestation of the TL behaviour, have been long awaited to be measured. Here, we present a waveform measurement for the pseudospin-charge separation process in a chiral TL liquid comprising quantum Hall edge channels 9-13 . The chargeand pseudospin-density waveforms are captured by utilizing a spin-resolved sampling scope that records the spin-up or -down component of the excitations. This experimental technique provides full information for time evolution of the 1D electron system, including not only propagation of TL eigenmodes but also their decay in a practical device 14 .Co-propagating spin-up and -down edge channels of the quantum Hall (QH) state at filling factor ν = 2 form a prototypical system for the study of TL physics. The TL eigenmodes have been identified by measuring interference of density waves 9 , shot noise generation [10][11][12] , and charge-density correlation between two paths in a Hong-Ou-Mandel experiment 13 . Dynamics of the charge-and spin-density excitations, that is, their excitation, propagation, and attenuation, are elementary processes of nonequilibrium phenomena in the 1D system. For investigating these processes, a waveform measurement for each density excitation is highly desirable. In this study, we developed a spin-resolved sampling scope comprising a spin filter and a time-resolved charge detector 15,16 , which enables one to perform the waveform measurement. We actually observe charge-and pseudospin-density excitations separated over a distance exceeding 200 µm. The TL parameters (group velocities of charge-(v C ) and pseudospin-density (v S ≤ v C ) waves and mixing angle θ, which is introduced later) are directly read out from the waveforms; this is the first experiment in which all the TL parameters are estimated from a single measurement. Moreover, attenuation of TL wavepackets is evaluated from distortion of the waveforms. These results give quantitative information on various non-equilibrium phenomena in QH edge channels-for example, heat transport 17-20 and decoherence in interferometers 21,22 .The 1D electron dynamics in the co-propagating channels are formulated by the wave equation for the spin-up and -down charge densities ρ ↑,↓ (x, t) 23-25where U X is the inter-channel interaction and v ↑ (v ↓ ) is the group velocity renormalized by the intra-channel interaction in the spin-up (down) channel. While conventional TL theory assumes v ↑ = v ↓ , we consider a more general ...

We demonstrated electrical spin injection from a half-metallic Heusler alloy Co 2 MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co 2 MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co 50 Fe 50 spin source, suggesting that the spin polarization of Co 2 MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel.

A clear spin-valve signal and a Hanle signal were observed in a Co 50 Fe 50 /n-GaAs Schottky tunnel junction through a four-terminal non-local geometry. The sign and magnitude of the spin-valve signal were strongly dependent on the bias current, suggesting that the spin polarization at the Co 50 Fe 50 /n-GaAs interface had strong energy dependence. A clear spin-valve signal was observed at temperatures up to 290 K. The magnitude of the spin-valve signal monotonically decreased by a factor of 7.9 as the temperature increased from 10 K to 290 K; this factor was significantly smaller than the factors reported for Fe/n-GaAs junctions which range from 35 to 80. The injection of spin-polarized electrons from a ferromagnet (F) into a semiconductor (SC) and the detection of spin-polarized electrons which transport through a SC channel have attracted much interest for creating viable semiconductor-based spintronics. The spin-valve measurement and Hanle-type spin precession measurement using a non-local four terminal device provide direct evidence for proving the spin injection and transport occur, and these measurements have been demonstrated in several systems, such as Fe/GaAs, The spin-signals observed at room temperature, however, were typically more than one order of magnitude smaller than those at low temperatures of around 10 K. The achievement of a much slower spin signal decay rate with increasing temperature is one of the most important steps towards realizing spin-injection devices which can operate at room temperature. In this paper, we discuss our observation of a clear spin-valve signal and a Hanle signal using a four-terminal non-local geometry in fully epitaxial Co 50 Fe 50 /n-GaAs Schottky tunnel junctions. We found that the spin-valve signal decreased by a factor of about 7.9 with increasing temperature from 10 K to 290 K, and this factor was significantly smaller than the factors reported for Fe/n-GaAs junctions which range from 35 to 80.

We have developed a nuclear magnetic resonance (NMR) system that uses spin injection from a highly polarized spin source. Efficient spin injection into GaAs from a half-metallic spin source of Mn-rich Co 2 MnSi enabled an efficient dynamic nuclear polarization of Ga and As nuclei in GaAs and a sensitive detection of NMR signals. Moreover, coherent control of nuclear spins, or the Rabi oscillation between two quantum levels formed at Ga nuclei, induced by a pulsed NMR has been demonstrated at a relatively low magnetic field of ∼0.1 T. This provides a novel all-electrical solid-state NMR system with the high spatial resolution and high sensitivity needed to implement scalable nuclear-spin-based qubits. Nuclear spins in semiconductors are an ideal system for implementing quantum bits (qubits) for quantum computation because they have an extremely long coherence time. The nuclear magnetic resonance (NMR) technique enables the control and detection of nuclear-spin qubits, and quantum algorism with seven qubits has been demonstrated in molecules in a liquid [1]. For large-scale integration, however, the implementation of qubits in solid-state materials, especially in semiconductors, is indispensable. Moreover, in conventional NMR techniques, a strong magnetostatic field should be applied to polarize nuclear spins, making it difficult to selectively control nuclear spins located within nanometer-sized regions. Furthermore, since the magnetic moment of a nuclear spin is three orders of magnitude smaller than that of an electron spin, the sensitivity of detecting nuclear spins through a pickup coil is quite low. Thus, there is a strong need to develop a novel NMR technique with high spatial resolution and high sensitivity to enable a future large-scale quantum computing system. From this point of view, dynamic nuclear polarization (DNP), where nuclear spins are dynamically polarized through a hyperfine interaction between nuclear spins and electron spins, has attracted much interest, since it can drastically increase the NMR signal. Several solid-state NMR devices based on different DNP techniques by optical [2][3][4] or electrical means [5][6][7] have recently been reported. Furthermore, coherent manipulation of nuclear spins, or the Rabi oscillation, which is a key factor for nuclear-spin-based qubits, has been demonstrated electrically in GaAs/AlGaAs quantum Hall systems [8][9][10] and optically in GaAs/AlGaAs quantum wells [11,12]. Although the optical method is suitable for clarifying the fundamental physics relevant to nuclear spins, it is restricted in its scalability because the spatial resolution is limited by the optical wavelength. Quantum Hall systems, on the other hand, require a relatively strong magnetic field of several tesla and a low temperature below 1 K to create the highly spin-polarized electrons necessary for the DNP and the detection of nuclear-spin states.An injection of spin-polarized electrons from a ferromagnetic electrode into a semiconductor also creates spinpolarized electronic states in a ...