Dongsung T. Park

Korea Advanced Institute of Science and Technology

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Hyung Kook Choi

Jeonbuk National University

Uh Jin Kim

Chonnam National University

Hyoungsoon Choi

Korea Advanced Institute of Science and Technology

Yunchul Chung

Pusan National University

Hwanchul Jung

Pusan National University

Seokyeong Lee

Yonsei University

H.-S. Sim

Korea Advanced Institute of Science and Technology

Chanuk Yang

Jeonbuk National University

V. Umansky

Weizmann Institute of Science

Bum-Kyu Kim

Korea Research Institute of Standards and Science

Cooperative Institutions

Korea Advanced Institute of Science and Technology

Korea Research Institute of Standards and Science

Jeonbuk National University

Pusan National University

Seoul National University

Weizmann Institute of Science

Daejeon University

Korea University of Science and Technology

Korea Institute of Science and Technology

Sejong University

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One-Lead Single-Electron Source with Charging Energy

Nano Letters (2022)

Sung Un Cho Wanki Park Bum-Kyu Kim Minky Seo Dongsung T. Park

Single-electron sources, formed by a quantum dot (QD), are key elements for realizing electron analogue of quantum optics. We develop a new type of single-electron source with functionalities that are absent in existing sources. This source couples with only one lead. By an AC rf drive, it successively emits holes and electrons cotraveling in the lead, as in the mesoscopic capacitor. Thanks to the considerable charging energy of the QD, however, emitted electrons have energy levels a few tens of millielectronvolts above the Fermi level, so that emitted holes and electrons are split by a potential barrier on demand, resulting in a rectified quantized current. The resulting pump map exhibits quantized triangular islands, in good agreement with our theory. We also demonstrate that the source can be operated with another tunable-barrier single-electron source in a series double QD geometry, showing parallel electron pumping by a common gate driving.

Mesoscopic physics

Fermi energy

10.1021/acs.nanolett.2c02893

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Significant energy relaxation of quantum dot emitted hot electrons

Physical Review Research (2021)

Dongsung T. Park Uh Jin Kim Dongkun Kim Hwanchul Jung Juho Choi

Through a series of transverse magnetic focusing experiments, we show that hot electrons in a two-dimensional electron gas system undergo an ultrafast relaxation when generated by a quantum dot (QD) instead of a quantum point contact (QPC). We find here that QPC hot electrons were well described by the non-interacting Fermi gas model for excitations up to 1.5 meV above the Fermi level of 7.44 meV, whereas QD hot electrons exhibited an energy loss quadratic to the excitation. The energy relaxation was a sizeable fraction of the tested excitations, up to about 55%. With the proposal that the hot electrons are relaxed by the QD immediately after emission, we present a toy model in which a capacitive coupling between the QD and its leads results in a finite, ultrafast energy relaxation.

Mesoscopic physics

Fermi energy

10.1103/physrevresearch.3.033015

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Observation of electronic modes in open cavity resonator

Nature Communications (2023)

Hwanchul Jung Dongsung T. Park Seokyeong Lee Uh Jin Kim Chanuk Yang

Abstract The resemblance between electrons and optical waves has strongly driven the advancement of mesoscopic physics, evidenced by the widespread use of terms such as fermion or electron optics. However, electron waves have yet to be understood in open cavity structures which have provided contemporary optics with rich insight towards non-Hermitian systems and complex interactions between resonance modes. Here, we report the realization of an open cavity resonator in a two-dimensional electronic system. We studied the resonant electron modes within the cavity and resolved the signatures of longitudinal and transverse quantization, showing that the modes are robust despite the cavity being highly coupled to the open background continuum. The transverse modes were investigated by applying a controlled deformation to the cavity, and their spatial distributions were further analyzed using magnetoconductance measurements and numerical simulation. These results lay the groundwork to exploring matter waves in the context of modern optical frameworks.

Mesoscopic physics

Optical cavity

Realization (probability)

10.1038/s41467-023-36012-2

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Channel-resolved wavefunctions of transverse magnetic focusing

Communications Physics (2024)

Seokyeong Lee Dongsung T. Park Uh Jin Kim Hwanchul Jung Yunchul Chung

Transverse magnetic focusing (TMF) is a staple technique in mesoscopic physics, used to study quasiparticles in a manner akin to mass spectrometry. However, the quantum nature of TMF has been difficult to appreciate due to several challenges in addressing the wavelike properties of the quasiparticles. Here, we report a numerical solution and experimental demonstration of the TMF wavefunction for the multichannel case, implemented using quantum point contacts in a two-dimensional electron gas. The wavefunctions could be understood as transverse modes of the emitter tracing a classical trajectory, and the geometric origins of multichannel effects were easily intuited from this simple picture. We believe our results may correspond to a near-field regime of TMF, in contrast to a far-field regime where the well-established semiclassical results are valid. Based on disorder analysis, we expect these results will apply to a wide range of realistic devices, suggesting that spatially coherent features even at the wavelength scale can be appreciated from TMF. Transverse magnetic focusing (TMF) has been widely used in mesoscopic physics, yet its quantum mechanical properties remain difficult to fully appreciate. Here, the authors present a numerical solution of TMF, analysed with channel-resolution and compared against experimental data, to expose the multichannel signatures of the TMF wavefunction.

