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Liquid Metallic Hydrogen at Static Conditions Liquid Metallic Hydrogen at Static Conditions The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:40046435 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA A DISSERTATION PRESENTED BY MOHAMED ZAGHOO To THE JOHN PAULSON SCHOOL OF ENGINEERING AND APPLIED SCIENCE IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSIPHY IN THE SUBJECT OF APPLIED PHYSICS HARVARD UNIVERSITY CAMBRIDGE, MASSACHUSETTS January 2017 ©2017 – MOHAMED ZAGHOO All RIGHTS RESERVED THESIS ADVISOR: PROFESSOR ISAAC F. SILVERA AUTHOR: MOHAMED ZAGHOO LIQUID METALLIC HYDROGEN AT STATIC CONDITIONS Abstract The search for dense hydrogen metallization is now almost eighty years old. Because of hydrogen’s fundamental significance as the benchmark system for most of the physical and chemical sciences as well as its astrophysical abundance, the problem has been dubbed as the holy grail of high-pressure physics. Despite a legion of experimental feats and a remarkable theoretical progress over the last century, the precise conditions, mechanism and nature of this metallization process remain elusive. This thesis reports the first production of metallic hydrogen in the liquid phase at bench-top experiments under static conditions and high temperatures. The nature of metallization and the mechanism of conduction are shown to be different than hitherto assumed. The electronic transport coefficients of this metallic fluid are revealed to be substantially higher than the only reported value in shockwave experiments. An isotope effect relating to deuterium dissociation under pressure is shown. The astrophysical implication of the work regarding our understanding of the dynamo action and thermal history models of giant planets are discussed. (iii) Table of contents Dedication (vii) Acknowledgements (viii) Preface 1-4 1. The hydrogen phase diagram 1.1 Hydrogen at high pressure: the solid and the liquid phases 5-10 1.2 The plasma phase transition 11-16 1.3 What is a metal at finite temperature? 17-19 - Minimum metallic conductivity 1.4 Experimental efforts 20-23 1.5 Problem statement 23 2. Experimental methods 2.1 Generating pressure: Diamond Anvil cell 28-31 - Atomic Layer deposition 31-34 2.2 Diamond treatment and Cryogenic loading 34-37 2.3 Pressure measurement: Ruby fluorescence and Raman scattering 37-42 - Hydrogen fundamental vibron - Diamond phonon line 2.4 Generating temperature: Laser heated absorber design 42-47 - Fabrication of high-quality thin films - Emittance of thin films versus bulk foils (iv) 2.5 Optical setup layout 47-54 2.6 Data Acquisition 55-56 2.7 Temperature measurement: Pyrometry techniques 57-71 - Transfer function 63-64 - Separation of Blackbody signal from Diamond Raman 64-69 - Errors and systematics in temperature determination 70-71! 3. Results: Signatures of an abrupt transition to metallic hydrogen 3.1 Heating curves: Observation of plateaus 73-77 3.2 Physical origin of the plateaus 77-81 - Enthalpy of dissociation: Energetic balance for dissociation - Increased reflection or absorption 3.3 Transmittance and reflectance analysis 81-90 - Thermotransmittance and thermoreflectance - Normalization and data analysis - Saturation of optical properties 3.4 Transport properties: Optical conductivity 90-98 - Simultaneous measurements of optical reflectance - Analysis of the optical reflectance within the Drude free-electron model - The plasma frequency, degree of dissociation, relaxation times - Minimum metallic conductivity 3.5 Dielectric properties and Drude coefficients of LMH 99-102 3.6 Smith-Drude conduction Model 102-104 (v) 3.7 Summary of optical conductivity 105-106 3.8 Discussion on transport properties 106-107 3.9 Discussion on the metallization phase boundary 108-114 4. Conclusions and prospects 4.1 The Metallization problem in the broader context 116 4.2 Prospects for future experimental efforts 116-118 4.3 Implication of the current results for planetary interiors 118-121 ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! "#$%! “To understand hydrogen is to understand all of physics” V. Weisskopf ! ! To my family ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! "#$$%! Acknowledgments I render infinite thanks to my supervisor, Ike Silvera, who introduced me to the field of high-pressure physics, in particular, the long-standing search for hydrogen metallization. Ike’s knowledge on the subject, fascination with the first element, as well his remarkably unabated diligence in this pursuit continues to be inspirational. Dense hydrogen posses some minor character defects, some of which are striking reactivity