APCTP-POSTECH Distinguished Lecture[09.07.06]
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"
“Carbon Nanotube Superconductivity: An Update”
ØSpeaker :Prof. Ping Sheng (HKUST, Clear Water Bay, Kowloon, Hong Kong)
ØPlace : #512, Hogil Kim Memorial Bldg., POSTECH
ØDate & Time : July 6 (Mon), 15:00 - 16:00
ØAbstract
Superconductivity in carbon nanotubes is a topic of intriguing interest. While the small-diameter nanotubes
Are predicted to have enhanced electron-phonon coupling—a key element responsible for nanotube
superconductivitythe associated increase in fluctuation effects is unfavorable to the manifestation of a
superconducting transition. The possibility of a Peierls transition in thin nanotubes is a further deterrent to
superconductivity. It follows that the existence of coupling between the nanotubes is important to the
realization of its superconducting behavior, since the transverse coherence can suppress fluctuations and
lower the Peierls transition temperature, thereby making the appearance of a superconducting transition
possible. Owing to its ordered and closely-spaced pore structure (with a 13.6 Å center-to-center
separation between the 0.7 nm diameter pores), the AFI zeolite (composition: Al12P12O48) with embedded
4-Å carbon nanotubes constitutes an ideal material for the observation of nanotube superconductivity.
In this talk I will describe the eight-year effort that resulted in the two new developments in 2007
(on improved sample fabrication) and 2008 (on making electrical contacts), leading to reasonably easy
observation of nanotube superconductivity with high reliability and repeatability. I n particular, we have
measured the specific heat signal for the superconducting transition as well as the resistive superconducting
transition. The coupled carbon nanotube arrays can yield both nearly 1D superconducting behavior as well
as the Josephson array behavior, with their attendant magnetic characteristics. The overall physical picture
that emerges is that of a coupled Josephson array consisting of aligned nanotubes crossing over from an
individually fluctuating 1D system to a coherent 3D superconductor, mediated by a Kosterlitz-Thouless (KT)
transition which establishes quasi long range order in the lateral plane perpendicular to the c-axis of the
nanotubes. The attainment of global coherence is seen at 5K and below, accompanied by the appearance
of a well-defined supercurrent gap at 2K. While the existence of the superconducting transition in nanotube
arrays is now beyond reasonable doubt, there are still many aspects of the data which have yet to be
theoretically understood. I will present some important lessons learned from the eight-year effort and what
they tell us about the mesoscopic electronic states in most carbon nanotubes. In particular, these lessons
may shed light on why nanotube superconductivity was not observed and/or confirmed earlier.
Contact Person : Prof. Wokyung Sung(054-279-2061, wsung@postech.ac.kr)"
“Carbon Nanotube Superconductivity: An Update”
ØSpeaker :Prof. Ping Sheng (HKUST, Clear Water Bay, Kowloon, Hong Kong)
ØPlace : #512, Hogil Kim Memorial Bldg., POSTECH
ØDate & Time : July 6 (Mon), 15:00 - 16:00
ØAbstract
Superconductivity in carbon nanotubes is a topic of intriguing interest. While the small-diameter nanotubes
Are predicted to have enhanced electron-phonon coupling—a key element responsible for nanotube
superconductivitythe associated increase in fluctuation effects is unfavorable to the manifestation of a
superconducting transition. The possibility of a Peierls transition in thin nanotubes is a further deterrent to
superconductivity. It follows that the existence of coupling between the nanotubes is important to the
realization of its superconducting behavior, since the transverse coherence can suppress fluctuations and
lower the Peierls transition temperature, thereby making the appearance of a superconducting transition
possible. Owing to its ordered and closely-spaced pore structure (with a 13.6 Å center-to-center
separation between the 0.7 nm diameter pores), the AFI zeolite (composition: Al12P12O48) with embedded
4-Å carbon nanotubes constitutes an ideal material for the observation of nanotube superconductivity.
In this talk I will describe the eight-year effort that resulted in the two new developments in 2007
(on improved sample fabrication) and 2008 (on making electrical contacts), leading to reasonably easy
observation of nanotube superconductivity with high reliability and repeatability. I n particular, we have
measured the specific heat signal for the superconducting transition as well as the resistive superconducting
transition. The coupled carbon nanotube arrays can yield both nearly 1D superconducting behavior as well
as the Josephson array behavior, with their attendant magnetic characteristics. The overall physical picture
that emerges is that of a coupled Josephson array consisting of aligned nanotubes crossing over from an
individually fluctuating 1D system to a coherent 3D superconductor, mediated by a Kosterlitz-Thouless (KT)
transition which establishes quasi long range order in the lateral plane perpendicular to the c-axis of the
nanotubes. The attainment of global coherence is seen at 5K and below, accompanied by the appearance
of a well-defined supercurrent gap at 2K. While the existence of the superconducting transition in nanotube
arrays is now beyond reasonable doubt, there are still many aspects of the data which have yet to be
theoretically understood. I will present some important lessons learned from the eight-year effort and what
they tell us about the mesoscopic electronic states in most carbon nanotubes. In particular, these lessons
may shed light on why nanotube superconductivity was not observed and/or confirmed earlier.
Contact Person : Prof. Wokyung Sung(054-279-2061, wsung@postech.ac.kr)"
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