Nematicity from mixed<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>S</mml:mi><mml:mo>±</mml:mo></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>d</mml:mi><mml:mrow><mml:msup><mml:mi>x</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:mo>−</mml:mo><mml:msup><mml:mi>y</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:msub></mml:mrow></mml:math>states in iron-based superconductors

Livanas, G.; Aperis, Alex; Kotetes, Panagiotis; Varelogiannis, G.

doi:10.1103/physrevb.91.104502

Cited by 25 publications

(28 citation statements)

References 72 publications

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“…By studying the temperature dependence of the orthorhombic distortion, we surprisingly find that, in contrast to most other Fe-based systems, superconductivity favors the distorted nematic state. This is in qualitative agreement to recent theoretical work [ 23,24], which predicts that orbital order increases T c , but is in strong contrast to the behavior found in other Fe-based systems. The heat capacity data show that S substitution leads to a slight increase in the electronic density of states and results in a significant residual density of states at T = 0 K.…”

Section: Introductionsupporting

confidence: 91%

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

Wang

Hardy

Wolf

et al. 2016

Physica Status Solidi (b)

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Superconducting iron chalcogenide FeSe has the simplest crystal structure among all the Fe‐based superconductors. Unlike other iron pnictides, FeSe exhibits no long‐range magnetic order accompanying the tetragonal‐to‐orthorhombic structural distortion, which raises the fundamental question about the role of magnetism and its associated spin fluctuations in mediating both nematicity and superconductivity. The extreme sensitivity of FeSe to external pressure suggests that chemical pressure, induced by substitution of Se by the smaller ion S, could also a be good tuning parameter to further study the coupling between superconductivity and nematicity and to obtain information on both the Fermi‐surface changes and the symmetry of the superconducting state. Here, we study the thermodynamic properties of Fe(Se1−xSx) for three compositions, x=0, 0.08, and 0.15, using heat‐capacity and thermal‐expansion measurements. With increasing S content, we observe a significant reduction of the tetragonal‐to‐orthorhombic transition temperature Ts. However, this suppression of Ts is counterintuitively accompanied by an enhancement of the orthorhombic distortion δ below Tc, which clearly indicates that superconductivity favors the nematic state. In parallel, the superconducting transition temperature Tc is sizeably enhanced, whereas the increase of the Sommerfeld coefficient γn is quite moderate. In the T→0 limit, an unusually large residual density of states is found for x>0 indicative of significant substitution‐induced disorder. We discuss these observations in the context of “s+d” superconducting‐state symmetry.

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Section: Introductionsupporting

confidence: 91%

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

Wang

Hardy

Wolf

et al. 2016

Physica Status Solidi (b)

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“…Note that an s AE d state was also found in the T ¼ 0 numerical results of Ref. [39]. As the nematic susceptibility further increases, sd changes sign and eventually the magnitude of ð sd À jjÞ 2 becomes large enough that the transition between s and d becomes first order as shown in Fig.…”

supporting

confidence: 73%

“…As we shall show, this coupling implies that (1) nematic order leads to an enhancement of the SC transition temperature; (2) superconductivity can lead to the appearance of a nematic phase; (3) an s þ d symmetry phase [similar to the one proposed in Ref. [39]] or a firstorder transition can separate the pure s þÀ and d-wave states; and (4) a softening of the shear modulus below T c is an experimental signature of proximity to the regime where s þÀ and d-wave SC states are degenerate. These results are robust and do not rely on any specific shape of the Fermi surface, as they follow from a general Ginzburg-Landau analysis based on a free energy that respects the gauge and rotational symmetries of the system…”

mentioning

confidence: 72%

Nematicity as a Probe of Superconducting Pairing in Iron-Based Superconductors

2013

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In several families of iron-based superconducting materials, a d-wave pairing instability may compete with the leading s-wave instability. Here, we show that when both states have comparable free energies, superconducting and nematic degrees of freedom are strongly coupled. Whereas nematic order causes a sharp nonanalytic increase in T(c), nematic fluctuations can change the character of the s-wave to d-wave transition, favoring an intermediate state that does not break time-reversal symmetry but does break tetragonal symmetry. The coupling between superconductivity and nematicity is also manifested in the strong softening of the shear modulus across the superconducting transition. Our results show that nematicity can be used as a diagnostic tool to search for unconventional pairing states in iron pnictides and chalcogenides.

