475 research outputs found
Mode-selective coupling of coherent phonons to the Bi2212 electronic band structure
Cuprate superconductors host a multitude of low-energy optical phonons. Using
time- and angle-resolved photoemission spectroscopy, we study coherent phonons
in BiSrCaYCuO. Sub-meV
modulations of the electronic band structure are observed at frequencies of
and THz. For the dominant mode at 3.94 THz, the
amplitude of the band energy oscillation weakly increases as a function of
momentum away from the node. Theoretical calculations allow identifying the
observed modes as CuO-derived phonons. The Bi- and Sr-derived
modes which dominate Raman spectra in the relevant frequency range are
absent in our measurements. This highlights the mode-selectivity for phonons
coupled to the near-Fermi-level electrons, which originate from CuO
planes and dictate thermodynamic properties.Comment: 7 pages, 3 figure
Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3
Using femtosecond time- and angle- resolved photoemission spectroscopy, we
investigated the nonequilibrium dynamics of the topological insulator Bi2Se3.
We studied p-type Bi2Se3, in which the metallic Dirac surface state and bulk
conduction bands are unoccupied. Optical excitation leads to a meta-stable
population at the bulk conduction band edge, which feeds a nonequilibrium
population of the surface state persisting for >10ps. This unusually long-lived
population of a metallic Dirac surface state with spin texture may present a
channel in which to drive transient spin-polarized currents
Reflection-based fibre-optic refractive index sensor using surface plasmon resonance
A reflection-based fibre-optic refractive index sensor using surface plasmon resonance (SPR) in a thin metal film sputtered on a bare core of a multimode optical fibre is presented. The sensing element of the SPR fibre-optic sensor is the core of a step-index optical fibre made of fused silica with a gold film double-sided sputtered on the whole core surface, including the core end face. Consequently, a terminated reflection-based sensing scheme to measure the refractive indices of liquids is realized. The sensing scheme uses a wavelength interrogation method and the refractive index of a liquid is sensed by measuring the position of the dip in the reflected spectral intensity distribution. As an example, the aqueous solutions of ethanol with refractive indices in a range from 1.333 to 1.363 are measured. In addition, the increase in the sensitivity of the SPR fibre-optic refractive index sensor with the decrease of the fibre sensing length is demonstrated
RKKY interactions in the regime of strong localization
We study the influence of strong nonmagnetic disorder on the
Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between diluted magnetic
moments in metals. We find that the probability distribution for the RKKY
interactions assumes strongly non-Gaussian form featuring long tails. Since
such distributions cannot be characterized by its moments, we define a
\textit{typical} value of the interaction amplitude, which we find to be
exponentially suppressed in presence of Anderson localization. Our results
present a plausible and physically transparent picture describing how Anderson
localization effectively eliminates the long range nature of the RKKY
interactions.Comment: 6 pages, published versio
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