We study the spin fluctuation mediated superconducting pairing gap in. Theory of spinfluctuation induced superconductivity in iron. Our analytical framework, based on the random phase approximation, allows for a selfconsistent calculation of material specific characteristics in the interacting, and more specifically, the superconducting state. Theories based on the coupling between spin fluctuations and fermionic quasiparticles are among the leading contenders to explain the origin of hightemperature superconductivity, but estimates of the strength of this interaction differ widely1.
The discovery of heavyfermion superconductivity in cecu2si2 was an. Theories based on the coupling between spin fluctuations and fermionic quasiparticles are among the leading contenders to explain the origin of hightemperature superconductivity, but estimates of the strength of this interaction differ widely. Spin and valencefluctuation mediated superconductivity in. The spin fluctuations are arguably the most promising candidate that can mediate such unconventional superconductivity. It is strong evidence that magnetic fluctuations are the ones doing the pairing. At high pressures, superconductivity is supposed to be mediated by valence fluctuations, in contrast to ambient pressure, where spin fluctuations most likely act as pairing glue. The superconducting transition temperature computed with this coupling constant exceeds 150 k, demonstrating that spin fluctuations have. Spin and charge transport in material with spindependent. However, superconductivity can also be derived from other types of elementary excitations. On the other hand, the separation between the onset of the second region sc ii, which corresponds to the sharp increase in t c around 12 gpa, and the disappearance of the afm order around 8 gpa indicates to a different mechanism for the emergence of the sc ii phase. The resistivity of pd, np, and pu as a function of temperature. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a.
Large triplet pairing mixing in the fflo state of spin. Pdf d and p wave superconductivity mediated by spin. Possible spinfluctuation mediated superconductivity in. We point out that superconductivity will be favored in the spin singlet channel and may be more easily realized around 25% hole doping. The origin of hightemperature superconductivity is still not clear, but it seems that instead of electronphonon attraction mechanisms, as in conventional superconductivity, one is dealing with genuine electronic mechanisms e. Pdf eliashberg theory for spinfluctuations mediated. The difference in the superconducting states between. Understanding repulsively mediated superconductivity of correlated electrons via massively parallel density matrix. Raising the critical temperature by disorder in unconventional. The mass enhancement and the quasiparticle decay rate exhibit in the normal state marginal fermi liquid behavior while in the superconducting state the quasiparticle.
This explains two of the wellknown systematic material dependences of t c in the cuprates. That is, there can be a local imbalance of up and down spin electrons for a short time span that is much larger than the average imbalance see fig. Strength of the spinfluctuationmediated pairing interaction in a high. Zayets spintronic research center, national institute of advanced industrial science and technology aist, umezono 111, tsukuba, ibaraki, japan received 28 june 2012. We compare predictions of the meanfield theory of superconductivity for metallic systems on the border of a density instability for cubic and tetragonal lattices. Nmr study of local hole distribution, spin fluctuation and. This suggests that the short range charge ordering may also contribute to an enhancement of spin fluctuation mediated superconductivity. Spinfluctuation theories of unconventional superconductivity.
Observation of doubledome superconductivity in potassium. However, the recent observation of strong incommensurate spin fluctuation 9, 10 indicates that more concrete evidence of fm spin fluctuation is needed. The small value of the electrical conductivity suggests that the charge transport takes place by polaron hopping. Strong orbital fluctuation arguably can be induced by phonons iron 19 or arsenic 20 atomic oscillation and mediate theswavestate,incontrastwiththeconventionalspin fluctuationmediated s wave state 21,22. Wehave performed neutron inelastic scattering experiments at t 10 and 20k. The spin fluctuations are arguably the most promising candidate that can mediate such. This problem remains outstanding because direct experimental. Pdf the superconducting ferromagnet ucoge researchgate.
The optimized eigenvalue of the linearized eliashberg equation, a measure for the strength of superconductivity, is not strongly affected by the bare width of the incipient band, but the parameter regime where superconductivity is optimized is wide when the incipient band is narrow, and in this sense, the coexistence of narrow and wide bands is. Revisit of the orbitalfluctuationmediated superconductivity in lifeas. Antiferromagnetic spin fluctuation and superconductivity. To date, however, the microscopic structure of this interface is still uncertain, which hampers an understanding of interfacial electron.