and diffusivity, rendering its confinement and interrogation exceedingly challenging. It, thus, took considerable faith from Ike, and my part, to stick with the search, despite the trials and tribulations of numerous failed attempts. Prof. Eric Mazur, my co-adviser, has been an incredible source of support along the years. I am very grateful to have worked along side postodcs like Ashkan Salamat, Ranga Dias and Ori Noked. All have made lasting contributions to the Ike’s lab and provided more than just knowledge on the knots and bolts of high pressure. Rachel husband was a latecomer to the team but is already a valuable impetus for our high-temperature high-pressure research efforts. I am very thankful to Prof. Melissa franklin, who truly embodies the notion of “elan vital” in science and otherwise. The Physics machine shop is very fortunate to host the likes of Stan Cotreau. Outside the pristine halls of Lyman, my extended family of friends and roommates have enriched my Harvard experience beyond my imagination. In particular, I am monumentally indebted to the best roommates anyone can hope for: Ahmed Badran, Mounir Koussa, Mohamed Helal, Rana Elkahwagy, Ahmed Omran, Sameh Galal and Mohamed El batran. Their company, friendship and support have not only made the work presented here possible but also more enjoyable. Cambridge would not have been the same without Nourhan Shabaan, Hytham Khalil and Salma Mohsen, whom words would not do justice. Nelly Elzayat, Alsherif Wahdan and Amr Omran provided warmth to some otherwise the very cold winters of 2012 and 2013. I wish to acknowledge my dear friends, community outreach and sport activity comrades: Mohamed Sherine, Edlyn Levine, and Greg Boursalian. The experience of working at the Harvard human rights Scholars at Risk committee, with Jane Unrue and others, was indeed truly humbling and deeply rewarding. ! ! ! ! ! ! "#$$$%! ! ! Preface THE FIRST METAL "Lets start at the very beginning, a very good place to start!" ~The Sound of Music Hydrogen is a colorless gas that when compressed…. Few research questions have ever captured the interest of condensed matter, planetary and plasma sciences more than Metallic Hydrogen (MH) [1-3]. For as long as the early days of the quantum theory of solids, the first element was expected, under sufficient compression, to undergo a phase transition into a metallic like state. It has been nearly 81 years since Wigner and Huntington (WH) first called the attention to this problem [1], yet the location of that phase transition, both in the solid and fluid state, let alone its nature and properties, remained an outstanding challenge. Starting from a body-centered cubic lattice of solid molecular hydrogen, WH calculated that under sufficient compression, the free energy of a dense atomic lattice, irrespective of its Bravais type, would be lower than its molecular counterpart. If so, the application of external pressure, calculated by WH to be 25 GPa or more, would drive a dissociative structural transition into a monoatmic phase with delocalized electrons. Because as a metal it is exceptional in possessing no bound electrons, so that the electron-ion interaction is due to the bare Coulomb attraction, and because of the light mass and high-phonon frequency of its ionic subsystem, MH has long been cited as the prototypical candidate for high, possibly room-temperature, superconductivity [2, 4]. The large zero-point motion of the nuclei is expected to persist at elevated pressures, possibly destructing any putative crystalline structure. This ! "! ! suggests a rather dramatic possibility: a liquid metallic ground state where the electronic and ionic systems could exhibit some exotic long-range ordering [5]. In its simplest form, this liquid ground state is considered a two-component Fermi liquid where the ions and the electrons share the same Fermi-surface yet have different Fermi temperatures and the system is imbued with some unusual transport properties [6]. Perhaps more interesting is the possibility of a liquid superconductivity state, should the lack of crystallinity prove amenable to the electrons pairing. At even lower temperatures, liquid metallic deuterium, owing to its spin-1 statistics, is conjectured to exhibit a more striking transition to a superfluid state in which the electrons could remain paired in a superconducting order while the deuterons would condense into a superfluid state [7]. At the other end of the temperature scale, the “hot” state of this metallic fluid constitutes 60-70% of Jupiter and Saturn planetary mass, making it the most abundant form of condensed
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