Quantum Phase Transitions in Disordered Magnets PDF Download

Author: David Nozadze
Publisher:
ISBN:
Category : Ferromagnetism
Languages : en
Pages : 152

View

Book Description
"We study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual spatial regions can order independently of the bulk system. In paper I, we study smeared quantum phase transitions in binary alloys A[subscript 1-x]B[subscript x] that are tuned by changing the composition x. We show that in this case the ordered phase is extended over all compositions x

Author: Subir Sachdev
Publisher: Cambridge University Press
ISBN: 113950021X
Category : Science
Languages : en
Pages : 521

View

Book Description
Describing the physical properties of quantum materials near critical points with long-range many-body quantum entanglement, this book introduces readers to the basic theory of quantum phases, their phase transitions and their observable properties. This second edition begins with a new section suitable for an introductory course on quantum phase transitions, assuming no prior knowledge of quantum field theory. It also contains several new chapters to cover important recent advances, such as the Fermi gas near unitarity, Dirac fermions, Fermi liquids and their phase transitions, quantum magnetism, and solvable models obtained from string theory. After introducing the basic theory, it moves on to a detailed description of the canonical quantum-critical phase diagram at non-zero temperatures. Finally, a variety of more complex models are explored. This book is ideal for graduate students and researchers in condensed matter physics and particle and string theory.

Author: Fawaz Y. Hrahsheh
Publisher:
ISBN:
Category : Ferromagnetism
Languages : en
Pages : 146

View

Book Description
"Disorder can have a wide variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this thesis we study the effects of disorder on several classical and quantum phase transitions in condensed matter systems. After a brief introduction, we study the ferromagnetic phase transition in a randomly layered Heisenberg magnet using large-scale Monte-Carlo simulations. Our results provide numerical evidence for the exotic infinite-randomness scenario. We study classical and quantum smeared phase transitions in substitutional alloys A[subscript 1-x]B[subscript x]. Our results show that the disorder completely destroys the phase transition with a pronounced tail of the ordered phase developing for all compositions x

Author: Gerard Perren
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: Subir Sachdev
Publisher: Cambridge University Press
ISBN: 9780521004541
Category : Mathematics
Languages : en
Pages : 374

View

Book Description
Quantum Phase Transitions is the first book to describe in detail the fundamental changes that can occur in the macroscopic nature of matter at zero temperature due to small variations in a given external parameter. The subject plays a central role in the study of the electrical and magnetic properties of numerous important solid state materials. The author begins by developing the theory of quantum phase transitions in the simplest possible class of non-disordered, interacting systems - the quantum Ising and rotor models. Particular attention is paid to their non-zero temperature dynamic and transport properties in the vicinity of the quantum critical point. Several other quantum phase transitions of increasing complexity are then discussed and clarified. Throughout, the author interweaves experimental results with presentation of theoretical models, and well over 500 references are included. The book will be of great interest to graduate students and researchers in condensed matter physics.

Author: Zhiyuan Yao
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
In this dissertation, we study the superfluid-insulator quantum phase transition in disordered boson systems. Recently, there has been considerable controversy over the validity of the scaling relations of the superfluid--Bose-glass quantum phase transition in three dimensions. Results from experimental and numerical studies on disordered quantum magnets contradict the scaling relations and the associated conventional scaling hypothesis for the singular part of the free energy. We determine various critical exponents of the superfluid--Bose-glass quantum phase transition in three-dimensional disordered Bose-Hubbard model through extensive Monte Carlo simulations. Our numerical study shows the previous studies on disordered quantum magnets were performed outside the quantum critical region, and our results for the critical exponents are in perfect agreement with previous theoretical predictions. We next move to study theoretically and numerically the superfluid-insulator quantum phase transition in one-dimensional disordered boson systems. While the superfluid-insulator transition in the weak disorder limit is well understood through the perturbative renormalization group study by Giamarchi and Schulz, transitions in the strong disorder regime are beyond the reach of this method. This problem was recently attacked by Altman et al. with the real space renormalization group method. They reached the conclusion that the superfluid-insulator transition in the strong disorder regime can be explained by the Coulomb blockade physics of weak links. However, their method is actually uncontrolled. Taking account of the crucial role of the hydrodynamic renormalization of weak links, finally, Pollet et al. put forward an asymptotically exact renormalization group theory of the superfluid-insulator transition. Based on this theory, we are able to provide an accurate description of the interplay between the well-known Giamarchi-Schulz criticality and the new weak-link criticality. A significant part of the ground-state phase diagram of one-dimensional disordered Bose-Hubbard model at unit filling is also determined numerically. In particular, we established the position of the multicritical point beyond which the new weak-link criticality takes over of the Giamarchi - Schulz criticality.

