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Author: Renyuan Liao
Publisher:
ISBN:
Category : Bose-Einstein condensation
Languages : en
Pages : 215
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Book Description
This dissertation covers my theoretical work in the field of pairing of fermions and BCS-BEC crossover behavior in various condensed matter systems. High temperature superconductors, heavy fermion systems, 2D semiconductors undergoing a semiconductor-superconductor transition, and ultracold atomic Fermi gases are examples of novel systems that provide us with a rich playground to study pairing phenomena such as superconductivity or superfluidity. In this dissertation, with ultracold fermions in mind, I attempt to address some of the outstanding theoretical issues regarding pairing of fermions for arbitrary interactions, and for arbitrary population and mass imbalance. In so doing, I explore pairing in Bose-Einstein condensation EC) and Bardeen-Cooper-Schrieffer CS) regimes, and the behavior at the BEC-BCS crossover. I investigate the stability of paired many-fermion ground states, e.g., superfluidity and phase separated states; and possible phase transitions between these ground states. The specific projects that I undertake at the mean-field level are: interplay of intra- and inter- species pairing correlations in determining s-wave pairing in spin-population imbalanced Fermi systems; p-wave pairing in systems with mismatched fermi surfaces; stability of "breached pairs" states with p-wave symmetry in BEC and BCS regimes; use of Bogoliubov-de Gennes equations to study spatial variation of the pairing order parameter; and superconductivity with unconventional pairing symmetries in 2D systems with an "inherent" gaps, such as in semiconducting systems. In the case of s-wave pairing in a spin-population imbalanced system, while the system phase separates into normal and superfluid components, I show that the inclusion of intra-species correlation stabilizes a supefluid phase, up to a critical polarization, on the BCS side. For S=1, ms=0 triplet p-wave pairing in a population imbalanced system, I obtain a rich phase diagram. In addition to the states Δ"1 propto Y1"1, a multitude of "mixed" SF states formed of linear combinations of Y1m's give global energy minimum under a phase stability condition. States with local minimum are also obtained. With increased polarization, the global minimum SF states may undergo a quantum phase transition to the local minimum SF states. I also study effects of finite temperature (T) and of mass imbalance (r) between the species. Though the features of the phase diagram are not changed qualitatively from the equal mass (r=1) case, the critical temperature Tc shows some interesting behavior for large polarization. Our p-wave pairing provides an arena to study "breached pairing" P), i.e., phase separation in momentum space. While this is not stable in BCS regime for s-wave pairing, I find that p-wave BP phases may be stable in both BCS and BEC regimes for arbitrary mass ratio, r. To explore many-body effects beyond mean-field, I study the effects of quantum fluctuations on equilibrium and pairing properties in BEC and BCS regimes and near the crossover (unitarity limit). I apply this to systems subjected to p-wave Feshbach resonance and compare with the results for the s-wave case. I also study the effects of these fluctuations on possible suppression of the superfluid transition temperature from dilute to dense regimes and at unitarity, and find the suppression factor of 2.2 to be quite robust, except close to unitarity. Specific systems to which my work may apply are population imbalanced cold atomic systems, 2D systems with "inherent gap", such as semiconducting systems, and strongly correlated Fermi systems close to the unitarity limit at the BEC-BCS crossover. My research utilizes method of many-body quantum field theory, quantum statistical mechanics, diagrammatic perturbation theory, notions of superconductivity and superfluidity at and beyond mean-field level. In many instances, I have developed detailed and reliable computer codes relevant to my work.