Possible mechanism to enhance spinfluctuationmediated. The occurrence of the meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. The good agreement of our theory with the experimental data evidences that the magnetic scenario for superconductivity in which cooper pairing is mediated by spin fluctuations. This interaction is extracted from the coqblinschrieffer model for a single kondolike localised. The challenge of unconventional superconductivity science. Theory of spin fluctuation induced superconductivity in ironbased superconductors junhua zhang iowa state university follow this and additional works at.
One possible origin of the dc conductivity change is a hopping distance andor hopping frequency modulation due to the. Role of valence fluctuations in the superconductivity of. We show that i d wave instability mediated by antiferromagnetic spin fluctuations is stronger than p wave instability mediated by ferromagnetic spin fluctuations both in 2d and 3d, and ii d wave instability in 2d is much stronger than that in 3d. Spin and chargefluctuation effects on dynamic conductivity.
We consider the problem of spin uctuation mediated pairing in a paramagnetic system, as well as a system in which spin density wave order is. The solid lines through the data points show the sum of the calculated spin fluctuation contribution and an experimentally determined, suitable nonmagnetic background ag for pd and th for np and pu. Developing a rigorous theory for any of these classes of materials has. This result had been naturally explained in terms of the orbital fluctuation scenario t. Spin state dependence of electrical conductivity of spin. Angle and frequency dependence of selfenergy from spin. In section 2 we will show that in the case of a material with spin dependent conductivity the requirement of spin and charge conservation leads to the spin charge transport equations, which are more complex than the valetfert equation. The superconducting properties are compatible with a d wave superconducting model, with a finite dos at the fermi level. We present a novel method for embedding spin and charge fluctuations in an anisotropic, multiband and fullbandwidth eliashberg treatment of superconductivity. B 90, 035104 2014, whereas an opposite result is obtained by the spin fluctuation scenario. The overall success of the theory in describing main properties of the hight c cuprates seems. Direct evidence for a magnetic felectron mediated in cecoin. Although spin fluctuations are believed to have an important role in the mechanism responsible for hightemperature superconductivity, it has been unclear whether the strength of. Our observation of a strongcoupling feature in the tunnelling conductivity, combined with recent inelastic neutron scattering data,14,15 strongly suggest a pairing interaction mediated by spin.
L735 october 1987 with 58 reads how we measure reads. Spintriplet pairing is tightly connected to an exotic pairing mechanism for superconductivity. Andrey chubukov university of wisconsinmadison iccmp workshop, nov. Superconducting and pseudogap transition temperatures in high. Citeseerx document details isaac councill, lee giles, pradeep teregowda. We found the dwave pairing with high t c mediated by strong kinematical interaction of electrons with spin fluctuations. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating cooper pairs, though with spin and angular. The calculations are based on the parameterisation of an effective interaction arising from the exchange of density fluctuations and assume that a single band is relevant for superconductivity.
Temperaturedependent reflectivity measurements in the frequency range 758000 cm 1 were performed on bafe 2 as 0. Pdf a spin fluctuation model for dwave superconductivity. On the other hand, the recent demonstrations of high temperature superconductivity in heavily electrondoped fese films or flakes through an alkalimetal potassium k. Characteristic signatures associated with both are distinct. Spin fluctuation theories of unconventional superconductivity theory winter school, tallahassee, january 7 20 andrey chubukov. Strength of the spinfluctuationmediated pairing interaction in. In the conventional superconductors, the cooper pairs are mediated by phonons, which is a process where only the correlations between the phonons and the charge properties of the electrons are needed. Spectral function and conductivity in the normal state of the cuprates. Because the antiferromagnetic phase is nearby, an interaction mediated by spin fluctuations is peaked at momenta at or near. Spin fluctuations federation of american scientists.
