THE PHYSICS OF ORGANIC SUPERCONDUCTORS AND CONDUCTORS

By RICHARD DAVIS

PART I HISTORICAL SURVEYS 1 1 HISTORICAL APPROACH TO ORGANIC SUPERCONDUCTIVITY 2 2 FROM SLIDING CHARGE DENSITY WAVE TO CHARGE ORDERING 16 3 FIELD INDUCED SPIN DENSITY WAVES AND DIMENSIONAL CROSSOVERS 24 4 CASCADE OF FISDW PHASES WAVE VECTOR QUANTIZATION AND ITS CONSEQUENCES 40 PART II GENERAL REVIEWS 45 5 LA TOUR DES SELS DE BECHGAARD 46 6 PHYSICAL PROPERTIES OF QUASI TWO DIMENSIONAL ORGANIC CONDUCTORS IN STRONG MAGNETIC FIELDS 85 7 MAGNETIC PROPERTIES OF ORGANIC CONDUCTORS AND SUPERCONDUCTORS AS DIMENSIONAL CROSSOVERS 123 8 LAYERED ORGANIC CONDUCTORS IN STRONG MAGNETIC FIELDS 181 9 HIGH FIELD MAGNETORESISTIVE EFFECTS IN REDUCED DIMENSIONALITY ORGANIC METALS AND SUPERCONDUCTORS 243 10 ENERGY AND DIELECTRIC RELAXATIONS IN BECHGAARD FABRE SALTS 273 11 FERROELECTRICITY AND CHARGE ORDERING IN QUASI 1D ORGANIC CONDUCTORS 309 12 INTERACTING ELECTRONS IN QUASI ONE DIMENSIONAL ORGANIC SUPERCONDUCTORS 352 CONTENTS PART III UNUSUAL PROPERTIES OF A METALLIC PHASE 408 13 UNUSUAL MAGIC ANGLES EFFECTS IN BECHGAARD SALTS 409 14 VERSATILE METHOD TO ESTIMATE DIMENSIONALITY OF Q1D FERMI SURFACE BY THIRD ANGULAR EFFECT 427 15 MICROWAVE SPECTROSCOPY OF Q1D AND Q2D ORGANIC CONDUCTORS 451 PART I HISTORICAL SURVEYS 1 1 HISTORICAL APPROACH TO ORGANIC SUPERCONDUCTIVITY WE GIVE A BRIEF ACCOUNT OF HOW THE SEARCH FOR SUPERCONDUCTIVITY IN ORGANIC MATTER MOTIVATED BY THE QUEST FOR HIGH TC SUPERCONDUCTORS HAS DEVELOPED SINCE THE 1960S EVEN IF THE MAXIMUM TC OF ORGANIC CONDUCTORS IN 2005 DOES NOT EXCEED 13 K THESE ARE PROTOTYPE SYSTEMS WHICH HAVE CONTRIBUTED REMARKABLY TO THE PROGRESSES IN THE PHYSICS OF LOW DIMENSIONAL CONDUCTORS 1 1 ONE DIMENSIONAL CONDUCTORS SUPERCONDUCTIVITY I E THE POSSIBILITY FOR ELECTRONS TO OW THROUGH A CON DUCTOR WITHOUT ANY ENERGY LOSS HAS BEEN THE FUEL FOR A VERY LARGE NUMBER OF INDUSTRIAL APPLICATIONS OF PHYSICS IN THE TWENTIETH CENTURY TO MENTION ONLY A FEW OF THEM WHICH ARE IMPORTANT IN CURRENT LIFE THERE ARE THE POWER LOSS ENERGY TRANSFER THE PRODUCTION OF VERY STRONG MAGNETIC ELDS FOR MEDICAL IMAGING OR FOR PLASMA CON NEMENT THE FUSION PROBLEM VOLTAGE STANDARDS PARTICLE ACCELERATORS AND MAGNETIC UX SENSORS THIS NEW STATE OF MATTER WAS DISCOVERED UNEXPECTEDLY IN 1911 IN MERCURY WITH A CRITICAL TEMPERATURE OF TC 4 15 K BY KAMERLINGH ONNES JUST AFTER HE HAD MASTERED THE LIQUEFACTION OF HELIUM 1 HOWEVER THE PHENOMENON OF SUPERCONDUCTIVITY IN PARTICULAR THE VALUE OF ITS TC IS STRONGLY DEPENDENT ON THE MATERIAL IN WHICH IT IS TO BE OBSERVED THEREFORE OVER THE YEARS A LOT OF NEW METALS AND INTERMETALLIC COMPOUNDS HAVE BEEN DISCOVERED WITH INCREASING VALUES OF TC REACHING A PLATEAU AT ABOUT 24 K IN THE 1960S 2 SEE FIG 1 1 THE ABSENCE OF ANY SATISFACTORY THEORY UNTIL 1957 DID NOT PREVENT APPLICA TIONS OF