Author: Renyuan Liao
Publisher:
ISBN:
Category : Bose-Einstein condensation
Languages : en
Pages : 215
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Book Description
This dissertation covers my theoretical work in the field of pairing of fermions and BCS-BEC crossover behavior in various condensed matter systems. High temperature superconductors, heavy fermion systems, 2D semiconductors undergoing a semiconductor-superconductor transition, and ultracold atomic Fermi gases are examples of novel systems that provide us with a rich playground to study pairing phenomena such as superconductivity or superfluidity. In this dissertation, with ultracold fermions in mind, I attempt to address some of the outstanding theoretical issues regarding pairing of fermions for arbitrary interactions, and for arbitrary population and mass imbalance. In so doing, I explore pairing in Bose-Einstein condensation EC) and Bardeen-Cooper-Schrieffer CS) regimes, and the behavior at the BEC-BCS crossover. I investigate the stability of paired many-fermion ground states, e.g., superfluidity and phase separated states; and possible phase transitions between these ground states. The specific projects that I undertake at the mean-field level are: interplay of intra- and inter- species pairing correlations in determining s-wave pairing in spin-population imbalanced Fermi systems; p-wave pairing in systems with mismatched fermi surfaces; stability of "breached pairs" states with p-wave symmetry in BEC and BCS regimes; use of Bogoliubov-de Gennes equations to study spatial variation of the pairing order parameter; and superconductivity with unconventional pairing symmetries in 2D systems with an "inherent" gaps, such as in semiconducting systems. In the case of s-wave pairing in a spin-population imbalanced system, while the system phase separates into normal and superfluid components, I show that the inclusion of intra-species correlation stabilizes a supefluid phase, up to a critical polarization, on the BCS side. For S=1, ms=0 triplet p-wave pairing in a population imbalanced system, I obtain a rich phase diagram. In addition to the states Δ"1 propto Y1"1, a multitude of "mixed" SF states formed of linear combinations of Y1m's give global energy minimum under a phase stability condition. States with local minimum are also obtained. With increased polarization, the global minimum SF states may undergo a quantum phase transition to the local minimum SF states. I also study effects of finite temperature (T) and of mass imbalance (r) between the species. Though the features of the phase diagram are not changed qualitatively from the equal mass (r=1) case, the critical temperature Tc shows some interesting behavior for large polarization. Our p-wave pairing provides an arena to study "breached pairing" P), i.e., phase separation in momentum space. While this is not stable in BCS regime for s-wave pairing, I find that p-wave BP phases may be stable in both BCS and BEC regimes for arbitrary mass ratio, r. To explore many-body effects beyond mean-field, I study the effects of quantum fluctuations on equilibrium and pairing properties in BEC and BCS regimes and near the crossover (unitarity limit). I apply this to systems subjected to p-wave Feshbach resonance and compare with the results for the s-wave case. I also study the effects of these fluctuations on possible suppression of the superfluid transition temperature from dilute to dense regimes and at unitarity, and find the suppression factor of 2.2 to be quite robust, except close to unitarity. Specific systems to which my work may apply are population imbalanced cold atomic systems, 2D systems with "inherent gap", such as semiconducting systems, and strongly correlated Fermi systems close to the unitarity limit at the BEC-BCS crossover. My research utilizes method of many-body quantum field theory, quantum statistical mechanics, diagrammatic perturbation theory, notions of superconductivity and superfluidity at and beyond mean-field level. In many instances, I have developed detailed and reliable computer codes relevant to my work.
