Superconductivity of κ-(BEDT–TTF)2 Cu[N(CN) 2]Br: Isotope Effect Revisited

1997 ◽  
Vol 488 ◽  
Author(s):  
M. Tokumoto ◽  
N. Kinoshita ◽  
Y. Tanaka ◽  
H. Anzai
Keyword(s):  
Transition Temperature ◽  
Isotope Effect ◽  
Volume Fraction ◽  
Organic Superconductors ◽  
Organic Superconductor ◽  
Superconducting Transition ◽  
Hydrogen Atoms ◽  
Superconducting Volume Fraction ◽  
Cooling Speed ◽  
Inverse Isotope Effect

AbstractIn 1991, we reported a normal isotope effect in organic superconductor κ-(BEDT–TTF)2Cu[N(CN)2]Br, when all the hydrogen atoms of BEDT – TTF were replaced with deuterium. In other words, Tc was depressed by as much as 0.9 K, in contrast to the “inverse isotope effect” commonly observed in 10K-class organic superconductors. Recently, it was reported that the deuterated κ-(BEDT–TTF)2Cu[N(CN)2]Br shows an insulating nature when cooled very rapidly. Therefore, it is necessary for us to reexamine the superconducting transition of both deuterated and undeuterated κ- (BEDT – TTF)2Cu[N(CN)2]Br by SQUID measurements with special attention to the cooling speed. We studied the effect of cooling rate ranging from 10 K/min down to as slow as 0.02 K/min, and observed a significant effect not only on the superconducting transition temperature Tc but also on the superconducting volume fraction.

scholarly journals Evolution of Shape and Volume Fraction of Superconducting Domains with Temperature and Anion Disorder in (TMTSF)2ClO4

Crystals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 72
Author(s):  
Kaushal K. Kesharpu ◽  
Vladislav D. Kochev ◽  
Pavel D. Grigoriev
Keyword(s):  
Cooling Rate ◽  
Annealing Time ◽  
Volume Fraction ◽  
Density Wave ◽  
Spin Density Wave ◽  
Finite Size ◽  
Organic Superconductors ◽  
Organic Superconductor ◽  
Sample Length ◽  
Sample Shape

In highly anisotropic organic superconductor (TMTSF)2ClO4, superconducting (SC) phase coexists with metallic and spin-density wave phases in the form of domains. Using the Maxwell-Garnett approximation (MGA), we calculate the volume ratio and estimate the shape of these embedded SC domains from resistivity data at various temperature and anion disorder, controlled by the cooling rate or annealing time of (TMTSF)2ClO4 samples. We found that the variation of cooling rate and of annealing time affect differently the shape of SC domains. In all cases the SC domains have oblate shape, being the shortest along the interlayer z-axis. This contradicts the widely assumed filamentary superconductivity along the z-axis, used to explain the anisotropic superconductivity onset. We show that anisotropic resistivity drop at the SC onset can be described by the analytical MGA theory with anisotropic background resistance, while the anisotropic Tc can be explained by considering a finite size and flat shape of the samples. Due to a flat/needle sample shape, the probability of percolation via SC domains is the highest along the shortest sample dimension (z-axis), and the lowest along the sample length (x-axis). Our theory can be applied to other heterogeneous superconductors, where the size d of SC domains is much larger than the SC coherence length ξ, e.g., cuprates, iron-based or organic superconductors. It is also applicable when the spin/charge-density wave domains are embedded inside a metallic background, or vice versa.

EFFECT OF COOLING RATE ON THE TRANSITION TEMPERATURE IN Bi–Pb–Sr–Ca–Cu–O SYSTEM

1990 ◽  
Vol 04 (04) ◽  
pp. 293-299
Author(s):  
YUGUI WANG ◽  
JINSONG WANG ◽  
NANLIN WANG ◽  
XINPING JIAO ◽  
GUCHANG HAN ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Specific Heat ◽  
Cooling Rate ◽  
Volume Fraction ◽  
Oxygen Deficiency ◽  
Ac Susceptibility ◽  
Rapid Quenching ◽  
Nominal Composition ◽  
Unit Cell Size ◽  
Superconducting Volume Fraction

