Author: Sharon Lynn Sessions
Publisher:
ISBN:
Category : Condensed matter
Languages : en
Pages : 450

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Book Description

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

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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: Ruizhe Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
The study of quantum phase transitions (QPT) is a promising route to comprehend the origin of unconventional properties in strongly correlated electron systems. Recent theories predict a new quantum critical point (QCP) in disordered itinerant system with exotic properties such as observable quantum Griffiths phase (QGP). The binary alloy Ni-V presents such QGP and looks like the best example to study a ferromagnetic QPT with controlled disorder. In this work, we investigate further Ni-V with advanced local methods using neutron scattering and [mu]SR techniques. Initial doubts on sample quality and sample-dependent impact on different magnetic phases and disordered scenarios can be resolved. A structural characterization indicates that the investigated Ni-V samples show a high-quality chemical structure with expected random atomic distribution. We provide direct evidence of the "disorder" with [mu]SR methods. We clarify essential details of the Ni-V phase diagram such as the nature and the boundaries of ferromagnetic and cluster glass phases. These new data reinforce the location of the QCP and the limits of the QGP in Ni-V. The main results are consistent with theories predicting an infinite randomness quantum critical point associated with a QGP.

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

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Book Description
Fermi-liquid theory is one of the standard models of condensed matter physics, supplying a valid explanation of the low temperature properties of many metals. However, non-Fermi-liquid behaviours arise in many itinerant systems that exhibit a zero temperature magnetic phase transition. This thesis is mainly concerned with such quantum critical points and is an investigation into the various phenomena seen in the phase diagram of itinerant ferromagnetic systems. We apply a standard theory of itinerant quantum criticality to a quantum-critical end-point in a three-dimensional ferromagnet, before speculating on ZrZn\(_2\) being a test-bed of our results. Then we consider two explanations for the appearance of a first-order phase transition at low temperatures and attempt to reconcile them with ZrZn\(_2\). Finally we concentrate on the wide range of novel states that appear instead of a pure quantum critical point. Such exotic phases are superconducting or magnetic in nature and we investigate whether the onset of ferromagnetic quantum critical fluctuations can give rise to a certain class of such states.

Author: Rastko Sknepnek
Publisher:
ISBN:
Category : Phase transformations (Statistical physics)
Languages : en
Pages : 246

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Book Description
"Quantum phase transitions occur at zero temperature as a function of some non-thermal parameter, e.g., pressure or chemical composition. In addition to being of fundamental interest, quantum phase transitions are important because they are believed to underlie a number of interesting low temperature phenomena. Quantum phase transitions differ from the classical phase transitions in many important aspects, two of them being (i) the mode-coupling effects and (ii) the behavior in the presence of disorder. We devote two projects of this dissertation to each of the two."--Abstract, p. iv.

Author: Raymond F Bishop
Publisher: World Scientific
ISBN: 9814489190
Category : Science
Languages : en
Pages : 520

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Book Description
Quantum many-body theory as a discipline in its own right dates largely from the 1950's. It has developed since then to its current position as one of the cornerstones of modern theoretical physics. The field remains vibrant and active, vigorous and exciting. Its most powerful techniques are truly universal. They are constantly expanding to find new fields of application, while advances continue to be made in the more traditional areas. To commemorate the impending 80th birthdays of its two co-inventors, Firtz Coester and Hermann Kümmel, one such technique, namely the coupled cluster method, was especially highlighted at this meeting, the eleventh in the series of International Conferences on Recent Progress in Many-Body Theories. The history of the coupled cluster method as told here mirrors in many ways both the development of the entire discipline of microscopic quantum many-body theory and the history of the series of conferences. The series itself is universally recognised as being the premier series of meetings in this subject area. Its proceedings have always summarised the current state of the art through the lectures of its leading practitioners. The present volume is no exception. No serious researcher in quantum many-body theory or in any field which uses it can afford to be without this volume.