SUPERCONDUCTIVITY WHICH DEVELOPED AFTER WORLD WAR II BUT THEY WERE ALL BOUND TO THE USE OF EXPENSIVE LIQUID HELIUM AS THE COOLING AGENT NECESSARY FOR THE STABILIZATION OF THE SUPERCONDUCTING STATE IN THE 1960S WHEN SUPERCONDUCTIVITY HAD ALREADY USED IN APPLICATIONS PEOPLE WERE THINKING ABOUT THE POSSIBILITY OF DISCOVERING NEW MATERIALS TO RELEASE THE CONSTRAINT OF USING LIQUID HELIUM TO REACH THE SUPERCONDUCTING STATE THEN CAME THE IDEA TO LOOK FOR MATERIALS OUT OF THE TRADITIONAL SERIES 2 FIG 1 1 EVOLUTION OF THE SUPERCONDUCTING CRITICAL TEMPERATURE IN METALS AND INTERMETALLIC COMPOUNDS CUPRATES AND ORGANIC CONDUCTORS 1 AND 2D CONDUCTORS OF METALS OR ALLOYS COMPOUNDS NAMELY NEW TYPES OF CONDUCTORS IN WHICH THE CONDUCTION WOULD PROCEED THROUGH THE TRANSPORT OF CHARGE BETWEEN MOLECULAR ORBITALS RATHER THAN ATOMIC ORBITALS ACTUALLY THE CONCEPT OF A SYNTHETIC METAL HAD ALREADY BEEN LAUNCHED BY MCCOY AND MOORE 3 SIMULTANEOUSLY WITH THE DISCOVERY OF SUPERCONDUCTIVITY IN MERCURY WHEN THEY PROPOSED TO PREPARE COM POSITE METALLIC SUBSTANCES FROM NON METALLIC CONSTITUENT ELEMENTS AS TO THE POSSIBILITY OF SUPERCONDUCTIVITY IN MATERIALS OTHER THAN METALS FRITZ LONDON IN 1937 4 WAS THE RST TO SUGGEST THAT COMPOUNDS WITH AROMATIC RINGS SUCH AS ANTHRACENE AND NAPHTALENE MIGHT EXHIBIT A CURRENT RUNNING FREELY AROUND THE RINGS UNDER A MAGNETIC ELD THE RST SUCCESSFUL ATTEMPT TO PROMOTE METAL LIKE CONDUCTION BETWEEN OPEN SHELL MOLECULAR SPECIES CAME OUT IN 1954 WITH THE SYNTHESIS OF THE MOLECULAR SALT OF PERYLENE OXIDIZED WITH BROMINE 5 ALTHOUGH THIS SALT WAS RATHER UNSTABLE IN THE EARLY 1960S RELATED TO THE QUEST FOR HIGHER TC LITTLE MADE AN IMPORTANT SUGGESTION 6 7 A NEW MECHANISM FOR SUPERCONDUCTIVITY EXPECTED TO LEAD TO A DRASTIC ENHANCEMENT OF THE SUPERCONDUCTING TC TO BE OBSERVED IN SPECIALLY DESIGNED MACROMOLECULES THE IDEA OF LITTLE WAS INDEED STRONGLY ROOTED IN THE ISOTOPE E ECT ONE OF THE GREATEST SUCCESSES OF THE THE ORY PROPOSED IN 1957 BY BARDEEN COOPER AND SCHRIE ER BCS 8 FOR THE INTERPRETATION OF SUPERCONDUCTIVITY IN MATERIALS KNOWN UP TO THAT DATE AND BASED ON THE PHONON MEDIATED ELECTRON PAIRING IN THE BCS THEORY THE ATTRAC TIVE INTERACTION BETWEEN ELECTRONS OR HOLES WHICH IS A PREREQUISITE FOR THE BOSE CONDENSATION OF ELECTRON PAIRS INTO THE SUPERCONDUCTING STATE RELIES ON THE MASS M OF THE IONS WHICH UNDERGO A SMALL DISPLACEMENT WHEN THE ELEC TRONS ARE PASSING CLOSE TO THEM NAMELY TC M 1 2 IT CAN BE NOTICED THAT FR OHLICH PROPOSED IN 1954 A MECHANISM FOR SUPERCONDUCTIVITY BASED ON THE 1D CASE 9 ALTHOUGH THE THEORY OF FR OHLICH HAS NOT BEEN ABLE TO ACCOUNT FOR THE SUPERCONDUCTIVITY OF METALS IT TURNED OUT TO BE QUITE SUCCESSFUL LATER FOR THE INTERPRETATION OF THE TRANSPORT PROPERTIES IN SOME 1D ORGANIC COMPOUNDS 3 THE PHYSICS OF ORGANIC SUPERCONDUCTORS AND CONDUCTORS