DOCSLIB.ORG

Attractive Fermi Polarons at Nonzero Temperatures with a Finite Impurity

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Attractive Fermi Polarons at Nonzero Temperatures with a Finite Impurity PHYSICAL REVIEW A 98, 013626 (2018) Attractive Fermi polarons at nonzero temperatures with a finite impurity concentration Hui Hu, Brendan C. Mulkerin, Jia Wang, and Xia-Ji Liu Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne, Victoria 3122, Australia (Received 29 June 2018; published 25 July 2018) We theoretically investigate how quasiparticle properties of an attractive Fermi polaron are affected by nonzero temperature and finite impurity concentration in three dimensions and in free space. By applying both non- self-consistent and self-consistent many-body T -matrix theories, we calculate the polaron energy (including decay rate), effective mass, and residue, as functions of temperature and impurity concentration. The temperature and concentration dependencies are weak on the BCS side with a negative impurity-medium scattering length. Toward the strong attraction regime across the unitary limit, we find sizable dependencies. In particular, with increasing temperature the effective mass quickly approaches the bare mass and the residue is significantly enhanced. At temperature T ∼ 0.1TF ,whereTF is the Fermi temperature of the background Fermi sea, the residual polaron-polaron interaction seems to become attractive. This leads to a notable down-shift in the polaron energy. We show that, by taking into account the temperature and impurity concentration effects, the measured polaron energy in the first Fermi polaron experiment [Schirotzek et al., Phys.Rev.Lett.102, 230402 (2009)] could be better theoretically explained. DOI: 10.1103/PhysRevA.98.013626 I. INTRODUCTION Experimentally, the first experiment on attractive Fermi polarons was carried out by the Zwierlein group at Mas- Over the past two decades, ultracold atomic gases have pro- sachusetts Institute of Technology (MIT) in 2009 using 6Li vided an ideal platform to understand the intriguing quantum many-body systems [1]. The simplest example is probably a atoms [20]. The polaron energy and residue were determined moving impurity immersed in a background medium that is by using radio-frequency (rf) spectroscopy, in the vicinity of often well understood [2,3]. In this so-called polaron problem, the unitary limit and in the strong attraction BEC regime. The the interaction between impurity and medium can be tuned attractive polaron picture was used later to understand the arbitrarily by using Feshbach resonances [4]. The motion of radio-frequency spectrum of a quasi-two-dimensional Fermi the impurity is then addressed by low-energy excitations of gas [21]. The existence of repulsive Fermi polarons was 40 the background medium and its fundamental properties are experimentally confirmed in 2012 by immersing K impurity profoundly affected [2]. In the case of fermionic impurity with inaFermiseaof6Li atoms near a narrow Feshbach resonance finite density and concentration, the emergence of a Fermi [22]orbyusing40K atoms in two dimensions [23]. Most liquid behavior is anticipated [5,6]. recently, a careful analysis of the quasiparticle properties of Theoretically, it turns out that the polaron problem can repulsive Fermi polarons in 6Li systems was performed at the be well approximately solved by using a variational ansatz European Laboratory for Non-linear Spectroscopy (LENS), that includes only one-particle-hole excitation, as proposed by Florence [24]. The experimental observation of attractive and Chevy in 2006 in his seminal work [7]. For a noninteracting repulsive Bose polarons has also been reported [25,26]. single-component Fermi sea as the background medium, when In all these experiments, the experimental data were com- the impurity-medium scattering length a is tuned to the unitary pared with the theoretical predictions of a single impurity limit (a →∞), Chevy’s ansatz predicts a polaron energy at zero temperature [2]. The unavoidable nonzero temper- EP −0.607εF [7,8], where εF is the Fermi energy of the ature and finite impurity concentration in real experiments Fermi sea, which is very close to the exact diagrammatic are anticipated to give negligible corrections. However, those Monte Carlo (Diag-MC) result of EP =−0.615(1)εF [9–12]. corrections have never been carefully examined, except the This perfect agreement may result from a nice cancellation of idealized case of 1D Fermi polarons [27], where the exact the higher-order contributions, as checked by the next order solution is available. A possible reason is that the current calculation with the inclusion of two-particle-hole excitations polaron theory relies heavily on Chevy’s variational approach [13]. The simple variational ansatz was later used to discover [7], which is unfortunately difficult to handle the nonzero repulsive Fermi polarons in the