1 / 19

Probes of Pairing in Strongly Interacting Fermions

Probes of Pairing in Strongly Interacting Fermions. Erich Mueller --Cornell University. Sourish Basu Stefan Baur Theja De Silva (Binghampton) Dan Goldbaum Kaden Hazzard. Outline. A tool: Doppler free spectroscopy Capabilities Challenges

ksena
Download Presentation

Probes of Pairing in Strongly Interacting Fermions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Probes of PairinginStrongly InteractingFermions Erich Mueller --Cornell University Sourish Basu Stefan Baur Theja De Silva (Binghampton) Dan Goldbaum Kaden Hazzard

  2. Outline • A tool: Doppler free spectroscopy • Capabilities • Challenges • Probing fermionic superfluidity near Feshbach resonance

  3. Abs Ketterle Group: Science 316, 867-870 (2007) “Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture” dn [kHz] Take-Home Message - I Chin et al. Science 20, 1128 (2004) • RF/Microwave spectroscopy does tell you details of the many-body state • Weak coupling -- density • Strong coupling -- complicated by final-state effects • Bimodal RF spectra in trapped Fermi gases not directly connected to pairing (trap effect) Decreasing T

  4. Take Home Message II • Homogeneous RF spectrum: two components -- bound-bound and bound-free • Final state effects are crucial -- qualitative role Bound-Free Bound-Bound Basu and Mueller, arXiv:0712.1007

  5. Context: Upcoming Cold Atom Physics Profound increase in complexity Ex: modeling condensed matter systems Big Question: How to probe?

  6. Atomic Spectroscopy I(w) [transfer rate] E w w w0 Narrow hyperfine spectral line in vacuum (Hz): in principle sensitive to details of many-body state (Eint~100kHz) (weak coupling) (weak coupling) Line shift proportional to density [Clock Shift]

  7. Spectrum gives histogram of density Applications BEC: Density bump Solid: condensedOpen: non-condensed Exp: (Kleppner group) PRL (1998) Theory: Killian, PRA (2000) Mott Shells: Exp: Ketterle group [Science, 313, 649 (2006)] Density Plateaus Thy: Hazzard and Mueller [arXiv:0708.3657]

  8. Pairs Spectrum knows about more than density! Jin group [Nature 424, 47 (2003)] Ex: RF dissociation - Potassium Molecules (Thermal, non-superfluid fermionic gas) Free atoms Initially weakly bound pairs in (and free atoms in these states) pairs Drive mf=-5/2 to mf=-7/2 Also see:Grimm group [Science 305, 1128 (2004)]Ketterle group [Science 300, 1723 (2003)

  9. Many-Body Simple limit I: Final state does not interact (V(ab)=0) • analogous to momentum resolved tunneling (or in some limits photoemission) • probe all single particle excitations Initial: ground state Final: single a-quasihole of momentum k single free b-atom Simple Limits II: Final state interacts same as initial (V(ab)=V(bb)), Ladder operator General Case: System specific

  10. Lithium near Feshbach resonance Innsbruck expt grp +NIST theory grp, PRL 94, 103201 (2005) Strongly interacting superfluid Strong final state interactions!!! BCS-BEC crossover

  11. Basu and Mueller, arXiv:0712.1007 Variational Model Idea: include all excitations consisting of single quasiparticles quasiholes “coherent contribution” -- should capture low energy structure a-b pairs -- excite from b to c Neglects multi-quasiparticle intermediate states (equivalent to BCS-RPA A. Perali, P. Pieri, G.C. Strinati, arXiv:0709.0817) [Exact if (final int)=(initial int) or if (final int)=0]

  12. Result Bound-Free Bound-Bound Experiment Many-body

  13. Typical spectra

  14. What about the trap? Most experiments show trap averaged lineshape Grimm group, Science 305, 1128 (2004) Bimodality:due to trap Thy: Kinnunen, Rodriguez, and Torma, Science 305, 1131 (2004); Heiselberg NJP 6, 137 (2004); Chin and Julienne, PRA 71, 012713;Ohashi and Griffin, PRA 72, 013601 (2005); He, Chen, and Levin, PRA 72, 011602 (2005); Yu and Baym, PRA 73, 063601 (2006);He, Chien, Chen, Levin, arXiv:0707.2625; Baym, Pethick, Yu, and Zwierlein, arXiv:0707.0859; Punk and Zwerger, arXiv:0707.0792;Perali, Pieri, Strinati, arXiv:0709.0817; Massignan, Bruun, and Stoof, arXiv:0709.3158

  15. Where spectral weight comes from Massignan, Bruun, and Stoof, ArXiv:0709.3158 (Neglects Final state interaction) Edge of cloud Calculation in normal state: Ndown<Nup More particles at center No superfluidity!! Pairing? Also see He, Chen and Levin, PRA 72, 011602 (2005)

  16. Highly polarized limit: only one down-spin particle Generic properties Assumption: local clock shift = (homogeneous spectrum peaks there) High temp: [Virial expansion: Ho and Mueller, PRL 92, 160404 (2004)] High density: Different a

  17. Bimodality nup ndn r Center of trap: highest down-spin density -- gives broad peak Edge of trap: low density, but a lot of volume -- All contribute at same detuning -- Gives power law-log singularity

  18. Quantitative Ketterle Group: Science 316, 867-870 (2007) Nozieres and Schmidt-Rink Mueller, ArXiv:0711.0182 Agreement: fortuitous, but gives scaling with parameters (no adjustable params)

  19. Summary • Trap leads to bimodal spectrum (model independent) regardless of pairing • Homogeneous spectrum can reveal pairing (bound-bound transition) but final state interactions are crucial

More Related