3,054 research outputs found
Aharonov-Casher effect in a two dimensional hole gas with spin-orbit interaction
We study the quantum interference effects induced by the Aharonov-Casher
phase in a ring structure in a two-dimensional heavy hole (HH) system with
spin-orbit interaction realizable in narrow asymmetric quantum wells. The
influence of the spin-orbit interaction strength on the transport is
investigated analytically. These analytical results allow us to explain the
interference effects as a signature of the Aharonov-Casher Berry phases. Unlike
previous studies on the electron two-dimensional Rashba systems, we find that
the frequency of conductance modulations as a function of the spin-orbit
strength is not constant but increases for larger spin-orbit splittings. In the
limit of thin channel rings (width smaller than Fermi wavelength), we find that
the spin-orbit splitting can be greatly increased due to quantization in the
radial direction. We also study the influence of magnetic field considering
both limits of small and large Zeeman splittings.Comment: 6 pages, 4 figure
Evidence for the band broadening across the ferromagnetic transition in CrNbSe
The electronic structure of CrNbSe is studied via optical
spectroscopy. We observe two low-energy interband transitions in the
paramagnetic phase, which split into four peaks as the compound enters the
ferromagnetic state. The band structure calculation indicates the four peaks
are interband transitions to the spin up Cr e states. We show that the peak
splitting below the Curie temperature is \emph{not} due to the exchange
splitting of spin up and down bands, but directly reflects a band broadening
effect in Cr-derived states upon the spontaneous ferromagnetic ordering.Comment: 6 pages, 5 figures, to be published in Phys. Rev.
Quantitative SERS Detection of Uric Acid via Formation of Precise Plasmonic Nanojunctions within Aggregates of Gold Nanoparticles and Cucurbit[n]uril
This work describes a rapid and highly sensitive method for the quantitative detection of an important biomarker, uric acid (UA), via surface-enhanced Raman spectroscopy (SERS) with a low detection limit of ~0.2 μM for multiple characteristic peaks in the fingerprint region, using a modular spectrometer. This biosensing scheme is mediated by the host-guest complexation between a macrocycle, cucurbit[7]uril (CB7), and UA, and the subsequent formation of precise plasmonic nanojunctions within the self-assembled Au NP: CB7 nanoaggregates. A facile Au NP synthesis of desirable sizes for SERS substrates has also been performed based on the classical citrate-reduction approach with an option to be facilitated using a lab-built automated synthesizer. This protocol can be readily extended to multiplexed detection of biomarkers in body fluids for clinical applications
SERS multiplexing of methylxanthine drug isomers via host-guest size matching and machine learning
Multiplexed detection and quantification of structurally similar drug molecules, methylxanthine MeX, incl. theobromine TBR, theophylline TPH and caffeine CAF, have been demonstrated via solution-based surface-enhanced Raman spectroscopy (SERS), achieving highly reproducible SERS signals with detection limits down to ∼50 nM for TBR and TPH, and ∼1 μM for CAF. Our SERS substrates are formed by aqueous self-assembly of gold nanoparticles (Au NPs) and supramolecular host molecules, cucurbit[n]urils (CBn, n = 7, 8). We demonstrate that the binding constants can be significantly increased using a host–guest size matching approach, which enables effective enrichment of analyte molecules in close proximity to the plasmonic hotspots. The dynamic range and the robustness of the sensing scheme can be extended using machine learning algorithms, which shows promise for potential applications in therapeutic drug monitoring, food processing, forensics and veterinary science
Soft optically-tuneable fluorescence phantoms based on gel wax and quantum dots: a tissue surrogate for fluorescence imaging validation
Fluorescence-guided brain tumour resection, notably using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) for high-grade gliomas, has been demonstrated to provide better tissue differentiation, thereby improving patient outcomes when compared to white-light guidance. Novel fluorescence imaging devices aiming to increase detection specificity and sensitivity and targeting applications beyond high-grade gliomas are typically assessed by measurements using tissue-mimicking optical phantoms. The field currently lacks adequate phantoms with well-characterised tuneable optical properties. In this study, we developed soft tissue-mimicking fluorescence phantoms (TMFP) highly suitable for this purpose. We investigated: 1) the ability to independently tune optical and fluorescent properties; 2) the stability of the fluorescence signal over time; and 3) the potential of the proposed phantoms for imaging device validation. The TMFP is based on gel-wax which is an optically transparent mineral-oil based soft material. We embedded TiO2 as scattering material, carbon black oil-paint as background absorber, and CdTe Quantum Dots (QDs) as fluorophore because of its similar fluorescence spectrum to PpIX. Scattering and absorption properties were measured by a spectrophotometer, while the fluorescence was assessed by a wide-field fluorescence imaging system (WFFI) and a spectrometer. We demonstrated that: 1) the addition of QDs didn’t alter the phantom’s scattering which was only defined by the concentration of TiO2, whereas its absorption was defined by both QDs and colour oil paint; 2) the measured fluorescence intensity was linearlyproportional to the concentration of QDs; 3) the fluorescence intensity was stable over time (up to eight months); and 4) the fluorescence signal measured by the WFFI were strongly correlated to spectrometer measurements