metastable upper branch [14] temperature and finite impurity concentration [28]. and to describe Bose polarons [15]. At the level of including The purpose of the present work is to address the effects two-particle-hole excitations, Chevy’s ansatz has also been of nonzero temperature and finite impurity concentration for applied to the medium systems with bosonic degrees of attractive Fermi polarons in three dimensions and in free freedom, such as a Bose-Einstein condensate (BEC) [16]ora space, by using both non-self-consistent [8,29–33] and self- Bardeen-Cooper-Schrieffer (BCS) superfluid [17,18]. In those consistent T -matrix theories [34–37]. In the limit of zero cases, the interplay between polarons and the resulting Efimov temperature and a single impurity and in three dimensions, the trimer was explored [16–19]. non-self-consistent T -matrix theory is shown to be equivalent 2469-9926/2018/98(1)/013626(9) 013626-1 ©2018 American Physical Society HUI HU, BRENDAN C. MULKERIN, JIA WANG, AND XIA-JI LIU PHYSICAL REVIEW A 98, 013626 (2018) to Chevy’s variational approach [8,32]. At weak attractions by using the well-established many-body T -matrix theories on the BCS side of the impurity and medium scattering [38–40], which amount to summing up all the ladder-type resonance, we find that the effects of nonzero temperature and diagrams. In this approximation, the self-energy of the finite impurity concentration are indeed negligible, confirming impurity atom is given by [8], the previous anticipation. However, across the resonance and (0) toward the strong attraction regime, a nonzero temperature = kB T G↑ (q − k,iνn − iωm)(q,iνn ), (5) may significantly reduce the effective mass and enhance the q,iνn residue of attractive Fermi polarons. The polaron energy also shows a considerable temperature dependence. In particular, where the vertex function can be written through the Bethe- Salpeter equation as at the typical experimental temperature T ∼ 0.1TF , where TF is the Fermi temperature of the Fermi sea, the polaron- 1 polaron interaction may become attractive, leading to a sizable (q,iνn ) = , (6) U −1 + χ(q,iν ) downshift in the polaron energy, which may be experimentally n resolved. Indeed, by taking into account the temperature and and the pair propagator χ(q,iνn)is impurity concentration effects, we find that the measured (0) polaron energy in the first Fermi polaron experiment at MIT χ = kB T G↑ (q − k,iνn − iωm)G↓(k,iωm ). (7) [20] could be better theoretically understood. k,iωm Here, ν ≡ 2nπk T with integer n are the bosonic Matsubara II. MANY-BODY T-MATRIX THEORIES OF ATTRACTIVE n B frequencies. Eqs. (4)–(7) form a closed set of equations, FERMI POLARONS which have to be solved self-consistently. We refer to it as We consider a two-component three-dimensional Fermi gas the self-consistent T -matrix theory, or the “G0↑G↓” theory of mass m with a large spin polarization (i.e., n↑ = n n↓), according to the structure in the pair propagator. We note which is described by the model Hamiltonian [7,8], that in a strong-coupling theory, the self-consistency does not necessarily guarantee a better or more accurate theory [39,40]. = − † + − † H [(k μ)ck↑ck↑ (k μ↓)ck↓ck↓] For attractive Fermi polarons, it is actually more useful to take k a non-self-consistent treatment of the many-body T -matrix U † † theory, as suggested by the comparison with numerically + ck↑cq−k↓cq−k ↓ck ↑, (1) V exact Diag-MC simulations [9–11,13] or exact Bethe ansatz q,k,k solutions [27]. That is, we simply use a noninteracting impurity 2 2 where k ≡ h¯ k /(2m), μ and μ↓ are the chemical potentials Green function, of spin-up and spin-down atoms, respectively, and U<0 1 is the bare attractive interatomic interaction strength, to be G(0)(k,iω ) = , ↓ m − − (8) renormalized in terms of the s-wave scattering length a, iωm (k μ↓) according to in the pair propagator Eq. (7). At zero temperature and in the 1 m m single-impurity limit, this non-self-consistent T -matrix theory = − . (2) U 4πh¯ 2a h¯ 2k2 or the “G0↑G0↓” theory exactly recovers Chevy’s variational k approach [8]. In the large spin polarization limit, we treat the spin-down In this work, we explore both non-self-consistent and self- atoms as impurities and assume that, at the first order of the consistent T -matrix theories, as both of them are not justified impurity concentration x = n↓/n, the background medium in the strong-coupling limit [39,40]. There is no reason to of spin-up atoms is not affected by interaction. As a result, expect that the self-consistent theory works better than the (0) μ can be taken as the chemical potential μ (T ) εF = non-self-consistent approach, or vice versa. The applicability h¯ 2(6π 2n)2/3/(2m) of an ideal Fermi gas at low temperatures of the two theories should be benchmarked by numerically and the thermal Green’s function of spin-up atoms is exact calculations such as Diag-MC simulations or accurate experimental measurements.
