Metallic bowtie nanoarchitectures can produce dramatic electric field enhancement, which is advantageous in single-molecule analysis and optical information processing. Plasmonic bowtie nanostructures were successfully constructed using a DNA origami-based bottom-up assembly strategy, which enables precise control over the geometrical configuration of the bowtie with an approximate 5 nm gap. A single Raman probe was accurately positioned at the gap of the bowtie. Single-molecule surface-enhanced Raman scattering (SM-SERS) of individual nanostructures, including ones containing an alkyne group, was observed. The design achieved repeatable local field enhancement of several orders of magnitude. This method opens the door on a novel strategy for the fabrication of metal bowtie structures and SM-SERS, which can be utilized in the design of highly-sensitive photonic devices.

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Experimental evidence on high-T c cuprates reveals ubiquitous charge density wave (CDW) modulations 1-10 , which coexist with superconductivity. Although the CDW had been predicted by theory 11-13 , important questions remain about the extent to which the CDW influences lattice and charge degrees of freedom and its characteristics as functions of doping and temperature. These questions are intimately connected to the origin of the CDW and its relation to the mysterious cuprate pseudogap 10,14 . Here, we use ultrahigh-resolution resonant inelastic X-ray scattering to reveal new CDW character in underdoped Bi 2.2 Sr 1.8 Ca 0.8 Dy 0.2 Cu 2 O 8+δ . At low temperature, we observe dispersive excitations from an incommensurate CDW that induces anomalously enhanced phonon intensity, unseen using other techniques. Near the pseudogap temperature T * , the CDW persists, but the associated excitations significantly weaken with an indication of CDW wavevector shift. The dispersive CDW excitations, phonon anomaly, and analysis of the CDW wavevector provide a comprehensive momentumspace picture of complex CDW behaviour and point to a closer relationship with the pseudogap state.With sufficient energy resolution, resonant inelastic X-ray scattering (RIXS) can be an ideal probe for revealing the CDW excitations in cuprates. By tuning the incident photon energy to the Cu L 3 -edge (Fig. 1a), the resonant absorption and emission processes can leave the system in excited final states, which couple to a variety of excitations arising from orbital, spin, charge, and lattice degrees of freedom 15 . Thus, information of these elementary excitations in energy and momentum space can be deduced from analysing the RIXS spectra as functions of the energy loss and the momentum transfer of the photons (Fig. 1a). This is highlighted by the pivotal role that RIXS has recently played in revealing orbital and magnetic excitations in cuprates [16][17][18][19][20] . In addition, RIXS provided the first X-ray scattering evidence for an incommensurate CDW in (Y,Nd)Ba 2 Cu 3 O 6+δ (ref. 4), owing to energy resolution that separated the quasi-elastic CDW signal (bright spot in Fig. 1b, limited by the instrumental resolution ∼130 meV) from other intense higher-energy excitations. Notably this quasi-elastic signal is asymmetric with respect to zero energy loss (Fig. 1c), which indicates the possible existence of additional low-energy excitations near the CDW wavevector (Q CDW ).In this work, we exploit the newly commissioned ultrahighresolution RIXS instrument at the European Synchrotron Radiation Facility to reveal these low-energy excitations near the CDW. We choose the double-layer cuprate Bi 2.2 Sr 1.8 Ca 0.8 Dy 0.2 Cu 2 O 8+δ (Bi2212), whose electronic structure has been extensively studied by surface-sensitive spectroscopy, such as scanning tunnelling microscopy 21 and angle-resolved photoemission 22 , and in which a short-range CDW order was recently reported 7,8 . With improved energy resolution up to 40 meV, we see additional features in the pre...

If the pseudogap and superconducting order parameters compete within a GinzburgLandau framework, this should be detectable as an abrupt change in the spectral-weight transfer at T c . To search for this signature, we performed measurements of the electronic states in Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly probes the occupied states of the single-particle spectral function. ARPES is an ideal tool for this study because it can resolve the strong momentum anisotropies of the pseudogap and superconducting gap, both of which become the largest at the antinode, the Fermi momentum (k F ) on the Brillouin zone boundary (Fig. 1b).We show in Fig. 1a a detailed temperature dependence of the ARPES spectra at the antinode of optimally-doped Bi2212 (denoted OP98, p ~ 0.160, T c = 98 K). Here, all the spectra are divided by the resolution-convolved Fermi-Dirac function (FD) to effectively remove the Fermi cutoff. At T << T c , the spectra show a "peak-dip-hump" structure which is typical for the cuprates near the antinode. While the peak (blue circles) is a signature of superconductivity, the dip (purple down triangles) and hump (red squares) are often associated with strong band renormalizations arising from electron-boson coupling. 21,22 Above T c , the spectra show a continued suppression of spectral intensity at the Fermi level (E F ), defining the pseudogap.1 Notably, the peak feature becomes weaker but survives above T c . There is no singular signature in the spectral lineshape at T c over a wide doping range (Supplementary Fig. 1 for complete dataset). The non-trivial evolution of the spectral lineshape has been making the interpretation of the pseudogap difficult.To investigate the nature of the peak, dip and hump, we show in Fig. 1c their energies as a function of temperature. The energy scale of the anomalously broad hump feature at T c < T < T* decreases with increasing temperature and hole doping ( Supplementary Fig. 1), suggesting that it arises from the pseudogap. The hump at T > T c continuously connects with that at T < T c (Fig. 1c), suggesting that not only the electron-boson coupling but also the pseudogap affects the hump energy at T < T c while simultaneously coexisting with the superconducting peak. Here, a simple addition of two gaps in quadrature does not reproduce the data and does not capture the mixed nature of the all spectral features as noted earlier. 15Next, we show in Figs. 1d-1f the spectral weight obtained by analyzing the spectral intensity I(ω) at the antinode (Fig. 1a), where ω is energy. and high-energy spectral weights, respectively Because the energy scale for superconductivity is < 50 meV, the opening of a superconducting gap at k F should push the 1 st moment energy away from E F in a narrow range, and have almost no effect on the low-and high-energy spectral weights.In contrast with the behavior expected for homogeneous superconductivity, the most striking signature in the current result is the spectral-weight singular...