Abstract Download (8.38MB)

Name (Title):
Xiao Hu ( Director, PI of MANA)
Affiliation:
International Center for Materials Nanoarchitectonics
(MANA), NIMS
Address:
Sengen 1-2-1, Tsukuba 305-0047, Japan
Email: Hu.Xiao@nims.go.jp
Home Page: http://www.nims.go.jp/cmsc/scm/index.html
Presentation Title:
Nano Superconductivity as a Novel Source of THz Electromagnetic Wave
Abstract:
Electromagnetic (EM) waves, ranging from the rf waves to γ ray, are deeply related with the
daily life. Below the visible lights, there locates the so-called terahertz (=10 12 Hertz, THz) band.
The EM waves in this range are very useful for genetic analysis, material inspection and
telecommunication, to name a few. Quantum cascade lasers based on super lattice of
semiconductors only provide THz EM waves in the pulse form and of fixed frequency, although
the power is fairly large. To seek continuous and strong sources of the THz EM waves is still a
matter of scientific challenge.
Superconductivity provides a unique way to generate
THz radiation due to the famous Josephson relations:
when a finite voltage is applied across two
superconducting electrodes with a thin gap (Josephson
junction), the phase difference across the junction
evolves with time in a velocity proportional to the
voltage (ac Josephson relation), and huge number of
Cooper pairs proportional to the sinusoidal function of
the phase difference tunnel across the junction (dc
Josephson relation). The tunneling of Cooper pairs is
accompanied by the emission of photons, or equivalently
EM waves. A voltage of 1mV emits the EM wave at
about half of 1THz.
Soon after the discovery of cuprate high-Tc superconductivity, it was demonstrated that a
single crystal of layered superconductors, such as Bi2Sr2CaCu2O8, behaves as a stack of intrinsic
Josephson junctions (IJJs). The IJJs are closely packed with a period of 1.5 nm, and their
homogeneity is guaranteed by the crystal structure down to the atomic scale, both very ideal for
getting strong radiations.
The challenge in exciting strong radiation is then to operate all the junctions coherently. One
way to achieve coherence is to build a cavity by a mesa of BSCCO single crystal. The cavity
resonance of the Josephson plasma will then force all the Josephson junctions to oscillate in
phase. By large-scale computer simulations and theoretical analysis on a model described by the
coupled sine-Gordon equations with large inductive coupling, we found that a novel dynamic
state can be stabilized by injecting c-axis dc currents, in which a π phase kink appears around the
junction center [1,2]. According to our estimate, this novel state can pump dc energy into THz
radiations with energy density larger than other known states by three orders.
This work is a collaboration with S.-Z. Lin and is supported by WPI Initiative on Materials
Nanoarchitectonics, MEXT and CREST, JST, Japan.
References:
[1] S.-Z. Lin and X. Hu, Phys. Rev. Lett. vol. 100, 247006 (2008)
[2] X. Hu and S.-Z. Lin, Phys. Rev. B, vol. 78, 134510 (2008)
CuO2 ����
1.53 nm
CuO2
CuO2
BSCCO-2212
single crystal
� ~600 junctions
Oral Presentation 19
19