Orbital Topology of Chiral Crystals for Orbitronics
Authors:
Kenta Hagiwara,
Ying-Jiun Chen,
Dongwook Go,
Xin Liang Tan,
Sergii Grytsiuk,
Kui-Hon Ou Yang,
Guo-Jiun Shu,
Jing Chien,
Yi-Hsin Shen,
Xiang-Lin Huang,
Fang-Cheng Chou,
Iulia Cojocariu,
Vitaliy Feyer,
Minn-Tsong Lin,
Stefan Blügel,
Claus Michael Schneider,
Yuriy Mokrousov,
Christian Tusche
Abstract:
Chirality is ubiquitous in nature and manifests in a wide range of phenomena including chemical reactions, biological processes, and quantum transport of electrons. In quantum materials, the chirality of fermions, given by the relative directions between the electron spin and momentum, is connected to the band topology of electronic states. Here, we show that in structurally chiral materials like…
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Chirality is ubiquitous in nature and manifests in a wide range of phenomena including chemical reactions, biological processes, and quantum transport of electrons. In quantum materials, the chirality of fermions, given by the relative directions between the electron spin and momentum, is connected to the band topology of electronic states. Here, we show that in structurally chiral materials like CoSi, the orbital angular momentum (OAM) serves as the main driver of a nontrivial band topology in this new class of unconventional topological semimetals, even when spin-orbit coupling is negligible. A nontrivial orbital-momentum locking of multifold chiral fermions in the bulk leads to a pronounced OAM texture of the helicoid Fermi arcs at the surface. Our findings highlight the pivotal role of the orbital degree of freedom for the chirality and topology of electron states, in general, and pave the way towards the application of topological chiral semimetals in orbitronic devices.
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Submitted 27 October, 2024;
originally announced October 2024.
Free-carrier relaxation and lattice heating in photoexcited bismuth thin films
Authors:
Y. M. Sheu,
Y. J. Chien,
C. Uher,
S. Fahy,
D. A. Reis
Abstract:
We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole (…
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We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole ($e-h$) recombination time is 12--26 ps and ambipolar diffusivity is 18--40 cm$^{2}$/s for carrier excitation up to $\sim 10^{19} \text{cm}^{-3}$. By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the $e-h$ plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation $\gtrsim 10^{20} \text{cm}^{-3}$.
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Submitted 16 November, 2012;
originally announced November 2012.