Load more

Recommended publications
  • Lecture 3: Fermi-Liquid Theory 1 General Considerations Concerning Condensed Matter
    Phys 769 Selected Topics in Condensed Matter Physics Summer 2010 Lecture 3: Fermi-liquid theory Lecturer: Anthony J. Leggett TA: Bill Coish 1 General considerations concerning condensed matter (NB: Ultracold atomic gasses need separate discussion) Assume for simplicity a single atomic species. Then we have a collection of N (typically 1023) nuclei (denoted α,β,...) and (usually) ZN electrons (denoted i,j,...) interacting ∼ via a Hamiltonian Hˆ . To a first approximation, Hˆ is the nonrelativistic limit of the full Dirac Hamiltonian, namely1 ~2 ~2 1 e2 1 Hˆ = 2 2 + NR −2m ∇i − 2M ∇α 2 4πǫ r r α 0 i j Xi X Xij | − | 1 (Ze)2 1 1 Ze2 1 + . (1) 2 4πǫ0 Rα Rβ − 2 4πǫ0 ri Rα Xαβ | − | Xiα | − | For an isolated atom, the relevant energy scale is the Rydberg (R) – Z2R. In addition, there are some relativistic effects which may need to be considered. Most important is the spin-orbit interaction: µ Hˆ = B σ (v V (r )) (2) SO − c2 i · i × ∇ i Xi (µB is the Bohr magneton, vi is the velocity, and V (ri) is the electrostatic potential at 2 3 2 ri as obtained from HˆNR). In an isolated atom this term is o(α R) for H and o(Z α R) for a heavy atom (inner-shell electrons) (produces fine structure). The (electron-electron) magnetic dipole interaction is of the same order as HˆSO. The (electron-nucleus) hyperfine interaction is down relative to Hˆ by a factor µ /µ 10−3, and the nuclear dipole-dipole SO n B ∼ interaction by a factor (µ /µ )2 10−6.
    [Show full text]
  • Unconventional Hund Metal in a Weak Itinerant Ferromagnet
    ARTICLE https://doi.org/10.1038/s41467-020-16868-4 OPEN Unconventional Hund metal in a weak itinerant ferromagnet Xiang Chen1, Igor Krivenko 2, Matthew B. Stone 3, Alexander I. Kolesnikov 3, Thomas Wolf4, ✉ ✉ Dmitry Reznik 5, Kevin S. Bedell6, Frank Lechermann7 & Stephen D. Wilson 1 The physics of weak itinerant ferromagnets is challenging due to their small magnetic moments and the ambiguous role of local interactions governing their electronic properties, 1234567890():,; many of which violate Fermi-liquid theory. While magnetic fluctuations play an important role in the materials’ unusual electronic states, the nature of these fluctuations and the paradigms through which they arise remain debated. Here we use inelastic neutron scattering to study magnetic fluctuations in the canonical weak itinerant ferromagnet MnSi. Data reveal that short-wavelength magnons continue to propagate until a mode crossing predicted for strongly interacting quasiparticles is reached, and the local susceptibility peaks at a coher- ence energy predicted for a correlated Hund metal by first-principles many-body theory. Scattering between electrons and orbital and spin fluctuations in MnSi can be understood at the local level to generate its non-Fermi liquid character. These results provide crucial insight into the role of interorbital Hund’s exchange within the broader class of enigmatic multiband itinerant, weak ferromagnets. 1 Materials Department, University of California, Santa Barbara, CA 93106, USA. 2 Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA. 3 Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. 4 Institute for Solid State Physics, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.
