TTerahertz radiation lies between microwaves and infrared light. It can be used to study materials and is also of interest for new detectors. One possible detector is the quantum point contact: an extremely narrow passage in a thin layer of mobile electrons. An applied voltage can narrow this passage to the point where electrons can barely pass through. When terahertz radiation hits the structure, the current through the constriction can increase dramatically.
A research team at TU Wien and its partners in Novosibirsk have now investigated how this effect depends on the frequency of the radiation. The study was published in Applied Physics Letters. The response was far from uniform: at certain frequencies, the electrical conductance increased particularly strongly. In the deep tunnelling regime, the relative enhancement at individual resonances reached a factor of approximately 10,000.
Where the strong resonances come from
One might expect the resonances to depend solely on the tiny constriction. Yet their frequencies remain unchanged when the researchers vary the voltage applied to the quantum point contact, thereby changing the tunnelling barrier. This points to the wider surroundings of the contact: collective electron oscillations, known as plasmons, can arise in the two-dimensional electron layer. At suitable frequencies, these oscillations enhance the electromagnetic field near the constriction – and thus the measured response to terahertz radiation.
Computer simulations confirm that the geometry and electron mobility shape the plasmon resonances. The structure therefore does not amplify all frequencies equally. By tailoring its surroundings, a quantum point contact could be made particularly sensitive to selected frequencies.
Two directions for further research
The resonances offer a route towards frequency-selective terahertz detectors. At the same time, they make it harder to investigate the intrinsic effect of radiation on transport through the quantum point contact: the response of the surroundings is superimposed on it. The team therefore proposes using electron layers with lower mobility for such fundamental experiments. In these layers, plasmon oscillations are more strongly damped, allowing the intrinsic response of the constriction to be isolated more effectively.
Original publication
D. A. Khudaiberdiev, M. L. Savchenko, A. Shuvaev, E. E. Rodyakina, A. Pimenov and Z. D. Kvon: “Plasmonic resonances in the terahertz photoresponse of quantum point contacts”, Applied Physics Letters 129, 102106 (2026). DOI: 10.1063/5.0347196, opens an external URL in a new window
Contact
Daniiar Khudaiberdiev & Andrei Pimenov
Institute of Solid State Physics
TU Wien
daniiar.khudaiberdiev@tuwien.ac.at