Superconductor-Insulator Phase Separation Induced by Rapid Cooling in kappa-(ET)_2Cu[N(CN)_2]Br

Abstract

We present measurements of the low temperature specific heat of single crystals of kappa-(ET)_2Cu[N(CN)_2]Br as a function of the cooling rate through the glasslike structure transition at $\sim$ 80K. We find that rapid cooling produces a small (< 4%) decrease in the superconducting transition temperature accompanied by a substantial (up to 50%) decrease in the normal-state electronic specific heat. A natural explanation of our data is that there is a macroscopic phase separation between superconducting and insulating regions in rapidly cooled samples.

4 pages, to appear in Phys. Rev. B (Rapid Comm)

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• Location of gap nodes in the organic superconductors $\kappa$-(ET)${}_2$Cu(NCS)${}_2$ and $\kappa$-(ET)${}_2$Cu[N(CN)${}_2$]Br determined by magnetocalorimetry
• Phase separation in a lattice model of a superconductor with pair hopping
• Mott metal-insulator transition induced by utilizing a glass-like structural ordering in low-dimensional molecular conductors
• Superconductivity in correlated BEDT-TTF molecular conductors: critical temperatures and gap symmetries
• The magnetic field induced phase separation in a model of a superconductor with local electron pairing
• Phase separation of superconducting phases in the Penson-Kolb-Hubbard model
• Insights from experiment and $abinitio$ calculations into the glass-like transition in the molecular conductor $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Cl
• Stretched exponential spin relaxation in organic superconductors
• Superconductivity and fluctuating magnetism in quasi two-dimensional kappa-(BEDT-TTF)2Cu[N(CN)2]Br probed with implanted muons