Transfer of optical spectral weight in magnetically ordered superconductors

Fernandes, Rafael M.; Schmalian, Joerg

doi:10.1103/physrevb.82.014520

Cited by 140 publications

(225 citation statements)

References 45 publications

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“…Moreover, this transition immediately indicates two distinct superconducting ground states. In our system, the robust T -linear behavior of δλ L (T ) on both sides of the purported QCP at x = 0.30 argues against a drastic change in the superconducting gap structure [2,39]. The fact that the zero-temperature extrapolation of the antiferromagnetic transition T N (x) into the dome [12] coincides with the location of the QCP ( Fig.…”

mentioning

confidence: 56%

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A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂

Hashimoto

Cho

Shibauchi

et al. 2012

Science

324

305

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In a superconductor, the ratio of the carrier density, n, to their effective mass, m * , is a fundamental property directly reflecting the length scale of the superfluid flow, the London penetration depth, λL. In two dimensional systems, this ratio n/m * (∼ 1/λ 2 L ) determines the effective Fermi temperature, TF . We report a sharp peak in the x-dependence of λL at zero temperature in clean samples of BaFe2(As1−xPx)2 at the optimum composition x = 0.30, where the superconducting transition temperature Tc reaches a maximum of 30 K. This structure may arise from quantum fluctuations associated with a quantum critical point (QCP). The ratio of Tc/TF at x = 0.30 is enhanced, implying a possible crossover towards the Bose-Einstein condensate limit driven by quantum criticality.In two families of high temperature superconductors, cuprates and iron-pnictides, superconductivity emerges in close proximity to an antiferromagnetically ordered state, and the critical temperature T c has a dome shaped dependence on doping or pressure [1][2][3]. What happens inside this superconducting dome is still a matter of debate [3][4][5]. In particular, elucidating whether a quantum critical point (QCP) is hidden inside it (Figs. 1A and B) may be key to understanding high-T c superconductivity [4,5]. A QCP marks the position of a quantum phase transition (QPT), a zero temperature phase transition driven by quantum fluctuations [7].The London penetration depth λ L is a property that may be measured at low temperature in the superconducting state to probe the electronic structure of the material, and look for signatures of a QCP. The absolute value of λ L in the zero-temperature limit immediately gives the superfluid density λ −2which is a direct probe of the superconducting state; here m * i and n i are the effective mass and concentration of the superconducting carriers in band i, respectively [8]. Measurements on high-quality crystals are necessary because impurities and inhomogeneity may otherwise wipe out the signatures of the QPT. Another advantage of this approach is that it does not require the application of a strong magnetic field, which may induce a different QCP or shift the zero-field QCP [9].BaFe 2 (As 1−x P x ) 2 is a particularly suitable system for penetration depth measurements as, in contrast to most other Fe-based superconductors, very clean [10] and homogeneous crystals of the whole composition series can be grown [11]. In this system, the isovalent substitution of P for As in the parent compound BaFe 2 As 2 offers an elegant way to suppress magnetism and induce superconductivity [11]. Non-Fermi liquid properties are apparent in the normal state above the superconducting dome ( Fig. 2A) [11,12] and de Haas-van Alphen (dHvA) oscillations [10] have been observed over a wide x range including the superconducting compositions, giving detailed information on the electronic structure. Because P and As are isoelectric, the system remains compensated for all values of x (i.e., volumes of the electron and hole Fermi surfaces...

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mentioning

confidence: 56%

“…2C), corresponding to the smaller volume of Fermi surface due to partial SDW gapping. The microscopic coexistence is also supported by the enhancement of λ 2 L (0) on approaching the QCP from the SDW side, which is not expected in the case of phase separation [14,39].…”

Section: Microscopic Coexistence Of Superconductivity and Sdw Ordmentioning

confidence: 82%

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂

Hashimoto

Cho

Shibauchi

et al. 2012

Science

324

305

View full text Add to dashboard Cite

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“…Moreover, this transition immediately indicates two distinct superconducting ground states. The strong temperature dependence of δλ L (T ) at low temperatures observed on both sides of the QCP argues against a drastic change in the superconducting gap structure [9,113]. The fact that the zero-temperature extrapolation of the AFM transition T N (x) into the dome coincides with the location of the QCP leads us to conclude that the QCP separates a pure superconducting phase and a superconducting phase coexisting with the SDW order ( Fig.…”

Section: F Continuous Quantum Phase Transition Inside the Domementioning

confidence: 87%

A Quantum Critical Point Lying Beneath the Superconducting Dome in Iron Pnictides

Shibauchi

Carrington

Matsuda

2014

Annu. Rev. Condens. Matter Phys.

