Quantum Criticality In Condensed Matter: Phenomena, Materials And Ideas In Theory And Experiment - 50th Karpacz Winter School Of Theoretical Physics

Phenomena, Materials and Ideas in Theory and Experiment

Janusz Jedrzejewski

• Publisher: WSPC
• Year: 2015
• ISBN:
  9789814704106
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

This volume comprises 8 articles written by lecturers of 50th Karpacz Winter School of Theoretical Physics and their collaborators. The contributing lecturers are outstanding researchers, and experts in various fields of physics, in particular in condensed matter, quantum phase transitions and quantum critical phenomena. The articles reflect the contents of the lectures given for school participants and cover various aspects of quantum phase transitions and quantum critical phenomena, from experimental to mathematical ones. For those wishing to get acquainted with the subject, extensive lists of references are provided in the articles.

Contents:

• The Enigma of the Pseudogap Phase of the Cuprate Superconductors (Debanjan Chowdhury and Subir Sachdev)
• Resonant Spin Excitations in Unconventional Heavy Fermion Superconductors and Kondo Lattice Comppounds (Peter Thalmeier and Alireza Akbari)
• Quantum Critical Heavy Fermion Metal YbRh 2 Si 2 (Gertrud Zwicknagl)
• Universality and Convergence of Energy Scales at Quantum Critical Points in Local and Lattice Models (A C Hewson, D J G Crow and Y Nishikawa)
• Beyond Particles: Unparticles in Strongly Correlated Electron Matter (Philip W Phillips)
• Fidelity Approach to Quantum Phase Transitions in Quantum Ising Model (Bogdan Damski)
• Dynamics of Quantum Phase Transitions: Quantum Kibble-Zurek Mechanism (Jacek Dziarmaga)
• Theory of Temporal Fluctuations in Isolated Quantum Systems (L Campos Venuti)

Readership: This book is suitable for graduate students and researchers who are interested in condensed matter, quantum phase transitions and quantum critical phenomena.
Key Features:

• Reviews of hot topics in condensed matter physics
• Unique, original presentations of discussed topics
• Prominent contributors

Resonant Spin Excitations in Unconventional Heavy Fermion
Superconductors and Kondo Lattice Compounds

Peter Thalmeier*

Max Planck Institute for Chemical Physics of Solids,
D-01187 Dresden, Germany
*E-mail: [email protected]
http://www.cpfs.mpg.de

Alireza Akbari

Asia Pacific Center for Theoretical Physics,
Dept. of Physics, and Max Planck POSTECH Center for Complex Phase Materials,
POSTECH, Pohang 790-784, Korea
E-mail: [email protected]
and
Max Planck Institute for Solid State Research,
D-70569 Stuttgart, Germany

The heavy quasiparticle bands in Kondo materials which originate in the hybridization of f- and conduction electrons exhibit numerous, sometimes coexisting, broken symmetry phases. Most notable are unconventional superconductivity, itinerant small moment antiferromagnetism and hidden order of higher order multipoles of f-electrons which all lead to a gapping of the heavy bands. In rare cases the chemical potential lies within the hybridization gap and the ground state is a Kondo semiconductor without ordering. The dynamical magnetic response of such gapped f-electron systems has been investigated with inelastic neutron scattering. It was found that collective spin exciton modes which are due to residual quasiparticle interactions appear below the threshold of superconducting or hidden order gap or directly the hybridzation gap. The spin exciton resonance is commonly located around a zone boundary vector

with nesting properties in the normal state. In the superconducting case its appearance gives a strong criterion for the gap symmetry requesting a sign change

due to the coherence factors. Therefore this many body effect with fundamental importance may also be used as a tool to discriminate between proposed gap models. While the spin resonance has been observed for many compounds we restrict our discussion here exclusively to the small group of f-electron superconductors CeCoIn₅, CeCu₂Si₂ and UPd₂Al₃, hidden order Kondo compounds CeB₆ and URu₂Si₂ as well as the Kondo semiconductor YbB₁₂.

Keywords: heavy fermion superconductors, Kondo lattice, feedback effect, spin exciton.

1. Introduction

The f-electron based heavy fermion systems, mostly intermetallic Ce- and U- compounds, are schematically described by Anderson-lattice type models which contain conduction electrons, localized f-electrons and a hybridization term. In mean-field approximation the effect of on-site f-electron correlations is taken into account by imposing a total on-site charge constraint on the average. Then the appearance of heavy hybridized bands and associated narrow density of states (DOS) peak around the Fermi level with a width of the order of the Kondo temperature T_K may be naturally explained¹. They are responsible for the typical heavy fermion anomalies in thermodynamic and transport quantities².

Furthermore residual interactions of the heavy quasiparticles which are on-site repulsive but inter-site attractive may lead to the formation of unconventional Cooper pairs and associated superconducting (SC) gap function^3,4. Its nontrivial symmetry implies the existence of nodes where the gap vanishes, leading to a power law behavior of the density of states (DOS) of SC quasiparticle excitations. The latter show up as power laws in the temperature dependence of physical quantities like specific heat, thermal conductivity and NMR relaxation which are the first typical signature of an unconventional superconductor. The unconventional gap symmetry not only modifies the low energy quasiparticle spectrum as compared to the f...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Preface
• The Enigma of the Pseudogap Phase of the Cuprate Superconductors
• Resonant Spin Excitations in Unconventional Heavy Fermion Superconductors and Kondo Lattice Compounds
• Quantum Critical Heavy Fermion Metal YbRh2Si2
• Universality and Convergence of Energy Scales at Quantum Critical Points in Local and Lattice Models
• Beyond Particles: Unparticles in Strongly Correlated Electron Matter
• Fidelity Approach to Quantum Phase Transitions in Quantum Ising Model
• Dynamics of Quantum Phase Transitions: Quantum Kibble-Zurek Mechanism
• Theory of Temporal Fluctuations in Isolated Quantum Systems