Experimentally observable signatures of odd-frequency pairing in multiband superconductors

Komendová, Lucia; Balatsky, Alexander V.; Black‐Schaffer, Annica M.

doi:10.1103/physrevb.92.094517

Cited by 58 publications

(87 citation statements)

References 60 publications

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“…Recently, an intriguing possibility of bulk odd-ω pairing was proposed for model two-band superconductors. Here an odd parity in the band index of the Cooper pair induces an odd-ω dependence [23,24]. We demonstrate odd-ω superconductivity in Sr 2 RuO 4 arising from a similar odd parity in the orbital index.…”

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confidence: 80%

“…If we also set η 2 = η 3 we lose the odd-ω signal altogether (and the intrinsic Kerr effect, see above). The overall structure of the other anomalous Green's functions, F 11 , F 22 , F 33 , and F even , remains largely unaffected by changing (η 2 − η 3 ) or η 23 .…”

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confidence: 83%

“…Moreover, the odd-ω component is finite only if there is finite inter-orbital pairing ∆ 12 or finite inter-orbital hybridization ǫ 12 . That either of these generate odd-ω pairing is not fully unexpected, since inter-band hybridization has been found to induce inter-band pairing [23]. In addition, an asymmetry in intra-orbital properties is needed for odd-ω superconductivity to appear, such that either ξ 1 = ξ 2 (for finite ∆ 12 ) or ∆ 1 = ∆ 2 (for finite ǫ 12 ).…”

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confidence: 99%

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Odd-Frequency Superconductivity in Sr2RuO4 Measured by Kerr Rotation

Komendová

Black‐Schaffer

2017

Phys. Rev. Lett.

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We establish the existence of bulk odd-frequency superconductivity in Sr2RuO4 and show that an intrinsic Kerr effect is a direct evidence of this state. We use both general two-and three-orbital models, as well as a realistic tight-binding description of Sr2RuO4 to demonstrate that odd-frequency pairing arises due to finite hybridization between different orbitals in the normal state, and is further enhanced by finite inter-orbital pairing.The layered perovskite strontium ruthenate Sr 2 RuO 4 hosts an exotic superconducting state at low temperatures [1], with experiments having established both spintriplet pairing [2,3] and broken time-reversal symmetry [4,5]. The strongest candidate for the spatial symmetry is chiral p-wave order, with d-vector d = ∆ 0ẑ (k x ± ik y ) [6,7], although the exact gap structure is still disputed [8][9][10][11]. For example, spontaneous edge currents, associated with chiral p-wave pairing, have so far not been found [12]. The situation is further complicated by the Fermi surface consisting of three bands originating from three hybridizing Ru 4d orbitals; electron-like γ-(from xy orbital) and β-bands (xz, yz orbitals) and hole-like α-band (xz and yz orbitals).In this work we establish that the multi-orbital nature of Sr 2 RuO 4 hosts bulk odd-frequency (odd-ω) superconductivity. Odd-ω superconductivity is a dynamical phenomenon where the fermionic nature of the Cooper pair is preserved due to an oddness in frequency (or equivalently time) [13,14]. It is well established to exist in superconductor-ferromagnet junctions [15][16][17][18][19] and also predicted for superconductor-normal metal junctions [20][21][22]. However, odd-ω superconductivity has remained elusive in bulk materials without external magnetic fields. Recently, an intriguing possibility of bulk odd-ω pairing was proposed for model two-band superconductors. Here an odd parity in the band index of the Cooper pair induces an odd-ω dependence [23,24]. We demonstrate odd-ω superconductivity in Sr 2 RuO 4 arising from a similar odd parity in the orbital index.Importantly, we also show that a finite Kerr rotation angle in clean Sr 2 RuO 4 is direct evidence of odd-ω superconductivity. Detecting the Kerr effect in superconducting Sr 2 RuO 4 was instrumental for establishing timereversal symmetry breaking [4]. Recently, it has also been shown that inter-orbital processes are needed for a finite Kerr rotation [25][26][27][28], unless invoking extrinsic impurity effects [29,30]. We find odd-ω superconductivity and Kerr rotation emerging from the same finite hybridization between different orbitals and supplemented by possible finite inter-orbital pairing.Two-orbital superconductor.-To establish odd-ω superconductivity in Sr 2 RuO 4 and its connection to the Kerr effect we start by studying a minimal two-orbital model. The general Bogoliubov-de Gennes Hamiltonian reads k Ψ † kĤ k Ψ k , wherêand Ψ † k = (c † k↑1 c † k↑2 c −k↓1 c −k↓2 ) for orbitals 1 and 2. The normal and superconducting parts of the Hamiltonian are, respectively,We...

