Specific heat in zero and applied magnetic fields of the organic superconductor. alpha. -di(bis(ethylenedithio)tetrathiafulvalene)-ammonium- tetra(thiocyanato)mercurate (. alpha. -(ET) sub 2 (NH sub 4 )Hg(SCN) sub 4 )

Journal Article · Sat Dec 01 04:00:00 EST 1990 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.42.9963· OSTI ID:5976153

Andraka, B; Stewart, G R ^[1]; Carlson, K D; Wang, H H; Vashon, M D; Williams, J M ^[2]

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1. Department of Physics, University of Florida, Gainesville, FL (USA)
2. Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, IL (USA)

Specific heats determined down to 0.3 K establish the existence of bulk superconductivity in a new {alpha}-phase superconducting salt, {alpha}-di(bis (ethylenedithio) tetrathiafulvalene)- ammonium -tetra(thiocyanato)mercurate ({alpha}-(ET){sub 2}(NH{sub 4})Hg(SCN){sub 4}) ({Tc}=1 K), a derivative of the organic radical-cation donor molecule bis(ethylenedithio)tetrathiafulvalene (ET). This salt is important because it establishes a new structural class of organic superconductors, the {alpha}-phase class. The anomaly in the specific heat {ital C} is distinct but broad with a maximum in {ital C}/{ital T} at 0.8 K. The measurements yield a normal-state Sommerfield coefficient of {gamma}=29{plus minus}2 mJ/K{sup 2} mol, which is essentially identical to those of other ET-based organic superconductors, and an approximate value {Delta}{ital C}/{gamma}{Tc}=1.1{plus minus}0.2, which is smaller than the BCS value of 1.43. A sharp but unexplained increase in {ital C}/{ital T} occurs below 0.7 K. Determinations of the temperature derivatives of the upper critical magnetic fields at {Tc}({minus}{ital dH}{sub {ital c}2}/{ital dT}), from specific heats measured in applied magnetic fields, yield an extremely large value larger than 3 T/K for {bold H}{parallel}{ital ac}, where {ital ac} denotes the crystallographic {ital ac} plane (which contains the tightly connected conducting layers of ET donor molecules), and a value of 0.1{plus minus}0.02 T/K for {bold H}{parallel}{ital b}{sup *}.

• DOE Contract Number: FG05-86ER45268; W-31109-ENG-38
• OSTI ID: 5976153
• Journal Information: Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 42:16; ISSN PRBMD; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
CRYSTAL STRUCTURE
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
HETEROCYCLIC COMPOUNDS
LAYERS
MAGNETIC FIELDS
MERCURY COMPOUNDS
NITRILES
ORGANIC COMPOUNDS
ORGANIC MERCURY COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANIC SUPERCONDUCTORS
PHYSICAL PROPERTIES
SPECIFIC HEAT
SUPERCONDUCTIVITY
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
TTF-TCNQ
ULTRALOW TEMPERATURE