Aspects of Quantum Criticality in Itinerant Electron Ferromagnetic Systems PDF Download

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

View

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: Martyn Laurence Lawley
Publisher:
ISBN:
Category :
Languages : en
Pages : 135

View

Book Description

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

View

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: Andreas W Rost
Publisher: Springer Science & Business Media
ISBN: 3642145248
Category : Science
Languages : en
Pages : 154

View

Book Description
Our department nominated this thesis for a Springer award because we regard it as an outstanding piece of work, carried out with a remarkable level of independence. Andreas Rost joined us in 2005, as one of the inaugural Prize Students of the Scottish Universities Physics Alliance. Our research group has been working on Sr Ru O , in collaboration with our colleagues in the group of Professor Y. Maeno 3 2 7 at Kyoto, since 1998. By early 2005 we had tantalising evidence that a novel phase was forming at very low temperatures, in an overall phase diagram dominated by quantum ?uctuations. We knew that comprehensive thermodynamic information would be needed in order to understand how this was happening, and that the demanding constraints of low temperature and high magnetic ?eld meant that bespoke apparatus would need to be constructed. Andreas had studied the speci?c heat of glasses below 50 mK during his diploma thesis work at Heidelberg, and was brimming with ideas about how to proceed. We gave him advice, and constantly discussed the physics with him, but quickly realised that the best way to proceed practically was to give him a budget, and let him take the main design decisions, double-checking with us from time to time.

Author: K.H.J. Buschow
Publisher: Elsevier
ISBN: 0444635386
Category : Science
Languages : en
Pages : 447

View

Book Description
Over the last few decades magnetism has seen an enormous expansion into a variety of different areas of research, notably the magnetism of several classes of novel materials that share with truly ferromagnetic materials only the presence of magnetic moments. Volume 23 of the Handbook of Magnetic Materials, like the preceding volumes, has a dual purpose. With contributions from leading authorities in the field, it includes a variety of self-contained introductions to a given area in the field of magnetism without requiring recourse to the published literature. It is also a reference for scientists active in magnetism research, providing readers with novel trends and achievements in magnetism. In each of these articles an extensive description is given in graphical as well as in tabular form, with much emphasis being placed on the discussion of the experimental material within the framework of physics, chemistry and material science. Comprises topical review articles written by leading authorities Introduces given topics in the field of magnetism Describes novel trends and achievements in magnetism

Author: Dieter Wagner
Publisher: Springer Science & Business Media
ISBN: 940115080X
Category : Science
Languages : en
Pages : 455

View

Book Description
A summary of recent developments in theoretical and experimental studies of fluctuation effects in itinerant electron magnets, focusing on novel physical phenomena: soft-mode spin fluctuations and zero-point effects, strong spin anharmonicity, magnetic frustrations in metals, fluctuation effects in Invar alloys and low-dimensional systems. All of these may be important for novel high-technology applications.

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

View

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: Daniel C. Cabra
Publisher: Springer Science & Business Media
ISBN: 3642104487
Category : Technology & Engineering
Languages : en
Pages : 380

View

Book Description
Condensed matter systems where interactions are strong are inherently difficult to analyze theoretically. The situation is particularly interesting in low-dimensional systems, where quantum fluctuations play a crucial role. Here, the development of non-perturbative methods and the study of integrable field theory have facilitated the understanding of the behavior of many quasi one- and two-dimensional strongly correlated systems. In view of the same rapid development that has taken place for both experimental and numerical techniques, as well as the emergence of novel testing-grounds such as cold atoms or graphene, the current understanding of strongly correlated condensed matter systems differs quite considerably from standard textbook presentations. The present volume of lecture notes aims to fill this gap in the literature by providing a collection of authoritative tutorial reviews, covering such topics as quantum phase transitions of antiferromagnets and cuprate-based high-temperature superconductors, electronic liquid crystal phases, graphene physics, dynamical mean field theory applied to strongly correlated systems, transport through quantum dots, quantum information perspectives on many-body physics, frustrated magnetism, statistical mechanics of classical and quantum computational complexity, and integrable methods in statistical field theory. As both graduate-level text and authoritative reference on this topic, this book will benefit newcomers and more experienced researchers in this field alike.

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

View

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: Dom Lal Kunwar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
The heavy fermions (HF) are strongly correlated electron systems consisting of intermetallic compounds of lanthanides and actinides ions with f -electrons unfilled shells. These systems are very rich in physics and the interplay between competing interactions results in various interesting physical phenomena such as heavy fermion behavior, unconventional superconductivity, non-Fermi-liquid behavior, coexistence of superconductivity and magnetism, and quantum criticality. The origin of such phenomena comes from the interaction of itinerant conduction states with the partially filled 4f - or 5f -electron states of rare earth elements. The study of such important physical phenomena can be possible by tuning the system using nonthermal control parameters, such as chemical composition, magnetic field, and applied pressure. So, studying the chemical pressure effect on heavy fermion systems with or without magnetic field is an intriguing idea to construct various phase diagrams and study their phase transitions. We performed heat capacity (HC), magnetoresistance (MR), and resistivity measurements on the Ce-based 115 and U-based 122 heavy fermion materials at low temperatures. We studied the nature of the quantum critical point, second-order phase transition, and the possible interplay between superconductivity and magnetism. First, we were motivated by the possibility of observing the coexistence of magnetism and unconventional superconductivity in the heavy fermion Ce1-xSmxCoIn5 alloys. We performed specific heat, MR, and resistivity measurements in different magnetic fields. We investigated how the samarium substitution on the cerium site affects the magnetic-field-tuned quantum criticality of stoichiometric CeCoIn5. We have observed Fermi-liquid to non-Fermi-liquid crossovers in the temperature dependence of the electronic specific heat and resistivity at higher external magnetic fields. We obtained the magnetic-field-induced quantum critical point (HQCP) by extrapolating the crossover temperature to zero temperature. Furthermore, we performed a scaling analysis of the electronic specific heat and confirmed the existence of the QCP. According to our findings, the magnitude of (HQCP) decreases as the samarium content rises and ultimately becomes zero. The electronic specific heat and resistivity data reveal a zero-field QCP for xcr = 0.15, which falls inside the antiferromagnetic and superconducting coexistence region. Next, we performed measurements of the heat capacity as a function of temperature in a single crystals URu2-xOsxSi2. Our experimental results show that the critical temperature of the second-order phase transition increases while the value of the Sommerfeld coefficient in the ordered state decreases with an increase in osmium concentration. We also observed the increase in the magnitude of the heat capacity at the critical temperature and a broadening of the critical fluctuations region with an increase in Os concentration. We analyze the experimental data using the Haule- Kotliar model, which identifies the 'hidden order' transition in the parent material URu2Si2 as a transition to a state with nonzero hexadecapolar moment. We showed that our experimental results are consistent with this model. In conclusion, we studied the interplay between superconductivity and magnetism in Ce based 115 and U based 122 single crystal alloys using heat capacity, magnetoresistivity, and resistivity measurements in both cryogenic systems including He-4 and He-3. The understating of various phenomena in these heavy fermions could be helpful in developing higher transition temperature superconductors, energy storage devices, quantum computers, and memory devices in the future.