Piatkový seminár fyziky - Jozef Strečka (22.1.2016)

v piatok 22.1.2016 o 14:00 hod. v miestnosti F2/272

18. 01. 2016 13.04 hod.
Od: Peter Markoš

Prednášajúci: doc RNDr. Jozef Strečka, PhD. (UPJŠ Košice)

Názov prednášky: Exotic quantum states of matter in frustrated spin systems: insights from rigorous and perturbation approaches

Termín: 22.1.2016, 14:00 hod., F2/272

After a brief introduction into statistical mechanics of two basic localized spin models, i.e. the Ising and Heisenberg model, theoretical and experimental motivation for an investigation of various geometrically frustrated spin systems will be clarified. The main part of the talk will be devoted to a rigorous analysis of three exactly solvable spin-1/2 Ising-Heisenberg models with a magnetic structure of: (i) the frustrated twoleg ladder, (ii) dimer-plaquette chain, and (iii) Shastry-Sutherland lattice. The frustrated Ising-Heisenberg two-leg ladder will be explored in connection with a quantum phase transition between a quantum ordered (Neel or stripe) phase and a disordered paramagnetic phase. The exactly solved spin-1/2 Ising-Heisenberg dimer-plaquette chain exhibits in a zero-temperature magnetization curve a few intermediate plateaus of quantum origin. In addition, it will be demonstrated that this frustrated spin model can be used as a useful starting ground for an investigation of the purely quantum Heisenberg dimer-plaquette chain within the many-body perturbation theory. Last but not least, the exact solution will be presented for the ground state of the spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice, which displays outstanding stripe and checkerboard ordering of singlet and triplet states within the one-third and one-half magnetization plateaus. The relevance of these theoretical implications for the experimental magnetization curve of polymeric coordination compound SrCu(BO3)2 will be discussed.