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“…Outside the SDW/nematic region, SC develops in the spin-singlet channel and in most of Fe-based superconductors has s−wave symmetry with a π phase shift between the SC order parameters on hole and on electron pockets ( s +− gap structure) 3,4 . It has been recently argued by several groups that the multiband structure of FeSCs allows for superconducting states with more exotic properties [5][6][7][8][9][10][11][14][15][16][17][18][19][20][21] . Of particular interest are SC states that break time-reversal symmetry (TRS), as such states have a plethora of interesting properties like, e.g., novel collective modes 12,13,15,20 .…”

Section: Introductionmentioning

confidence: 99%

Time-Reversal Symmetry Breaking Superconductivity in the Coexistence Phase with Magnetism in Fe Pnictides

2014

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We argue that superconductivity in the coexistence region with spin-density-wave (SDW) order in weakly doped Fe-pnictides differs qualitatively from the ordinary s +− state outside the coexistence region, as it develops an additional gap component which is a mixture of intra-pocket singlet (s ++ ) and inter-pocket spin-triplet pairings (the t−state). The coupling constant for the t−channel is proportional to the SDW order and involves interactions that do not contribute to superconductivity outside of the SDW region. We argue that the s +− and t−type superconducting orders coexist at low temperatures, and the relative phase between the two is in general different than 0 or π, manifesting explicitly the breaking of the time-reversal symmetry promoted by long-range SDW order. We show that this exotic state emerges already in the simplest model of Fe-pnictides, with one hole pocket and two symmetry-related electron pockets. We argue that in some parameter range time-reversal gets broken even before long-range superconducting order develops. IntroductionIron-based superconductors (FeSCs) have been the subject of intense study since 20081 . Their rich phase diagram includes the regions of superconductivity (SC), spin density wave (SDW), nematic order, and a region where SDW, SC, and nematic order coexist 2 . Outside the SDW/nematic region, SC develops in the spin-singlet channel and in most of Fe-based superconductors has s−wave symmetry with a π phase shift between the SC order parameters on hole and on electron pockets ( s +− gap structure) 3,4 . It has been recently argued by several groups that the multiband structure of FeSCs allows for superconducting states with more exotic properties 5-11,14-21 . Of particular interest are SC states that break time-reversal symmetry (TRS), as such states have a plethora of interesting properties like, e.g., novel collective modes 12,13,15,20 . TRS-broken states emerge when the phase differences ψ i between SC order parameters on different Fermi surfaces (FS) are not multiples of π.The two current proposals for TRS breaking in FeSCs are s + id 5,[9][10][11]19 and s + is states 6,15,20,21 . The first emerges when attractions in the d−wave and s−wave channels are of near-equal strength. The second emerges when there is a competition between different s +− states favored by inter-pocket and intra-pocket interactions. Both of these proposals were, however, argued to be applicable only to strongly hole or electron-doped FeSCc. For weakly/moderately doped FeSCs the common belief is that s +− superconductivity is robust. In this communication we argue that an exotic state which breaks TRS can emerge already at low doping, in a range where SC is known [22][23][24][25][26][27][28][29][30] to emerge from a pre-existing SDW state. Previous works on SC in the coexistence region focused on the SDW-induced modification of the form of s +− gap 31-37 . We argue that there is another effect -SDW order also induces attraction in another pairing channel, for which the order parameter is an admix...

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Nematicity from mixedS±+dx2−y2states in iron-based superconductors

Cited by 25 publications

References 72 publications

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

Nematicity as a Probe of Superconducting Pairing in Iron-Based Superconductors

Time-Reversal Symmetry Breaking Superconductivity in the Coexistence Phase with Magnetism in Fe Pnictides

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Nematicity from mixedS±+dx2−y2states in iron-based superconductors

Cited by 25 publications

References 72 publications

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se1−xSx)

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se1−xSx)

Nematicity as a Probe of Superconducting Pairing in Iron-Based Superconductors

Time-Reversal Symmetry Breaking Superconductivity in the Coexistence Phase with Magnetism in Fe Pnictides

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Resources

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Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

Superconductivity‐enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)