LIST OF RESEARCHERS
Junghyun Shin (active), Dr. Sunkyu Park (08-17)
QUANTUM PHASE TRANSITION IN SUPERCONDUCTING THIN FILMS
Two-dimensional (2D) superconductors have received many attentions due to their interesting physical phenomena under a disorder, electric and magnetic field. They also have a close relation with 2D characteristics of high-Tc superconductors because of their layered structures. In general, 2D superconducting systems show superconductor-insulator transition. This type of transition is a clear example of quantum phase transition between the ground states at zero temperature due to a quantum fluctuation. At zero temperature, one ground state can be abruptly changed to another one by varying the physical parameter such as pressure, disorder, and magnetic field.
- Researchers: Dr. Sun-Gyu Park
- Results: S. Park and E. Kim, arxiv:1401.3947 (submitted)
VORTEX DYNAMICS IN 2D SUPERCONDUCTORS
In our group, we have studied behaviors of the superconducting tantalum (Ta) thin films according to disorders, magnetic fields and temperature. The superconductor-insulator transition occurs when disorder is changed or when magnetic field is applied to the Ta thin-film. Surprisingly, Ta thin films show an intermediate ground state between superconductor and insulator. This unexpected phase behaves like a metal with a finite resistance at zero temperature limit. Despite of discussions over a decade, the physical mechanism underlying this mysterious phase are still in controversy. Here we are focused on vortex dynamics as prospective mechanism of intermediate phase. 2D superconductor systems below critical temperature have vortices as excitations. The number of vortices can be manipulated by magnetic field, while its velocity is controlled by electric field due to Lorentz force. With a combination of these two parameters, 2D superconducting systems show various vortex dynamics. The finite resistance at zero temperature limit of an intermediate phase in Ta thin film can be understood in terms of vortex dynamics. We are studying various vortex dynamics and testing the above hypothesis for Ta thin film by using a challenging fabrication and measurement technique.
- Researchers: Dr. Sun-Gyu Park, Junghyun Shin