599 research outputs found
Two-channel conduction in YbPtBi
We investigated transport, magnetotransport, and broadband optical properties
of the half-Heusler compound YbPtBi. Hall measurements evidence two types of
charge carriers: highly mobile electrons with a temperature-dependent
concentration and low-mobile holes; their concentration stays almost constant
within the investigated temperature range from 2.5 to 300 K. The optical
spectra (10 meV - 2.7 eV) can be naturally decomposed into contributions from
intra- and interband absorption processes, the former manifesting themselves as
two Drude bands with very different scattering rates, corresponding to the
charges with different mobilities. These results of the optical measurements
allow us to separate the contributions from electrons and holes to the total
conductivity and to implement a two-channel-conduction model for description of
the magnetotransport data. In this approach, the electron and hole mobilities
are found to be around 50000 and 10 cm/Vs at the lowest temperatures (2.5
K), respectively.Comment: 6 page
Pressure-dependent optical investigations of -(BEDT-TTF)I: tuning charge order and narrow gap towards a Dirac semimetal
Infrared optical investigations of -(BEDT-TTF)I have been
performed in the spectral range from 80 to 8000~cm down to temperatures
as low as 10~K by applying hydrostatic pressure. In the metallic state, ~K, we observe a 50\% increase in the Drude contribution as well as the
mid-infrared band due to the growing intermolecular orbital overlap with
pressure up to 11~kbar. In the ordered state, , we extract how
the electronic charge per molecule varies with temperature and pressure:
Transport and optical studies demonstrate that charge order and metal-insulator
transition coincide and consistently yield a linear decrease of the transition
temperature by ~K/kbar. The charge disproportionation
diminishes by /kbar and the optical gap between
the bands decreases with pressure by -47~cm/kbar. In our high-pressure
and low-temperature experiments, we do observe contributions from the massive
charge carriers as well as from massless Dirac electrons to the low-frequency
optical conductivity, however, without being able to disentangle them
unambiguously.Comment: 13 pages, 17 figures, submitted to Phys. Rev.
The Normal Red Letter, volume 6, number 1, October (1904)
https://red.mnstate.edu/normalredletter/1032/thumbnail.jp
On the correspondence between the classical and quantum gravity
The relationship between the classical and quantum theories of gravity is
reexamined. The value of the gravitational potential defined with the help of
the two-particle scattering amplitudes is shown to be in disagreement with the
classical result of General Relativity given by the Schwarzschild solution. It
is shown also that the potential so defined fails to describe whatever
non-Newtonian interactions of macroscopic bodies. An alternative interpretation
of the -order part of the loop corrections is given directly in terms
of the effective action. Gauge independence of that part of the one-loop
radiative corrections to the gravitational form factors of the scalar particle
is proved, justifying the interpretation proposed.Comment: Latex 2.09, 3 ps. figures, 17 page
Compositional variation of thin PZT films near morphotropic phase boundary: experiment and simulation
The work was partly supported by the Ministry for Education and Science (Russian Federation) (Grant No 16.2811.2017/4.6) and RFBR (Grant No 16-02-00632)
Optical conductivity and penetration depth in MgB2
The complex conductivity of a MgB2 film has been investigated in the
frequency range 4 cm^{-1}< nu < 30 cm^{-1} and for temperatures 2.7 K < T <300
K. The overall temperature dependence of both components of the complex
conductivity is reminiscent of BCS-type behavior, although a detailed analysis
reveals a number of discrepancies. No characteristic feature of the isotropic
BCS gap temperature evolution is observed in the conductivity spectra in the
superconducting state. A peak in the temperature dependence of the real part of
the conductivity is detected for frequencies below 9 cm^{-1}. The
superconducting penetration depth follows a T^2 behavior at low temperatures.Comment: 4 pages, 4 figure
Observation of non-local dielectric relaxation in glycerol
Since its introduction, liquid viscosity and relaxation time have been
considered to be an intrinsic property of the system that is essentially local
in nature and therefore independent of system size. We perform dielectric
relaxation experiments in glycerol, and find that this is the case at high
temperature only. At low temperature, increases with system size and
becomes non-local. We discuss the origin of this effect in a picture based on
liquid elasticity length, the length over which local relaxation events in a
liquid interact via induced elastic waves, and find good agreement between
experiment and theory
Universal relationship between the penetration depth and the normal-state conductivity in YBaCuO
The absolute values of the conductivity in the normal state sigma_n and of
the low temperature penetration depths lambda(0) were measured for a number of
different samples of the YBaCuO family. We found a striking correlation between
sigma_n and 1/lambda^2, regardless of doping, oxygen reduction or defects, thus
providing a simple method to predict the superconducting penetration depth and
to have an estimate of the sample quality by measuring the normal-state
conductivity.Comment: 7 pages, 1 figure, Europhys. Lett., accepte
Cerebellar anaplastic astrocytoma in adult patients: 15 consecutive cases from a single institution and literature review
Adult cerebellar anaplastic astrocytomas (cAA) are rare entities and their clinical and genetic appearances are still ill defined. Previously, malignant gliomas of the cerebellum were combined and reviewed together (cAA and cerebellar glioblastomas (cGB), that could have possibly affected overall survival (OS) and progression-free survival (PFS). We present characteristics of 15 adult patients with cAA and compared them to a series of 45 patients with a supratentorial AA (sAA) in order to elicit the effect of tumor location on OS and PFS. The mean age at cAA diagnosis was 39.3 years (range 19–72). A history of neurofibromatosis type I was noted in 1 patient (6.7%). An IDH-1 mutation was identified in 6/15 cases and a methylated MGMT promoter in 5/15 cases. Patients in study and control groups were matched in age, sex and IDH-1 mutation status. Patients in a study group tended to present with longer overall survival (50 vs. 36.5 months), but the difference did not reach statistical significance. In both cAA and supratentorial AA groups presence of the IDH-1 mutation remains a positive predictor for the prolonged survival. The present study suggests that adult cAA constitute a group of gliomas with relatively higher rate of IDH-1 mutations and prognosis similar to supratentorial AA. The present study is the first to systematically compare cAA and supratentorial AA with respect to their genetic characteristics and suggests that both groups show a similar survival prognosis
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