Author: Sara Ubaid-Kassis
Publisher:
ISBN:
Category : Ferromagnetism
Languages : en
Pages : 114

View

Book Description
The study of quantum phase transitions (QPT) provides a new route to find and understand unconventional phases in condensed matter physics. The presently studied alloy, Ni(1-x)Vx, offers an opportunity to investigate a ferromagnetic quantum phase transition, a transition from a ferromagnetic ordered state into a paramagnetic state at T = 0 K, by varying the vanadium concentration, x. Magnetization and transport measurements are used to probe the critical behavior of the phase transition and characterize the onset of "unconventional behavior" such as non-Fermi liquid behavior, which signals a deviation from Fermi liquid theory, a fundamental concept in metals. Towards 11.2 % vanadium, the Curie temperature (Tc) is reduced to zero from its pure nickel value of Tc = 627 K. The critical behavior of the phase transition in samples with the higher nickel content (x 11%) at a finite Tc essentially follows theories as expected for weak itinerant magnets. The samples with more vanadium (x 11.2%) do not show a conventional ferromagnetic transition or the typical properties of an ordinary paramagnet. Instead, we see evidence for power laws with unusual exponents in the temperature dependence of the magnetization and the resistivity due to an inhomogeneous magnetic moment distribution. We compare our data findings with recent theories addressing a new critical scenario, quantum phase transitions with disorder. One signature is a Quantum Griffiths' phase which is observed as power laws with non-universal exponents heading towards a T-> 0 instability. At very low temperatures, the quantum Griffiths phase in Ni-V leads to the formation of a frozen cluster glass phase. To our knowledge, our compound is the first to experimentally show all signatures of a quantum Griffiths phase in an extended regime, and therefore provides an ideal model system for a disordered itinerant 3-d Heisenberg system.

Author: Robert Alan Pelcovits
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: Praveen Chaddah
Publisher: CRC Press
ISBN: 1351651935
Category : Science
Languages : en
Pages : 243

View

Book Description
This book introduces new concepts in the phenomenon of 1st order phase transitions. It discusses the concept of kinetic arrest at a certain temperature, with this temperature being dependent on the second control variable (magnetic field, or pressure). It discusses interesting manifestations of this phenomenon when the 1st order transition is broadened, i.e. occurs over a finite range of temperatures. Many examples of this phenomenon, observed recently in many materials, will also be discussed.

Author: Vladimir Dobrosavljevic
Publisher: Oxford University Press
ISBN: 0191642169
Category : Science
Languages : en
Pages :

View

Book Description
Quantum phase transitions describe the violent rearrangement of electrons or atoms as they evolve from well defined excitations in one phase to a completely different set of excitations in another. The chapters in this book give insights into how a coherent metallic or superconducting state can be driven into an incoherent insulating state by increasing disorder, magnetic field, carrier concentration and inter-electron interactions. The problem necessarily involves many interacting particles and therein lies the challenge to develop a multi-faceted theory. Experiments probing microscopic structure, transport, charge and spin dynamics provide important clues. What sets this book apart is a strong dialog between experiment and theory that has the potential to solve some major issues in many-body physics. The ideas and methods developed here are bound to have repercussions in all spheres of physics.