1,085 research outputs found
Thin n-in-p planar pixel sensors and active edge sensors for the ATLAS upgrade at HL-LHC
Silicon pixel modules employing n-in-p planar sensors with an active
thickness of 200 m, produced at CiS, and 100-200 m thin active/slim
edge sensor devices, produced at VTT in Finland have been interconnected to
ATLAS FE-I3 and FE-I4 read-out chips. The thin sensors are designed for high
energy physics collider experiments to ensure radiation hardness at high
fluences. Moreover, the active edge technology of the VTT production maximizes
the sensitive region of the assembly, allowing for a reduced overlap of the
modules in the pixel layer close to the beam pipe. The CiS production includes
also four chip sensors according to the module geometry planned for the outer
layers of the upgraded ATLAS pixel detector to be operated at the HL-LHC. The
modules have been characterized using radioactive sources in the laboratory and
with high precision measurements at beam tests to investigate the hit
efficiency and charge collection properties at different bias voltages and
particle incidence angles. The performance of the different sensor thicknesses
and edge designs are compared before and after irradiation up to a fluence of
.Comment: In proceedings of the 10th International Conference on Position
Sensitive Detectors, PSD10 201
Quantum critical properties of the Bose-Fermi Kondo Model in a large-N limit
Studies of non-Fermi liquid properties in heavy fermions have led to the
current interest in the Bose-Fermi Kondo model. Here we use a dynamical large-N
approach to analyze an SU(N)xSU() generalization of the model. We
establish the existence in this limit of an unstable fixed point when the
bosonic bath has a sub-ohmic spectrum (|\omega|^{1-\epsilon} \sgn \omega,
with ). At the quantum critical point, the Kondo scale vanishes
and the local spin susceptibility (which is finite on the Kondo side for \kappa
<1) diverges. We also find an \omega/T scaling for an extended range (15
decades) of \omega/T. This scaling violates (for ) the
expectation of a naive mapping to certain classical models in an extra
dimension; it reflects the inherent quantum nature of the critical point.Comment: 4 pages; v2: included clarifying discussions on why the omega/T
scaling (for epsilon >=1/2) violates the naive mapping to classical models in
an extra dimension and the implications of this observation about the nature
of the QCP; v3: shortened to conform to the PRL length limi
Thermoelectric transport through strongly correlated quantum dots
The thermoelectric properties of strongly correlated quantum dots, described
by a single level Anderson model coupled to conduction electron leads, is
investigated using Wilson's numerical renormalization group method. We
calculate the electronic contribution, , to the thermal conductance,
the thermopower, , and the electrical conductance, , of a quantum dot as
a function of both temperature, , and gate voltage, , for strong,
intermediate and weak Coulomb correlations, , on the dot. For strong
correlations and in the Kondo regime, we find that the thermopower exhibits two
sign changes, at temperatures and with
. Such sign changes in are particularly sensitive
signatures of strong correlations and Kondo physics. The relevance of this to
recent thermopower measurements of Kondo correlated quantum dots is discussed.
We discuss the figure of merit, power factor and the degree of violation of the
Wiedemann-Franz law in quantum dots. The extent of temperature scaling in the
thermopower and thermal conductance of quantum dots in the Kondo regime is also
assessed.Comment: 21 pages, 12 figures; published versio
Kondo Insulator to Semimetal Transformation Tuned by Spin-Orbit Coupling
Recent theoretical studies of topologically nontrivial electronic states in
Kondo insulators have pointed to the importance of spin-orbit coupling (SOC)
for stabilizing these states. However, systematic experimental studies that
tune the SOC parameter in Kondo insulators remain elusive.
The main reason is that variations of (chemical) pressure or doping strongly
influence the Kondo coupling and the chemical potential --
both essential parameters determining the ground state of the material -- and
thus possible tuning effects have remained unnoticed. Here
we present the successful growth of the substitution series
CeBi(PtPd) () of the archetypal
(noncentrosymmetric) Kondo insulator CeBiPt. The Pt-Pd substitution
is isostructural, isoelectronic, and isosize, and therefore likely to leave
and essentially unchanged. By contrast, the large mass
difference between the element Pt and the element Pd leads to a large
difference in , which thus is the dominating tuning
parameter in the series. Surprisingly, with increasing (decreasing
), we observe a Kondo insulator to semimetal transition,
demonstrating an unprecedented drastic influence of the SOC. The fully
substituted end compound CeBiPd shows thermodynamic signatures of a
recently predicted Weyl-Kondo semimetal.Comment: 6 pages, 5 figures plus Supplemental Materia
Comment on "Zeeman-Driven Lifshitz Transition: A Model for the Experimentally Observed Fermi-Surface Reconstruction in YbRh2Si2"
In Phys. Rev. Lett. 106, 137002 (2011), A. Hackl and M. Vojta have proposed
to explain the quantum critical behavior of YbRh2Si2 in terms of a
Zeeman-induced Lifshitz transition of an electronic band whose width is about 6
orders of magnitude smaller than that of conventional metals. Here, we note
that the ultra-narrowness of the proposed band, as well as the proposed
scenario per se, lead to properties which are qualitatively inconsistent with
the salient features observed in YbRh2Si2 near its quantum critical point.Comment: 3 page
Magnetic field-induced quantum critical point in YbPtIn and YbPtIn single crystals
Detailed anisotropic (Hab and Hc) resistivity and
specific heat measurements were performed on online-grown YbPtIn and
solution-grown YbPtIn single crystals for temperatures down to 0.4 K,
and fields up to 140 kG; Hab Hall resistivity was also measured on
the YbPtIn system for the same temperature and field ranges. All these
measurements indicate that the small change in stoichiometry between the two
compounds drastically affects their ordering temperatures (T
K in YbPtIn, and K in YbPtIn). Furthermore, a field-induced
quantum critical point is apparent in each of these heavy fermion systems, with
the corresponding critical field values of YbPtIn (H around
35-45 kG and H kG) also reduced compared to the analogous
values for YbPtIn (H kG and H kG
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