    [Show full text]
  • Landau Effective Interaction Between Quasiparticles in a Bose-Einstein Condensate
    PHYSICAL REVIEW X 8, 031042 (2018) Landau Effective Interaction between Quasiparticles in a Bose-Einstein Condensate A. Camacho-Guardian* and Georg M. Bruun Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Aarhus C, Denmark (Received 19 December 2017; revised manuscript received 28 February 2018; published 15 August 2018) Landau’s description of the excitations in a macroscopic system in terms of quasiparticles stands out as one of the highlights in quantum physics. It provides an accurate description of otherwise prohibitively complex many-body systems and has led to the development of several key technologies. In this paper, we investigate theoretically the Landau effective interaction between quasiparticles, so-called Bose polarons, formed by impurity particles immersed in a Bose-Einstein condensate (BEC). In the limit of weak interactions between the impurities and the BEC, we derive rigorous results for the effective interaction. They show that it can be strong even for a weak impurity-boson interaction, if the transferred momentum- energy between the quasiparticles is resonant with a sound mode in the BEC. We then develop a diagrammatic scheme to calculate the effective interaction for arbitrary coupling strengths, which recovers the correct weak-coupling results. Using this scheme, we show that the Landau effective interaction, in general, is significantly stronger than that between quasiparticles in a Fermi gas, mainly because a BEC is more compressible than a Fermi gas. The interaction is particularly large near the unitarity limit of the impurity-boson scattering or when the quasiparticle momentum is close to the threshold for momentum relaxation in the BEC.
    [Show full text]
  • Electron-Electron Interactions(Pdf)
    Contents 2 Electron-electron interactions 1 2.1 Mean field theory (Hartree-Fock) ................ 3 2.1.1 Validity of Hartree-Fock theory .................. 6 2.1.2 Problem with Hartree-Fock theory ................ 9 2.2 Screening ..................................... 10 2.2.1 Elementary treatment ......................... 10 2.2.2 Kubo formula ............................... 15 2.2.3 Correlation functions .......................... 18 2.2.4 Dielectric constant ............................ 19 2.2.5 Lindhard function ............................ 21 2.2.6 Thomas-Fermi theory ......................... 24 2.2.7 Friedel oscillations ............................ 25 2.2.8 Plasmons ................................... 27 2.3 Fermi liquid theory ............................ 30 2.3.1 Particles and holes ............................ 31 2.3.2 Energy of quasiparticles. ....................... 36 2.3.3 Residual quasiparticle interactions ................ 38 2.3.4 Local energy of a quasiparticle ................... 42 2.3.5 Thermodynamic properties ..................... 44 2.3.6 Quasiparticle relaxation time and transport properties. 46 2.3.7 Effective mass m∗ of quasiparticles ................ 50 0 Reading: 1. Ch. 17, Ashcroft & Mermin 2. Chs. 5& 6, Kittel 3. For a more detailed discussion of Fermi liquid theory, see G. Baym and C. Pethick, Landau Fermi-Liquid Theory : Concepts and Ap- plications, Wiley 1991 2 Electron-electron interactions The electronic structure theory of metals, developed in the 1930’s by Bloch, Bethe, Wilson and others, assumes that electron-electron interac- tions can be neglected, and that solid-state physics consists of computing and filling the electronic bands based on knowldege of crystal symmetry and atomic valence. To a remarkably large extent, this works. In simple compounds, whether a system is an insulator or a metal can be deter- mined reliably by determining the band filling in a noninteracting cal- culation.
