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Research Overview
LIST OF RESEARCHERS
Dr. Seong Jang (10-19), Dr. Jungil Lee (07-16)
GRAPHENE: A CARBON FLATLAND
Graphene is a monolayer hexagonal lattice of carbon atoms. It has triggered a huge research field of science and engineering due to its extraordinary physical properties and possibility as the new candidate for the replacement of silicon semiconductor. Graphene has distinctive band structure (gapless, massless and valley degeneracy) and shows many interesting electronic phenomena such as Klein tunneling, quantum Hall effect with different integers, specular Andreev reflection and etc.
NANO-CONSTRICTED GRAPHENE DEVICES
We investigated the fabrication of a nano-constricted graphene quantum dot device. A suspended graphene device was first prepared by using well-developed polymer based methods [1]. Application of sufficiently large electric current at low temperatures induces dramatic constrictions in graphene devices [2-3]. Adequate control of the current annealing condition allows us to carry out the fine tuning of conductance of the devices. The conductance spectroscopy demonstrates the evolution of the coulomb blockade effect as well as progressive change in the the quantum dot energy.
- Researcher: Dr. Jungil Lee
- Results: J. I. Lee, S. Jang, S. Cho and E. Kim, Current Applied Physics 16, 731 (2016)
ANDREEV REFLECTION AT GRAPHENE-SUPERCONDUCTOR INTERFACES
We are especially interested in Andreev reflection which occurs at the interface between graphene and superconductor. Due to the special electronic band structure of graphene, it is theoretically predicted that Andreev reflection occurs in specular way which is contrast to other material where it occurs in retro-reflective way [4]. Recently, it is predicted that the period of magneto-resistance oscillation in a ring shaped graphene can distinguish the type of Andreev reflection in a device [5]. In order to measure this, we are fabricating a number of graphene devices on boron nitride crystals in order to avoid charge inhomogeneity and low mobility in the device, which allows comparable transport properties to that of suspended graphene [6]. We do both of sample fabrication and measurement. Our graphene device fabrication is based on typical electron beam lithography process. Graphene devices are measured at very low temperature and high magnetic field in homebuilt cryogen-free dilution refrigerator equipped with superconducting magnet.
- Researcher: Dr. Seong Jang
REFERENCES
[1] N. Tombros et al., Journal of Applied Physics 109, 093702 (2011)
[2] N. Tombros et al., Nature Physics 7, 697 (2011)
[3] A. Barreiro et al., Nano Letters 12, 6096 (2012)
[4] C. W. J. Beenakker, Phys. Rev. Lett. 97, 067007 (2006)
[5] J. Schelter et al., Phys. Rev. Lett. 108, 106603 (2012)
[6] C. R. Dean et al., Nat. Nanotechnol. 5, 722-726 (2010)
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