Abstract
Realising and probing topological superfluids is a key goal for fundamental science, with exciting technological promises. Here, we show that chiral $p_x+ip_y$ pairing in a two-dimensional topological superfluid can be detected through circular dichroism, namely, as a difference in the excitation rates induced by a clockwise and counter-clockwise circular drive. For weak pairing, this difference is to a very good approximation determined by the Chern number of the superfluid, whereas there is a non-topological contribution scaling as the superfluid gap squared that becomes signifiant for stronger pairing. This gives rise to a competition between the experimentally driven goal to maximise the critical temperature of the superfluid, and observing a signal given by the underlying topology. Using a combination of strong coupling Eliashberg and Berezinskii-Kosterlitz-Thouless theory, we analyse this tension for an atomic Bose-Fermi gas, which represents a promising platform for realising a chiral superfluid. We identify a wide range of system parameters where both the critical temperature is high and the topological contribution to the dichroic signal is dominant.
Highlights
The realization and manipulation of topological superfluids and superconductors is presently one of the most actively pursued goals in physics
We show that chiral px + ipy pairing in a two-dimensional topological superfluid can be detected through circular dichroism, namely, as a difference in the excitation rates induced by a clockwise and counterclockwise circular drive
We identify a wide range of system parameters where both the critical temperature is high and the topological contribution to the dichroic signal is dominant
Summary
The realization and manipulation of topological superfluids and superconductors is presently one of the most actively pursued goals in physics. The fermions form Cooper pairs with chiral symmetry by exchanging sound modes in the BEC, and the system offers sufficient flexibility so that one can tune the superfluid critical temperature to be within experimental reach Such a Bose-Fermi mixture has been realized using 173Yb-7Li atoms, which constitutes an important step towards an unequivocal realization of a topological px + ipy superfluid [10]. Contrary to the chiral edge modes of single-particle band structures, which have been detected in experiments [12], the observation of Majorana states [13,14] is complicated by their small number and their particle-hole nature It was recently proposed [15,16] and experimentally demonstrated [17] that the topologically invariant Chern number can be detected in atomic gases through circular dichroism, namely, by analyzing excitation rates upon applying a circular drive. Our results demonstrate that the dichroic probe offers an experimentally promising pathway to detect topological superfluidity
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