Observation of non-Fermi liquid behavior in hole-dopedLiFe1−xVxAs

Abstract

We synthesized a series of V-doped LiFe1−xVxAs single crystals. The superconducting transition temperature Tc of LiFeAs decreases rapidly at a rate of 7 K per 1% V. The Hall coefficient of LiFeAs switches from negative to positive with 4.2% V doping, showing that V doping introduces hole carriers. This observation is further confirmed by the evaluation of the Fermi surface volume measured by angle-resolved photoemission spectroscopy (ARPES), from which a 0.3 hole doping per V atom introduced is deduced. Interestingly, the introduction of holes does not follow a rigid band shift. We also show that the temperature evolution of the electrical resistivity as a function of doping is consistent with a crossover from a Fermi liquid to a non-Fermi liquid. Our ARPES data indicate that the non-Fermi liquid behavior is mostly enhanced when one of the hole dxz/dyz Fermi surfaces is well nested by the antiferromagnetic wave vector to the inner electron Fermi surface pocket with the dxy orbital character. The magnetic susceptibility of LiFe1−xVxAs suggests the presence of strong magnetic impurities following V doping, thus providing a natural explanation to the rapid suppression of superconductivity upon V doping.

Evolution of superconductivity and antiferromagnetic order in Ba(Fe$_{0.92-x}$Co$_{0.08}$V$_x$)$_2$As$_2$

“…The T c suppression rate is calculated to be 7.4 K/1%V (Fig. 1(d)), similar as that in previous reports about magnetic impurity doped Fe-based superconductors such as V-doped LiFeAs [14], Cr-doped Ba(Fe,Ni) 2 As 2 [15] or Mn-doped Ba 0.5 K 0.5 Fe 2 As 2 [16]. On the other hand, the phase diagram of Ba(Fe,Co) 2 As 2 has been extensively studied in early publications [5,17], consensus has been reached about the existence of a weak short-range incommensurate AFM order in the slightly under doped region.…”

Strong local moment antiferromagnetic spin fluctuations in V-doped LiFeAs

“…We report the magnetic excitations in hole-doped nonsuperconducting LiFe 0.955 V 0.045 As, which has nearly nested hole-electron Fermi surfaces with d xz/yz and d xy orbital characters, respectively, and exhibits non-Fermi-liquid behavior [30]. We observe enhanced commensurate magnetic fluctuations at antiferromagnetic (AF) wave vectors, suggesting that the non-Fermi-liquid behavior is intimately associated with magnetic fluctuations.…”

“…Such a difference may be rooted in the different sites of the dopants. Since Vanadium is directly introduced into the FeAs layer while K + is not, the Fe-As bond length is affected by V-doping [30] and a high spin state is favored in V-doped LiFeAs. With increasing V-doping, the nesting condition improves between the inner hole Fermi surface with d xz/yz orbital character and the inner electron pocket mainly derived from d xy orbital character [30].…”

“…Since Vanadium is directly introduced into the FeAs layer while K + is not, the Fe-As bond length is affected by V-doping [30] and a high spin state is favored in V-doped LiFeAs. With increasing V-doping, the nesting condition improves between the inner hole Fermi surface with d xz/yz orbital character and the inner electron pocket mainly derived from d xy orbital character [30]. Therefore, the enhanced inter-orbital scattering between d xz/yz and d xy orbitals, which suppresses superconductivity [32], favors the "spin mixing" process [ Fig.…”

“…In the case of LiFeAs family, ARPES experiments indicate that doping V into Fe sites actually introduces hole carriers with a rate of 0.3 hole per V dopant and selectively enlarges the inner hole Fermi surface [ Fig. 1(b)] [30], even though the doping-induced impurity and disorder effects might still play a role in the transport and susceptibility measurements with higher V-doping ratio. Although hole-doping via K substitution in Ba 1−x K x Fe 2 As 2 induces superconductivity, less than 2% V-doping in LiFe 1−x V x As quickly suppresses the superconductivity in pure LiFeAs, even with a perfect nesting condition established between the inner hole and electron Fermi pockets at x = 0.084 [see arrows in Fig.…”