Observation of a linearly dispersing collective mode in a quantum Hall ferromagnet - art. no. 036803

Double-layer two-dimensional electron systems can exhibit a fascinating col lective phase believed to display both quantum ferromagnetism and excitonic superfluidity. This unusual phase has recently been found to exhibit tunne ling phenomena reminiscent of the Josephson effect. A key element of the th eoretical understanding of this bizarre quantum fluid is the existence of l inearly dispersing Goldstone collective modes. Using the method of tunnelin g spectroscopy, we have demonstrated the existence of these modes. We find the measured velocity to be in reasonable agreement with theoretical estima tes.