Author: Mark Gower Alford
Publisher: World Scientific
ISBN: 9812773045
Category : Science
Languages : en
Pages : 298
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Book Description
Cooper pairing of fermions is a profound phenomenon that has become very important in many different areas of physics in the recent past. This book brings together, for the first time, experts from various fields involving Cooper pairing, at the level of BCS theory and beyond, including the study of novel states of matter such as ultracold atomic gases, nuclear systems at the extreme, and quark matter with application to neutron stars. Cross-disciplinary in nature, the book will be of interest to physicists in many different specialties, including condensed matter, nuclear, high-energy, and astrophysics. The emphasis is on novel issues beyond ordinary BCS theory such as pairing in asymmetric systems, the polarization effect, and higher spin pairing. These topics are rarely treated at the textbook level and all of them are the subjects of intensive ongoing research. The book also considers various new techniques widely used in current research that differ significantly from the conventional condensed matter approaches described in the standard literature. Sample Chapter(s). Chapter 1: Color Superconductivity in Dense, but not Asymptotically Dense, Quark Matter (1,976 KB). Contents: Color Superconductivity in Dense, But Not Asymptotically Dense, Quark Matter (M Alford & K Rajagopal); Larkin-Ovchinnikov-Fulde-Ferrell Phases in QCD (G Nardulli); Phase Diagram of Neutral Quark Matter at Moderate Densities (S B Rster et al.); Spontaneous Nambu-Goldstone Current Generation Driven by Mismatch (M Huang); The CFL Phase and m s: An Effective Field Theory Approach (T Schnfer); Nuclear Superconductivity in Compact Stars: BCS Theory and Beyond (A Sedrakian & J W Clark); Pairing Properties of Dressed Nucleons in Infinite Matter (W H Dickhoff & H Mther); Pairing in Higher Angular Momentum States: Spectrum of Solutions of the 3 P 2 - 3 F 2 Pairing Model (M V Zverev et al.); Four-Particle Condensates in Nuclear Systems (G RApke & P Schuck); Realization, Characterization, and Detection of Novel Superfluid Phases with Pairing Between Unbalanced Fermion Species (K Yang); Phase Transition in Unbalanced Fermion Superfluids (H Caldas). Readership: Researchers and graduate students in the areas of condensed matter, nuclear and particle physics."
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Wilhelm Zwerger
Publisher: Springer Science & Business Media
ISBN: 3642219772
Category : Science
Languages : en
Pages : 543
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Book Description
Recent experimental and theoretical progress has elucidated the tunable crossover, in ultracold Fermi gases, from BCS-type superconductors to BEC-type superfluids. The BCS-BEC Crossover and the Unitary Fermi Gas is a collaborative effort by leading international experts to provide an up-to-date introduction and a comprehensive overview of current research in this fast-moving field. It is now understood that the unitary regime that lies right in the middle of the crossover has remarkable universal properties, arising from scale invariance, and has connections with fields as diverse as nuclear physics and string theory. This volume will serve as a first point of reference for active researchers in the field, and will benefit the many non-specialists and graduate students who require a self-contained, approachable exposition of the subject matter.
Author: Markus Bartenstein
Publisher:
ISBN: 9783816768821
Category :
Languages : en
Pages : 166
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Book Description
Author: Armen Sedrakian
Publisher: World Scientific
ISBN: 9812569073
Category : Science
Languages : en
Pages : 297
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Book Description
Cooper pairing of fermions is a profound phenomenon that has become very important in many different areas of physics in the recent past. This book brings together, for the first time, experts from various fields involving Cooper pairing, at the level of BCS theory and beyond, including the study of novel states of matter such as ultracold atomic gases, nuclear systems at the extreme, and quark matter with application to neutron stars. Cross-disciplinary in nature, the book will be of interest to physicists in many different specialties, including condensed matter, nuclear, high-energy, and astrophysics. The emphasis is on novel issues beyond ordinary BCS theory such as pairing in asymmetric systems, the polarization effect, and higher spin pairing. These topics are rarely treated at the textbook level and all of them are the subjects of intensive ongoing research. The book also considers various new techniques widely used in current research that differ significantly from the conventional condensed matter approaches described in the standard literature.
Author: Menderes Iskin
Publisher:
ISBN:
Category : Bose-Einstein condensation
Languages : en
Pages :
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Book Description
This thesis focuses on the analysis of Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) evolution in ultracold superfluid Fermi gases when the interaction between atoms is varied. The tuning of attractive interactions permits the ground state of the system to evolve from a weak fermion attraction BCS limit of loosely bound and largely overlapping Cooper pairs to a strong fermion attraction limit of tightly bound small bosonic molecules which undergo BEC. This evolution is accompanied by anomalous behavior of many superfluid properties, and reveals several quantum phase transitions. This thesis has two parts: In the first part, I analyze zero and nonzero orbital angular momentum pairing effects, and show that a quantum phase transition occurs for nonzero angular momentum pairing, unlike the s-wave case where the BCS to BEC evolution is just a crossover. In the second part, I analyze two-species fermion mixtures with mass and population imbalance in continuum, trap and lattice models. In contrast with the crossover physics found in the mass and population balanced mixtures, I demonstrate the existence of phase transitions between normal and superfluid phases, as well as phase separation between superfluid (paired) and normal (excess) fermions in imbalanced mixtures as a function of scattering parameter and mass and population imbalance.
