^{75} As NMR study of single crystals of the heavily overdoped pnictide superconductors Ba_{1−x} K_{x} Fe_{2} As_{2} ( x=0.7 and 1)

from Recent Articles in Phys. Rev. B by S. W. Zhang, L. Ma, Y. D. Hou, J. Zhang, T.-L. Xia, G. F. Chen, J. P. Hu, G. M. Luke, and W. Yu

We performed ⁷⁵As NMR studies on two overdoped high-quality Ba_1−xK_xFe₂As₂ (x=0.7 and 1.0) single crystals. In the normal states, we found a dramatic increase in the spin-lattice relaxation (1/⁷⁵T₁) from the x=0.7 to the x=1.0 samples. In KFe₂As₂, the ratio of 1/⁷⁵T₁TK_n², where ⁷⁵K_n is the Knight shift, increases as temperature drops. These results indicate the existence of another type of spin fluctuations in KFe₂As₂ which is accustomed to being treated as a simple Fermi liquid. In the superconducting state, the temperature scalings of 1/⁷⁵T₁ below T_c in the overdoped samples are significantly different from those in the under or optimally doped ones. A power-law scaling behavior 1/⁷⁵T₁T∼T^0.5 is observed, which indicates universal strong low-energy excitations in the overdoped hole-type superconductors.

Quantum interface between light and nuclear spins in quantum dots

from Recent Articles in Phys. Rev. B by Heike Schwager, J. Ignacio Cirac, and Géza Giedke

The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum-communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum dot strongly coupled to a high-finesse optical cavity. By adiabatically eliminating the electron a direct effective coupling is achieved. Depending on the laser field applied, interactions that enable either write-in or read-out are obtained.

nhomogeneous nuclear spin flips: Feedback mechanism between electronic states in a double quantum dot and the underlying nuclear spin bath

from Recent Articles in Phys. Rev. B by M. Stopa, J. J. Krich, and A. Yacoby

We discuss a feedback mechanism between electronic states in a two-electron double quantum dot and the underlying nuclear spin bath. We analyze two pumping cycles for which this feedback provides a force for the Overhauser fields of the two dots to either equilibrate or diverge. Which of these effects is favored depends on the g factor and Overhauser coupling constant of the material. The strength of the effect increases with the ratio of Overhauser coupling to electron exchange energy and also increases as the external magnetic field decreases.