Spin Motion in Electron Transmission through Ultrathin Ferromagnetic Films Accessed by Photoelectron Spectroscopy
Ab initio and model calculations demonstrate that the spin motion of
electrons transmitted through ferromagnetic films can be analyzed in detail by
means of angle- and spin-resolved core-level photoelectron spectroscopy. The
spin motion appears as precession of the photoelectron spin polarization around
and as relaxation towards the magnetization direction. In a systematic study
for ultrathin Fe films on Pd(001) we elucidate its dependence on the Fe film
thickness and on the Fe electronic structure. In addition to elastic and
inelastic scattering, the effect of band gaps on the spin motion is addressed
in particular.Comment: 4 pages, 5 figure
Spin Diode Based on Fe/MgO Double Tunnel Junction
We demonstrate a spin diode consisting of a semiconductor free nano-scale
Fe/MgO-based double tunnel junction. The device exhibits a near perfect
spin-valve effect combined with a strong diode effect. The mechanism consistent
with our data is resonant tunneling through discrete states in the middle
ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent
transparency. The observed magneto-resistance is record high, ~4000%,
essentially making the structure an on/off spin-switch. This, combined with the
strong diode effect, ~100, offers a new device that should be promising for
such technologies as magnetic random access memory and re-programmable logic.Comment: 14 page
The physical characteristics of the gas in the disk of Centaurus A using the Herschel Space Observatory
We search for variations in the disk of Centaurus A of the emission from
atomic fine structure lines using Herschel PACS and SPIRE spectroscopy. In
particular we observe the [C II](158 m), [N II](122 and 205 m), [O
I](63 and 145 m) and [O III](88 m) lines, which all play an important
role in cooling the gas in photo-ionized and photodissociation regions. We
determine that the ([C II]+[O I])/ line ratio, a proxy for the
heating efficiency of the gas, shows no significant radial trend across the
observed region, in contrast to observations of other nearby galaxies. We
determine that 10 - 20% of the observed [C II] emission originates in ionized
gas. Comparison between our observations and a PDR model shows that the
strength of the far-ultraviolet radiation field, , varies between
and and the hydrogen nucleus density varies between
and cm, with no significant radial trend in
either property. In the context of the emission line properties of the
grand-design spiral galaxy M51 and the elliptical galaxy NGC 4125, the gas in
Cen A appears more characteristic of that in typical disk galaxies rather than
elliptical galaxies.Comment: Accepted for publication in the Astrophysical Journal. 22 pages, 10
figures, 5 table
Herschel and JCMT observations of the early-type dwarf galaxy NGC 205
We present Herschel dust continuum, James Clerk Maxwell Telescope CO(3-2)
observations and a search for [CII] 158 micron and [OI] 63 micron spectral line
emission for the brightest early-type dwarf satellite of Andromeda, NGC 205.
While direct gas measurements (Mgas ~ 1.5e+6 Msun, HI + CO(1-0)) have proven to
be inconsistent with theoretical predictions of the current gas reservoir in
NGC 205 (> 1e+7 Msun), we revise the missing interstellar medium mass problem
based on new gas mass estimates (CO(3-2), [CII], [OI]) and indirect
measurements of the interstellar medium content through dust continuum
emission. Based on Herschel observations, covering a wide wavelength range from
70 to 500 micron, we are able to probe the entire dust content in NGC 205
(Mdust ~ 1.1-1.8e+4 Msun at Tdust ~ 18-22 K) and rule out the presence of a
massive cold dust component (Mdust ~ 5e+5 Msun, Tdust ~ 12 K), which was
suggested based on millimeter observations from the inner 18.4 arcsec. Assuming
a reasonable gas-to-dust ratio of ~ 400, the dust mass in NGC 205 translates
into a gas mass Mgas ~ 4-7e+6 Msun. The non-detection of [OI] and the low
L_[CII]-to-L_CO(1-0) line intensity ratio (~ 1850) imply that the molecular gas
phase is well traced by CO molecules in NGC 205. We estimate an atomic gas mass
of 1.5e+4 Msun associated with the [CII] emitting PDR regions in NGC 205. From
the partial CO(3-2) map of the northern region in NGC 205, we derive a
molecular gas mass of M_H2 ~ 1.3e+5 Msun. [abridged]Comment: 16 pages, 7 figures, accepted for publication in MNRA
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