Superconductivity and spin-density waves: organic superconductors

Psaltakis, G.C.; Fenton, E.W.

doi:10.1088/0022-3719/16/20/015

Cited by 81 publications

(64 citation statements)

References 11 publications

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“…The coupling in the t−channel is a combination of interactions that do not contribute to s +− SC in the paramagnetic state. A real admixture between these singlet and triplet SC states, s ± t, has been discussed in the SDW/SC coexistence region of organics, cuprates, and heavy fermions [38][39][40][41][42][43][44] . Here, however, we found that the situation is different -s ± t state exists only near T c , while at low T , the relative phase between the two SC components is different from 0 or π, i.e., the order parameter has s + e iθ t form.…”

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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Section: Introductionmentioning

confidence: 99%

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

2014

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“…One may think of a general Ginzburg-Landau theory with antiferromagnetic and superconducting order parameters like those considered in [12]. The Freedericksz transition is, of course, the result of having two states close in energy, and it may be present even within mean field theories that consider general competition between spin-density wave and dSC states.…”

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confidence: 99%

Proximity Effect and Josephson Coupling in the SO(5) Theory of High-TcSuperconductivity

et al. 1998

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We consider proximity effect coupling in Superconducting/Antiferromagnetic/Superconducting (S-A-S) sandwiches using the recently developed SO(5) effective theory of high temperature superconductivity. We find that, for narrow junctions, the A region acts like a strong superconductor, and that there is a critical junction thickness which depends on the effective SO(5) coupling constants and on the phase difference across the junction, at which the A region undergoes a Freedericksz-like transition to a state which is intermediate between superconductor and antiferromagnet. For thick junctions, the current-phase relation is sinusoidal, as in standard S-N-S and S-I-S junctions, but for thin junctions it shows a sharp break in slope at the Freedericksz point.

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“…In an exact diagonalization study of the t − J model [13], the dynamical correlation functions of the π−operators have been calculated and found to be non-zero. The existence of both AF and triplet pairing amplitude with net momentum Q was reported earlier in the mean-field study of a pairing Hamiltonian in the context of the heavy fermions and organic superconductors [8,14], although the conditions under which the triplet amplitude appears and the modifications of the phase boundaries due to this triplet amplitude were not dealt with. In a recent investigation, Kyung [15] considered explicit mean-field pairing interactions in the singlet and triplet channel with a repulsive on-site interaction to stabilize the d-wave SC state (over s-wave) and discussed the coexistence of a dynamically generated triplet SC pair amplitude and AF long range order (LRO).…”

Section: Introductionmentioning

confidence: 90%

Antiferromagnetism and superconductivity in a model with extended pairing interactions

2001

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The competition between antiferromagnetism and the d + id superconducting state is studied in a model with near and next near neighbour interactions in the absence of any on-site repulsion. A mean field study shows that it is possible to have simultaneous occurrence of an antiferromagnetic and a singlet d + id superconducting state in this model. In addition, such a coexistence generates a triplet d + id superconducting order parameter with centre of mass momentum Q = (π, π) dynamically having the same orbital symmetry as the singlet superconductor. Inclusion of next nearest neighbour hopping in the band stabilises the d xy superconducting state away from half filling, the topology of the phase diagram, though, remains similar to the near neighbour model. In view of the very recent observation of a broad region of coexistence of antiferrmagnetic and unconventional superconducting states in organic superconductors, the possibility of observation of the triplet state has been outlined.

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Superconductivity and spin-density waves: organic superconductors

Cited by 81 publications

References 11 publications

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

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

Proximity Effect and Josephson Coupling in the SO(5) Theory of High-TcSuperconductivity

Antiferromagnetism and superconductivity in a model with extended pairing interactions

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