DISORDER EFFECTS IN FRUSTRATED MAGNETS AND ABSORBING STATE TRANSITIONS

<p>"Correlation, topology, and disorder can fundamentally affect the properties of interacting many-particle systems. After a short introduction which covers the basic concepts of phase transitions and scaling as well as the physics of Josephson junctions, the dissertation focuses on three separate projects.</p> <p>The first project is motivated by the stripe and nematic phases observed e.g. in cuprate superconductors and iron pnictides. To understand the effects of disorder on such phases, we have investigated the behavior of the diluted J₁-J₂ Ising model. Spinless impurities generate a random-field disorder for the spin-density (stripe) order parameter, which destroys the stripe phase. Combining symmetry arguments, percolation theory and Monte Carlo simulations, we show that a weak spatial interaction anisotropy restores the stripe phase. Moreover, we determine the phase diagram and explain it using percolation theory. We also analyze the critical behavior of the transition into the stripe phase.</p> <p>Many-particle systems far from thermal equilibrium can undergo abrupt transitions between different steady states which resemble thermal transitions. In the second project, we have studied the absorbing-state phase transition of the 1-D contact process, which can be understood as a model of epidemic spreading, under the combined influence of spatial and temporal disorders. We discuss the stability of the directed percolation universality class against such disorder, and then perform Monte Carlo simulations to confirm our theory. We also investigate the Griffiths singularities that accompany the nonequilibrium transition.</p> <p>In the third project, we have constructed unconventional Josephson junctions by coupling superconducting Nb leads to the surface states of a SmB₆ crystal. We have found a robust critical current at low temperatures which responds to out-of-phase magnetic fields. This behaviour significantly deviates from the usual Fraunhofer patterns, forming so-called Shaphiro steps. We have also found the effects of Kondo breakdown in our devices, as well as the coexistence of magnetism with superconductivity at the SmB₆ surface"--Abstract, p. iv</p>

Name thesis:degree_name

Ph. D. in Physics

Grantor

Missouri University of Science and Technology

Author dc:creator

• Ye, Xuecheng

• Physical Sciences and Mathematics
• Physics

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3246

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4251