Jia Dai

Simultaneous optimization of spin fluctuations and superconductivity under pressure in an iron-based superconductor.

We present a high-pressure NMR study of the overdoped iron pnictide superconductor NaFe0.94Co0.06As. The low-energy antiferromagnetic spin fluctuations in the normal state, manifest as the Curie-Weiss upturn in the spin-lattice relaxation rate 1/(75)T1T, first increase strongly with pressure but fall again at P>Popt=2.2  GPa. Neither long-ranged magnetic order nor a structural phase transition is encountered up to 2.5 GPa. The superconducting transition temperature Tc shows a pressure dependence identical to the spin fluctuations. Our observations demonstrate that magnetic correlations and superconductivity are optimized simultaneously as a function of the electronic structure, thereby supporting very strongly a magnetic origin of superconductivity.

Microscopic Coexistence of Superconductivity and Antiferromagnetism in Underdoped Ba(Fe(1-x)Ru(x))2As2.

We use (75)As nuclear magnetic resonance to investigate the local electronic properties of Ba(Fe(1-x)Ru(x))(2)As(2) (x = 0.23). We find two phase transitions: to antiferromagnetism at T(N) ≈ 60 K and to superconductivity at T(C) ≈ 15 K. Below T(N), our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4μ(B)/Fe. The spin-lattice relaxation rate 1/(75)T(1) is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below T(C), 1/(75)T(1) on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity.

Local spin fluctuations in iron-based superconductors:Se77andRb87NMR measurements on Tl0.47Rb0.34Fe1.63Se2

We report nuclear magnetic resonance (NMR) studies of the intercalated iron selenide superconductor (Tl, Rb)

Phase separation, competition, and volume-fraction control in NaFe1-xCoxAs

_{y}

Microscopic Coexistence of Superconductivity and Antiferromagnetism in Underdoped Ba(Fe1-xRux)(2)As-2

Fe

Quenched Fe moment in the collapsed tetragonal phase of Ca1-xPrxFe2As2

_{2-x}

Microscopic Coexistence of Superconductivity and Antiferromagnetism in UnderdopedBa(Fe1−xRux)2As2

Se

Mermin-Wagner physics, (H,T) phase diagram, and candidate quantum spin-liquid phase in the spin-1/2 triangular-lattice antiferromagnet Ba 8 CoNb 6 O 24

_2

NMR Evidence for Two Spin-Fluctuation Components and their Linear Scaling with Superconductivity in Fe Superconductors

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NMR Studies of the Candidate Topological Superconductor Sn

T_c = 32