6,550 research outputs found
NIR spectroscopy of the Sun and HD20010 - Compiling a new linelist in the NIR
Context: Effective temperature, surface gravity, and metallicity are basic
spectroscopic stellar parameters necessary to characterize a star or a
planetary system. Reliable atmospheric parameters for FGK stars have been
obtained mostly from methods that relay on high resolution and high
signal-to-noise optical spectroscopy. The advent of a new generation of high
resolution near-IR spectrographs opens the possibility of using classic
spectroscopic methods with high resolution and high signal-to-noise in the NIR
spectral window. Aims: We aim to compile a new iron line list in the NIR from a
solar spectrum to derive precise stellar atmospheric parameters, comparable to
the ones already obtained from high resolution optical spectra. The spectral
range covers 10 000 {\AA} to 25 000 {\AA}, which is equivalent to the Y, J, H,
and K bands. Methods: Our spectroscopic analysis is based on the iron
excitation and ionization balance done in LTE. We use a high resolution and
high signal-to-noise ratio spectrum of the Sun from the Kitt Peak telescope as
a starting point to compile the iron line list. The oscillator strengths (log
gf) of the iron lines were calibrated for the Sun. The abundance analysis was
done using the MOOG code after measuring equivalent widths of 357 solar iron
lines. Results: We successfully derived stellar atmospheric parameters for the
Sun. Furthermore, we analysed HD20010, a F8IV star, from which we derived
stellar atmospheric parameters using the same line list as for the Sun. The
spectrum was obtained from the CRIRES- POP database. The results are compatible
with the ones found in the literature, confirming the reliability of our line
list. However, due to the quality of the data we obtain large errors.Comment: 9 pages and 9 figure
The surface-state of the topological insulator BiSe revealed by cyclotron resonance
To date transport measurements of topological insulators have been dominated
by the conductivity of the bulk, leading to substantial difficulties in
resolving the properties of the surface. To this end, we use high magnetic
field, rf- and microwave-spectroscopy to selectively couple to the surface
conductivity of BiSe at high frequency. In the frequency range of a few
GHz we observe a crossover from quantum oscillations indicative of a small 3D
Fermi surface, to cyclotron resonance indicative of a 2D surface state
Field-induced Bose-Einstein Condensation of triplons up to 8 K in Sr3Cr2O8
Single crystals of the spin dimer system Sr3Cr2O8 have been grown for the
first time. Magnetization, heat capacity, and magnetocaloric effect data up to
65 T reveal magnetic order between applied fields of Hc1 ~ 30.4 T and Hc2 ~ 62
T. This field-induced order persists up to ~ 8 K at H ~ 44 T, the highest
observed in any quantum magnet where Hc2 is experimentally-accessible. We fit
the temperature-field phase diagram boundary close to Hc1 using the expression
Tc = A(H-Hc1)^v. The exponent v = 0.65(2), obtained at temperatures much
smaller than 8 K, is that of the 3D Bose-Einstein condensate (BEC) universality
class. This finding strongly suggests that Sr3Cr2O8 is a new realization of a
triplon BEC where the universal regimes corresponding to both Hc1 and Hc2 are
accessible at He-4 temperatures.Comment: 4 pages, 3 figures, accepted by PR
Fermion scattering off electroweak phase transition kink walls with hypermagnetic fields
We study the scattering of fermions off a finite width kink wall during the
electroweak phase transition in the presence of a background hypermagnetic
field. We derive and solve the Dirac equation for such fermions and compute the
reflection and transmission coefficients for the case when the fermions move
from the symmetric to the broken symmetry phase. We show that the chiral nature
of the fermion coupling with the background field in the symmetric phase
generates an axial asymmetry in the scattering processes. We discuss possible
implications of such axial charge segregation for baryon number generation.Comment: 9 pages, 3 Postscript figures, uses RevTeX4. Expanded discussion,
published versio
Dilepton low suppression as an evidence of the Color Glass Condensate
The dilepton production is investigated in proton-nucleus collisions in the
forward region using the Color Glass Condensate approach. The transverse
momentum distribution (), more precisely the low region, where the
saturation effects are expected to increase, is analyzed. The ratio between
proton-nucleus and proton-proton differential cross section for RHIC and LHC
energies is evaluated, showing the effects of saturation at small , and
presenting a Cronin type peak at moderate . These features indicate the
dilepton as a most suitable probe to study the properties of the saturated
regime and the Cronin effect.Comment: 10 pages, 8 figures, replaced with the version to appear in Physical
Review
Influence of the Magnetic Field on the Fermion Scattering off Bubble and Kink Walls
We investigate the scattering of fermions off domain walls at the electroweak
phase transition in presence of a magnetic field. We consider both the bubble
wall and the kink domain wall. We derive and solve the Dirac equation for
fermions with momentum perpendicular to the walls, and compute the transmission
and reflection coefficients. In the case of kink domain wall, we briefly
discuss the zero mode solutions localized on the wall. The possibile role of
the magnetic field for the electroweak baryogenesis is also discussed.Comment: 11 pages and 3 eps figure
The Wilson renormalization group for low x physics: towards the high density regime
We continue the study of the effective action for low physics based on a
Wilson renormalization group approach. We express the full nonlinear
renormalization group equation in terms of the average value and the average
fluctuation of extra color charge density generated by integrating out gluons
with intermediate values of . This form clearly exhibits the nature of the
phenomena driving the evolution and should serve as the basis of the analysis
of saturation effects at high gluon density at small .Comment: 14 pages, late
Cooper pairing and finite-size effects in a NJL-type four-fermion model
Starting from a NJL-type model with N fermion species fermion and difermion
condensates and their associated phase structures are considered at nonzero
chemical potential and zero temperature in spaces with nontrivial
topology of the form and . Special
attention is devoted to the generation of the superconducting phase. In
particular, for the cases of antiperiodic and periodic boundary conditions we
have found that the critical curve of the phase transitions between the chiral
symmetry breaking and superconducting phases as well as the corresponding
condensates and particle densities strongly oscillate vs ,
where is the length of the circumference . Moreover, it is shown that
at some finite values of the superconducting phase transition is shifted to
smaller values both of and particle density in comparison with the case
of .Comment: 13 pages, 13 figures; minor changes; new references added; version
accepted to PR
Controllable chirality-induced geometrical Hall effect in a frustrated highly-correlated metal
A current of electrons traversing a landscape of localized spins possessing
non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to
a Hall voltage independent of the spin-orbit coupling within the material--a
geometrical Hall effect. We show that the highly-correlated metal UCu5
possesses an unusually large controllable geometrical Hall effect at T<1.2K due
to its frustration-induced magnetic order. The magnitude of the Hall response
exceeds 20% of the \nu=1 quantum Hall effect per atomic layer, which translates
into an effective magnetic field of several hundred Tesla acting on the
electrons. The existence of such a large geometric Hall response in UCu5 opens
a new field of inquiry into the importance of the role of frustration in
highly-correlated electron materials.Comment: article and supplemental informatio
- …