Time reversal symmetry breakdown in normal and superconducting states in frustrated three-band systems

Bojesen, Troels Arnfred; Babaev, Egor; Sudbø, Asle

doi:10.1103/physrevb.88.220511

Cited by 64 publications

(55 citation statements)

References 21 publications

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“…On the other hand, for two-band systems there are indications that if one of the bands is strongly in BCS regime E F ≫ |∆| then the behavior of system as a whole is closer to BCS type 28 . For multiband superconductors allowing for the s + is state to occur, fluctuations have been shown to lead to new phases 67,68 and re-entrant phase transitions 69 . Moreover, softening of Leggett modes 53,57 suggests that close to the s + is state boundaries fluctuations become progressively more important.…”

Section: Ertiesmentioning

confidence: 99%

s+is superconductivity with incipient bands: Doping dependence and STM signatures

et al. 2017

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Motivated by the recent observations of small Fermi energies and comparatively large superconducting gaps, present also on bands not crossing the Fermi energy (incipient bands) in iron-based superconductors, we analyze the doping evolution of superconductivity in a four-band model across the Lifshitz transition including BCS-BEC crossover effects on the shallow bands. Similar to the BCS case, we find that with hole doping the phase difference between superconducting order parameters of the hole bands change from 0 to π through an intermediate s + is state, breaking time-reversal symmetry (TRS). The transition, however, occurs in the region where electron bands are incipient and chemical potential renormalization in the superconducting state leads to a significant broadening of the s + is region. We further present the qualitative features of the s + is state that can be observed in scanning tunneling microscopy (STM) experiments, also taking incipient bands into account.

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Section: Ertiesmentioning

confidence: 99%

s+is superconductivity with incipient bands: Doping dependence and STM signatures

et al. 2017

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“…Domain walls between BTRS states is also highly important in rotational response of 3 He [17]. Aspects of topological defects of s + is states received attention only recently [18][19][20][21]. The remaining question is how domain walls can be created and observed in s + is superconductors.…”

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confidence: 99%

Domain Walls and Their Experimental Signatures ins+isSuperconductors

Garaud

Babaev

2014

Phys. Rev. Lett.

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Arguments were recently advanced that hole-doped Ba1−xKxFe2As2 exhibits s+is state at certain doping. Spontaneous breaking of time reversal symmetry in s + is state, dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in s+is state. We find that in this state the domain walls can have dipole-like magnetic signature (in contrast to the uniform magnetic signature of domain walls p + ip superconductors).We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and be observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm s + is state.The recently discovered iron-based superconductors [1] may exhibit new physics originating in the possible frustration of inter-band couplings between more than two superconducting components [2][3][4][5]. For a two-band superconductor, inter-band Josephson interaction either locks or anti-locks phases, so that the ground state interband phase difference is respectively 0 or π. Similarly, for more than two bands, each inter-band coupling favours (anti-)locking of the two corresponding phases. However, these Josephson terms can collectively compete so that optimal phases are neither locked nor anti-locked. There, the resulting frustrated phase differences are neither 0 nor π. Since it is not invariant under complex conjugation, such a ground state spontaneously breaks the TimeReversal Symmetry (TRS) [2,3]. This is the s + is state, with the spontaneously Broken Time-Reversal Symmetry (BTRS), that recently received strong theoretical support in connection with hole-doped Ba 1−x K x Fe 2 As 2 , [5]. There are also other scenarios for BTRS states in pnictides [6,7], and related multi-component states may possibly exist in other classes of materials [8].Symmetrywise, these BTRS states break the U(1) × Z 2 symmetry. The topological defects associated with the breakdown of a discrete Z 2 symmetry are domain walls (DW) segregating regions of different broken states [9]. Other superconductors with BTRS and having domain walls are the chiral p-wave superconductors. There are evidences for such superconductivity in Sr 2 RuO 4 [10]. For that material, it is predicted that domain walls have magnetic signature and thus can be detected by measuring the magnetic field (see e.g. [11,12]). These signatures were searched for in surface probes measurements, but were not experimentally detected [13]. This led to intense theoretical investigation of possible mechanisms for the field suppression (see e.g. [14]). The problem of interaction of vortices and domain walls in these systems and magnetization process was studied in [15,16]. Domain walls between BTRS states is also highly important in rotational response of 3 He [17]. Aspects of topological defects of s + is states received attention only recently [18][19][20][21]. The remaining question is how domain walls can be created and observed in s + is superco...

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“…The lattice version of an n-band superconductor in the London limit is given by (when the energy density is summed over the entire lattice) 11,12 …”

Section: Reduced Three-band Model and Its Interpretationmentioning

confidence: 99%

“…We do this by carrying out single-site and cluster mean-field calculations, 9,10 and compare them to results of largescale Monte-Carlo simulations, going well beyond what has previously been obtained in the literature. 11,12 In so doing, we identify a source of strong fluctuation effects other than low dimensionality, namely frustration in the phases of the superconducting order parameters due to interband Josephson couplings.…”

Section: Introductionmentioning

confidence: 99%

Fluctuation Effects in Phase-Frustrated Multiband Superconductors

Bojesen

Sudbø

2015

J Supercond Nov Magn

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We compare the phase-diagrams of an effective theory of a three-dimensional multi-band superconductor obtained within standard and cluster mean-field theories, and in large-scale Monte Carlo simulations. In three dimensions, mean field theory fails in locating correctly the positions of the phase transitions, as well as the character of the transitions between the different states. A cluster mean-field calculations taking into account order-parameter fluctuations in a local environment improves the results considerably for the case of extreme type-II superconductors where gauge-field fluctuations are negligible. The large fluctuations in the multi-component superconducting order parameter originate with strong frustration due to interband Josephson-couplings. A novel chiral metallic phase found in previous works using large scale Monte-Carlo computations, is not obtained either within the single-site mean-field theory or the improved cluster mean-field theory of order parameter fluctuations. In three-dimensional superconductors, this unusual metallic phase originates with gauge-field fluctuations.

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Time reversal symmetry breakdown in normal and superconducting states in frustrated three-band systems

Cited by 64 publications

References 21 publications

s+is superconductivity with incipient bands: Doping dependence and STM signatures

s+is superconductivity with incipient bands: Doping dependence and STM signatures

Domain Walls and Their Experimental Signatures ins+isSuperconductors

Fluctuation Effects in Phase-Frustrated Multiband Superconductors

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