The resistance and ac susceptibility measurements show that cooling rate of the cast-annealing samples in heat treatment process has some effect on the 110 K superconducting phase in Bi–Pb–Sr–Ca–Cu–O system. Rapid quenching of the sample in air from 845°C causes oxygen deficiency in lattice and brings about a trifling change of unit cell size along c-axis direction. The dc magnetization and specific heat anomaly ∆c measurements demonstrate that fast cooling rate can reduce the transition temperature of high T c phase and the lower critical field, and weaken the pinning forces for vertex lines. The peak value of specific heat anomaly of the sample with nominal composition of Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 4.5 O y is still small in comparison with YBa 2 Cu 3 O 7. From the magnetization curve we can estimate that the superconducting volume fraction is about 20%.

scholarly journals On the “inverse” isotope effect in organic superconductors: new findings and implications

2001 ◽  
Vol 120 (1-3) ◽  
pp. 713-714 ◽  
Author(s):  
Aravinda M. Kini ◽  
John A. Schlueter ◽  
Brian H. Ward ◽  
Urs W. Geiser ◽  
H.Hau Wang
Keyword(s):  
Isotope Effect ◽  
Organic Superconductors ◽  
New Findings ◽  
Inverse Isotope Effect

THEORY OF THE ISOTOPE EFFECT AND SUPERCONDUCTING TRANSITION TEMPERATURE IN HIGH-Tc OXIDES

2011 ◽  
Vol 25 (26) ◽  
pp. 2069-2078 ◽  
Author(s):  
A. BECHLAGHEM ◽  
D. BOURBIE
Keyword(s):  
Experimental Data ◽  
Transition Temperature ◽  
Fermi Level ◽  
Isotope Effect ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
Van Hove Singularity ◽  
High Tc ◽  
Analytical Expressions

Analytical expressions for the superconducting transition temperature Tc and the isotope coefficient α have been obtained for the case where the Fermi level is close to the van Hove singularity. In this approach, we consider two interactions, the first related to the phonons and the second relevant to the magnetic excitations. Our result shows that the isotope coefficient α decreases with the superconducting transition temperature Tc in qualitative agreement with experimental data.

scholarly journals Isotopeneffekt und Druckkoeffizient der Übergangstemperatur zur Supraleitung in der Eliashberg-Theorie / Isotope Effect and Pressure Coefficient of the Superconducting Transition Temperature within the Eliashberg-Theory

1975 ◽  
Vol 30 (2) ◽  
pp. 250-255
Author(s):  
W. Kessel
Keyword(s):  
Transition Temperature ◽  
Isotope Effect ◽  
Superconducting Transition Temperature ◽  
Pressure Coefficient ◽  
Volume Control ◽  
Superconducting Transition ◽  
Eliashberg Equations ◽  
Eliashberg Theory ◽  
Fundamental Parameters ◽  
Experimental Values

Abstract Isotope Effect and Pressure Coefficient of the Superconducting Transition Temperature within the Eliashberg-Theory Starting from the observation that both the mass of the ions and their volume control the phonon frequencies by stretching the phonon spectrum, the change of the Eliashberg-equations of the theory of superconductivity regarding these stretchings is considered. General expressions for the isotopic exponent and the pressure coefficient of the transition temperature are derived in which only derivatives of the transition temperature with respect to the fundamental parameters of the theory are involved. A comparison with experimental values shows that lead is not the metal with the highest transition temperature possible under the simple metals.

SOME DEUTERIUM ISOTOPE EFFECTS: I. WATER SOLVOLYSIS OF METHYL-d3 ESTERS

1960 ◽  
Vol 38 (2) ◽  
pp. 222-232 ◽  
Author(s):  
J. A. Llewellyn ◽  
R. E. Robertson ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Hydrogen Atoms ◽  
Deuterium Isotope Effect ◽  
Methyl Group ◽  
Out Of Plane ◽  
Thermodynamic Effects ◽  
Inverse Isotope Effect ◽  
Activated Complex

The α-deuterium isotope effect has been examined for the solvolysis of a series of esters containing a fully deuterated methyl group. The possible sources of the effect have been divided into "thermodynamic" effects which appear to favor more rapid reaction of the protium compound and "zero point" effects where stiffening of out-of-plane vibrations may account for the direction of the observed isotope effects. It appears that the inverse isotope effect may be a measure of the spatial restrictions placed on the hydrogen atoms on the carbon atom in the activated complex.

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