The optical properties and functionalities of single-walled carbon nanotubes (SWNTs) are currently attracting considerable attention. New techniques such as alignment of carbon nanotubes have been introduced to elucidate their 1D nature. These techniques include magnetic-field alignment, [1] chemical vapor deposition, [2] and mechanical stretching.[3] Indeed, aligned SWNTs have already provided the opportunity to carry out polarization-dependent spectroscopic studies [4][5][6] and experiments on the directionally dependent Aharanov-Bohm effect in magnetic fields. [7,8] On the other hand, lower frequency regions (gigahertz, terahertz, and far infrared) of the electromagnetic spectrum, which are related to the electrodynamic response of metallic and narrow-gap semiconductors, have been less investigated and are less understood. [9][10][11] This is particularly true for the anisotropic spectral response, though it is crucial for understanding the low-energy electronic structure and carrier dynamics in SWNTs, as well as for exploring polarization-sensitive terahertz applications. In this communication, we report the preparation of aligned SWNTs embedded in polyethylene and their optical properties over a broad frequency range (6-33 000 cm -1 ). The oriented films reveal rich, novel properties involving strong anisotropy as well as morphology and doping dependencies. The discussion based on these results has uncovered intriguing aspects on the infrared response of SWNTs as well as possible functionalities in the terahertz region of the electromagnetic spectrum.We have employed two kinds of SWNTs: laser-ablationgrown SWNTs and commercially available high-pressure CO disproportionation (HiPCO) SWNTs, abbreviated hereafter as L-SWNTs and H-SWNTs. The former was purified by a conventional method, [12] whereas the latter was used as purchased without purification. From a Kataura plot, [13] which relates transitions between van Hove singularities and tube diameter, we have extracted average diameters of 1.4 and 0.95 nm, respectively. Among the three techniques for nanotube alignment, the mechanical stretching of SWNT/polymer composites [14] offers the best flexibility, assuming that the matrix is transparent in the region of interest. Here, we have selected polyethylene as the matrix. All of our SWNTs are bundled; no isolation processes were employed to separate individual tubes. The degree of orientation of our samples has been determined by polarized Raman spectroscopy utilizing a He-Ne laser (633 nm) excitation source. Because resonance Raman scattering is detectable only for polarization parallel to the tube axis, this technique is ideal for determining the degree of alignment in SWNT/polymer composites. [15,16] The maximum entropy analysis [17,18] showed that approximately 90 % of SWNTs are within 25°of the stretching direction, indicating a rather high degree of alignment. A similar degree of alignment was reproducibly obtained both for L-and H-SWNTs. Figure 1 displays the polarized absorption spectra of LSWNTs (top)...

A central characteristic of living beings is the ability to learn from and respond to their environment leading to habit formation and decision making. This behavior, known as habituation, is universal among all forms of life with a central nervous system, and is also observed in single-cell organisms that do not possess a brain. Here, we report the discovery of habituation-based plasticity utilizing a perovskite quantum system by dynamical modulation of electron localization. Microscopic mechanisms and pathways that enable this organismic collective charge-lattice interaction are elucidated by first-principles theory, synchrotron investigations, ab initio molecular dynamics simulations, and in situ environmental breathing studies. We implement a learning algorithm inspired by the conductance relaxation behavior of perovskites that naturally incorporates habituation, and demonstrate learning to forget: a key feature of animal and human brains. Incorporating this elementary skill in learning boosts the capability of neural computing in a sequential, dynamic environment.

We present X-ray crystal truncation rods measurements of Pt(111) surface under electrochemical conditions. Analyses of crystal truncation rods reveal that surface oxide formation buckles the top surface layer of platinum to two different heights at the potential (0.95 V vs RHE) below the so-called place-exchange potential. While the anti-Bragg intensity, sensitive to the top surface layer, drops in response to the anodic charge transfers, its responses to the cathodic charge transfers are significantly delayed. Implications to the surface oxidation and reduction behaviors are discussed.

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Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we combine measurements of transmon qubit relaxation times (T1) with spectroscopy and microscopy of the polycrystalline niobium films used in qubit fabrication. By comparing films deposited using three different techniques, we reveal correlations between T1 and intrinsic film properties such as grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Qubit and resonator measurements show signatures of two-level system defects, which we propose to be hosted in the grain boundaries and surface oxides. We also show that the residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.