Freiburg 2019 – wissenschaftliches Programm
FM 59.6: Talk
Mittwoch, 25. September 2019, 15:15–15:30, 3043
Quantum phases and quantum phase transitions in frustrated networks of Josephson junctions — •Mikhail Fistul1,2 and Alexei Andreanov1 — 1Center for Theoretical Physics of Complex Systems, Institute for Basic Science (IBS), Daejeon, Republic of Korea — 2National University of Science and Technology MISiS, Russian Quantum Center, Moscow, Russia
We present a theoretical study of spatial correlations of Josephson phases in frustrated quantum networks of Josephson junctions. We focus on one-dimensional sawtooth chains where frustration arises due to the Josephson couplings having alternating signs in a single lattice cell of our model. The classical nonlinear dynamics of such system  shows the crossover from non-frustrated to frustrated regimes at the critical value of frustration, fc. Such crossover is characterized by the thermodynamic spatial correlation functions of phases on vertices, ϕn, i.e. C(n−m)=⟨ cos(ϕn−ϕm) ⟩ displaying the transition from long- to short-range spatial correlations.
In the quantum regime using a direct mapping to the classical one- or two-dimensional lattices of spins with alternating sign long-range interactions, we obtain the zero temperature phase diagram (√Ec/EJ)-f, where Ec and EJ are the charge and Josephson coupling energies, respectively. The various macroscopic quantum phases, e.g. quantum vortices/antivortices, quantum vortex-antivortex pairs, quantum superposition states, quantum strip phases, are discussed.
 A. Andreanov and M. V. Fistul, J. Phys. A: Math. Theor. 52, 105101 (2019).