It seems clear, anyway, that the main physics in the hight c cuprates occurs in the cuo 2 planes, involving the electrons in the 3d xy22orbitals of copper ions and 2p x and 2p y. Recently the theory has been extended to deal with the spin fluctuaionmediated superconductivity with anisotropic order parameters in strongly correlated. In the iron pnictidechalcogenide superconductors, one of the proposed pictures for the pairing is through exchanging the antiferromagnetic spin fluctuations with the two electrons on the electron hole pockets. At lower temperatures, there is clear evidence that cecoin 5 is an unconventional superconductor with a nodal energy gap 30 33 possibly with d. Pdf boosting tc with disorder in spinfluctuation mediated. A selfconsistent microscopic theory for the 2d hubbard hamiltonian and additional electronphonon interaction yields below t c a gap in the quasiparticle decay rate as well as in the spin and charge fluctuation spectra. Based on the above analysis, we will in this paper consider a phononmediated pairing mechanism for the superconductivity in na xcoo 2yh o. Developments of the theory of spin fluctuations and spin fluctuation. Close relationship between superconductivity and the bosonic. Request pdf lectures on the spin pairing mechanism in hightemperature. Materials science copyright 2020 picoscale structural. The larger characteristic energy of spin fluctuations well ac counts for its higher tc in the mechanism proposed by moriya et al. Spinfluctuationmediated pairing symmetry on the metallic. Charge density wave cdw, the periodic modulation of the electronic charge density, will open a gap on the fermi surface that commonly leads to decreased or vanishing conductivity.
We study the spinfluctuationmediated superconducting pairing gap in a. Abanov department of physics, university of wisconsin, madison, wisconsin 53706 received 4 september 2000. Here, we analyse the charge and spin excitation spectra determined by. Chargefluctuationmediated superconductivity in the dp. These amount that the best situation is the antiferromagnetic fluctuation mediated in 2d. We argue that most mn atoms are segregated within nanometersized regions of magnetic precipitate and form the alloy, or compound, mnsi 2z with z. Density fluctuation mediated superconductivity arxiv. Spectral function and conductivity in the normal state of the. Spin and charge transport in materials with spin dependent conductivity v. Unconventional superconductivity in pucoga 5 nature. Theory suggests that the spintriplet pairing for the unconventional super conductivity in sr 2 ruo 4 is mediated by exchange of fm spin fluctuations 8. Enhancement of spinfluctuationmediated superconductivity. Antiferromagnetic spin fluctuations and superconductivity in. Spin triplet superconductivity, which is generally difficult to be realised as opposed to singlet, is theoretically discussed in terms of i dimensionality and fermiology, ii pairing interaction mediated by spin fluctuations vs.
We note that a recent arpes study rules out an extrinsic origin 5 16 of the replica band. Spinfluctuationmediated superconductivity article pdf available in journal of physics c solid state physics 2028. Spinfluctuation mediated hightemperature ferromagnetism in. Superconductivity from repulsion lecture 3 superconductivity.
Although spin fluctuations are believed to have an important role in the mechanism responsible for hightemperature superconductivity, it has been unclear whether the strength of their coupling. In this sense, orbital distillation is a key for enhancing t c. During the past few decades, several new classes of superconductors have been discovered that do not appear to be related to traditional superconductors. Any material exhibiting these properties is a superconductor. The spectra have been found to be described in energy by a singlelorentzian function and analyzed on the basis of the so calledselfconsistent renormalization scr theory. Spin fluctuation mediated pairing symmetry on the metallic kagome lattice. Fermi surface is favorable for spin fluctuation mediated dwave superconductivity, and the mixing of the dz2 orbital character in the fermi surface degrades superconductivity 1,2. Spinfluctuation mediated thermal conductivity around the. Superconductivity and charge density wave in zrte 3. The wiedemannfranz law is observed at low temperatures t 0 k. In hightc superconductors, spin fluctuations are supposed to provide the necessary. Spinfluctuation exchange study of superconductivity in. In 1986, it was discovered that some cuprateperovskite ceramic materials have a critical temperature above 90 k.
Spin fluctuations and pairing symmetry in axfe2yse2. Electronic spectrum and superconductivity are studied within the extended hubbard model which includes intersite coulomb repulsion and electronphonon interaction. As will be seen below, thiswx also reflects when the cuo chain mediated cou. Details of pairingpairbreaking in a particular system depend on. A qualitative explanation for the occurrence of super conductivity in itinerant ferromagnets is offered by spin fluctuation models 7,8. Vedic physics theory posits that super conductivity occurs amidst the 18 types of quarks in the thaamic type of matter, known as the substratum, a. For repulsive interaction u, the dominant term is in the spin channel. We present evidence that ucoge is a pwave superconductor and argue that superconductivity is mediated by critical ferromagnetic spin fluctuations. Abstract we consider an swave superconductor in the vicinity of a secondorder ferromagnetic fm or spin densitywave sdw quantum critical point qcp, where the superconductivity and magnetism arise from separate mechanisms. Specifically, super conductivity occurs at at an approximate phase related velocity, between the 4th. Phononmediated unconventional superconductivity in naxcoo2y. The most remarkable characteristics in lifeas gap structure would be that the largest gap emerges on the tiny holepockets around z point. Spin and valence fluctuation mediated superconductivity in pressurised fe and cecu2sige2 article in physica b condensed matter 359361. With increasing temperature, a deviation from the wiedemannfranz law.
