212 research outputs found
The Mutual Effect of Reciprocally Moving Geokhod and Geological Environment Studied by the Discrete Element Method in Software PFC3D 5.00
A numerical experiment procedure of geokhod traverse in the geological environment, based on software PFC3D 5.00 is presented in the paper; the interpretation of numerical experiment results is provided
Cyclotron resonance of extremely conductive 2D holes in high Ge content strained heterostructures
Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels
Temperature-driven single-valley Dirac fermions in HgTe quantum wells
We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe
quantum wells below and above the critical well thickness . Our results,
obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K,
clearly indicate a change of the band-gap energy with temperature. The quantum
well wider than evidences a temperature-driven transition from
topological insulator to semiconductor phases. At the critical temperature of
90 K, the merging of inter- and intra-band transitions in weak magnetic fields
clearly specifies the formation of gapless state, revealing the appearance of
single-valley massless Dirac fermions with velocity of
ms. For both quantum wells, the energies extracted from
experimental data are in good agreement with calculations on the basis of the
8-band Kane Hamiltonian with temperature-dependent parameters.Comment: 5 pages, 3 figures and Supplemental Materials (4 pages
Temperature-dependent magnetospectroscopy of HgTe quantum wells
We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up
to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and
inter-band transitions from zero-mode Landau levels, which split from the
bottom conduction and upper valence subbands, and merge under the applied
magnetic field. To describe experimental results, realistic
temperature-dependent calculations of Landau levels have been performed. We
show that although our samples are topological insulators at low temperatures
only, the signature of such phase persists in optical transitions at high
temperatures and high magnetic fields. Our results demonstrate that
temperature-dependent magnetospectroscopy is a powerful tool to discriminate
trivial and topological insulator phases in HgTe quantum wells
Emission spectra of terahertz quantum cascade laser
We calculated energy levels, wave functions, and energies of radiative transitions in terahertz
quantum cascade lasers based on GaAs/Al0.15Ga0.85As heterostructures. Current-voltage characteristics
and current dependences of laser radiation intensity were measured, and the maximum
operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade
lasers were measured for different temperatures, and the effect of intensity “pumping” from lowfrequency
modes to high-frequency modes was found to happen in the case of an increase in the
current and time delay of the signal capture, which is explained by heating of the sample during
a pulse of the current. Application of the lasers for registration of impurity photoconductivity
signals in semiconductor heterostructures was demonstrated
Mid-Rapidity Direct-Photon Production in p+p Collisions at sqrt(s) = 200 GeV
A measurement of direct photons in p+p collisions at sqrt(s)=200 GeV is
presented. A photon excess above background from pi^0 --> gamma+gamma, eta -->
gamma+gamma, and other decays is observed in the transverse momentum range 5.5
< p_T < 7 GeV/c. The result is compared to a next-to-leading-order perturbative
QCD calculation. Within errors, good agreement is found between the QCD
calculation and the measured result.Comment: 330 authors, 7 pages text, RevTeX, 2 figures, 2 tables. Submitted to
Physical Review D. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Deuteron and antideuteron production in Au+Au collisions at sqrt(s_NN)=200 GeV
The production of deuterons and antideuterons in the transverse momentum
range 1.1 < p_T < 4.3 GeV/c at mid-rapidity in Au + Au collisions at
sqrt(s_NN)=200 GeV has been studied by the PHENIX experiment at RHIC. A
coalescence analysis comparing the deuteron and antideuteron spectra with those
of protons and antiprotons, has been performed. The coalescence probability is
equal for both deuterons and antideuterons and increases as a function of p_T,
which is consistent with an expanding collision zone. Comparing (anti)proton
yields p_bar/p = 0.73 +/- 0.01, with (anti)deuteron yields: d_bar/d = 0.47 +/-
0.03, we estimate that n_bar/n = 0.64 +/- 0.04.Comment: 326 authors, 6 pages text, 5 figures, 1 Table. Submitted to PRL.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Scaling properties of proton and anti-proton production in sqrt(s_NN) = 200 GeV Au + Au collisions
We report on the yield of protons and anti-protons, as a function of
centrality and transverse momentum, in Au+Au collisions at sqrt(s_NN) = 200 GeV
measured at mid-rapidity by the PHENIX experiment at RHIC. In central
collisions at intermediate transverse momenta (1.5 < p_T < 4.5 GeV/c) a
significant fraction of all produced particles are protons and anti-protons.
They show a centrality-scaling behavior different from that of pions. The
p-bar/pion and p/pion ratios are enhanced compared to peripheral Au+Au, p+p,
and electron+positron collisions. This enhancement is limited to p_T < 5 GeV/c
as deduced from the ratio of charged hadrons to pi^0 measured in the range 1.5
< p_T < 9 GeV/c.Comment: 325 authors, 6 pages text, 4 figures, RevTeX 4. Minor changes to text
and figures to meet PRL length restrictions; no changes to figures;
resubmitted to PRL. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Suppressed pi^0 Production at Large Transverse Momentum in Central Au+Au Collisions at sqrt(s_NN) = 200 GeV
Transverse momentum spectra of neutral pions in the range 1 < p_T < 10 GeV/c
have been measured at mid-rapidity by the PHENIX experiment at RHIC in Au+Au
collisions at sqrt(s_NN) = 200 GeV. The pi^0 multiplicity in central reactions
is significantly below the yields measured at the same sqrt(s_NN) in peripheral
Au+Au and p+p reactions scaled by the number of nucleon-nucleon collisions. For
the most central bin, the suppression factor is ~2.5 at p_T = 2 GeV/c and
increases to ~4-5 at p_T ~= 4 GeV/c. At larger p_T, the suppression remains
constant within errors. The deficit is already apparent in semi-peripheral
reactions and increases smoothly with centrality.Comment: 326 authors, 6 pages text, RevTeX, 3 figures, 2 tables. Submitted to
PRL. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
A Detailed Study of High-pT Neutral Pion Suppression and Azimuthal Anisotropy in Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV
Measurements of neutral pion production at midrapidity in sqrt(s_NN) = 200
GeV Au+Au collisions as a function of transverse momentum, p_T, collision
centrality, and angle with respect to reaction plane are presented. The data
represent the final pi^0 results from the PHENIX experiment for the first RHIC
Au+Au run at design center-of-mass-energy. They include additional data
obtained using the PHENIX Level-2 trigger with more than a factor of three
increase in statistics over previously published results for p_T > 6 GeV/c. We
evaluate the suppression in the yield of high-p_T pi^0's relative to point-like
scaling expectations using the nuclear modification factor R_AA. We present the
p_T dependence of R_AA for nine bins in collision centrality. We separately
integrate R_AA over larger p_T bins to show more precisely the centrality
dependence of the high-p_T suppression. We then evaluate the dependence of the
high-p_T suppression on the emission angle \Delta\phi of the pions with respect
to event reaction plane for 7 bins in collision centrality. We show that the
yields of high-p_T pi^0's vary strongly with \Delta\phi, consistent with prior
measurements. We show that this variation persists in the most peripheral bin
accessible in this analysis. For the peripheral bins we observe no suppression
for neutral pions produced aligned with the reaction plane while the yield of
pi^0's produced perpendicular to the reaction plane is suppressed by more than
a factor of 2. We analyze the combined centrality and \Delta\phi dependence of
the pi^0 suppression in different p_T bins using different possible
descriptions of parton energy loss dependence on jet path-length averages to
determine whether a single geometric picture can explain the observed
suppression pattern.Comment: 330 authors, pages text, RevTeX4, figures, tables. Submitted to
Physical Review C. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
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