arXiv subjects

O. J. Taylor

Publications and source records attributed to O. J. Taylor.

5 recordsLinked to original sources

arXiv2010

Location of gap nodes in the organic superconductors $κ$-(ET)$_2$Cu(NCS)$_2$ and $κ$-(ET)$_2$Cu[N(CN)$_2$]Br determined by magnetocalorimetry

We report specific heat measurements of the organic superconductors $κ$-(ET)$_2$Cu(NCS)$_2$ and $κ$-(ET)$_2$Cu[N(CN)$_2$]Br. When the magnetic field is rotated in the highly conducting planes at low temperature ($T\simeq 0.4$ K), we observe clear oscillations of specific heat which have a strong fourfold component. The observed strong field and temperature dependence of this fourfold component identifies it as originating from nodes in the superconducting energy gap which point along the in-plane crystal axes ($d_{xy}$ symmetry)

cond-mat.supr-con↗

arXiv2008

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

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.

cond-mat.supr-con↗

arXiv2007

Specific heat measurements of the gap structure of the organic superconductors kappa-(ET)_2Cu[N(CN)_2]Br and kappa-(ET)_2Cu(NCS)_2

We present high resolution heat capacity measurements for the organic superconductors kappa-(ET)_2Cu[N(CN)_2]Br and kappa-(ET)_2Cu(NCS)_2 in fields up to 14 T. We use the high field data to determine the normal state specific heat and hence extract the behavior of the electronic specific heat C_{el} in the superconducting state in zero and finite fields. We find that in both materials for T/T_c<0.3, C_{el}(H=0)\sim T^2 indicating d-wave superconductivity. Our data are inconsistent with s-wave behavior, but may be fitted to a strong coupling d-wave model over the full temperature range.

cond-mat.supr-con↗

arXiv2005

de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2

We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al doped crystals of MgB$_2$. We have measured crystals with $\sim 7.5$% Al which have a $T_c$ of 33.6 K, ($\sim 14$% lower than pure MgB$_2$). dHvA frequencies for the $σ$ tube orbits in the doped samples are lower than in pure MgB$_2$, implying a $16\pm2%$ reduction in the number of holes in this sheet of Fermi surface. The mass of the quasiparticles on the larger $σ$ orbit is lighter than the pure case indicating a reduction in electron-phonon coupling constant $λ$. These observations are compared with band structure calculations, and found to be in excellent agreement.

cond-mat.supr-con↗

arXiv2005

Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2

We report measurements of the temperature dependent anisotropies ($γ_λ$ and $γ_ξ$) of both the London penetration depth $λ$ and the upper critical field of MgB$_2$. Data for $γ_λ=λ_c/λ_a$ was obtained from measurements of $λ_{a}$ and $λ_c$ on a single crystal sample using a tunnel diode oscillator technique. $γ_ξ=H_{c2}^{\parallel c}/H_{c2}^{\bot c}$ was deduced from field dependent specific heat measurements on the same sample. $γ_λ$ and $γ_ξ$ have opposite temperature dependencies, but close to $T_c$ tend to a common value ($γ_λ\simeq γ_ξ=1.75\pm0.05$). These results are in good agreement with theories accounting for the two gap nature of MgB$_2$

cond-mat.supr-con↗