Kyuil Cho

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe2(As1–xPx)2

A Spike Inside the Dome The transition temperature Tc of iron-based superconductors has a dome-shaped dependence on chemical doping, and the superconductivity that develops underneath may obscure a potential quantum critical point (QCP) residing at absolute zero. With the aim of detecting signatures of this quantum criticality, Hashimoto et al. (p 1554; see the Perspective by Sachdev) measured the penetration depth of the pnictide series BaFe2(As1−xPx)2 as a function of x. A sharp peak right around the point where Tc has a maximum (x = 0.30) was observed, implying that the superfluid density diminishes sharply where one would expect it to be the most robust. This unusual finding is interpreted as a sign of a QCP at x = 0.30. A quantum critical point may be lurking inside the superconducting dome of a pnictide series. In a superconductor, the ratio of the carrier density, n, to its effective mass, m*, is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, λL. In two-dimensional systems, this ratio n/m* (~1/λL2) determines the effective Fermi temperature, TF. We report a sharp peak in the x-dependence of λL at zero temperature in clean samples of BaFe2(As1–xPx)2 at the optimum composition x = 0.30, where the superconducting transition temperature Tc reaches a maximum of 30 kelvin. This structure may arise from quantum fluctuations associated with a quantum critical point. The ratio of Tc/TF at x = 0.30 is enhanced, implying a possible crossover toward the Bose-Einstein condensate limit driven by quantum criticality.

Superconducting phase diagram and FFLO signature in λ -(BETS) 2 GaCl 4 from rf penetration depth measurements

We report the phase diagram of

Nodeless multiband superconductivity in stoichiometric single-crystalline CaKFe4As4

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Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

-(BETS)

Precision global measurements of London penetration depth in FeTe0.58Se0.42

_2

Complex superconductivity in the noncentrosymmetric compound Re6Zr

GaCl

The structural and magnetic phase transitions in Ca0.73La0.27FeAs2 with electron overdoped FeAs layers.

_4

Comparative Study of the Effects of Electron Irradiation and Natural Disorder in Single Crystals of SrFe2(As1-xPx)2 Superconductor (x=0.35)

from rf penetration depth measurements with a tunnel diode oscillator in a pulsed magnetic field. We examined four samples with 1100 field sweeps in a range of angles with the magnetic field parallel and perpendicular to the conducting planes. In the parallel direction,

Nodal superconductivity in isovalently substituted SrFe 2 (As 1 − x P x ) 2 pnictide superconductor at the optimal doping x = 0.35

H_{c2}

Environmental stability and anisotropic resistivity of Co-doped Na 1 − δ Fe 1 − x Co x As

appears to include a tricritical point at 1.6 K and 10 T with a phase line that increases to 11 T as the temperature is decreased to} 500 mK. The second phase line forms a clearly defined high field low temperature region satisfying several of the conditions of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We show remarkably good fits of