75 research outputs found
Buildup and dephasing of Floquet-Bloch bands on subcycle time scales
Strong light fields have created spectacular opportunities to tailor novel
functionalities of solids. Floquet-Bloch states can form under periodic driving
of electrons and enable exotic quantum phases. On subcycle time scales,
lightwaves can simultaneously drive intraband currents and interband
transitions, which enable high-harmonic generation (HHG) and pave the way
towards ultrafast electronics. Yet, the interplay of intra- and interband
excitations as well as their relation with Floquet physics have been key open
questions as dynamical aspects of Floquet states have remained elusive. Here we
provide this pivotal link by pioneering the ultrafast buildup of Floquet-Bloch
bands with time- and angle-resolved photoemission spectroscopy. We drive
surface states on a topological insulator with mid-infrared fields - strong
enough for HHG - and directly monitor the transient band structure with
subcycle time resolution. Starting with strong intraband currents, we observe
how Floquet sidebands emerge within a single optical cycle; intraband
acceleration simultaneously proceeds in multiple sidebands until high-energy
electrons scatter into bulk states and dissipation destroys the Floquet bands.
Quantum nonequilibrium calculations explain the simultaneous occurrence of
Floquet states with intra- and interband dynamics. Our joint experiment-theory
study opens up a direct time-domain view of Floquet physics and explores the
fundamental frontiers of ultrafast band-structure engineering.Comment: 45 pages, 4 figures, 10 extended data figure
Beyond quantitative and qualitative traits: three telling cases in the life sciences
This paper challenges the common assumption that some phenotypic traits are quantitative while others are qualitative. The distinction between these two kinds of traits is widely influential in biological and biomedical research as well as in scientific education and communication. This is probably due to both historical and epistemological reasons. However, the quantitative/qualitative distinction involves a variety of simplifications on the genetic causes of phenotypic variability and on the development of complex traits. Here, I examine three cases from the life sciences that show inconsistencies in the distinction: Mendelian traits (dwarfism and pigmentation in plant and animal models), Mendelian diseases (phenylketonuria), and polygenic mental disorders (schizophrenia). I show that these traits can be framed both quantitatively and qualitatively depending, for instance, on the methods through which they are investigated and on specific epistemic purposes (e.g., clinical diagnosis versus causal explanation). This suggests that the received view of quantitative and qualitative traits has a limited heuristic power—limited to some local contexts or to the specific methodologies adopted. Throughout the paper, I provide directions for framing phenotypes beyond the quantitative/qualitative distinction. I conclude by pointing at the necessity of developing a principled characterisation of what phenotypic traits, in general, are
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