2012.10.01

Seminar Room 205, Faculty of Engineering building 4, Hongo Campus

Prof. Mads Brandbyge
         Dept. of micro and nanotechnology,
         Tech. Univ. of Denmark (DTU), Denmark

Title：Semi-Classical Langevin and NEGF Approach to Atomic Dynamics in Non-Equilibrium Nanosystems

Abstract：
The influence of an electronic current on atomic dynamics is an important and intriguing problem in nanoelectronics. We have developed an approach based on the semi-classical Langevin equation(SCLE) to investigate the excitation of atomic dynamics in a nanoconductor in the presence of electrical current[1, 2, 3]. In the SCLE description the nonequilibrium electronic environment is described like an effective "bath" influencing the atomic dynamics causing fluctuations and dissipation. We will discuss how this formalism is related to the NEGF method, and compare results for e.g. vibrational heating based on the two approaches. The SCLE approach allows us to identify the forces acting on the atoms due to the electronic current. We show how the current can cause several types of instabilities in a nanoconductor which ultimately can lead to contact breakdown. These include run-away behavior due to excitation of "water-wheel" modes[4, 2, 3], and a laserlike amplification of the phonons for contacts with a n-p-junction character[5].

[1] M. Brandbyge and P. Hedegård. Phys. Rev. Lett., 72, 2919, 1994.
[2] Jing Tao Lü, M. Brandbyge, and P. Hedegård. Nano Lett., 10, 1657, 2010.
[3] Jing-Tao Lü, M. Brandbyge, P. Hedegård, T. N. Todorov, and D.
Dundas. Phys. Rev.
B, 85, 245444, 2012.
[4] Daniel Dundas, Eunan J. McEniry, and Tchavdar N. Todorov. Current-driven atomic waterwheels. Nature Nanotech., 4(2):99-102, FEB 2009.
[5] Jing Tao Lü, P. Hedegård, and M. Brandbyge. Phys. Rev. Lett., 107, 046801,2011.

Schedule：13:30-15:00 Oct. 1, 2012 (Mon.) Place：Room 205, Engineering Bld #4, Hongo Campus Attached file： The 115th open seminar.pdf