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confidence: 80%

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confidence: 83%

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confidence: 99%

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Odd-Frequency Superconductivity in Sr2RuO4 Measured by Kerr Rotation

Komendová

Black‐Schaffer

2017

Phys. Rev. Lett.

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“…An advantage of studying odd-ω pairing in multiband superconductors is that these systems do not have to be engineered to generate odd-ω pair amplitudes since interband scattering can arise from disorder or it can be intrinsic to the system if the Cooper pairs are composed of electrons corresponding to particular orbitals while the quasiparticles of the system emerge from a linear combination of these orbitals 40 , as is the case in Sr 2 RuO 4 42 . Thus, it is expected that bulk odd-ω pairing should be ubiquitous in multiband superconductors.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, it has been shown that superconductors with multiple bands close to the Fermi level, like MgB 2 29-33 and iron-based superconductors [34][35][36][37][38] , will possess odd-ω pairing in the presence of interband hybridization [39][40][41][42] . An advantage of studying odd-ω pairing in multiband superconductors is that these systems do not have to be engineered to generate odd-ω pair amplitudes since interband scattering can arise from disorder or it can be intrinsic to the system if the Cooper pairs are composed of electrons corresponding to particular orbitals while the quasiparticles of the system emerge from a linear combination of these orbitals 40 , as is the case in Sr 2 RuO 4 42 .…”

Section: Introductionmentioning

confidence: 99%

Pair symmetry conversion in driven multiband superconductors

Triola

Balatsky

2017

Phys. Rev. B

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It was recently shown that odd-frequency superconducting pair amplitudes can be induced in conventional superconductors subjected to a spatially nonuniform time-dependent drive. It has also been shown that, in the presence of interband scattering, multiband superconductors will possess bulk odd-frequency superconducting pair amplitudes. In this work we build on these previous results to demonstrate that by subjecting a multiband superconductor with interband scattering to a timedependent drive even-frequency pair amplitudes can be converted to odd-frequency pair amplitudes and vice versa. We will discuss the physical conditions under which these pair symmetry conversions can be achieved and possible experimental signatures of their presence.

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The Role of Odd‐Frequency Pairing in Multiband Superconductors

2020

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Recent progress in the understanding of multiband superconductivity and its relationship to odd‐frequency pairing are reviewed herein. The discussion begins by reviewing the emergence of odd‐frequency pairing in a simple two‐band model, providing a brief pedagogical overview of the formalism. Several examples of multiband superconducting systems are examined, in each case describing both the origin of the band degree of freedom and the nature of the odd‐frequency pairing. Throughout, it is attempted to convey a unified picture of how odd‐frequency pairing emerges in these materials and propose that similar mechanisms are responsible for odd‐frequency pairing in several analogous systems: layered 2D heterostructures, double quantum dots, double nanowires, Josephson junctions, and systems described by isolated valleys in momentum space. In addition, experimental probes of odd‐frequency pairing in multiband systems are reviewed, focusing on hybridization gaps in the electronic density of states, paramagnetic Meissner effect, and Kerr effect.

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Experimentally observable signatures of odd-frequency pairing in multiband superconductors

Cited by 58 publications

References 60 publications

Odd-Frequency Superconductivity in Sr2RuO4 Measured by Kerr Rotation

Odd-Frequency Superconductivity in Sr2RuO4 Measured by Kerr Rotation

Pair symmetry conversion in driven multiband superconductors

The Role of Odd‐Frequency Pairing in Multiband Superconductors

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