Developments of the theory of spin fluctuations and spin. Link between spin fluctuations and cooper pairing in copper. The initial hint came from the fact that all of the ferromagnetic superconductors are very close to the border between a. Neutron spin resonance in the 112type ironbased superconductor. Optical and resistivity data indicate the development of a pseudogap below tu for the transport in the cdirection,14.
Oct 26, 2005 in this article we first discuss very briefly some developments in the theory of magnetism of metals leading to the spin fluctuation theory and then go on to discuss recent theories of spin fluctuation mediated superconductivity which are now considered to be appropriate as applied to hight c cuprates, organic and heavy electron. Using the fluctuation exchange approximation, this idea is confirmed for the hubbard on a lattice with. The source of the superconductivity of these materials is likely different from the electronion interactions that are at the heart of conventional superconductivity. Recent microscopic studies on the hubbard model have shown that the s z 0 triplet pairing is mixed with singlet pairing in the fflo state of the hubbard model on the twoleg laddertype lattice, and also on the square lattice, where dwave superconductivity is mediated by spin fluctuations. In order to identify the most favorable situation for superconductivity in the repulsive singleband hubbard model, we have studied instabilities for dwave pairing mediated by antiferromagnetic spin fluctuations and ppairing mediated by ferromagnetic fluctuations with the fluctuation exchange approximation in both two dimensions and three dimensions. Strong interplay between stripe spin fluctuations, nematicity and. We have obtained the direct experimental evidence that the same proportionality relation between t 0 and t c holds in upd 2 al 3 as observed in high t c cuprates, strongly suggesting that the superconductivity in upd 2 al 3 is mediated by the spin fluctuations. Direct neutron observation of spin fluctuations in related compounds lda calculations indicate proximity to quantum critical point there is growing evidence that sf have a role in the superconductivity. Based on this finding, the linenode symmetry can be explained naturally as spin fluctuation mediated superconductivity. In these systems the valence and magnetic critical points, at p v and p c, respectively, are well separated. Eveniftheyarenotthedominantcoupling mechanism, orbital fluctuations have been shown to strengthen pairing in spin fluctuationmediated coupling 24. Separate tuning of nematicity and spin fluctuations to. Summary and discussion we have investigated the chargefluctuation mediated superconductivity in the simplest dp model described by the infinite intraatomic coulomb repulsion and the nearestneighbor dp hybridization with the help of the auxiliary particle method to gether with the 1in expansion method.
It was believed from the start that fluctuating magnetism may play a key role in the superconductivity of ferromagnetic superconductors. A novel, purely dynamical spinfluctuationmediated pairing interaction is proposed and. Ferromagnetism stabilized by lattice distortion at the. Lectures on the spin pairing mechanism in hightemperature. In the theoretical part, we address spin uctuation mediated pairing in the weakcoupling limit by a systematic study of the oneband hubbard model. Spin and charge transport in materials with spindependent. Spinfluctuation mediated superconductivity and magnetic. Characteristic signatures associated with both phenomena are distinct. Spin fluctuations and hightemperature superconductivity.
Spinfluctuationmediated superconductivity iopscience. We propose that if there are two small pocketlike fermi surfaces, and the spin susceptibility is pronounced around a wave vector \\bf q that bridges the two pockets, the spin singlet superconductivity mediated by spin fluctuations may have a high transition temperature. Here we analyze the charge and spin excitation spec. Boosting tc with disorder in spinfluctuation mediated unconventional superconductors. These strong spin fluctuations are consistent with linenode symmetry in spinfluctuationmediated superconductors 25,26. In the case of spin fluctuation mediated dwave superconductivity, a critical energy. Designing 2d topological scs 2d topological sc oddparity sc of spinless fermions majorana bound state strategies. The spinuctuation theory for the high superconductivity.
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