Transverse magnetic

10.1038/s42005-024-01902-4

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Exploring Guest-Dependent Photoconductivity in a Donor-Containing Metal–Organic Framework

The Journal of Physical Chemistry C (2021)

Sanggyu Chong Dongsung T. Park Jihan Kim

In this computational study, intercalation of tetracyano acceptor guest molecules in In2(OH2)TBAPy (TBAPy = 1,3,6,8-tetrakis(4-carboxyphenyl)pyrene) is proposed as a strategy to induce photoconductivity in a previously insulating metal–organic framework (MOF). Analysis of the resulting MOF systems shows that photoconductivity is imparted by the completion of through-space charge transport pathways composed of newly inserted tetracyano acceptor molecules and pyrene donor moieties of the MOF linker. Substitution of Al3+ for In3+ and perylene for pyrene is subsequently suggested to further optimize the charge transfer between donors and acceptors, leading to a significant enhancement in the optoelectronic behavior. These results show that adaptation of known donor–acceptor chemistry from other materials (e.g., molecular cocrystals) can be a simple, yet effective strategy to design new electroactive MOFs. Furthermore, our findings demonstrate that rational modifications of MOFs based on their chemical tunability can lead to additional control over electroactivity in these materials.

Photoconductivity

Acceptor

Linker

Tetracyanoethylene

10.1021/acs.jpcc.0c11190

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Numerical Reconstruction of 2D Magnetic Focusing Experiments

arXiv (Cornell University) (2020)

Dongsung T. Park Seokyeong Lee Uh Jin Kim Yunchul Chung Hyoungsoon Choi

Spatial aspects in quantum mechanics are often difficult to model in geometrically intricate settings that are typical of mesoscopic physics. In such cases, predicting the device behaviors is a vital but difficult challenge. Transverse magnetic focusing (TMF) is a prime example where a classically simple effect becomes difficult to approach in the quantum regime. Here, we have simulated a realistic TMF device and compared the results to those from experiments performed on GaAs/AlGaAs two-dimensional electron gas systems. Unlike previous studies, device features such as quantum point contacts and disorder were realized within the simulation. The simulated and experimental focusing spectra showed good agreement, and the analysis was extended to multichannel and energy-modulated scenarios. By revisiting the energy-modulated simulation with a quantum dot (QD) emitter, we confirmed that the unique geometry of a QD does not affect the focusing spectra, thereby validating the feasibility of such experiments in the study of monoenergetic excitations.

10.48550/arxiv.2005.13841

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Cryogenic transimpedance amplifier based on a commercial operational amplifier

Journal of the Korean Physical Society (2023)

Chanuk Yang Inan Choi Hwanchul Jung Dongsung T. Park Hyung Kook Choi

Transimpedance amplifier

Dilution refrigerator

Direct-coupled amplifier

Instrumentation amplifier

Y-factor

Operational transconductance amplifier

FET amplifier

10.1007/s40042-023-00917-4

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Semiclassical Broadening in Quantum Dot Thermometry

Journal of the Korean Physical Society (2020)

Uh Jin Kim Hyung Kook Choi Dongsung T. Park

Coulomb blockade

Semiclassical physics

Johnson–Nyquist noise

Thermal fluctuations

10.3938/jkps.77.489

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Robust quantum point contact via trench gate modulation

Scientific Reports (2020)

Dongsung T. Park Seokyeong Lee Uh Jin Kim Hyoungsoon Choi Hyung Kook Choi

Quantum point contacts (QPC) are a primary component in mesoscopic physics and have come to serve various purposes in modern quantum devices. However, fabricating a QPC that operates robustly under extreme conditions, such as high bias or magnetic fields, still remains an important challenge. As a solution, we have analyzed the trench-gated QPC (t-QPC) that has a central gate in addition to the split-gate structure used in conventional QPCs (c-QPC). From simulation and modelling, we predicted that the t-QPC has larger and more even subband spacings over a wider range of transmission when compared to the c-QPC. After an experimental verification, the two QPCs were investigated in the quantum Hall regimes as well. At high fields, the maximally available conductance was achievable in the t-QPC due to the local carrier density modulation by the trench gate. Furthermore, the t-QPC presented less anomalies in its DC bias dependence, indicating a possible suppression of impurity effects.

Mesoscopic physics

Modulation (music)

10.1038/s41598-020-76790-z

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Citations (4)