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تسجيل مستخدم جديدMagnetic instabilities in quasi-one-dimensional Cr-based material
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The magnetic response of a K2Cr3As3 sample has been studied by means of dc magnetization measurements as a function of magnetic field (H) at different temperatures ranging from 5 K up to 300 K. Looking at the magnetic hysteresis loops m(H), a diamagnetic behavior of the sample has been inferred at temperatures higher than 60 K, whereas at lower temperatures the sample shows a hysteresis loop compatible with the presence of ferrimagnetism. Moreover, several spike-like magnetization jumps, both positive and negative, have been observed at certain fields in the range -1000 Oe < H < 1000 Oe, regardless of the temperature considered. The field position of the magnetization jumps has been studied at different temperatures, and their distribution can be described by a Lorentzian curve.
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Recently a new family of Cr-based A2Cr3As3 (A = K, Rb, Cs) superconductors were reported, which own a rare quasi-one-dimensional (Q1D) crystal structure with infinite (Cr3As3)2- chains and exhibit intriguing superconducting characteristics possibly d
erived from spin-triplet electron pairing. The crystal structure of A2Cr3As3 is actually a slight variation of the hexagonal TlFe3Te3 prototype although they have different lattice symmetry. Here we report superconductivity in a 133-type KCr3As3 compound that belongs to the latter structure. The single crystals of KCr3As3 were prepared by the deintercalation of K ions from K2Cr3As3 crystals which were grown from a high-temperature solution growth method, and it owns a centrosymmetric lattice in contrast to the non-centrosymmetric K2Cr3As3. After annealing at a moderate temperature, the KCr3As3 crystals show bulk superconductivity at 5 K revealed by electrical resistivity, magnetic susceptibility and heat capacity measurements. The discovery of this KCr3As3 superconductor provides a different structural instance to study the exotic superconductivity in these Q1D Cr-based superconductors.
Following the discovery of superconductivity in quasi-one-dimensional K$_2$Cr$_3$As$_3$ containing [(Cr$_3$As$_3$)$^{2-}$]$_{infty}$ chains [J. K. Bao et al., arXiv: 1412.0067 (2014)], we succeeded in synthesizing an analogous compound, Rb$_2$Cr$_3$A
s$_3$, which also crystallizes in a hexagonal lattice. The replacement of K by Rb results in an expansion of $a$ axis by 3%, indicating a weaker interchain coupling in Rb$_2$Cr$_3$As$_3$. Bulk superconductivity emerges at 4.8 K, above which the normal-state resistivity shows a linear temperature dependence up to 35 K. The estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit by a factor of two. Furthermore, the electronic specific-heat coefficient extrapolated to zero temperature in the mixed state increases with $sqrt{H}$, suggesting existence of nodes in the superconducting energy gap. Hence Rb$_2$Cr$_3$As$_3$ manifests itself as another example of unconventional superconductor in the Cr$_3$As$_3$-chain based system.
We present neutron total scattering and density functional theory studies on quasi-one-dimensional superconducting K$_2$Cr$_3$As$_3$ revealing a frustrated structural instability. Our first principles calculations find a significant phonon instabilit
y which, under energy minimization, corresponds to a frustrated orthorhombic distortion. In diffraction studies we find large and temperature independent atomic displacement parameters which pair distribution analyses confirms and shows as resulting from highly localized orthorhombic distortions of the CrAs sublattice and coupled K displacements. These results suggest a far more complex phase diagram than previously assumed for this unusual superconductor with the likelihood of subtle interplays of structure, electron-phonon and magnetic interactions.
We report the discovery of bulk superconductivity (SC) at 6.1 K in a quasi-one-dimensional (Q1D) chromium pnictide K$_2$Cr$_3$As$_3$ which contains [(Cr$_3$As$_3$)$^{2-}$]$_{infty}$ double-walled subnano-tubes with face-sharing Cr$_{6/2}$ (As$_{6/2}$
) octahedron linear chains in the inner (outer) wall. The material has a large electronic specific-heat coefficient of 70$sim$75 mJ K$^{-2}$ mol$^{-1}$, indicating significantly strong electron correlations. Signature of non-Fermi liquid behavior is shown by the linear temperature dependence of resistivity in a broad temperature range from 7 to 300 K. Unconventional SC is preliminarily manifested by the estimated upper critical field exceeding the Pauli limit by a factor of three to four. The title compound represents a rare example that possibly unconventional SC emerges in a Q1D system with strong electron correlations.
We report $^{75}$As NMR measurements on the new quasi one-dimensional superconductor K$_{2}$Cr$_{3}$As$_{3}$ ($T_{c} sim 6.1$~K) [J. K. Bao et al., Phys. Rev. X {bf 5}, 011013 (2015)]. We found evidence for strong enhancement of Cr spin fluctuations
above $T_c$ in the [Cr$_{3}$As$_{3}$]$_{infty}$ double-walled subnano-tubes based on the nuclear spin-lattice relaxation rate $1/T_{1}$. The power law temperature dependence, $1/T_{1}T sim T^{-gamma}$ ($gamma sim 0.25$), is consistent with the Tomonaga-Luttinger liquid. Moreover, absence of the Hebel-Slichter coherence peak of $1/T_{1}$ just below $T_{c}$ suggests unconventional nature of superconductivity.
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