Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userReemergeing electronic nematicity in heavily hole-doped Fe-based superconductors
94
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In correlated electrons system, quantum melting of electronic crystalline phase often gives rise to many novel electronic phases. In cuprates superconductors, melting the Mott insulating phase with carrier doping leads to a quantum version of liquid crystal phase, the electronic nematicity, which breaks the rotational symmetry and exhibits a tight twist with high-temperature superconductivity. Recently, the electronic nematicity has also been observed in Fe-based superconductors. However, whether it shares a similar scenario with its cuprates counterpart is still elusive. Here, by measuring nuclear magnetic resonance in CsFe2As2, a prototypical Fe-based superconductor perceived to have evolved from a Mott insulating phase at 3d5 configuration, we report anisotropic quadruple broadening effect as a direct result of local rotational symmetry breaking. For the first time, clear connection between the Mott insulating phase and the electronic nematicity can be established and generalized to the Fe-based superconductors. This finding would promote a universal understanding on electronic nematicity and its relation with high-temperature superconductivity.
rate research
Read More
Although Fe-based superconductors are multiorbital correlated electronic systems, previous nuclei magnetic resonance (NMR) measurement suggests that a single spin-fluid model is sufficient to describe its spin behavior. Here, we firstly observed the breakdown of single spin-fluid model in a heavily hole-doped Fe-based superconductor CsFe2As2 by site-selective NMR measurement. At high temperature regime, both of Knight shift and nuclei spin-lattice relaxation at 133Cs and 75As nuclei exhibit distinct temperature-dependent behavior, suggesting the breakdown of single spin-fluid model in CsFe2As2. This is ascribed to the coexistence of both localized and itinerant spin degree of freedom at 3d orbits, which is consistent with orbital-selective Mott phase. However, single spin-fluid behavior is gradually recovered by developing a coherent state among 3d orbits with decreasing temperature. A Kondo liquid scenario is proposed for the low-temperature coherent state. The present work sets strong constraint on the theoretical model for Fe-based superconductors.
We study the dynamical quasiparticle scattering by spin and charge fluctuations in Fe-based pnictides within a five-orbital model with on-site interactions. The leading contribution to the scattering rate is calculated from the second-order diagrams with the polarization operator calculated in the random-phase approximation. We find one-particle scattering rates which are highly anisotropic on each Fermi surface sheet due to the momentum dependence of the spin susceptibility and the multi-orbital composition of each Fermi pocket. This fact, combined with the anisotropy of the effective mass, produces disparity between electrons and holes in conductivity, the Hall coefficient, and the Raman initial slope, in qualitative agreement with experimental data.
We report high-resolution neutron scattering measurements of the low energy spin fluctuations of KFe$_{2}$As$_{2}$, the end member of the hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ family with only hole pockets, above and below its superconducting transition temperature $T_c$ ($sim$ 3.5 K). Our data reveals clear spin fluctuations at the incommensurate wave vector ($0.5pmdelta$, 0, $L$), ($delta$ = 0.2)(1-Fe unit cell), which exhibit $L$-modulation peaking at $L=0.5$. Upon cooling to the superconducting state, the incommensurate spin fluctuations gradually open a spin-gap and form a sharp spin resonance mode. The incommensurability ($2delta$ = 0.4) of the resonance mode ($sim1.2$ meV) is considerably larger than the previously reported value ($2delta$ $approx0.32$) at higher energies ($gesim6$ meV). The determination of the momentum structure of spin fluctuation in the low energy limit allows a direct comparison with the realistic Fermi surface and superconducting gap structure. Our results point to an $s$-wave pairing with a reversed sign between the hole pockets near the zone center in KFe$_{2}$As$_{2}$.
Recent experiments reported an unusual nematic behavior of heavily hole-doped pnictides $A$Fe$_{2}$As$_{2}$, with alkali $A$ = Rb, Cs. In contrast to the $B_{2g}$ nematic order of the parent $Ae$Fe$_{2}$As$_{2}$ compounds (with alkaline earth $Ae$ = Sr, Ba), characterized by unequal nearest-neighbor Fe-Fe bonds, in the hole-doped systems nematic order is observed in the $B_{1g}$ channel, characterized by unequal next-nearest-neighbor Fe-Fe (diagonal Fe-As-Fe) bonds. In this work, using density functional theory, we attribute this behavior to the evolution of the magnetic ground state along the series $Ae_{1-x}A_{x}$Fe$_{2}$As$_{2}$, from single stripes for small $x$ to double stripes for large $x$. Our simulations using the reduced Stoner theory show that fluctuations of Fe moments are essential for the stability of the double-stripe configuration. We propose that the change in the nature of the magnetic ground state is responsible for the change in the symmetry of the vestigial nematic order that it supports.
A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature ($T_{rm c}$). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving nonmagnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe overlap with each other, the effects of two orders on superconductivity remain perplexing. Here we construct the three-dimensional electronic phase diagram, temperature ($T$) against pressure ($P$) and isovalent S-substitution ($x$), for FeSe$_{1-x}$S$_{x}$, in which we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended nonmagnetic tetragonal phase emerges, where we find a striking enhancement of $T_{rm c}$. The completed phase diagram uncovers two superconducting domes with similarly high $T_{rm c}$ on both ends of the dome-shaped antiferromagnetic phase. The $T_{rm c}(P,x)$ variation implies that nematic fluctuations unless accompanying magnetism are not relevant for high-$T_{rm c}$ superconductivity in this system.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
