Fengyan Wei

Unusual superconducting state at 49 K in electron-doped CaFe2As2 at ambient pressure

We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at 49 K, which has a low critical field < 4 Oe, and the other at 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr, or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase detected will be discussed.

Evidence for multiple gaps in the specific heat of LiFeAs crystals

The zero-field specific heat of LiFeAs was measured on several single crystals selected from a bulk sample. A sharp

Absence of zero-energy surface bound states in CuxBi2Se3studied via Andreev reflection spectroscopy

\ensuremath{\Delta}{C}_{\text{p}}/{T}_{\text{c}}

Lower critical field, anisotropy, and two-gap features of LiFeAs

anomaly

Disorder-induced bulk superconductivity in ZrTe3single crystals via growth control

\ensuremath{\approx}20\text{ }\text{mJ}/\text{mole}\text{ }{\text{K}}^{2}

Two-gap features in the specific heat of (M,K)Fe2As2 (M = Ba, Sr)

was observed. The value appears to be between those of

Carrier contribution to the specific heat coefficient of Sr 1 − x K x Fe 1 − x As 2

\text{SmFeAs}({\text{O}}_{0.9}{\text{F}}_{0.1})

Doping dependence of phase-separation morphology in (Sr,K)Fe2As2

and

Possible Interface Superconductivity in Rare-earth Doped CaFe2As2 and Undoped CaFe2As2

({\text{Ba}}_{0.6}{\text{K}}_{0.4}){\text{Fe}}_{2}{\text{As}}_{2}

Defect-induced Superconductivity up to 49 K in (Ca1-xRx)Fe2As2

but bears no clear correlation with their Sommerfeld coefficients. The electronic specific heat below