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Laser Physics

Quasiresonant tunneling of phonons in bosonic superfluid-insulator- superfluid junctions

Ippei Danshita, Nobuhiko Yokoshi, Susumu Kurihara

Published Feb 1, 2005• 2 citations
OpenAlex

Abstract

We investigate the quasiresonant tunneling of phonon excitations across a potential barrier spatially separating two condensates with different macroscopic phases. We confirm that the quasiresonant tunneling occurs through the quasibound state. The quasibound state is induced by a potential well created by the condensate density. We analyze the relation between the phase difference φ of two condensates and the transmission coefficient T by solving the Bogoliubov-de Gennes equations. As a result, the transmission coefficient T is found to depend strongly on (p because of the φ dependence of the quasibound state.

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•Feb 6, 2008•0 citations
We investigate the quasiresonant tunneling of phonon excitations across a potential barrier spatially separating two condensates with different macroscopic phases. We confirm that the quasiresonant tunneling occurs through the quasibound state. The quasibound state is induced by a potential well created by the condensate density. We analyze the relation between the phase difference φ of two condensates and the transmission coefficient T by solving the Bogoliubov-de Gennes equations. As a result, the transmission coefficient T is found to depend strongly on (p because of the φ dependence of the quasibound state.
We consider the tunnelling of phonon excitations across a potential barrier spatially separating two condensates with different macroscopic phases. We analyse the relation between the phase difference φ of the two condensates and the transmission coefficient T by solving the Bogoliubov equations. It is found that T strongly depends on φ, and that the perfect transmission of low-energy excitations disappears when the phase difference reaches the critical value which gives the maximum supercurrent of the condensate. We also discuss the feasibility of observing the phase differences in experiments.
We discuss the tunneling of phonon excitations across a potential barrier separating two condensate bulks. It is shown that the strong barrier proves to be transparent for the excitations at low energy εεε. Moreover, the transmission is reduced with increasing εεε in contrast to the standard dependence. This anomalous behavior is due to an existence of the quasiresonance interaction. The origin of this interaction is a result of the formation of the special well determined by the density distribution of condensate in the vicinity of a high barrier.
We discuss the tunneling of phonon excitations across a potential barrier separating two condensates. It is shown that a strong barrier proves to be transparent for the excitations at low energy epsilon. Moreover, the transmission is reduced with increasing epsilon in contrast to the standard dependence. This anomalous behavior is due to the existence of a quasiresonance interaction. The origin of this interaction is a result of the formation of a special well determined by the density distribution of the condensate in the vicinity of a high barrier.
We study the tunneling of Bogoliubov excitations through a barrier in a Bose-Einstein condensate. We extend our previous work [S. Tsuchiya and Y. Ohashi, Phys. Rev. A 78, 013628 (2008)] to the case when condensate densities are different between the left and right of the barrier potential. In the framework of the Bogoliubov mean-field theory, we calculate the transmission probability and phase shift, as well as the energy flux and quasiparticle current carried by Bogoliubov excitations. We find that Bogoliubov phonons twist the condensate phase due to a back-reaction effect, which induces the Josephson supercurrent. While the total current given by the sum of quasiparticle current and induced supercurrent is conserved, the quasiparticle current flowing through the barrier potential is shown to be remarkably enhanced in the low-energy region. When the condensate densities are different between the left and right of the barrier, the excess quasiparticle current, as well as the induced supercurrent, remains finite far away from the barrier. We also consider the tunneling of excitations and atoms through the boundary between the normal and superfluid regions. We show that supercurrent can be generated inside the condensate by injecting free atoms from outside. On the other hand, atoms are emitted when the Bogoliubov phonons propagate toward the phase boundary from the superfluid region.
We clarify the origin of anomalous tunneling [Yu. Kagan et al. Phys. Rev. Lett. 90 (2003) 130402] i.e. the perfect transmission at low energy limit of tunneling of phonon excitations across the potential barrier separating two Bose condensates. The perfect transmission is a consequence of the coincidence of the wave function of the excited state at low energy limit and the macroscopic wave function of the condensate. We show that the perfect transmission at low energy occurs even at finite temperatures within the scheme of Popov approximation.
We investigate tunneling properties of Bogoliubov phonons in a Bose-Einstein condensate. We find the anomalous enhancement of the quasiparticle current JqJ_{\rm q}Jq​ carried by Bogoliubov phonons near a potential barrier, due to the supply of the excess current from the condensate. This effect leads to the increase of quasiparticle transmission probability in the low energy region found by Kovrizhin {\it et al.}. We also show that the quasiparticle current twists the phase of the condensate wavefunction across the barrier, leading to a finite Josephson supercurrent JsJ_{\rm s}Js​ through the barrier. This induced supercurrent flows in the opposite direction to the quasiparticle current so as to cancel out the enhancement of JqJ_{\rm q}Jq​ and conserve the total current J=Jq+JsJ=J_{\rm q}+J_{\rm s}J=Jq​+Js​.