    [Show full text]
  • Non-Fermi Liquids in Oxide Heterostructures
    UC Santa Barbara UC Santa Barbara Previously Published Works Title Non-Fermi liquids in oxide heterostructures Permalink https://escholarship.org/uc/item/1cn238xw Journal Reports on Progress in Physics, 81(6) ISSN 0034-4885 1361-6633 Authors Stemmer, Susanne Allen, S James Publication Date 2018-06-01 DOI 10.1088/1361-6633/aabdfa Peer reviewed eScholarship.org Powered by the California Digital Library University of California Reports on Progress in Physics KEY ISSUES REVIEW Non-Fermi liquids in oxide heterostructures To cite this article: Susanne Stemmer and S James Allen 2018 Rep. Prog. Phys. 81 062502 View the article online for updates and enhancements. This content was downloaded from IP address 128.111.119.159 on 08/05/2018 at 17:09 IOP Reports on Progress in Physics Reports on Progress in Physics Rep. Prog. Phys. Rep. Prog. Phys. 81 (2018) 062502 (12pp) https://doi.org/10.1088/1361-6633/aabdfa 81 Key Issues Review 2018 Non-Fermi liquids in oxide heterostructures © 2018 IOP Publishing Ltd Susanne Stemmer1 and S James Allen2 RPPHAG 1 Materials Department, University of California, Santa Barbara, CA 93106-5050, United States of America 062502 2 Department of Physics, University of California, Santa Barbara, CA 93106-9530, United States of America S Stemmer and S J Allen E-mail: [email protected] Received 18 July 2017, revised 25 January 2018 Accepted for publication 13 April 2018 Published 8 May 2018 Printed in the UK Corresponding Editor Professor Piers Coleman ROP Abstract Understanding the anomalous transport properties of strongly correlated materials is one of the most formidable challenges in condensed matter physics.
    [Show full text]
  • Boiling a Unitary Fermi Liquid
    PHYSICAL REVIEW LETTERS 122, 093401 (2019) Editors' Suggestion Featured in Physics Boiling a Unitary Fermi Liquid Zhenjie Yan,1 Parth B. Patel,1 Biswaroop Mukherjee,1 Richard J. Fletcher,1 Julian Struck,1,2 and Martin W. Zwierlein1 1MIT-Harvard Center for Ultracold Atoms, Department of Physics, and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 2D´epartement de Physique, Ecole Normale Sup´erieure/PSL Research University, CNRS, 24 rue Lhomond, 75005 Paris, France (Received 1 November 2018; published 6 March 2019) We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a classical Boltzmann gas at high temperatures. Radio-frequency spectroscopy gives access to the energy, lifetime, and short-range correlations of Fermi polarons at low temperatures T. In this regime, we observe a characteristic T2 dependence of the spectral width, corresponding to the quasiparticle decay rate expected for a Fermi liquid. At high T, the spectral width decreases again towards the scattering rate of the classical, unitary Boltzmann gas, ∝ T−1=2. In the transition region between the quantum degenerate and classical regime, the spectral width attains its maximum, on the scale of the Fermi energy, indicating the breakdown of a quasiparticle description. Density measurements in a harmonic trap directly reveal the majority dressing cloud surrounding the minority spins and yield the compressibility along with the effective mass of Fermi polarons. DOI: 10.1103/PhysRevLett.122.093401 Landau’s Fermi liquid theory provides a quasiparticle the quantum critical region.
    [Show full text]
  • Singular Fermi Liquids, at Least for the Present Case Where the Singularities Are Q-Dependent
    Singular Fermi Liquids C. M. Varmaa,b, Z. Nussinovb, and Wim van Saarloosb aBell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, U.S.A. 1 bInstituut–Lorentz, Universiteit Leiden, Postbus 9506, 2300 RA Leiden, The Netherlands Abstract An introductory survey of the theoretical ideas and calculations and the ex- perimental results which depart from Landau Fermi-liquids is presented. Common themes and possible routes to the singularities leading to the breakdown of Landau Fermi liquids are categorized following an elementary discussion of the theory. Sol- uble examples of Singular Fermi liquids include models of impurities in metals with special symmetries and one-dimensional interacting fermions. A review of these is followed by a discussion of Singular Fermi liquids in a wide variety of experimental situations and theoretical models. These include the effects of low-energy collective fluctuations, gauge fields due either to symmetries in the hamiltonian or possible dynamically generated symmetries, fluctuations around quantum critical points, the normal state of high temperature superconductors and the two-dimensional metallic state. For the last three systems, the principal experimental results are summarized and the outstanding theoretical issues highlighted. Contents 1 Introduction 4 1.1 Aim and scope of this paper 4 1.2 Outline of the paper 7 arXiv:cond-mat/0103393v1 [cond-mat.str-el] 19 Mar 2001 2 Landau’s Fermi-liquid 8 2.1 Essentials of Landau Fermi-liquids 8 2.2 Landau Fermi-liquid and the wave function renormalization Z 11
    [Show full text]
  • UC Berkeley UC Berkeley Electronic Theses and Dissertations
