## Kathryn Levin

Ph.D., Harvard, 1970.

Professor, Dept. Physics, James Franck Inst., and the College.

Research: *Theoretical physics, solid state physics.*

See Prof. Levin's CV and publications

Papers from x-arXiv/cond-mat

Our work is based on many body quantum field theory and is closely tied to experiments. Our more recent research has been in the two theoretical fields of high temperature cuprate superconductors and ultracold atomic gas superfluids. We were among the first to investigate the more extended version of BCS (Bardeen Cooper Schrieffer) theory to the so called ‘‘crossover" between BCS and Bose Einstein condensation (BEC). Our original motivation was to understand anomalies in high temperature superconductors where, because of the small size of the Cooper pairs, one would expect that these materials are in the ‘‘crossover" region, intermediate between very loosely and very tightly bound pairs. [Pairing of fermions through an attractive interaction is an essential ingredient of superconductivity.] In the cuprates much more could be going on as well, but minimally one has to include these effects. And they surely give rise to so-called ‘‘pseudogap" effects, that is, an anomalous normal state above the transition temperature. Understanding the origin of this pseudogap still remains a central focus of the cuprate field.

Fortunately, in 2003 it was shown that there is a very nice laboratory for studying BCS- BEC crossover, and verifying some of our ideas about high temperature superconductors. This is in the ultracold Fermi gases which have attracted enormous attention to the concept of BCS-BEC crossover. We were in a rather unique position having a theory of the cuprates (there are literally hundreds in the literature) which has a clear realization in a laboratory. We have continued to work in this cold atom field making predictions and arriving at an a posteriori understanding of a vast treasure trove of experiments. Most recently (in 2014) we anticipated quite precisely the experimental story involving a long sequence of equilibrating steps associated with these superfluids when they are driven violently from equilibrium via ‘‘phase imprinting".

With the recent emphasis on topological order, we have begun to contribute to this field, by looking at spin-orbit effects in Fermi gas superfluids. Our focus is on calculating whether the transition temperatures are in a reasonable, physically accessible range, and also how one can probe these systems through precisely calculated correlation functions.

**Selected Publications:**

- Signatures of Pairing and spin-orbit coupling in correlation functions of Fermi gases, Chien-Te Wu, Brandon M. Anderson, Rufus Boyack and K. Levin [ArXiv 1503.05454]
- Phase Imprinting in Equilibrating Fermi Gases: The Transience of Vortex Rings and Other Defects, Peter Scherpelz, Karmela Padavic, Adam Rancon, Andreas Glatz, Igor Aranson and K Levin Phys. Rev. Lett. 113, 125301 (2014).
- Unified Treatment of Fermi pockets and arcs scenarios for the cuprates: Sum rule con- sistent response functions of the pseudogap Peter Scherpelz, Adam Rancon, Yan He and K. Levin PRB 90, 060506(R) (2014)
- Theory of Fluctuating Charge Ordering in the Pseudogap Phase of the Cuprates Via A Preformed Pair Approach, Yan He, Peter Scherpelz and K. Levin Phys. Rev. B 88, 064516 (2013)
- "Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energyof Angle Resolved Photoemission" Temperature Superconductors" Dan Wulin and K. Levin Phys. Rev. 86, 184513 (2012)
- Perfect fluids and Bad Metals: Insights from Ultracold Fermi gases. Hao Guo, D. Wulin, Chih-Chun Chien and K. Levin New Journal of Physics 13, 075011 (2011).
- Microscopic Approach to Viscosities in Superfluid Fermi Gases: From BCS to BEC. H. Guo, D. Wulin, Chih-Chun Chien, K. Levin Phys. Rev. Lett. 107, 020403 (2011).
- Establishing the Presence of Coherence in Atomic Fermi Superfluids: Spin Flip and Spin-Preserving Bragg Scattering at Finite Temperatures, Hao Guo, Chih-Chun Chien and K. Levin Phys. Rev. Lett 105, 120401 (2010).
- "BCS-BEC Crossover: From High Temperature Superconductors to Ultracold Super- fluids." Qijin Chen, Jelena Stajic, Shina Tan and K. Levin Physics Reports 412, 1 (2005).
- Heat Capacity of a strongly-Interacting Fermi Gas." J. Kinast, A. Turlapov, J.E. Thomas, Qijin Chen, Jelena Stajic, Science 307, 1296 (2005).