Spin-flip transitions between Zeeman sublevels in semiconductor quantum dots

We have studied spin-flip transitions between Zeeman sublevels in GaAs electron quantum dots. Several different mechanisms which originate from spin-orbit coupling are shown to be responsible for such processes. It is shown that spin-lattice relaxation for the electron localized in a quantum dot is much less effective than for the free electron. The spin-flip rates due to several other mechanisms not related to the spin-orbit interaction are also estimated.Comment: RevTex, 7 pages (extended journal version, PRB, in press

Coupling molecular spin states by photon-assisted tunneling

Artificial molecules containing just one or two electrons provide a powerful platform for studies of orbital and spin quantum dynamics in nanoscale devices. A well-known example of these dynamics is tunneling of electrons between two coupled quantum dots triggered by microwave irradiation. So far, these tunneling processes have been treated as electric dipole-allowed spin-conserving events. Here we report that microwaves can also excite tunneling transitions between states with different spin. In this work, the dominant mechanism responsible for violation of spin conservation is the spin-orbit interaction. These transitions make it possible to perform detailed microwave spectroscopy of the molecular spin states of an artificial hydrogen molecule and open up the possibility of realizing full quantum control of a two spin system via microwave excitation.Comment: 13 pages, 9 figure

Orthogonal Cherenkov sound in spin-orbit coupled systems

Conventionally the Cherenkov sound is governed by {\it orbital} degrees of freedom and is excited by {\it supersonic} particles. Additionally, it usually has a {\it forward} nature with a conic geometry known as the Cherenkov cone whose axis is oriented {\it along} the {\it supersonic} particle motion. Here we predict Cherenkov sound of a unique nature entirely resulting from the electronic {\it spin} degree of freedom and demonstrate a fundamentally distinct Cherenkov effect originating from essentially {\it subsonic} electrons in two-dimensional gases with both Bychkov-Rashba and Dresselhaus spin-orbit interactions. Specifically, we show that the axis of the conventional {\it forward} Cherenkov cone gets a nontrivial {\it quarter-turn} and at the same time the sound distribution strongly localizes around this rotated axis being now {\it orthogonal} to the {\it subsonic} particle motion. Apart from its fundamentally appealing nature, the orthogonal Cherenkov sound could have applications in planar semiconductor technology combining spin and acoustic phenomena to develop, {\it e.g.}, acoustic amplifiers or sound sources with a flexible spin dependent orientation of the sound propagation.Comment: 7 pages, 4 figure