Observation of Leggett’s Collective Mode in a Multiband<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>MgB</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>Superconductor

Blumberg, G.; Mialitsin, Aleksej; Dennis, B. S.; Klein, Miles V.; Zhigadlo, N. D.; Karpiński, J.

doi:10.1103/physrevlett.99.227002

Cited by 136 publications

(141 citation statements)

References 29 publications

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“…Its double-gap structure originates from an electronic structure around the Fermi energy that comprises σ and π bands [33][34][35] . Observation of the Leggett mode in MgB 2 has been reported with tunneling spectroscopy 36 , Raman spectroscopy 37,38 and angle-resolved photoemission spectroscopy 39 , while no report has so far been made for the Higgs mode. A more recent family of superconductors, the iron pnictides with high T c s, also have multi-orbital and multi-gap structures, where the electron correlation is suggested 40,41 to bring about s ± and s ++ pairings depending on the chemical composition and/or doping level 42,43 .…”

Section: Introductionmentioning

confidence: 99%

Theory of light-induced resonances with collective Higgs and Leggett modes in multiband superconductors

2017

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We theoretically investigate coherent optical excitations of collective modes in two-band BCS superconductors, which accommodate two Higgs modes and one Leggett mode corresponding, respectively, to the amplitude and relative-phase oscillations of the superconducting order parameters associated with the two bands. We find, based on a mean-field analysis, that each collective mode can be resonantly excited through a nonlinear light-matter coupling when the doubled frequency of the driving field coincides with the frequency of the corresponding mode. Among the two Higgs modes, the higher-energy one exhibits a sharp resonance with light, while the lower-energy mode has a broadened resonance width. The Leggett mode is found to be resonantly induced by a homogeneous ac electric field because the leading nonlinear effect generates a potential offset between the two bands that couples to the relative phase of the order parameters. The resonance for the Leggett mode becomes sharper with increasing temperature. All of these light-induced collective modes along with density fluctuations contribute to the third-harmonic generation. We also predict an experimental possibility of optical detection of the Leggett mode.

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Section: Introductionmentioning

confidence: 99%

Theory of light-induced resonances with collective Higgs and Leggett modes in multiband superconductors

2017

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“…We stress that this is an estimate as the dip location is slightly affected by functional form of the self energy. The vertex corrections for Raman spectroscopy 25,30 and ARPES are almost certainly different and can potentially explain the the difference between the Leggett mode energy measured by the two techniques. Previous electron spectroscopy studies reported the value of the Leggett mode energy of 3.9-4.0 meV, consistent with our results.…”

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confidence: 99%

“…Previous electron spectroscopy studies reported the value of the Leggett mode energy of 3.9-4.0 meV, consistent with our results. While the bare mode was calculated to have a frequency of 5.1-6.2meV 25,30 , if the experimentally measured ∆ π = 1.5meV is used, the calculated frequencies decrease to 3.8-4.5meV. More theoretical efforts will be required to fully understand the origin of the difference.…”

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confidence: 99%

“…Inelastic neutron scattering studies have reported optical phonon modes at ∼35, 55, 75, 85 and 100 meV 28 , while Raman scattering reports a single, broad asymmetric peak at 75meV, attributed to the E 2g mode, as well as a sharp peak at 2∆ σ = 12meV due to a pair breaking excitation 29 . As a bonus, due to its multi-gap nature, MgB 2 also contains another exotic collective mode that can couple to the electrons: the Leggett mode [21][22][23][24][25] . This mode is a longitudinal fluctuation corresponding to equal and opposite displacements of the two condensates.…”

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confidence: 99%

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Strong interaction between electrons and collective excitations in the multiband superconductorMgB2

et al. 2015

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We use a tunable laser ARPES to study the electronic properties of the prototypical multiband BCS superconductor MgB 2 . Our data reveal a strong renormalization of the dispersion (kink) at ∼65 meV, which is caused by coupling of electrons to the E 2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB 2 does not change significantly across T c . More interestingly, we observe strong coupling to a second, lower energy collective mode at binding energy of 10 meV. This excitation vanishes above T c and is likely a signature of the elusive Leggett mode.

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“…Investigations of the Leggett modes in multi-band superconductor have already attracted intensive interests [24][25][26][27][28][29]. It is only until very recently years that some evidences of its existence have been observed experimentally in multi-band superconductors MgB 2 , by tunneling spectroscopy techniques [30], Raman spectroscopy [31], and angle-resolved photoemission spectroscopy [32]. In the case of cold atom system, the Leggett modes have so far not been observed experimentally.…”

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confidence: 99%

Collective modes in a two-band superfluid of ultracold alkaline-earth-metal atoms close to an orbital Feshbach resonance

2017

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We discuss the collective modes in an alkaline-earth Fermi gas close to an orbital Feshbach resonance. Unlike the usual Feshbach resonance, the orbital Feshbach resonance in alkaline-earth atoms realizes a two-band superfluid system where the fermionic nature of both the open and the closed channel has to be taken into account. We show that apart from the usual Anderson-Bogoliubov mode which corresponds to the oscillation of total density, there also appears the long-sought Leggett mode corresponding to the oscillation of relative density between the two channels. The existence of the phonon and the Leggett modes and their evolution are discussed in detail. We show how these collective modes are reflected in the density response of the system. [5][6][7], is that there are two clock states, the electronic s-and p-states, both of which have zero electronic angular momentum J = 0. As a result, there is no hyperfine coupling between the electronic and nuclear spins. The inter-atomic interactions which depend (primarily) on the electronic configurations thus become independent of nuclear spins. This realizes the so-called SU (N ) symmetries, where N is the number of nuclear spin components [8][9][10][11][12][13][14][15]. The OFR relies on the atoms residing on both the s and p-states which possess slight different Landé g-factors [16,17], thus allowing tuning by external magnetic field.

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Observation of Leggett’s Collective Mode in a MultibandMgB2Superconductor

Cited by 136 publications

References 29 publications

Theory of light-induced resonances with collective Higgs and Leggett modes in multiband superconductors

Theory of light-induced resonances with collective Higgs and Leggett modes in multiband superconductors

Strong interaction between electrons and collective excitations in the multiband superconductorMgB2

Collective modes in a two-band superfluid of ultracold alkaline-earth-metal atoms close to an orbital Feshbach resonance

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