Author: Kathy Levin
Publisher: Elsevier
ISBN: 0444538623
Category : Science
Languages : en
Pages : 225
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Book Description
The rapidly developing topic of ultracold atoms has many actual and potential applications for condensed-matter science, and the contributions to this book emphasize these connections. Ultracold Bose and Fermi quantum gases are introduced at a level appropriate for first-year graduate students and non-specialists such as more mature general physicists. The reader will find answers to questions like: how are experiments conducted and how are the results interpreted? What are the advantages and limitations of ultracold atoms in studying many-body physics? How do experiments on ultracold atoms facilitate novel scientific opportunities relevant to the condensed-matted community? This volume seeks to be comprehensible rather than comprehensive; it aims at the level of a colloquium, accessible to outside readers, containing only minimal equations and limited references. In large part, it relies on many beautiful experiments from the past fifteen years and their very fruitful interplay with basic theoretical ideas. In this particular context, phenomena most relevant to condensed-matter science have been emphasized. Introduces ultracold Bose and Fermi quantum gases at a level appropriate for non-specialists Discusses landmark experiments and their fruitful interplay with basic theoretical ideas Comprehensible rather than comprehensive, containing only minimal equations
Author: M. Inguscio
Publisher: IOS Press
ISBN: 1607503182
Category : Science
Languages : en
Pages : 933
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Book Description
The field of cold atomic gases faced a revolution in 1995 when Bose-Einstein condensation was achieved. Since then, there has been an impressive progress, both experimental and theoretical. The quest for ultra-cold Fermi gases started shortly after the 1995 discovery, and quantum degeneracy in a gas of fermionic atoms was obtained in 1999. The Pauli exclusion principle plays a crucial role in many aspects of ultra-cold Fermi gases, including inhibited interactions with applications to precision measurements, and strong correlations. The path towards strong interactions and pairing of fermions opened up with the discovery in 2003 that molecules formed by fermions near a Feshbach resonance were surprisingly stable against inelastic decay, but featured strong elastic interactions. This remarkable combination was explained by the Pauli exclusion principle and the fact that only inelastic collisions require three fermions to come close to each other. The unexpected stability of strongly interacting fermions and fermion pairs triggered most of the research which was presented at this summer school. It is remarkable foresight (or good luck) that the first steps to organize this summer school were already taken before this discovery. It speaks for the dynamics of the field how dramatically it can change course when new insight is obtained. The contributions in this volume provide a detailed coverage of the experimental techniques for the creation and study of Fermi quantum gases, as well as the theoretical foundation for understanding the properties of these novel systems.
Author: Karl-Heinz Bennemann
Publisher: OUP Oxford
ISBN: 0191029998
Category : Science
Languages : en
Pages : 657
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Book Description
Volume 2 of Novel Superfluids continues the presentation of recent results on superfluids, including novel metallic systems, superfluid liquids, and atomic/molecular gases of bosons and fermions, particularly when trapped in optical lattices. Since the discovery of superconductivity (Leyden, 1911), superfluid 4He (Moscow and Cambridge, 1937), superfluid 3He (Cornell, 1972), and observation of Bose-Einstein Condensation (BEC) of a gas (Colorado and MIT, 1995), the phenomenon of superfluidity has remained one of the most important topics in physics. Again and again, novel superfluids yield surprising and interesting behaviors. The many classes of metallic superconductors, including the high temperature perovskite-based oxides, MgB2, organic systems, and Fe-based pnictides, continue to offer challenges. The technical applications grow steadily. What the temperature and field limits are remains illusive. Atomic nuclei, neutron stars and the Universe itself all involve various aspects of superfluidity, and the lessons learned have had a broad impact on physics as a whole.
