Speaker
Description
We investigate odd-in-time—or odd-frequency—pairing of fermions in equilibrium systems within the particle-number-conserving framework of Penrose, Onsager and Yang, where superfluid order is defined by macrosocopic eigenvalues of reduced density matrices. We show that odd-frequency pair correlations are synonymous with even fermion-exchange symmetry in a time-dependent correlation function that generalises the two-body reduced density matrix [1]. Macroscopic even-under-fermion-exchange pairing is found to emerge from conventional Penrose-Onsager-Yang condensation in two-body or higher-order reduced density matrices through the symmetry-mixing properties of the Hamiltonian. We identify and characterise a transformer matrix responsible for producing macroscopic even fermion-exchange correlations that coexist with a conventional Cooper-pair condensate, while a generator matrix is shown to be responsible for creating macroscopic even fermion-exchange correlations from hidden orders such as a multi-particle condensate. The transformer scenario is illustrated using the spin-imbalanced Fermi superfluid as an example. The generator scenario is demonstrated by the composite-boson condensate arising for itinerant electrons coupled to magnetic excitations. Structural analysis of the transformer and generator matrices is shown to provide general conditions for odd-frequency pairing order to arise in a given system.
References
[1] Thompson, K., U. Zülicke, M. Governale, and J. Brand. “Odd-Frequency Superfluidity from a Particle-Number-Conserving Perspective.” arXiv, March 10, 2024. https://doi.org/10.48550/arXiv.2403.06325.
Relevant publications (optional)
Thompson, K., U. Zülicke, M. Governale, and J. Brand. “Odd-Frequency Superfluidity from a Particle-Number-Conserving Perspective.” arXiv, March 10, 2024. https://doi.org/10.48550/arXiv.2403.06325.
Reynolds, L. A., E. Schwartz, U. Ebling, M. Weyland, J. Brand, and M. F. Andersen. “Direct Measurements of Collisional Dynamics in Cold Atom Triads.” Physical Review Letters 124, no. 7 (February 18, 2020): 073401. https://doi.org/10.1103/PhysRevLett.124.073401.
Yang, Mingrui, Matija Čufar, Elke Pahl, and Joachim Brand. “Polaron-Depleton Transition in the Yrast Excitations of a One-Dimensional Bose Gas with a Mobile Impurity.” Condensed Matter 7, no. 1 (January 26, 2022): 15. https://doi.org/10.3390/condmat7010015.
Short bio (50 words) or link to website
Professor Brand completed obtained his PhD from the University of Heidelberg. After a postdoctoral research fellowship at the University of Washington and the Max Planck Institute for the Physics of Complex Systems he joined Massey University in 2006.
| Career stage | Professor |
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