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Full-Text Articles in Physics
Theory Of Smeared Quantum Phase Transitions, Jose A. Hoyos, Thomas Vojta
Theory Of Smeared Quantum Phase Transitions, Jose A. Hoyos, Thomas Vojta
Physics Faculty Research & Creative Works
We present an analytical strong-disorder renormalization group theory of the quantum phase transition in the dissipative random transverse-field Ising chain. For Ohmic dissipation, we solve the renormalization flow equations analytically, yielding asymptotically exact results for the low-temperature properties of the system. We find that the interplay between quantum fluctuations and Ohmic dissipation destroys the quantum critical point by smearing. We also determine the phase diagram and the behavior of observables in the vicinity of the smeared quantum phase transition.
Effects Of Dissipation On A Quantum Critical Point With Disorder, Jose A. Hoyos, Chetan Kotabage, Thomas Vojta
Effects Of Dissipation On A Quantum Critical Point With Disorder, Jose A. Hoyos, Chetan Kotabage, Thomas Vojta
Physics Faculty Research & Creative Works
We study the effects of dissipation on a disordered quantum phase transition with O(N) order-parameter symmetry by applying a strong-disorder renormalization group to the Landau-Ginzburg-Wilson field theory of the problem. We find that Ohmic dissipation results in a nonperturbative infinite-randomness critical point with unconventional activated dynamical scaling while super-Ohmic damping leads to conventional behavior. We discuss applications to the superconductor-metal transition in nanowires and to the Hertz theory of the itinerant antiferromagnetic transition.
Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta
Percolation Transition And Dissipation In Quantum Ising Magnets, Jose A. Hoyos, Thomas Vojta
Physics Faculty Research & Creative Works
We study the effects of dissipation on a randomly diluted transverse-field Ising magnet close to the percolation threshold. For weak transverse fields, a percolation quantum phase transition separates a superparamagnetic cluster phase from an inhomogeneously ordered ferromagnetic phase. The properties of this transition are dominated by large frozen and slowly fluctuating percolation clusters. This leads to a discontinuous magnetization-field curve and exotic hysteresis phenomena as well as highly singular behavior of magnetic susceptibility and specific heat. We compare our results to the smeared transition in generic dissipative random quantum Ising magnets. We also discuss the relation to metallic quantum magnets …
Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta
Slow Dynamics At The Smeared Phase Transition Of Randomly Layered Magnets, Shellie Huether, Ryan Kinney, Thomas Vojta
Physics Faculty Research & Creative Works
We investigate a model for randomly layered magnets, viz., a three-dimensional Ising model with planar defects. The magnetic phase transition in this system is smeared because static long-range order can develop on isolated rare spatial regions. Here, we report large-scale kinetic Monte Carlo simulations of the dynamical behavior close to the smeared phase transition, which we characterize by the spin (time) autocorrelation function. In the paramagnetic phase, its behavior is dominated by Griffiths effects similar to those in magnets with point defects. In the tail region of the smeared transition the dynamics is even slower: the autocorrelation function decays like …
Critical Behavior And Griffiths Effects In The Disordered Contact Process, Thomas Vojta, Mark Dickison
Critical Behavior And Griffiths Effects In The Disordered Contact Process, Thomas Vojta, Mark Dickison
Physics Faculty Research & Creative Works
We study the nonequilibrium phase transition in the one-dimensional contact process with quenched spatial disorder by means of large-scale Monte Carlo simulations for times up to 109 and system sizes up to 107 sites. In agreement with recent predictions of an infinite-randomness fixed point, our simulations demonstrate activated (exponential) dynamical scaling at the critical point. The critical behavior turns out to be universal, even for weak disorder. However, the approach to this asymptotic behavior is extremely slow, with crossover times of the order of 104 or larger. In the Griffiths region between the clean and the dirty critical points, we …
Quantum Griffiths Effects In Itinerant Heisenberg Magnets, Thomas Vojta, Jörg Schmalian
Quantum Griffiths Effects In Itinerant Heisenberg Magnets, Thomas Vojta, Jörg Schmalian
Physics Faculty Research & Creative Works
We study the influence of quenched disorder on quantum phase transitions in itinerant magnets with Heisenberg spin symmetry, paying particular attention to rare disorder fluctuations. In contrast to the Ising case where the Landau damping of the spin fluctuations suppresses the tunneling of the rare regions, the Heisenberg system displays strong power-law quantum Griffiths singularities in the vicinity of the quantum critical point. We discuss these phenomena based on general scaling arguments, and we illustrate them by an explicit calculation for O(N) spin symmetry in the large-N limit. We also discuss broad implications for the classification of quantum phase transitions …
Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta
Smeared Phase Transition In A Three-Dimensional Ising Model With Planar Defects: Monte Carlo Simulations, Rastko Sknepnek, Thomas Vojta
Physics Faculty Research & Creative Works
We present results of large-scale Monte Carlo simulations for a three-dimensional Ising model with short-range interactions and planar defects, i.e., disorder perfectly correlated in two dimensions. We show that the phase transition in this system is smeared, i.e., there is no single critical temperature, but different parts of the system order at different temperatures. This is caused by effects similar to but stronger than Griffiths phenomena. In an infinite-size sample there is an exponentially small but finite probability to find an arbitrary large region devoid of impurities. Such a rare region can develop true long-range order while the bulk system …