408 research outputs found
Tunneling into the normal state of Pr(2-x)CexCuO4
The temperature dependence of the tunneling conductance was measured for
various doping levels of Pr(2-x)CexCuO4 using planar junctions. A normal state
gap is seen at all doping levels studied, x=0.11 to x=0.19. We find it to
vanish above a certain temperature T*. T* is greater than Tc for the underdoped
region and it follows Tc on the overdoped side. This behavior suggests finite
pairing amplitude above Tc on the underdoped side
Human Rights Environment And Development In South Asia
The fundamental importance of the issue of Human Rights and the environment to any society is deeply appreciated today
Hyperspectral Infrared Imaging of Surface Phonon-polaritons in SrTiO3
Polaritons have a demonstrated impact on nanophotonic applications in the midinfrared through visible spectral range. Surface phonon-polaritons (SPhPs) offer a way to bring the potential of polaritons to the longer infrared wavelengths. Strontium titanate (STO) is a perovskite polar dielectric with diverse technologically advantageous properties and it can support SPhPs in a uniquely broad spectral range of the far infrared. Despite these advantages, STO has mostly been overlooked as a nanophotonic material. In this work we investigate SPhP propagation in STO in the far-infrared through midinfrared spectral range using broadband, near-field nanospectroscopy. We developed a tabletop, laser sustained plasma light source that enabled us to obtain amplitude and phase resolved hyperspectral line scan maps of SPhPs across the surface of the STO sample. Analytical modeling of experimental data reveals the dispersion characteristics of SPhPs in STO. This work establishes STO as a platform for perovskite-based broadband far-infrared and terahertz nanophotonics
Partially Metal-Coated Tips for Near-Field Nanospectroscopy
Scanning probes with functional optical responses are key components of scanning near-field optical microscopes. For nanospectroscopy performed at IR and terahertz (THz) frequencies, one major challenge is that the commonly used metal-coated silicon tips yield nonadjustable coupling efficiency across the spectrum, which greatly limits the signal-to-noise ratio. Here, we test the possibility of a generic design scheme for wavelength-selective tip enhancement via finite-element numerical modeling. We employ a Si-based tip with various gold-coating lengths on the top, yielding a customizable near-field field strength at the tip apex. Calculations show a wavelength-dependent enhancement factor of the metal-coated tip due to the geometrical antenna resonances, which can be precisely tuned throughout a broad spectral range from visible to terahertz frequencies by adjusting the length of the metal coating. By changing the coating pattern into a chiral helical structure on an achiral tip, we also demonstrate the usefulness of coating-length effect in designing high-performance enantiomeric near-field scanning. Our methods and findings offer interesting perspectives for developing near-field optical probes, pushing the detection and resolution limits of tip-enhanced near-field detections, such as fluorescence, Raman, IR, and THz nanospectroscopies
Strong electron-boson coupling in the iron-based superconductor BaFe1.9Pt0.1As2 revealed by infrared spectroscopy
Understanding the formation of Cooper pairs in iron-based superconductors is
one of the most important topics in condensed matter physics. In conventional
superconductors, the electron-phonon interaction leads to the formation of
Cooper pairs. In conventional strong-coupling superconductors like lead (Pb),
the features due to electron-phonon interaction are evident in the infrared
absorption spectra. Here we investigate the infrared absorption spectra of the
iron arsenide superconductor BaFe1.9Pt0.1As2. We find that this superconductor
has fully gapped (nodeless) Fermi surfaces, and we observe the strong-coupling
electron-boson interaction features in the infrared absorption spectra. Through
modeling with the Eliashberg function based on Eliashberg theory, we obtain a
good quantitative description of the energy gaps and the strong-coupling
features. The full Eliashberg equations are solved to check the
self-consistency of the electron-boson coupling spectrum, the largest energy
gap, and the transition temperature (Tc). Our experimental data and analysis
provide compelling evidence that superconductivity in BaFe1.9Pt0.1As2 is
induced by the coupling of electrons to a low-energy bosonic mode that does not
originate solely from phonons.Comment: 9 pages, 5 figute
Random Field Driven Spatial Complexity at the Mott Transition in VO2
We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric universal properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system
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