Competition between superconductivity and nematic order: Anisotropy of superconducting coherence length

Moon, Eun-Gook; Sachdev, Subir

doi:10.1103/physrevb.85.184511

Cited by 31 publications

(22 citation statements)

References 33 publications

(42 reference statements)

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“…The twofold symmetry of the vortex core state can be understood by the difference between SC coherence length ξ along the a and b directions, being attributed to the strong impact of the nematic order on SC [42,43].…”

Section: Fig 3 (A) Temperature Dependence Of the Splitmentioning

confidence: 99%

Nematicity and in-plane anisotropy of superconductivity inβ−FeSedetected bySe77nuclear magnetic resonance

Baek

Efremov

et al. 2016

Phys. Rev. B

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The recent study of 77 Se nuclear magnetic resonance (NMR) in a β-FeSe single crystal proposed that ferro-orbital order breaks the 90• C4 rotational symmetry, driving nematic ordering. Here, we report an NMR study of the impact of small strains generated by gluing on nematic state and spin fluctuations. We observe that the local strains strongly affect the nematic transition, considerably enhancing its onset temperature. On the contrary, no effect on low-energy spin fluctuations was found. Furthermore we investigate the interplay of the nematic phase and superconductivity. Our study demonstrates that the twinned nematic domains respond unequivalently to superconductivity, evidencing the twofold C2 symmetry of superconductivity in this material. The obtained results are well understood in terms of the proposed ferro-orbital order.Many experiments have established the existence of nematic order -a state that spontaneously breaks the rotational symmetry while time-reversal invariance is preserved -in Fe-based superconductors (FeSCs) [1][2][3][4][5][6][7][8]. Although whether spin or orbital degrees of freedom drive the nematic order is still under debate [9][10][11][12][13][14][15], it is widely believed that a nematic instability is an important characteristic of the normal state from which superconductivity emerges. Therefore establishing the mechanism of the nematic order will help to elucidate the Cooper pair glue in FeSCs.In most FeSCs, the nematic state arises in the vicinity of a spin-density wave state. The temperature (T ) interval separating them is small. As a result the strong interaction of various degrees of freedom hides the nature of the nematic order. The only exception is β-FeSe which has a PbO-type crystal structure. The nematic order occurs at T nem ≈ 91 K and at a lower temperature of T c ≈ 9 K SC sets in. The absence of static magnetism in the whole interval of temperature together with its simple structure [16] make β-FeSe the primary object for investigation of nematicity and its interplay with SC [14,[17][18][19][20][21][22][23][24][25][26]. To other spectacular properties of β-FeSe belongs the dramatic increase in T c under pressure [27,28] or by growing mono layer films on substrates [29][30][31].The band structure of β-FeSe is typical for FeSC [32,33]. The low energy is given by two hole bands around the Γ point and two electron bands around the M point. The nesting between the electron and the hole bands advocates strong spin fluctuations (SFs) at low T which indeed were observed in nuclear magnetic resonance (NMR) and neutron studies at T ≪ T nem . However no enhancement of SFs was found close to the nematic transition. It led to the suggestion that nematic state in β-FeSe is driven by orbital degrees of freedom [34][35][36][37].In this Rapid Communication, we report the investigations of nematic order in the normal and superconducting states of β-FeSe. We show that gluing the sample introduces random local strains (defects) and significantly smears out the otherwise sharp nematic tran...

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Section: Fig 3 (A) Temperature Dependence Of the Splitmentioning

confidence: 99%

Nematicity and in-plane anisotropy of superconductivity inβ−FeSedetected bySe77nuclear magnetic resonance

Baek

Efremov

et al. 2016

Phys. Rev. B

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“…The same spin fluctuations [7], possibly combined with orbital degrees of freedom [13][14][15][16], can give rise to an emergent electronically driven breaking of rotational symmetry [17][18][19], often referred to as nematic order [20]. The interplay between s þÀ and d-wave superconductivity has been extensively studied [8][9][10]12,[21][22][23] as has the interplay between s þÀ and nematic order [24][25][26][27], but the coupling of all three seems not to have previously been considered. Here, we show that such a coupling can have dramatic effects, qualitatively changing the phase diagram, increasing the SC transition temperature T c , and helping to distinguish an s-d competition from other proposed phases.…”

mentioning

confidence: 99%

“…The change from s þÀ to d-wave superconductivity in the absence of nematicity [21,31] and the interplay between nematicity and a single SC order parameter [24][25][26] have been studied. On general grounds, one expects that a single superconducting order parameter Á couples to a nematic order parameter ' via the biquadratic term Á 2 ' 2 in the free energy [27].…”

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confidence: 99%

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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“…An additional important remark is that part of these conclusions are based in the assumption of the validity of the GL formalism, under discussions in these materials 47 . Assuming this framework, full time dependent GL calculations, as well as a model for the interaction between nematic DBs and superconducting vortices are necessary to rigorously quantify our experimental results.…”

Section: Discussionmentioning

confidence: 99%

Nematicity in the superconducting mixed state of strain detwinned underdoped Ba( Fe1−xCox)2As2

et al. 2019

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Evidence of nematic effects in the mixed superconducting phase of slightly underdoped Ba(Fe1−xCox)2As2 is reported. We have found strong in-plane resistivity anisotropy for crystals in different strain conditions. For these compositions, there is no magnetic long range order, so the description may be ascribed to the interplay between the superconducting and nematic order parameters. A piezoelectric-based apparatus is used to apply tensile or compressive strain to tune nematic domain orientation in order to examine intrinsic nematicity. Measurements are done under a rotating magnetic field and the analysis of the angular dependence of physical quantities identifies the cases in which the sample is detwinned. Furthermore, the angular dependence of the data allows us to evaluate the effects of nematicity on the in-plane superconductor stiffness. Our results show that although nematicity contributes in a decisive way in the conduction properties, its contributions to the anisotropy properties of the stiffness of the superconducting order parameter is not as significant in these samples.

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Competition between superconductivity and nematic order: Anisotropy of superconducting coherence length

Cited by 31 publications

References 33 publications

Nematicity and in-plane anisotropy of superconductivity inβ−FeSedetected bySe77nuclear magnetic resonance

Nematicity and in-plane anisotropy of superconductivity inβ−FeSedetected bySe77nuclear magnetic resonance

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

Nematicity in the superconducting mixed state of strain detwinned underdoped Ba( Fe1−xCox)2As2

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