Solving strongly correlated fermions Anatoly Kuklov, (CSI, CUNY), (DMR-) PHY-1005527

1. Stress induced roughening of superclimbing dislocationsAnatoly Kuklov, (CSI, CUNY),(DMR-) PHY-1005527Boris V. Svistunov, (UMass, Amherst),(DMR-) PHY-1005543 Solid 4He continues puzzling researchers by its unusual properties for more than 50 years. In particular, some dislocations – linear defects of crystalline structure – in solid 4He have superfluid core so that atoms can flow without any resistance along it. With the help of Monte-Carlo simulations, we have found that imposing a small external stress on so called superclimbing edge dislocation can induce its roughening, so that it becomes able to climb with the help of the superflow along its core. Such roughening proceeds as a phase transition even at finite temperature which usually does not happen in 1D systems. As a result, the maximum speed of the superflow becomes significantly suppressed at the roughening temperature. We believe this effect can explain the suppression of the superflow through solid 4He observed by Ray & Hallock in the “Umass-Sandwich” experiment in 2010. The maximum superflow speed Vs versus temperature T (divided by its T=0 value). The curves are shown for several values of external stress F (given in the inset magnifying the dip structure). The transition results in a very narrow dip at T/To ~ 0.05, where To ~ 1K stands for a temperature at which the core superfluidity vanishes

2. Solving strongly correlated fermions Anatoly Kuklov, (CSI, CUNY),(DMR-) PHY-1005527 Boris V. Svistunov, (UMass, Amherst),(DMR-) PHY-1005543 Resonantly interacting cold fermions is a strongly correlated system of interest to condensed-matter, statistical, and high-energy physics because of its fundamental connections to high-Tc superconductivity, neutron matter, rich phase diagram, and polaron physics. For the first time this many-body problem was solved in the normal phase by the bold diagrammatic Monte Carlo (BDMC) technique which performs stochastic summation of millions of fully dressed irreducible Feynman diagrams. Excellent agreement with highly accurate thermodynamic data from MIT for 6Li at a Feshbach resonance establishes BDMC as a reliable unbiased theoretical tool for dealing with strongly correlated quantum matter. Pressure of the unitary gas in the normal phase normalized to the ideal Fermi gas pressure vs chemical potential. High precision data for 6Li atoms from the MIT group of M. Zweirlein (red points) perfectly agree with the theoretical calculation (blue points). Third-order virial expansion is shown by blue curve.

3. Solving strongly correlated fermions: Broader impacts Anatoly Kuklov, (CSI, CUNY),(DMR-) PHY-1005527 Boris V. Svistunov, (UMass, Amherst),(DMR-) PHY-1005543 Quantum magnetism Condensed matter Nuclear matter Particle physics There are numerous examples of key systems in nearly all disciplines of natural science: Standard model, Coulomb gas, localization, Hubbard model, charged polymers, just to name a few. Remarkably, it is possible to express answers for all of them in terms of series of Feynman diagrams. By demonstrating that new Monte Carlo methods can compute contributions from millions of irreducible self-consistent diagrams and reliably extrapolate answers to the infinite diagram order opens the door to solution of some of the most challenging problems across many fields. Results are obtained for thermodynamic (and finite) systems at any temperature, lattice, continuous, short-range, and long-range models can be dealt with by the same approach. FF FF Road to solution Feynman diagrams = Materials science Quantum chemistry Statistical mechanics Polymer science

4. Synergetic activities: Two international workshops Anatoly Kuklov, (CSI, CUNY),(DMR-) PHY-1005527 Boris V. Svistunov (UMass, Amherst),(DMR-) PHY-1005543 Organization of the International workshop Nonstandard superfluids and insulatorsat ICTP, Trieste, July 18-22, 2011. Recent years have seen remarkable progress in creating, exploring, and understanding novel states of matter which are found in realistic materials, prepared in table-top experiments, and imagined in theoretical models. These states challenge established dogmas, call for development of new physical concepts and methods of observation/detection, and have enormous potential for technological applications. The workshop brought together active researchers in the field to discuss its current status, address existing controversies and strategies for their resolution. It fostered closer collaboration between the theoretical and experimental groups including the design of next-generation experiments and first-principles simulations to test new ideas. Organization of the International workshop Supersolidity 2011 at the Graduate Center, CUNY, New York, June 7-10, 2011. (http://mcwa.csi.cuny.edu/supersolid). Among the most exciting discoveries in condensed matter physics in the last several years are the torsional oscillator anomaly (Kim & Chan, 2004) and the observation of a direct superflow through solid 4He (Ray & Hallock, 2008). These phenomena may be revealing a unique state of matter – supersolid in free space, that is, a substance made of simple 4He atoms which is simultaneously a solid and a superfluid. This workshop has provided an exciting opportunity for the international community of scientists to learn and exchange ideas on the latest developments around the world in the research of supersolidity phenomena and the fundamental nature of quantum solids in general.