180 research outputs found
Quantitative analysis on electric dipole energy in Rashba band splitting
We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime.1131Ysciescopu
Linear scaling relationship of N\'{e}el temperature and dominant magnons in pyrochlore ruthenates
We present a systematic Raman spectroscopy study on a series of pyrochlore
ruthenates, a system which is not yet clearly settled on its magnetic origin
and structure. Apart from the Raman-active phonon modes, new peaks that appear
in the energy range of 15 - 35 meV below the N\'{e}el temperature are assigned
as one-magnon modes. The temperature evolution of one-magnon modes displays no
significant thermal dependence in mode frequencies while the intensities
decrease monotonically. Remarkably, one-magnons from all compounds show similar
characteristics with a single dominant peak at lower energy and weaker side
peaks at a couple of meV higher energy. Most importantly, we uncover a striking
proportionality between the dominant magnon mode energies and the N\'{e}el
temperatures. Our results suggest the Ru ions may have similar or the same
magnetic phase in all pyrochlore ruthenates of our study. We have thus found an
avenue for directly tuning the magnetic exchange interaction by the selection
of the -site ion
Experimental observation of hidden Berry curvature in inversion-symmetric bulk 2H-WSe2
We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the
surface sensitivity of angle resolved photoemission (ARPES). The symmetry in
the electronic structure of transition metal dichalcogenides is used to
uniquely determine the local orbital angular momentum (OAM) contribution to the
circular dichroism (CD) in ARPES. The extracted CD signals for the K and K'
valleys are almost identical but their signs, which should be determined by the
valley index, are opposite. In addition, the sign is found to be the same for
the two spin-split bands, indicating that it is independent of spin state.
These observed CD behaviors are what are expected from Berry curvature of a
monolayer of WSe2. In order to see if CD-ARPES is indeed representative of
hidden Berry curvature within a layer, we use tight binding analysis as well as
density functional calculation to calculate the Berry curvature and local OAM
of a monolayer WSe2. We find that measured CD-ARPES is approximately
proportional to the calculated Berry curvature as well as local OAM, further
supporting our interpretation.Comment: 6 pages, 3 figure
phonon anomaly driven by Fermi surface instability at intermediate temperature in YBaCuO
We performed temperature- and doping-dependent high-resolution Raman
spectroscopy experiments on YBaCuO to study
phonons. The temperature dependence of the real part of the phonon self-energy
shows a distinct kink at above due to softening,
in addition to the one due to the onset of the superconductivity. is clearly different from the pseudogap temperature with a maximum in the
underdoped region. The region between and
resembles that of superconducting fluctuation or charge density wave order.
While the true origin of the phonon softening is not known, we
can attribute it to a gap on the Fermi surface due to an electronic order. Our
results may reveal the role of the phonon not only in the
superconducting state but also in the intertwined orders in multilayer copper
oxide high- superconductors.Comment: 5 pages, 4 figure
Optical biochemical sensor based on half-circled microdisk laser diode
In this study, a half-circled cavity based microdisk laser diode is proposed and demonstrated experimentally for an integrated photonic biochemical sensor. Conventional microdisk sensors have limitations in optical coupling and reproducibility. In order to overcome these drawbacks, we design a novel half-circled micro disk laser (HC-MDL) which is easy to manufacture and has optical output directionality. The Q-factor of the fabricated HC-MDL was measured as 7.72 × 106 using the self-heterodyne method and the side mode suppression ratio was measured as 23 dB. Moreover, gas sensing experiments were performed using the HC-MDL sensor. A wavelength shift response of 14.21 pm was obtained for 100 ppb dimethyl methylphosphonate (DMMP) gas and that of 14.70 pm was obtained for 1 ppm ethanol gas. These results indicate the possibility of highly sensitive gas detection at ppb levels using HC-MDL. This attractive feature of the HC-MDL sensor is believed to be very useful for a wide variety of optical biochemical sensor applications. © 2017 Optical Society of America.1
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