Author: Una Karahasanovic
Publisher:
ISBN:
Category : Condensed matter
Languages : en
Pages : 236

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Book Description
The formation of new phases close to itinerant electron quantum critical points has been observed experimentally in many compounds. We present a unified analytical model that explains the emergence of new types of phases around itinerant ferromagnetic quantum critical points. The central idea of our analysis is that certain deformations of the Fermi surface enhance the phase-space available for low-energy quantum fluctuations and so self-consistently lower the free energy. Using this quantum order-by-disorder mechanism, we find instabilities towards the formation of a spiral ferromagnet and spin-nematic phase close to an itinerant ferromagnetic quantum critical point. Further, we employ the quantum order-by-disorder mechanism to describe the partially ordered phase of MnSi. Using the simplest model of a Stoner-like helimagnetic transition, we show that quantum fluctuations naturally lead to the formation of an unusual phase near to the putative quantum critical point that shares many of the observed features of the partially ordered phase in MnSi. In particular, we predict an angular dependence of neutron scattering that is in good agreement with neutron-scattering data.

Author: John Karkheck
Publisher: Springer Science & Business Media
ISBN: 940114365X
Category : Science
Languages : en
Pages : 512

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Book Description
Recent years have witnessed a resurgence in the kinetic approach to dynamic many-body problems. Modern kinetic theory offers a unifying theoretical framework within which a great variety of seemingly unrelated systems can be explored in a coherent way. Kinetic methods are currently being applied in such areas as the dynamics of colloidal suspensions, granular material flow, electron transport in mesoscopic systems, the calculation of Lyapunov exponents and other properties of classical many-body systems characterised by chaotic behaviour. The present work focuses on Brownian motion, dynamical systems, granular flows, and quantum kinetic theory.

Author: Yurij Holovatch
Publisher: World Scientific
ISBN: 9811216231
Category : Science
Languages : en
Pages : 294

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Book Description
This book is the sixth volume of reviews on advanced problems of phase transitions and critical phenomena, with the first five volumes appearing in 2004, 2007, 2012, 2015, and 2018. It aims to provide an overview of those aspects of criticality and related topics that have attracted much attention due to the recent contributions. The six chapters discuss criticality of complex systems, where the new, emergent properties appear via collective behaviour of simple elements. Since all complex systems involve cooperative behaviour between many interconnected components, the field of phase transitions and critical phenomena provides a very natural conceptual and methodological framework for their study.As for the previous volumes, this book is based on the review lectures that were given in Lviv (Ukraine) at the 'Ising lectures' — a traditional annual workshop on phase transitions and critical phenomena which aims to bring together scientists working in the field of phase transitions with university students and those who are interested in the topic.The level of presentation makes the book readable both for professionals and the students in the field. On a larger scale, the book may contribute to promoting and deepening studies of phase transitions and critical phenomena.

Author: Raymond F. Bishop
Publisher: World Scientific
ISBN: 9812777849
Category : Science
Languages : en
Pages : 520

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Book Description
Quantum many-body theory as a discipline in its own right dates largely from the 1950's. It has developed since then to its current position as one of the cornerstones of modern theoretical physics. The field remains vibrant and active, vigorous and exciting. Its most powerful techniques are truly universal. They are constantly expanding to find new fields of application, while advances continue to be made in the more traditional areas. To commemorate the impending 80th birthdays of its two co-inventors, Firtz Coester and Hermann Kummel, one such technique, namely the coupled cluster method, was especially highlighted at this meeting, the eleventh in the series of International Conferences on Recent Progress in Many-Body Theories. The history of the coupled cluster method as told here mirrors in many ways both the development of the entire discipline of microscopic quantum many-body theory and the history of the series of conferences. The series itself is universally recognised as being the premier series of meetings in this subject area. Its proceedings have always summarised the current state of the art through the lectures of its leading practitioners. The present volume is no exception. No serious researcher in quantum many-body theory or in any field which uses it can afford to be without this volume.