6 research outputs found
Non-saturating large magnetoresistance in semimetals
The rapidly expanding class of quantum materials known as {\emph{topological
semimetals}} (TSM) display unique transport properties, including a striking
dependence of resistivity on applied magnetic field, that are of great interest
for both scientific and technological reasons. However, experimental signatures
that can identify or discern the dominant mechanism and connect to available
theories are scarce. Here we present the magnetic susceptibility (), the
tangent of the Hall angle () along with magnetoresistance in four
different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb and
TaSb, all of which exhibit non-saturating large MR. We find that the
distinctly different temperature dependences, and the values of
in phosphides and antimonates serve as empirical criteria to
sort the MR from different origins: NbP and TaP being uncompensated semimetals
with linear dispersion, in which the non-saturating magnetoresistance arises
due to guiding center motion, while NbSb and TaSb being {\it
compensated} semimetals, with a magnetoresistance emerging from nearly perfect
charge compensation of two quadratic bands. Our results illustrate how a
combination of magnetotransport and susceptibility measurements may be used to
categorize the increasingly ubiquitous non-saturating large magnetoresistance
in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions,
6 figure
Semiconductor thermal and electrical properties decoupled by localized phonon resonances
Thermoelectric materials convert heat into electricity through thermally
driven charge transport in solids, or vice versa for cooling. To be competitive
with conventional energy-generation technologies, a thermoelectric material
must possess the properties of both an electrical conductor and a thermal
insulator. However, these properties are normally mutually exclusive because of
the interconnection of the scattering mechanisms for charge carriers and
phonons. Recent theoretical investigations on sub-device scales have revealed
that silicon membranes covered by nanopillars exhibit a multitude of local
phonon resonances, spanning the full spectrum, that couple with the
heat-carrying phonons in the membrane and collectively cause a reduction in the
in-plane thermal conductivitywhile, in principle, not affecting the
electrical properties because the nanopillars are external to the pathway of
voltage generation and charge transport. Here this effect is demonstrated
experimentally for the first time by investigating device-scale suspended
silicon membranes with GaN nanopillars grown on the surface. The nanopillars
cause up to 21 % reduction in the thermal conductivity while the electrical
conductivity and the Seebeck coefficient remain unaffected, thus demonstrating
an unprecedented decoupling in the semiconductor's thermoelectric properties.
The measured thermal conductivity behavior for coalesced nanopillars and
corresponding lattice-dynamics calculations provide further evidence that the
reductions are mechanistically tied to the phonon resonances. This finding
breaks a longstanding trade-off between competing properties in
thermoelectricity and paves the way for engineered high-efficiency solid-state
energy recovery and cooling
FDG-PET/CT(A) imaging in large vessel vasculitis and polymyalgia rheumatica: joint procedural recommendation of the EANM, SNMMI, and the PET Interest Group (PIG), and endorsed by the ASNC
Large vessel vasculitis (LVV) is defined as a disease mainly affecting the large arteries, with two major variants, Takayasu arteritis (TA) and giant cell arteritis (GCA). GCA often coexists with polymyalgia rheumatica (PMR) in the same patient, since both belong to the same disease spectrum. FDG-PET/CT is a functional imaging technique which is an established tool in oncology, and has also demonstrated a role in the field of inflammatory diseases. Functional FDG-PET combined with anatomical CT angiography, FDG-PET/CT(A), may be of synergistic value for optimal diagnosis, monitoring of disease activity, and evaluating damage progression in LVV. There are currently no guidelines regarding PET imaging acquisition for LVV and PMR, even though standardization is of the utmost importance in order to facilitate clinical studies and for daily clinical practice. This work constitutes a joint procedural recommendation on FDG-PET/CT(A) imaging in large vessel vasculitis (LVV) and PMR from the Cardiovascular and Inflammation & Infection Committees of the European Association of Nuclear Medicine (EANM), the Cardiovascular Council of the Society of Nuclear Medicine and Molecular Imaging (SNMMI), and the PET Interest Group (PIG), and endorsed by the American Society of Nuclear Cardiology (ASNC). The aim of this joint paper is to provide recommendations and statements, based on the available evidence in the literature and consensus of experts in the field, for patient preparation, and FDG-PET/CT(A) acquisition and interpretation for the diagnosis and follow-up of patients with suspected or diagnosed LVV and/or PMR. This position paper aims to set an internationally accepted standard for FDG-PET/CT(A) imaging and reporting of LVV and PMR