Confined electrons collectively oscillate in response to light, resulting in a plasmon resonance whose frequency is determined by the electron density and the size and shape of the confinement structure. Plasmons in metallic particles typically occur in the classical regime where the characteristic quantum level spacing is negligibly small compared to the plasma frequency. In doped semiconductor quantum wells, quantum plasmon excitations can be observed, where the quantization energy exceeds the plasma frequency. Such intersubband plasmons occur in the mid- and far-infrared ranges and exhibit a variety of dynamic many-body effects. Here, we report the observation of intersubband plasmons in carbon nanotubes, where both the quantization and plasma frequencies are larger than those of typical quantum wells by three orders of magnitude. As a result, we observed a pronounced absorption peak in the near-infrared. Specifically, we observed the near-infrared plasmon peak in gated films of aligned single-wall carbon nanotubes only for probe light polarized perpendicular to the nanotube axis and only when carriers are present either in the conduction or valence band. Both the intensity and frequency of the peak were found to increase with the carrier density, consistent with the plasmonic nature of the resonance. Our observation of gate-controlled quantum plasmons in aligned carbon nanotubes will not only pave the way for the development of carbon-based near-infrared optoelectronic devices but also allow us to study the collective dynamic response of interacting electrons in one dimension.
We investigate dynamic properties of bouncing and penetration in colliding binary and ternary Bose-Einstein condensates comprised of different Zeeman or hyperfine states of 87 Rb. Through the application of magnetic field gradient pulses, two-or three-component condensates in an optical trap are spatially separated and then made to collide. The subsequent evolutions are classified into two categories: repeated bouncing motion and mutual penetration after damped bounces. We experimentally observed mutual penetration for immiscible condensates, bouncing between miscible condensates, and domain formation for miscible condensates. From numerical simulations of the Gross-Pitaevskii equation, we find that the penetration time can be tuned by slightly changing the atomic interaction strengths. Multicomponent Bose-Einstein condensates (BECs) in dilute atomic gases are an attractive system for studying hydrodynamics of multicomponent quantum fluids owing to their unprecedented controllability. One of the significant properties characterizing multicomponent fluid systems is their miscibility; different fluids are either mutually miscible or phase separation occurs. In multicomponent BECs, the miscibility is determined by inter-and intra-species atomic interaction strengths [1] and, importantly, they can be experimentally controlled using Feshbach resonances [2,3] and Rabi coupling [4,5]. Multicomponent BECs with various degrees of miscibility are also available by choosing the internal states [6] or atomic species [7]. Employing such adjustability and selectability, intriguing phenomena that depend on the degree of miscibility have been experimentally observed, e.g., soliton generation in a counterflow of miscible fluids [8,9] The condition for miscibility in multicomponent BECs is determined by linear stability analysis of a static or steady state, and is not naively applicable to dynamical situations. Let us consider a situation in which two wave packets of different BECs collide with each other. One may think that the two wave packets pass through each other without much reflection for miscible BECs, while for immiscible BECs they do not. However, we will show that these simple predictions from the miscibility do not apply to a highly dynamic situation.In this Rapid Communication, we generate multicomponent BECs with various degrees of miscibility by utilizing the rich spin degrees of freedom of the 87 Rb atom, and investigate the dynamical properties of bouncing and penetration in colliding binary and ternary BECs in an optical trap. We observed various dynamics, including bouncing between miscible BECs and mutual penetration of immiscible BECs, which seems counterintuitive at first glance. In miscible and weakly immiscible binary and ternary systems, after a few bounces, BECs mutually penetrate and create the domain structure. In contrast, in the case of a relatively strongly immiscible system, binary BECs continue to bounce. Such repetitive bouncing motion between atoms has been observed only in a Tonks-Girardeau ga...
We report the thermoelectric properties of WS2 nanotube networks. By using electrolyte-gating techniques, we turned on a conducting channel in the macroscopic networks of WS2 nanotubes in both the hole and electron regions and evaluated the thermoelectric properties of the networks. We manipulated the P- and N-type Seebeck coefficients in the WS2 nanotube networks by changing the shifts in the gate voltage potentials. The power factor of the WS2 nanotube networks increased as the gate voltage shifted and exhibited a high thermoelectric performance approaching that of single-crystalline WS2 flakes.
The values of the interspecies scattering length a 1,2 and the degree of miscibility a between |1, −1 and |1,0 in Table I and Fig. 2 are incorrect. The correct values should be a 1,2 = 100.40a 0 [1,2] and a = −0.0023. Due to this correction, the ground state for |1, −1 and |1,0 is changed from weakly immiscible to weakly miscible. Even though this change is made, our claim "observation of the mutual penetration for immiscible condensates" remains unaltered since the mutual penetration for immiscible condensates is observed in the three-component system as shown in Fig. 6 and numerically confirmed as shown in Fig. 4. Therefore, the corrections do not affect the conclusions of the paper.[1] E.
The presence of hopping carriers and grain boundaries can sometimes lead to anomalous carrier types and density overestimation in Hall-effect measurements. Previous Hall-effect studies on carbon nanotube films reported unreasonably large carrier densities without independent assessments of the carrier types and densities. Here, we have systematically investigated the validity of Hall-effect results for a series of metallic, semiconducting, and metal–semiconductor-mixed single-wall carbon nanotube films. With carrier densities controlled through applied gate voltages, we were able to observe the Hall effect both in the n- and p-type regions, detecting opposite signs in the Hall coefficient. By comparing the obtained carrier types and densities against values derived from simultaneous field-effect-transistor measurements, we found that, while the Hall carrier types were always correct, the Hall carrier densities were overestimated by up to four orders of magnitude. This significant overestimation indicates that thin films of one-dimensional SWCNTs are quite different from conventional hopping transport systems.
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