55 research outputs found
Specific heat and magnetization of a ZrB12 single crystal: characterization of a type II/1 superconductor
We measured the specific heat, the magnetization, and the magnetoresistance
of a single crystal of ZrB12, which is superconducting below Tc ~ 6 K. The
specific heat in zero field shows a BCS-type superconducting transition. The
normal- to superconducting-state transition changes from first order (with a
latent heat) to second order (without latent heat) with increasing magnetic
field, indicating that the pure compound is a low-kappa, type-II/1
superconductor in the classification of Auer and Ullmaier [J. Auer and H.
Ullmaier, Phys. Rev.B 7, 136 (1973)]. This behavior is confirmed by
magnetization measurements. The H-T phase diagram based on specific-heat and
magnetization data yields Hc2(0) =550 G for the bulk upper critical field,
whereas the critical field defined by vanishing resistance is a surface
critical field Hc3(0) ~ 1000 G.Comment: 17 pages, 8 figures, submitted to PR
Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6
The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys.
Rev.
Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions
We have studied the effect of Lu substitution on the spin dynamics of the
Kondo insulator YbB12 to clarify the origin of the spin-gap response previously
observed at low temperature in this material. Inelastic neutron spectra have
been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25,
0.90 and 1.0. The data indicate that the disruption of coherence on the Yb
sublattice primarily affects the narrow peak structure occurring near 15-20 meV
in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV
remain almost unaffected. It is inferred that the latter features reflect
mainly local, single-site processes, and may be reminiscent of the inelastic
magnetic response reported for mixed-valence intermetallic compounds. On the
other hand, the lower component at 15 meV is most likely due to dynamic
short-range magnetic correlations. The crystal-field splitting in YbB12
estimated from the Er3+ transitions measured in a Yb0.9Er0.1B12 sample, has the
same order of magnitude as other relevant energy scales of the system and is
thus likely to play a role in the form of the magnetic spectral response.Comment: 16 pages in pdf format, 9 figures. v. 2: coauthor list updated; extra
details given in section 3.2 (pp. 6-7); one reference added; fig. 5 axis
label change
The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy
We have investigated the intermediate valence narrow-gap semiconductor SmB6
at low temperatures using both conventional spear-anvil type point contacts as
well as mechanically controllable break junctions. The zero-bias conductance
varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the
spectral anomalies, which are related to the different activation energies and
band gaps of SmB6, did not depend on the the contact size. Two different
regimes of charge transport could be distinguished: Contacts with large zero -
bias conductance are in the diffusive Maxwell regime. They had spectra with
only small non-linearities. Contacts with small zero - bias conductance are in
the tunnelling regime. They had larger anomalies, but still indicating a finite
45 % residual quasiparticle density of states at the Fermi level at low
temperatures of T = 0.1 K. The density of states derived from the tunelling
spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and
Ed = 4.5 meV wide gaps, respectively.Comment: 9 pages incl. 13 figure
Contemporary management of primary parapharyngeal space tumors
The parapharyngeal space is a complex anatomical area. Primary parapharyngeal tumors are rare tumors and 80% of them are benign. A variety of tumor types can develop in this location; most common are salivary gland neoplasm and neurogenic tumors. The management of these tumors has improved greatly owing to the developments in imaging techniques, surgery, and radiotherapy. Most tumors can be removed with a low rate of complications and recurrence. The transcervical approach is the most frequently used. In some cases, minimally invasive approaches may be used alone or in combination with a limited transcervical route, allowing large tumors to be removed by reducing morbidity of expanded approaches. An adequate knowledge of the anatomy and a careful surgical plan is essential to tailor management according to the patient and the tumor. The purpose of the present review was to update current aspects of knowledge related to this more challenging area of tumor occurrence.Peer reviewe
International Consensus Statement on Rhinology and Allergy: Rhinosinusitis
Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICARâRS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICARâRSâ2021 as well as updates to the original 140 topics. This executive summary consolidates the evidenceâbased findings of the document. Methods: ICARâRS presents over 180 topics in the forms of evidenceâbased reviews with recommendations (EBRRs), evidenceâbased reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICARâRSâ2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidenceâbased management algorithm is provided. Conclusion: This ICARâRSâ2021 executive summary provides a compilation of the evidenceâbased recommendations for medical and surgical treatment of the most common forms of RS
Substitution Effect of Non-magnetic Rare-earth ion R (R = Lu, Sc, Y and Zr) of Kondo Semiconductor YbB 12
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