Sangwook Ha
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Sangwook Ha has a total of 7 co-authors. Here are the top co-authors by number of shared publications:
- Joonho Jang
Department of Physics and Astronomy Seoul National University 08826 Seoul Korea
2 shared publications Baeksan Jang
Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University , Seoul 08826
1 shared publication- Hangyeol Park
Department of Physics and Astronomy Seoul National University Seoul South Korea
1 shared publication - Hyeokjun Heo
Department of Physics and Astronomy and Institute of Applied Physics, Seoul National University 1 , Seoul 08826, South Korea
1 shared publication - Namkyung Lee
Department of Physics and Astronomy, Seoul National University 1 , Seoul 08826
1 shared publication - Seungwon Jung
Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University , Seoul 08826
1 shared publication
Latest Publications
- 1 September 2025
- Published by AIP Publishing in Review of Scientific Instruments
- Vol. 96 (9)
Cryogen-free variable-temperature Kelvin probe force microscopy for probing local chemical potential in van der Waals heterostructures
We report the development of a variable-temperature Kelvin probe force microscopy (KPFM) system based on a Gifford–McMahon cryocooler, which enables stable and highly sensitive operation across a broad temperature range. The system integrates a custom-designed phase-locked loop, automatic gain control, and compact passive vibration isolation stages, effectively suppressing mechanical vibrations intrinsic to cryostats. We demonstrate the system’s performance using a monolayer graphene (MLG) device encapsulated in hexagonal boron nitride, serving as a benchmark platform to validate spatial resolution and CPD sensitivity. Despite the presence of a dielectric encapsulation layer, our system achieves high CPD sensitivity. Temperature-dependent measurements further confirm the capability to resolve subtle changes in chemical potential near the charge neutrality point, consistent with the known electronic structure of MLG. This work establishes a variable temperature KPFM platform suitable for investigating temperature-dependent quantum electronic phases in van der Waals heterostructures.
- 1 September 2025
- Published by AIP Publishing in Review of Scientific Instruments
- Vol. 96 (9)
Cryogen-free variable-temperature Kelvin probe force microscopy for probing local chemical potential in van der Waals heterostructures
We report the development of a variable-temperature Kelvin probe force microscopy (KPFM) system based on a Gifford–McMahon cryocooler, which enables stable and highly sensitive operation across a broad temperature range. The system integrates a custom-designed phase-locked loop, automatic gain control, and compact passive vibration isolation stages, effectively suppressing mechanical vibrations intrinsic to cryostats. We demonstrate the system’s performance using a monolayer graphene (MLG) device encapsulated in hexagonal boron nitride, serving as a benchmark platform to validate spatial resolution and CPD sensitivity. Despite the presence of a dielectric encapsulation layer, our system achieves high CPD sensitivity. Temperature-dependent measurements further confirm the capability to resolve subtle changes in chemical potential near the charge neutrality point, consistent with the known electronic structure of MLG. This work establishes a variable temperature KPFM platform suitable for investigating temperature-dependent quantum electronic phases in van der Waals heterostructures.
- 15 June 2022
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 131 (23) , 233901
Magneto-optical measurements of mesoscopic Nb superconducting structures using a ferromagnetic metal indicator layer
Imaging local magnetic fields produced by nano- and micrometer-scale superconductors has become a vital tool that can not only reveal crucial information on the vortex dynamics and order parameters of the superconducting materials but also visualize the working mechanism of superconducting devices made for quantum information. Here, we performed measurements of the magnetic field distributions of mesoscopic superconducting structures with various geometries by combining a thin ferromagnetic metal layer as a magneto-optical sensing element that responds to the environmental magnetic fields and a custom-made sensitive Sagnac interferometer. The sensitivity of the technique enables the observation of magnetic flux jumps due to individual vortex entries into nanostructured superconductors. In addition, with the control of incident power at a focused laser spot, we induce thermally driven movement of vortices that leaves a trace of a microscopic optical heating pattern.
- 15 June 2022
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 131 (23) , 233901
Magneto-optical measurements of mesoscopic Nb superconducting structures using a ferromagnetic metal indicator layer
Imaging local magnetic fields produced by nano- and micrometer-scale superconductors has become a vital tool that can not only reveal crucial information on the vortex dynamics and order parameters of the superconducting materials but also visualize the working mechanism of superconducting devices made for quantum information. Here, we performed measurements of the magnetic field distributions of mesoscopic superconducting structures with various geometries by combining a thin ferromagnetic metal layer as a magneto-optical sensing element that responds to the environmental magnetic fields and a custom-made sensitive Sagnac interferometer. The sensitivity of the technique enables the observation of magnetic flux jumps due to individual vortex entries into nanostructured superconductors. In addition, with the control of incident power at a focused laser spot, we induce thermally driven movement of vortices that leaves a trace of a microscopic optical heating pattern.