Recent progress on superconductors with time-reversal symmetry breaking

Ghosh, S. K.; Smidman, M.; Shang, T.; Annett, James F.; Hillier, A. D.; Quintanilla, Jorge; Yuan, Huiqiu

doi:10.1088/1361-648x/abaa06

Cited by 111 publications

(105 citation statements)

References 225 publications

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“…This strongly suggests that the additional relaxation below T c is not due to rapidly fluctuating fields 18 , but rather associated with very weak fields which are static or quasistatic on the time-scale of muon life-time. The spontaneous static magnetic field arising just below T c is so intimately connected with superconductivity that we can safely say its existence is direct evidence for TRS-breaking superconducting state in LaPt 3 P. From the change Δ λ ZF = λ ZF ( T ≈ 0) − λ ZF ( T > T c ) we can estimate the corresponding spontaneous internal magnetic field at the muon site B int ≈ Δ λ ZF / γ μ = 0.22(4) G for sample-A and 0.18(2) G for sample-B, which are very similar to that of other TRS-breaking SCs 19 . Here, γ μ /(2 π ) = 13.55 kHz/G is the muon gyromagnetic ratio.…”

Section: Resultssupporting

confidence: 62%

“…129) with point group D 4 h . From the group theoretical classification of the SC order parameters within the Ginzburg-Landau theory 19 , 24 , the only possible superconducting instabilities with strong SOC, which can break TRS spontaneously at T c correspond to the two 2D irreducible representations, E g and E u , of D 4 h . Non-symmorphic symmetries can give rise to additional symmetry-required nodes on the Brillouin zone boundaries along the high symmetry directions.…”

Section: Discussionmentioning

confidence: 99%

“…We compute the quasi-particle excitation spectrum for the two TRS-breaking states on a generic single-band spherical Fermi surface using the Bogoliubov-de Gennes mean-field theory 19 , 24 . The chiral d -wave singlet state leads to an energy gap given by .…”

Section: Discussionmentioning

confidence: 99%

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Chiral singlet superconductivity in the weakly correlated metal LaPt3P

et al. 2021

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Chiral superconductors are novel topological materials with finite angular momentum Cooper pairs circulating around a unique chiral axis, thereby spontaneously breaking time-reversal symmetry. They are rather scarce and usually feature triplet pairing: a canonical example is the chiral p-wave state realized in the A-phase of superfluid He3. Chiral triplet superconductors are, however, topologically fragile with the corresponding gapless boundary modes only weakly protected against symmetry-preserving perturbations in contrast to their singlet counterparts. Using muon spin relaxation measurements, here we report that the weakly correlated pnictide compound LaPt3P has the two key features of a chiral superconductor: spontaneous magnetic fields inside the superconducting state indicating broken time-reversal symmetry and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt3P is a chiral d-wave singlet.

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Section: Resultssupporting

confidence: 62%

Section: Discussionmentioning

confidence: 99%

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Chiral singlet superconductivity in the weakly correlated metal LaPt3P

et al. 2021

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“…129) with point group D 4h . From the group theoretical classification of the SC order parameters within the Ginzburg-Landau theory [15,20], the only possible superconducting instabilities with strong SOC which can break TRS spontaneously at T c correspond to the two 2D irreducible representations, E g and E u , of D 4h [21]. The superconducting ground state in the E g channel is a pseudospin chiral d-wave singlet state with gap function ∆(k) = ∆ 0 k z (k x + ik y ) where ∆ 0 is an amplitude independent of k. While the E u order parameter is a pseudospin nonunitary chiral p-wave triplet state with…”

Section: Discussionmentioning

confidence: 99%

Chiral singlet superconductivity in the weakly correlated metal LaPt3P

Biswas⃰

Ghosh

Zhao

et al. 2020

Preprint

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Topological superconductors (SCs) are novel phases of matter with nontrivial bulk topology. They host at their boundaries and vortex cores zero-energy Majorana bound states, potentially useful in fault-tolerant quantum computation [1]. Chiral SCs [2] are particular examples of topological SCs with finite angular momentum Cooper pairs circulating around a unique chiral axis, thus spontaneously breaking time-reversal symmetry (TRS). They are rather scarce and usually feature triplet pairing: best studied examples in bulk materials are UPt<3> and Sr<2>RuO<4> proposed to be f-wave and p-wave SCs respectively, although many open questions still remain [2]. Chiral triplet SCs are, however, topologically fragile with the gapless Majorana modes weakly protected against symmetry preserving perturbations in contrast to chiral singlet SCs [3, 4]. Using muon spin relaxation (μSR) measurements, here we report that the weakly correlated pnictide compound LaPt<3>P has the two key features of a chiral SC: spontaneous magnetic fields inside the superconducting state indicating broken TRS and low-temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt<3>P is chiral d-wave singlet.

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“…The breaking of time reversal symmetry (TRS) in the superconducting state is manifested by the spontaneous appearance of magnetic fields below the superconducting transition temperature T c . This requires the superconducting order parameter to have multiple components with nontrivial phase differences, and hence TRS breaking is a signature of unconventional superconductivity beyond the s-wave pairing state of Bardeen-Cooper-Schrieffer (BCS) theory [1,2]. TRS breaking in the superconducting state was first reported in a few strongly correlated electron systems, such as U 1−x Th x Be 13 [3], UPt 3 [4], and Sr 2 RuO 4 [5].…”

Section: Introductionmentioning

confidence: 99%

Nodeless superconductivity in Lu5−xRh6Sn18+x with broken time reversal symmetry

Wang

Nie

et al. 2021

Phys. Rev. B

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Evidence for broken time reversal symmetry (TRS) has been found in the superconducting states of the R 5 Rh 6 Sn 18 (R = Sc, Y, Lu) compounds with a centrosymmetric caged crystal structure, but the origin of this phenomenon is unresolved. Here, we report neutron diffraction measurements of single crystals with R = Lu, as well as measurements of the temperature dependence of the magnetic penetration depth using a self-induced tunnel-diode-oscillator (TDO)-based technique, together with band structure calculations using density functional theory. Neutron diffraction measurements reveal that the system crystallizes in a tetragonal caged structure, and that one of the nominal Lu sites in the Lu 5 Rh 6 Sn 18 structure is occupied by Sn, yielding a composition Lu 5−x Rh 6 Sn 18+x (x = 1). The low temperature penetration depth shift λ(T) exhibits an exponential temperature dependence below around 0.3T c , giving clear evidence for fully gapped superconductivity. The derived superfluid density is reasonably well accounted for by a single-gap s-wave model, whereas agreement cannot be found for models of TRS breaking states with two-component order parameters. Moreover, band structure calculations reveal multiple bands crossing the Fermi level, and indicate that the aforementioned TRS breaking states would be expected to have nodes on the Fermi surface, in contrast to the observations.

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Recent progress on superconductors with time-reversal symmetry breaking

Abstract: The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.

Cited by 111 publications

References 225 publications

Chiral singlet superconductivity in the weakly correlated metal LaPt3P

Chiral singlet superconductivity in the weakly correlated metal LaPt3P

Chiral singlet superconductivity in the weakly correlated metal LaPt3P

Nodeless superconductivity in Lu5−xRh6Sn18+x with broken time reversal symmetry

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