    UC Berkeley UC Berkeley Electronic Theses and Dissertations Title Quantum Phenomena in Interacting Many-Body Systems: Topological Protection, Localization, and Non-Fermi Liquids Permalink https://escholarship.org/uc/item/9kw3g8gg Author Bahri, Yasaman Publication Date 2017 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California Quantum Phenomena in Interacting Many-Body Systems: Topological Protection, Localization, and Non-Fermi Liquids by Yasaman Bahri A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Ashvin Vishwanath, Chair Professor Joel Moore Professor K. Birgitta Whaley Spring 2017 Quantum Phenomena in Interacting Many-Body Systems: Topological Protection, Localization, and Non-Fermi Liquids Copyright 2017 by Yasaman Bahri 1 Abstract Quantum Phenomena in Interacting Many-Body Systems: Topological Protection, Localization, and Non-Fermi Liquids by Yasaman Bahri Doctor of Philosophy in Physics University of California, Berkeley Professor Ashvin Vishwanath, Chair This dissertation establishes and investigates new phenomena in diverse interacting many- body quantum systems guided by three distinct, but complementary, themes: (i) symmetry and topology, (ii) localization, and (iii) non-Fermi liquids. The first theme concerns how the interplay of symmetry and topology can offer robust protection for a many-body system. We investigate low-dimensional quantum fermionic mod- els from a general structural perspective. These phases can exhibit fractionalized Majorana zero-energy modes on their boundary. We devise experimentally relevant nonlocal measure- ments that can be used to detect these topological phases. While our primary focus is on quantum systems, topologically protected behavior can arise in classical mechanical models as well.
    [Show full text]
  • Probing Luttinger Liquid Plasmons in Single Walled Carbon Nanotubes
    Probing Luttinger Liquid Plasmons in Single Walled Carbon Nanotubes By Sheng Wang A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Feng Wang, Chair Professor Michael F. Crommie Professor Eli Yablonovitch Spring 2020 Abstract Probing Luttinger Liquid Plasmons in Single Walled Carbon Nanotubes By Sheng Wang Doctor of Philosophy in Physics University of California, Berkeley Professor Feng Wang, Chair Single walled carbon nanotubes (SWNTs) are one-dimensional (1D) rolled-up hollow cylinders composed of graphene sheets. Since their discovery about three decades ago, they have been one of the most fascinating and unique nanoscale structures. There have been tremendous and still ongoing research on SWNTs for both fundamental science as well as technological devices. SWNTs have been a good platform to study electron-electron interaction in solid state systems, including Coulomb blockage effect and Luttinger liquid formulism. SWNTs exhibit unique electrical, mechanical and thermal properties, making them potentially useful in a variety of applications including nano-electronics, optics, energy storage, and nanomedicine. Notably, carbon nanotube field-effect transistor-based digital circuits may be a viable route for next- generation beyond-silicon electronic systems for post-Moore’s Law era. Recent major advance includes a 16-bit computer built entirely from carbon nanotube transistors. Despite the intense established research, SWNTs have never ceased to surprise researchers with their emerging properties and potential applications. During the past decade, advances in the synthesis and processing have enabled the controlled growth of high quality ultralong SWNTs on different substrates even with desirable chirality.
    [Show full text]
  • Breakdown of Fermi-Liquid Theory in a Copper-Oxide Superconductor
    articles Breakdown of Fermi-liquid theory in a copper-oxide superconductor R. W. Hill*, Cyril Proust*³, Louis Taillefer*, P. Fournier²³ & R. L. Greene² * Canadian Institute for Advanced Research, Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada ² Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742, USA ............................................................................................................................................................................................................................................................................ The behaviour of electrons in solids is well described by Landau's Fermi-liquid theory, which predicts that although electrons in a metal interact, they can still be treated as well de®ned fermions, which are called `quasiparticles'. At low temperatures, the ability of quasiparticles to transport heat is given strictly by their ability to transport charge, as described by a universal relation known as the Wiedemann±Franz law, which hitherto no material has been known to violate. High-temperature superconductors have long been thought to fall outside the realm of Fermi-liquid theory, as suggested by several anomalous properties, but this has yet to be shown conclusively. Here we report an experimental test of the Wiedemann±Franz law in the normal state of a copper-oxide superconductor, (Pr,Ce)2CuO4, which reveals that the elementary excitations that carry heat in this material are not fermions. This is compelling evidence for the breakdown of Fermi-liquid theory in high-temperature superconductors. Landau's Fermi-liquid theory is the de®nitive theory of electrons in Theoretically, electrons are predicted to obey the WF law at T ! 0 metals1, or more generally fermions in condensed matter, and is a in a very wide range of environments4: in both three dimensions or major landmark of twentieth-century physics.