388

380

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Whether a quantum critical point (QCP) lies beneath the superconducting dome has been a long-standing issue that remains unresolved in many classes of unconventional superconductors, notably cuprates, heavy fermion compounds and most recently iron-pnictides. The existence of a QCP may offer a route to understand: the origin of their anomalous non-Fermi liquid properties, the microscopic coexistence between unconventional superconductivity and magnetic or some exotic order, and ultimately the mechanism of superconductivity itself. The isovalent substituted iron-pnictide BaFe2(As1−xPx)2 offers a new platform for the study of quantum criticality, providing a unique opportunity to study the evolution of the electronic properties in a wide range of the phase diagram. Recent experiments in BaFe2(As1−xPx)2 have provided the first clear and unambiguous evidence of a second order quantum phase transition lying beneath the superconducting dome.

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“…In this case, it is straightforward to conclude that ⌬ = ͉⌬ 1 ͉ = ͉⌬ 2 ͉. Moreover, using formula ͑37͒, it follows that a s,11 = a s, 22 and u s,1 = u s,2 . Thus, independently of the relative sign between the Cooperpair wave functions of the two bands, they have the same SC Ginzburg-Landau coefficients, meaning that the thermodynamic properties of the "pure" s ++ and s +− states will be the same.…”

Section: A Particle-hole Symmetric Casementioning

confidence: 90%

“…In particular, optical conductivity measurements show a considerable Drude weight as well as a pronounced midinfrared peak below the Néel transition temperature T N , consistent with the itinerant picture. 21,22 Furthermore, band-structure calculations reveal that the crystalline field is unable to significantly split the energy levels in order to localize 3d electrons. 23 Also, several theoretical models demonstrate the adequacy of the itinerant description.…”

Section: Introductionmentioning

confidence: 99%

Competing order and nature of the pairing state in the iron pnictides

2010

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We show that the competition between magnetism and superconductivity can be used to determine the pairing state in the iron arsenides. To this end we demonstrate that the itinerant antiferromagnetic phase (AFM) and the unconventional $s^{+-}$ sign-changing superconducting state (SC) are near the borderline of microscopic coexistence and macroscopic phase separation, explaining the experimentally observed competition of both ordered states. In contrast, conventional $s^{++}$ pairing is not able to coexist with magnetism. Expanding the microscopic free energy of the system with competing orders around the multicritical point, we find that static magnetism plays the role of an intrinsic interband Josephson coupling, making the phase diagram sensitive to the symmetry of the Cooper pair wavefunction. We relate this result to the quasiparticle excitation spectrum and to the emergent SO$(5)$ symmetry of systems with particle-hole symmetry. Our results rely on the assumption that the same electrons that form the ordered moment contribute to the superconducting condensate and that the system is close to particle-hole symmetry. We also compare the suppression of SC in different regions of the FeAs phase diagram, showing that while in the underdoped side it is due to the competition with AFM, in the overdoped side it is related to the disappearance of pockets from the Fermi surface.Comment: 24 pages, 13 figures; revised versio

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Transfer of optical spectral weight in magnetically ordered superconductors

Cited by 140 publications

References 45 publications

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂

A Quantum Critical Point Lying Beneath the Superconducting Dome in Iron Pnictides

Competing order and nature of the pairing state in the iron pnictides

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Transfer of optical spectral weight in magnetically ordered superconductors

Cited by 140 publications

References 45 publications

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe 2 (As 1– x P x ) 2

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe 2 (As 1– x P x ) 2

A Quantum Critical Point Lying Beneath the Superconducting Dome in Iron Pnictides

Competing order and nature of the pairing state in the iron pnictides

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A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂

A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe ₂ (As _1– _x P _x ) ₂