Pseudogap-like phase in Ca(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ revealed by ${}^{75}$As NQR

Abstract

We report ${}^{75}$As NQR measurements on single crystalline Ca(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ ($0\le x\le 0.09$). The nuclear spin-lattice relaxation rate $T_1^{-1}$ as a function of temperature $T$ and Co dopant concentration $x$ reveals a normal-state pseudogap-like phase below a crossover temperature $T^{\ast }$ in the under- and optimally-doped region. The resulting $x$-$T$ phase diagram shows that, after suppression of the spin-density-wave order, $T^{\ast }$ intersects $T_c$ falling to zero rapidly near the optimal doping regime. Possible origins of the pseudogap behavior are discussed.

published in Physical Review B (regular article)

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