646 research outputs found
Quasiparticle dynamics and phonon softening in FeSe superconductors
Quasiparticle dynamics of FeSe single crystals revealed by dual-color
transient reflectivity measurements ({\Delta}R/R) provides unprecedented
information on Fe-based superconductors. The amplitude of fast component in
{\Delta}R/R clearly tells a competing scenario between spin fluctuations and
superconductivity. Together with the transport measurements, the relaxation
time analysis further exhibits anomalous changes at 90 K and 230 K. The former
manifests a structure phase transition as well as the associated phonon
softening. The latter suggests a previously overlooked phase transition or
crossover in FeSe. The electron-phonon coupling constant {\lambda} is found to
be 0.16, identical to the value of theoretical calculations. Such a small
{\lambda} demonstrates an unconventional origin of superconductivity in FeSe.Comment: Final published version; 5 pages; 4 figure
Thermal dosimetry characteristics of deep regional heating of non-muscle invasive bladder cancer.
PURPOSE: The aim of this paper is to report thermal dosimetry characteristics of external deep regional pelvic hyperthermia combined with intravesical mitomycin C (MMC) for treating bladder cancer following transurethral resection of bladder tumour, and to use thermal data to evaluate reliability of delivering the prescribed hyperthermia dose to bladder tissue.
MATERIALS AND METHODS: A total of 14 patients were treated with MMC and deep regional hyperthermia (BSD-2000, Sigma Ellipse or Sigma 60). The hyperthermia objective was 42° ± 2 °C to bladder tissue for ≥40 min per treatment. Temperatures were monitored with thermistor probes and recorded values were used to calculate thermal dose and evaluate treatment. Anatomical characteristics were examined for possible correlations with heating.
RESULTS: Combined with BSD-2000 standard treatment planning and patient feedback, real-time temperature monitoring allowed thermal steering of heat sufficient to attain the prescribed thermal dose to bladder tissue within patient tolerance in 91.6% of treatments. Mean treatment time for bladder tissue \u3e40 °C was 61.9 ± 11.4 min and mean thermal dose was 21.3 ± 16.5 CEM43. Average thermal doses obtained in normal tissues were 1.6 ± 1.2 CEM43 for the rectum and 0.8 ± 1.3 CEM43 in superficial normal tissues. No significant correlation was seen between patient anatomical characteristics and thermal dose achieved in bladder tissue.
CONCLUSIONS: This study demonstrates that a hyperthermia prescription of 42° ± 2 °C for 40-60 min can be delivered safely to bladder tissue with external radiofrequency phased array applicators for a typical range of patient sizes. Using the available thermometry and treatment planning, the BSD-2000 hyperthermia system was shown to be an effective method of focusing heat regionally around the bladder with good patient tolerance
Spatial Symmetry of Superconducting Gap in YBa2Cu3O7-\delta Obtained from Femtosecond Spectroscopy
The polarized femtosecond spectroscopies obtained from well characterized
(100) and (110) YBa2Cu3O7-\delta thin films are reported. This bulk-sensitive
spectroscopy, combining with the well-textured samples, serves as an effective
probe to quasiparticle relaxation dynamics in different crystalline
orientations. The significant anisotropy in both the magnitude of the
photoinduced transient reflectivity change and the characteristic relaxation
time indicates that the nature of the relaxation channel is intrinsically
different in various axes and planes. By the orientation-dependent analysis,
d-wave symmetry of the bulk-superconducting gap in cuprate superconductors
emerges naturally.Comment: 8 pages, 4 figures. To be published in Physical Review B, Rapid
Communication
Spatially-resolved relaxation dynamics of photoinduced quasiparticles in underdoped YBaCuO
The spatially-resolved relaxation characteristics of photoinduced
quasiparticles (QPs) in CuO planes of underdoped YBCO are disclosed by
polarized fs time-resolved spectroscopy. The relaxation time (tau) along b axis
diverges at Tc, and appears to be governed by a temperature-dependent gap
Delta(T) at T Tc, a monotonic increase of tau with
decreasing T along the b axis and ab diagonal was observed and can be
attributed to a temperature-independent gap Delta. The results lend
support to recombination dominant scenario of QP dynamics. However, the QP
thermalization may take part along the nodal direction in the highly underdoped
samples.Comment: 16 pages, 4 figures. To be published in Physical Review B, Brief
Repor
Unveiling the hidden nematicity and spin subsystem in FeSe
The nematic order (nematicity) is considered one of the essential ingredients
to understand the mechanism of Fe-based superconductivity. In most Fe-based
superconductors (pnictides), nematic order is reasonably close to the
antiferromagnetic order. In FeSe, in contrast, a nematic order emerges below
the structure phase transition at T_s = 90 K with no magnetic order. The case
of FeSe is of paramount importance to a universal picture of Fe-based
superconductors. The polarized ultrafast spectroscopy provides a tool to probe
simultaneously the electronic structure and the magnetic interactions through
quasiparticle dynamics. Here we show that this approach reveals both the
electronic and magnetic nematicity below and, surprisingly, its fluctuations
far above Ts to at least 200 K. The quantitative pump-probe data clearly
identify a correlation between the topology of the Fermi surface (FS) and the
magnetism in all temperature regimes, thus providing profound insight into the
driving factors of nematicity in FeSe and the origin of its uniqueness.Comment: Supplementary Information include
3D visualizations of nano-scale phase separation and ultrafast dynamic correlation between phases in (Na0.32K0.68)0.95Fe1.75Se2
Phase separation of metallic and antiferromagnetic (AFM) insulating phases in
alkaline iron selenides (AxFe2-ySe2) continues to attract intense interest
because the relationship between two peculiar features probably is a key to
clarifying the pairing mechanism of AxFe2-ySe2 superconductors. Here we report
that the 3D visualizations of nano-scale phase separation in
(Na0.32K0.68)0.95Fe1.75Se2 single crystals are revealed by hybrid
focused-ion-beam scanning electron microscopy and the superconducting paths are
fully percolative in 3D. Moreover, the phase-related ultrafast dynamics in
(Na0.32K0.68)0.95Fe1.75Se2 is studied by dual-color pump-probe spectroscopy.
The anomalous changes in the electron and acoustic phonon components of
transient reflectivity change ({\Delta}R/R) identify two characteristic
temperatures T*~100 K (the onset temperature of coupling between nano-metallic
and AFM phases) and TH~230 K (the onset temperature of
metallic-interface-phase). An energy-transfer channel between the nano-metallic
and AFM phases is inferred. This proposed channel provides a new insight into
the pairing mechanism of alkaline iron selenide superconductors.Comment: 17 pages, 5 figures; Physical Review Materials, in pres
Fabrication and Low Temperature Thermoelectric Properties of Na_xCoO_2 (x = 0.68 and 0.75) Epitaxial Films by the Reactive Solid-Phase Epitaxy
We have fabricated Na_xCoO_2 thin films via lateral diffusion of sodium into
Co_3O_4 (111) epitaxial films (reactive solid-phase epitaxy: Ref. 4). The
environment of thermal diffusion is key to the control of the sodium content in
thin films. From the results of x-ray diffraction and in-plane resistivity, the
epitaxial growth and the sodium contents of these films were identified. The
thermoelectric measurements show a large thermoelectric power similar to that
observed in single crystals. The quasiparticle scattering rate is found to
approach zero at low temperatures, consistent with the small residual
resistivity, indicating high quality of the Na_xCoO_2 thin films.Comment: 16 pages. 4 figures. To appear in Applied Physics Letter
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