    [Show full text]
  • Propagation of Shear Stress in Strongly Interacting Metallic Fermi Liquids Enhances Transmission of Terahertz Radiation D
    www.nature.com/scientificreports OPEN Propagation of shear stress in strongly interacting metallic Fermi liquids enhances transmission of terahertz radiation D. Valentinis1,2, J. Zaanen3 & D. van der Marel1* A highlight of Fermi-liquid phenomenology, as explored in neutral 3He, is the observation that in the collisionless regime shear stress propagates as if one is dealing with the transverse phonon of a solid. The existence of this “transverse zero sound” requires that the quasiparticle mass enhancement exceeds a critical value. Could such a propagating shear stress also exist in strongly correlated electron systems? Despite some noticeable diferences with the neutral case in the Galilean continuum, we arrive at the verdict that transverse zero sound should be generic for mass enhancement higher than 3. We present an experimental setup that should be exquisitely sensitive in this regard: the transmission of terahertz radiation through a thin slab of heavy-fermion material will be strongly enhanced at low temperature and accompanied by giant oscillations, which refect the interference between light itself and the “material photon” being the actual manifestation of transverse zero sound in the charged Fermi liquid. Te elucidation of the Fermi liquid as a unique state of matter is a highlight of twentieth century physics 1. It has a precise identity only at strictly zero temperature. At times large compared to /(kBT) it can be adiabatically con- tinued to the high-temperature limit and it is therefore indistinguishable from a classical fuid—the “collision-full regime”. However, at energies ω>kBT (the “collisionless regime”) the unique nature of the zero-temperature state can be discerned, being diferent from either the non-interacting Fermi gas or a thermal fuid.
    [Show full text]
  • The “Old” Marginal Fermi Liquid “Theory”
    The “old” marginal Fermi liquid “theory” Peter Littlewood University of Cambridge [email protected] Review: Les Houches, Session LVI (1991), ed Doucot and Zinn-Justin, p 69-148, Elsevier (1995) Outline • Selected experimental data on cuprate superconductors – Phase diagram – Resistivity, tunnelling, Raman scattering, optical conductivity, superconductivity, • Phenomenology of a non Fermi liquid • Remarks Phenomenology of high-Tc superconductors Underdoped Overdoped Fermi liquid Resistivity Metallic but 2 Non-Fermi r ~ T liquid c , g ~ const Fermi Temperature Pseudogap liquid? Temperature Non-Fermi liquid 1/t=max(T,w) Antiferromagnet No long-lived quasiparticles Superconductor Spin glass Carrier concentration Pseudo-gap destroys portions of Mott insulator statesof density Electronic Fermi surface La2CuO4 Temperature Resistivity Martin et al Phys. Rev. B 41:846 (1990 ) Resistivity is very large, linear in T, non- Bi - 2201 saturating Implies strong local (back-)scattering Mean free path is a lattice constant or less - -- is this a meaningful concept? Cu Optical conductivity Orenstein et al. PRB 42, 6342 (1990) Reflectivity YBCO Drude metal Scattering rate is frequency dependent Divergent effective mass (Kramers-Kronig) Schlesinger et al. PRL 65, 801 (1990) Inelastic light scattering Cooper et al PRB 47, 8233 (1993) Slakey et al., PRB 42, 3764 (1991) “2-magnon” light scattering peak in insulator evolves to a flat continuum in metal Lower cutoff of spectrum is kB T Much larger than conventional metal ~ q2 (Galilean invariance) But with strong
    [Show full text]