1,987 research outputs found
Magneto-Optics of Exciton Rydberg States in a Monolayer Semiconductor
We report 65 tesla magneto-absorption spectroscopy of exciton Rydberg states
in the archetypal monolayer semiconductor WSe. The strongly field-dependent
and distinct energy shifts of the 2s, 3s, and 4s excited neutral excitons
permits their unambiguous identification and allows for quantitative comparison
with leading theoretical models. Both the sizes (via low-field diamagnetic
shifts) and the energies of the exciton states agree remarkably well with
detailed numerical simulations using the non-hydrogenic screened Keldysh
potential for 2D semiconductors. Moreover, at the highest magnetic fields the
nearly-linear diamagnetic shifts of the weakly-bound 3s and 4s excitons provide
a direct experimental measure of the exciton's reduced mass, .Comment: To appear in Phys. Rev. Lett. Updated version (25 jan 2018) now
includes detailed supplemental discussion of Landau levels, Rydberg exciton
energies, exciton mass, Dirac Hamiltonian, nonparabolicity, and dielectric
effect
Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS and MoS to 65 Tesla
We report circularly-polarized optical reflection spectroscopy of monolayer
WS and MoS at low temperatures (4~K) and in high magnetic fields to
65~T. Both the A and the B exciton transitions exhibit a clear and very similar
Zeeman splitting of approximately 230~eV/T (), providing
the first measurements of the valley Zeeman effect and associated -factors
in monolayer transition-metal disulphides. These results complement and are
compared with recent low-field photoluminescence measurements of valley
degeneracy breaking in the monolayer diselenides MoSe and WSe. Further,
the very large magnetic fields used in our studies allows us to observe the
small quadratic diamagnetic shifts of the A and B excitons in monolayer WS
(0.32 and 0.11~eV/T, respectively), from which we calculate exciton
radii of 1.53~nm and 1.16~nm. When analyzed within a model of non-local
dielectric screening in monolayer semiconductors, these diamagnetic shifts also
constrain and provide estimates of the exciton binding energies (410~meV and
470~meV for the A and B excitons, respectively), further highlighting the
utility of high magnetic fields for understanding new 2D materials.Comment: 9 pages, 5 figure
Magneto-reflection spectroscopy of monolayer transition-metal dichalcogenide semiconductors in pulsed magnetic fields
We describe recent experimental efforts to perform polarization-resolved
optical spectroscopy of monolayer transition-metal dichalcogenide
semiconductors in very large pulsed magnetic fields to 65 tesla. The
experimental setup and technical challenges are discussed in detail, and
temperature-dependent magneto-reflection spectra from atomically thin tungsten
disulphide (WS) are presented. The data clearly reveal not only the valley
Zeeman effect in these 2D semiconductors, but also the small quadratic exciton
diamagnetic shift from which the very small exciton size can be directly
inferred. Finally, we present model calculations that demonstrate how the
measured diamagnetic shifts can be used to constrain estimates of the exciton
binding energy in this new family of monolayer semiconductors.Comment: PCSI-43 conference (Jan. 2016; Palm Springs, CA
Terahertz dynamics of a topologically protected state: quantum Hall effect plateaus near cyclotron resonance in a GaAs/AlGaAs heterojunction
We measure the Hall conductivity of a two-dimensional electron gas formed at
a GaAs/AlGaAs heterojunction in the terahertz regime close to the cyclotron
resonance frequency by employing a highly sensitive Faraday rotation method
coupled with electrical gating of the sample to change the electron density. We
observe clear plateau-and step-like features in the Faraday rotation angle vs.
electron density and magnetic field (Landau-level filling factor), which are
the high frequency manifestation of quantum Hall plateaus - a signature of
topologically protected edge states. The results are compared to a recent
dynamical scaling theory.Comment: 18 pages, 3 figure
Beak colour dynamically signals changes in fasting status and parasite loads in king penguins
This research was funded by the French Polar Institute (IPEVâResearch Program 119) and the French National Centre for Scientific Research (CNRS-INEE). Field logistic support was provided by Terres Australes et Antarctiques Françaises. Q.S. was funded by a doctoral fellowship from the MinistĂšre Français de lâEducation SupĂ©rieur et de la Recherche. We thank all over-wintering assistants: Benoit Gineste, Sylvia Pardonnet, Laureline Durand, Emilie Lefol and HĂ©di Saadaoui for field work and Emilio Rojas for helpful discussion on the analyses. We apologize to our stick insect (Carausius morosus) for bearing with VAVâs inquisitive curiosity during our debates on color ornaments in king penguins. We sincerely thank the editor and 2 anonymous reviewers for their helpful comments on a previous version of the paper.Peer reviewedPostprin
Correlation in telomere lengths between feathers and blood cells in pied flycatchers
We are grateful to Toni Laaksonen, Pauliina Teerikorpi, Ville Ojala, Wiebke Schuett, Corinna Adrian and Marie Hardenbicker for their help in the field, and two anonymous reviewers for constructive comments on the manuscript. This research was financially supported by the Turku Collegium for Science and Medicine (grant to AS) and Societas Pro Fauna et Flora Fennica, The Kuopio Naturalistsâ Society, and Finnish Cultural Foundation Varsinais-Suomi regional fund (grants to TK). The authors declare to have no conflict of interests. Dataset used in this study will be publicly accessible on Figshare https://figshare.com/s/dffa03e1e91c2e57dc13).Peer reviewedPostprin
Hole-LO phonon interaction in InAs/GaAs quantum dots
We investigate the valence intraband transitions in p-doped self-assembled
InAs quantum dots using far-infrared magneto-optical technique with polarized
radiation. We show that a purely electronic model is unable to account for the
experimental data. We calculate the coupling between the mixed hole LO-phonon
states using the Fr\"ohlich Hamiltonian, from which we determine the polaron
states as well as the energies and oscillator strengths of the valence
intraband transitions. The good agreement between the experiments and
calculations provides strong evidence for the existence of hole-polarons and
demonstrates that the intraband magneto-optical transitions occur between
polaron states
The oxidative debt of fasting : evidence for short to medium-term costs of advanced fasting in adult king penguins
This research was funded by the French Polar Institute (IPEVâResearch Program 119) and the French National Centre for Scientific Research (CNRS-INEE). We are especially grateful to Dominic L. Cram and one anonymous reviewer for helpful comments on the paper. Field logistic support was provided by Terres Australes et Antarctiques Françaises. QS was funded by a doctoral fellowship from the MinistĂšre Français de lâEducation SupĂ©rieur et de la Recherche.Peer reviewedPublisher PD
High speed development of new chemical synthesis and materials at molecular-level: Methods and approaches
Recent success of advanced computational chemistry, in example for the prediction of chemical reactivity and materials properties, reflects its reputation as a valuable and widely accepted means to tackle problems in academia. The development of new simulation methods and new computer architectures enables an enormous improvement of the productivity of research and development of new chemical synthesisand materials. These advances can be achieved in terms of less time, material, and staff compared to traditional lab experiments. Especially, approaches like virtual high throughput screenings (vHTS) are highly scalable and allow fast and deep insights into new promising system modifications. Consequently, the time to market and risk of new product development can be decreased significantly. These characteristicspaved the way for the successful application in industry nowadays
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