Report on
QS2C Theory Forum: International Symposium on
“Strongly Correlated Quantum Science”

This symposium was held by the budget of

The Theory Forum, one of the activities in the program “Quantum Science of Strongly Correlated Systems” (Core Researcher: Prof. Yoshinori Tokura, University of Tokyo and RIKEN) in “World–Leading Innovative R&D on Science and Technology (FIRST Program)” funded for 5 years (2010–2014) by the Japan Society for the Promotion of Science.

Organizers are R. Arita, A. Furusaki, N. Kawakami, H. Kawamura,
N. Nagaosa (Chair), and M. Ueda (alphabetical order). The scope of this workshop was to discuss the following themes in condensed matter physics;

  • Topological aspects of condensed matter
  • Spintronics and physics of spin systems
  • Bose condensation and cold atoms
  • First-principles calculations
  • Strong correlation
  • Superconductivity

The majority of the speakers were the theorists, and we also invited some distinguished experimentalists as guests.

On the first day (Jan. 26), there were one oral session and the poster preview session. In the first oral session “Spin Physics”, several recent issues in experiments and theories of spintronics and statistical mechanics of spin systems have been discussed including the role of spin orbit interaction in the current driven domain wall motion of ferromagnets, giant spin Hall effect, spin motive force, and the formation of spin textures and phase diagram in frustrated magnets. The topological nature of the spin systems was the common issue through all the presentations in this session, on which many interesting arguments were there. In the poster preview session, all the poster presentations were summarized within one minute for each. All the previews were well organized within the scheduled time slot.

On the second day (Jan. 27), there were 3 oral sessions and poster session. In the first oral session “Topological States”, recent experimental advances on topological insulators and topological superconductors, new theoretical formalism to define the quantum entanglement, and a theory of the new quantum state, i.e., the partially Kondo screened state coexisting with the ferromagnetic moment have been discussed. In the second oral session “Topological States”, the theoretical proposal and the experimental confirmation of “crystalline topological insulator”, topological interacting bosonic states, and odd frequency pairing and topological superconductors were discussed. The fruitful interplay between theories and experiments is impressive in this field.

In the afternoon, we had the poster session. Including the lunch time and break, more than 3 hours were available for the intensive discussion. Actually, the poster session site was crowded and vivid discussion was made all during this time period between young people and senior people.

In the third oral session “Quantum Coherence”, the experimental advances on unconventional p-wave superconductor Sr2RuO4, theoretical proposal and experimental detection of Berry/Zak phase in cold atom system, theoretical proposal to realize the Majorana fermion by the proximity effect between semiconductor and superconductor, and the thermal responses of topological superconductors have been discussed. The role of the quantum phase is the key and penetrating issue of these problems, and one could get some unified view during this session.

On the third day (Jan. 28), there were 4 oral sessions. In the first session “Electron Correlation”, the experimental study of the topological Hall effect in magnets, theory of anyon bose condensation in quantum spin system, and the topological aspects of He3 have been discussed. In the second session “Electron Correlation”, a new theory of the resonating valence bond state, theoretical proposals and experimental study of “valleytronics”, and the prediction of the superconducting Tc by the first-principles calculation have been reported. In the third session “Quantum Coherence”, a theory of a non-Fermi liquid in the spin chains coupled to metal, topological superconductors, and classification theory of BEC with spin-orbit interaction have been discussed. In the last session “Cold Atoms”, the diagrammatic quantum Monte Carlo method for many body systems, relaxation of disordered quantum system, topological excitations in cold atom systems have been discussed.

On the fourth day (Jan. 29), there are 3 oral sessions including one for contributed talks. In the first session “Topological States”, the recent advances on the spectroscopy of topological insulators, and the NMR and transport study of the Dirac fermions in organic conductor have been reported. In the second session for contributed talks, topological aspect of the magnon system, experimental study of magnetically doped topological insulators, theoretical proposals for silicene, universal three-body parameter in cold atom system, Lorenz microscope study of skyrmion system, and the spin nematic and spin density wave in spin system have been reported.

In the last session “Electron Correlation”, the experimental progress on the quantum critical phenomena in strongly correlated system, theoretical study on the nonlinear dispersion in Tomonaga-Luttinger liquid, a theoretical study of the real-time quantum dynamics in terms of Floquet theory, and a simulation of Skyrmion dynamics in magnets have been discussed.

To summarize, this symposium covered many of the hot topics in current condensed matter theory. Especially, the common issues among electronic systems, spin systems, and cold atoms were highlighted such as the topological states, generalized group theory, entanglement, and quantum dynamics. With the active participation of top researchers in this field, fruitful and stimulating discussion has been done during the symposium.

Jan. 30, 2013 Naoto Nagaosa