Zener tunneling of light in an optical superlattice
- PDF / 276,184 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 93 Downloads / 165 Views
B5.8.1
Zener tunneling of light in an optical superlattice Mher Ghulinyan, Zeno Gaburro, and Lorenzo Pavesi INFM and Dipartimento di Fisica, University of Trento, Italy Claudio J. Oton, Departamento de Fisica Basica, University of La Laguna, Tenerife, Spain Costanza Toninelli and Diederik S. Wiersma INFM & European Laboratory for Nonlinear Spectroscopy, Florence, Italy ABSTRACT We report on the observation of resonant Zener tunnelling of light waves in an optical superlattice. The one dimensional (1D) structures are made in free-standing porous silicon and are designed specifically to exhibit two photonic minibands. A controlled optical path gradient has been maintained over the sample thickness which resulted in tilting of photonic minibands and formation of optical Wannier-Stark ladders. At a certain value of optical gradient the two minibands couple within the extension of the structure and a resonant tunnelling channel through the superlattice forms, resulting in a very high transmission peak. Ultrafast time resolved transmission experiments were performed: excitation of the Wannier-Stark states causes the appearance of photonic Bloch oscillations, which are strongly damped when Zener tunneling modes are excited. The observed phenomenon is the optical analogue of resonant Zener tunnelling in an electronic superlattice. INTRODUCTION The electrical charge transport phenomena in solids lay in the basics of functionality of semiconductor electrical devices. Among the various transport phenomena the electrical Zener breakdown of solids has been one of the most intriguing topics. Originally formulated by Zener in 1934 [1], the problem suggests that at high electric fields a quantum particle in a crystal can be accelerated to higher energy bands without extra energy by simply tunnelling through the forbidden energy region. This theory predicts a tunnelling event of a particle into a continuum of states of the other energy band and is known in the literature as non-resonant Zener tunnelling. On the other hand, resonant tunnelling of charge carriers can be realized between Wannier-Stark ladders (WSL) of different energy bands [2]. A WSL is formed in the energy spectrum of particles as a set of equidistant states when electric field is applied to a crystal. These are not stationary states and, therefore, are localized in space. The experimental proof of Zener tunnelling phenomena was delayed for several decades, because of the experimental difficulties arising with the very high electric fields needed to tilt enough energy bands of usual crystals. Resonant Zener tunnelling was observed for the first time in electronic superlattices [3]. The typical bandwidth in a superlattice is in the order of some 100 meV therefore the observation of Zener tunnelling between energy minibands is possible at much lower electric fields. Since the invention of superlattices [4] an intensive research has been carried out for observing WSLs [5] and Zener breakdown [6, 7]. The analogies between transport phenomena of electrons in semiconducto
Data Loading...
