Coexistence of incommensurate magnetism and superconductivity in Fe_{1+y}Se_xTe_{1-x}
R. Khasanov, M. Bendele, A. Amato, P. Babkevich, A. T. Boothroyd, A. Cervellino, K. Conder, S. N. Gvasaliya, H. Keller, H. -H. Klauss, H. Luetkens, E. Pomjakushina, B. Roessli
We report an investigation into the superconducting and magnetic properties of Fe_{1+y}Se_{x}Te_{1-x} single crystals by magnetic susceptibility, muon spin rotation, and neutron diffraction. We find three regimes of behavior in the phase diagram for 0\leq x\leq 0.5: (i) commensurate magnetic order for x< 0.1, (ii) bulk superconductivity for $x\lesssim 0.1$, and (iii) a range \sim 0.25\leq x\leq 0.45 in which superconductivity coexists with static incommensurate magnetic order. The results are qualitatively consistent with a two-band mean-field model in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.
We study the nonequilibrium dynamics of an electronic model with competing spin-density-wave and unconventional superconductivity in the context of iron pnictides. Focusing on the collisionless regime, we find that magnetic and superconducting order parameters may coexist dynamically after a sudden quench, even though the equilibrium thermodynamic state supports only one order parameter. We consider various initial conditions concomitant with the phase diagram and in a certain regime identify different oscillatory amplitude modes with incommensurate frequencies for magnetic and superconducting…
Tuning the superconducting and magnetic properties in Fe_ySe_0.25Te_0.75 by varying the Fe-content
用X射线衍射、SQUID磁强计、μ子自旋旋转和弹性中子衍射研究了Fe $_{y}$ Se $_{0.25}$ Te $_{0.75}$单晶（$0.9\leq y \leq1.1$）的超导和磁性。添加$y<1$的样品表现出体超导电性和无公度磁性的共存。$y\geq 1$的磁序仍然是无公度的，但随着Fe含量的增加，超导电性被抑制，磁相关长度增加。结果表明，Fe $_{y}$ Se $_{1-x}$ Te $_{x}$的超导性能和磁性能不仅可以通过改变Se/Te比来调节，而且可以通过改变Fe含量来调节。
To elucidate the spin dynamics of La$_{2-x}$Sr$_x$CuO$_4$, which couples with the charge degree of freedom, the spin excitations spanning the characteristic energy ($E_{\rm cross}$ $\sim$35-40 meV) are investigated for underdoped $x$ = 0.10 and optimally doped (OP) $x$ = 0.16 through inelastic neutron scattering measurements. Analysis based on a two-component picture of high-quality data clarified the possible coexistence of uprightly standing incommensurate (IC) excitations with gapless commensurate (C) excitations in the energy-momentum space. The IC component weakens the intensity toward $E…
Modulated superconductivity due to vacancy and magnetic order in $A_x$Fe$_{2-x/2}$Se$_2$ [$A=$Cs, K, (Tl,Rb), (Tl,K)] iron-selenide superconductors
本文计算了铁硒化物超导体的“调制”超导态。零动量$d-$波配对打破了$I4/mmm$空间群的常规BaFe $_2$ Se $_2$类晶体的平移对称性。当Fe空位形成有序状态时，这种配对状态变得相容，并且晶体对称性变为低温$I4/m$对称性。对于在$Q_v=(1/5, 3/5)$在K $_{0.82(2)}$ Fe $_{1.626(3)}$ Se $_2$的一个无公度空位顺序的具体情况下，我们发现，它诱导块棋盘形反铁磁相波矢量${\bf Q}_m=4{\bf Q}_v$。空位有序和磁有序的共存导致了一个重建的基态，它自然地耦合到$d-$波超导在一个统一的相位，我们建议将是一个一般的耦合所有的铁硒化物超导体。我们的结果与迄今为止的大量实验数据一致。因此，我们建议，不可分割性导致多个相的均匀共存，作为一个可行的替代方案，在高- $T_c$超导体的纳米级相分离，并发挥重要作用，在增强超导性。
We introduce a McMillan-Ginzburg-Landau theory to describe the cooperative coexistence of charge-density and superconducting order in two-dimensional crystals. With a free-energy that explicitly accounts for the competition between commensurate and incommensurate ground states, we are able to map the transition between these phases and monitor the development of discommensurations in the near-commensurate regime. Attributing the enhancement of superconducting order to density-wave fluctuations, we propose a coupling scheme that yields a phase diagram in qualitative agreement with experiments i…
The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La$_{1.93}$Sr$_{0.07}$CuO$_4$, a superconductor with a transition temperature of $T_c = 20$~K. At $T\ll T_c$, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below $\sim10$~K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpecte…
The concept of intertwined orders has been introduced to describe the cooperative relationship between antiferromagnetic spin correlations and electron (or hole) pair correlations that develop in copper-oxide superconductors. This contrasts with systems in which, for example, charge-density-wave (CDW) order competes for Fermi surface area with superconductivity. La$_{2-x}$Ba$_x$CuO$_4$ with $x=0.125$ provides an example in which the ordering of spin stripes coincides with the onset of two-dimensional superconducting correlations. The apparent frustration of the interlayer Josephson coupling ha…
