Ultrafast Umklapp-assisted electron-phonon cooling in magic-angle twisted bilayer graphene

Jake Dudley Mehew; Rafael Luque Merino; Hiroaki Ishizuka; Alexander Block; Jaime Díez Mérida; Andrés Díez Carlón; Kenji Watanabe; Takashi Taniguchi; Leonid S. Levitov; Dmitri K. Efetov; Klaas-Jan Tielrooij

doi:10.1126/sciadv.adj1361

Journal article Ultrafast Umklapp-assisted electron-phonon cooling in magic-angle twisted bilayer graphene

; ; ; ; ; ;

;

; ; ;

Download file (1.36 MB)
Download as zip (1.2 MB)

Collection

Citation

Jake Dudley Mehew, Rafael Luque Merino, Hiroaki Ishizuka, Alexander Block, Jaime Díez Mérida, Andrés Díez Carlón, Kenji Watanabe, Takashi Taniguchi, Leonid S. Levitov, Dmitri K. Efetov, Klaas-Jan Tielrooij. Ultrafast Umklapp-assisted electron-phonon cooling in magic-angle twisted bilayer graphene. Science Advances. 2024, 10 (6), eadj1361. https://doi.org/10.1126/sciadv.adj1361

(BibTeX)

Description:

(abstract)

Scattering between particles represents a crucial class of microscopic physical processes that govern transport properties and excited-state relaxation phenomena, among others. In crystals, as well as normal scattering, the discrete translation symmetry allows Umklapp scatter- ing events that do not conserve momentum. Phonon-phonon Umklapp scattering is a ubiquitous process that governs the thermal conductiv- ity of semiconductors and insulators, while electron-electron Umklapp scattering is only observed in ultraclean systems, usually at low temper- atures. In contrast, Umklapp scattering between electrons and phonons has not been demonstrated experimentally. Here we reveal the occurrence of electron-phonon Umklapp scattering in twisted bilayer graphene near the magic angle using time- and frequency-resolved photocurrent mea- surements. In magic-angle twisted bilayer graphene, a dramatic speedup of hot carrier cooling occurs: the cooling time is a few picoseconds from room temperature down to 5 K, where in pristine graphene coupling to acoustic phonons takes nanoseconds. Our theoretical calculations show that this ultrafast cooling is the result of the formation of a super- lattice with low-energy moir ́e phonons, spatially compressed electronic Wannier orbitals, and a reduced superlattice Brillouin zone, enabling Umklapp scattering and thus overcoming electron-phonon momentum mismatch. These results demonstrate the ability to engineer electron- phonon coupling in twistronic systems, and could contribute to the fundamental understanding of their transport properties, while enabling applications in thermal management and ultrafast photodetection.

Rights: