Abstract
Mesoscopic quantum dots (QDs) are ubiquitous in quantum devices as reliable sources of hot electrons. However, we have observed an unexpectedly significant energy relaxation of QD-emitted hot electrons up to $\ensuremath{\approx}55%$ of its excitation $\ensuremath{\le}1.5\phantom{\rule{4pt}{0ex}}\mathrm{meV}$ from the Fermi level. The energetics of hot electrons were obtained through transverse magnetic focusing over a few microns using both QD and quantum point contact (QPC) emitters. Unlike the QPC counterparts, QD emissions deviated substantially from Fermi gas predictions---the focusing peak appeared at lower magnetic fields, and excessive broadening was observed. The phenomenon was modeled by a capacitive interaction transferring energy from the hot electron to the QD. Model simulations reproduced the key experimental features, implying the presence of a strong yet overlooked relaxation mechanism that is intrinsic to QD emissions. Our observation calls for the prudent use of QDs as single electron sources.
Highlights
Condensed matter physics provides a powerful framework for understanding the vast array of macroscopic systems— band metals, superconductors, and topological insulators, just to list a few [1,2,3]
In support of previous reports that quantum point contact (QPC) hot electrons act as Fermi gas quasiparticles [21,32], we found that both the√peak positions and widths of the QPC spectra scaled with EF + EDC, blue circles in Figs. 3(e) and 3(f)
Our relaxation mechanism originates from a generic capacitive interaction, we expect it to be inconsequential during QPC emissions for two major reasons
Summary
Condensed matter physics provides a powerful framework for understanding the vast array of macroscopic systems— band metals, superconductors, and topological insulators, just to list a few [1,2,3]. QPC-emitted hot electrons differ in their relaxations, the reasons as to how much and why the differences emerge have yet to be fully understood. Such characteristics are especially important at low magnetic fields, where a wide range of device applications would realistically operate. We report the observation of strong energy relaxation in two-dimensional (2D) QD-emitted hot electrons at low magnetic fields. Using the energy scaling properties of transverse magnetic focusing (TMF) [20,21,22,23], the energetic mean and standard deviation were obtained for both QD- and QPCemitted hot electrons with initial excitations ranging from 0 to 1.5 meV. The model simulation presented similar energy statistics and produced a TMF spectrum analogous to experimental measurements, indicating that QD hot electrons can be significantly relaxed immediately after emission by exciting the electrons left in the QD
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