Effective action approach to the Leggett's mode in two-band superconductors

Sharapov, S. G.; Gusynin, V. P.; Beck, H. P.

doi:10.1140/epjb/e2002-00356-9

Cited by 95 publications

(112 citation statements)

References 25 publications

(70 reference statements)

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“…We further ignore differences in the microscopic charge distribution of Wannier orbitals between α and β bands. In this approximation, it is known that the Leggett mode at zero momentum is not affected by the Anderson-Higgs (AH) mechanism [22][23][24]28 , since the interband charge transfer associated with the Leggett mode does not induce an electric current in real space. Hence the Leggett mode is not coupled linearly to electromagnetic fields, and survives at low energies.…”

Section: Pseudospin Representation For Two-band Superconductorsmentioning

confidence: 99%

“…For d-wave superconductors such as high-T c cuprates, it has been group-theoretically shown 21 that they can accommodate additional amplitude (Higgs) modes coming from multiple irreducible representations of the k-dependent gap function with the D 4 point-group symmetry. As for the phase modes, multi-gap superconductors are predicted to have an out-of-phase mode between the two components of the gap function [22][23][24][25][26][27][28][29][30] , called "Leggett mode".…”

Section: Introductionmentioning

confidence: 99%

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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: Pseudospin Representation For Two-band Superconductorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2017

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“…Comparing Fig.4 (c) with Fig.4 (d), the spectral weight of Leggett mode diminishes after merging into the continuum. 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].…”

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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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“…In multigap superconductors a collective mode called the Leggett's mode [18][19][20] appears in the low energy region, which is an out-of-phase oscillation mode of the superconducting phases. In Ref.…”

Section: Macroscopic Quantum Tunneling (Mqt)mentioning

confidence: 99%

Macroscopic quantum tunneling in multigap superconducting Josephson junctions: Enhancement of escape rate via quantum fluctuations of the Josephson-Leggett mode

2011

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We theoretically study the macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multigap superconductor such as and ironbased superconductors and MgB 2 . In such a Josephson junction more than one phase difference is defined. We clarify their phase dynamics and construct a theory for the MQT in the multigap Josephson junctions. The dynamics of the phase differences are strongly affected by the JosephsonLeggett mode, which is the out-of-phase oscillation mode of the phase differences. The escape rate is calculated in terms of the effective action renormalized by the Josephson-Leggett mode at zero-temperature limit. We successfully predict drastic enhancement of the escape rate when the frequency of the Josephson-Leggett mode is less than the Josephson-plasma frequency.PACS numbers: 74.50.+r Macroscopic quantum tunneling (MQT)1-4 is a counterintuitive phenomenon in quantum mechanics appearing in a macroscopic level and has been observed in various fields of physics such as condensed matters, nuclei, cosmology, etc. This phenomenon has still attracted a great interest in physics communities. In particular, the MQT in Josephson junctions, which is observed in a switching event at low temperature 3,4 , has been intensively studied because it is promising for applications to a Josephson phase qubit 5-7 .In this paper we explore the physics of MQT in an unexplored type of Josephson junctions which has multiple tunneling channels. Such a Josephson junction can be fabricated by using recently discovered iron-based superconductors 8-10 or MgB 2 11-13 , because these superconductors are multiband ones having more than one disconnected Fermi surfaces and the superconducting gap can be individually well defined on each Fermi surface. In a Josephson junction made of multigap superconductors one may expect that the superconducting tunneling current has multiple channels between the two superconducting electrodes 14-17 . We construct a theory for the quantum switching (i.e., MQT) in Josephson junctions with multiple tunneling channels. To our knowledge no theory has been formulated for the MQT in multigap systems. The theory predicts that the escape rate, i.e., the rate of quantum tunneling, is drastically enhanced compared with that in conventional single-channel systems.In multigap superconductors a collective mode called the Leggett's mode18-20 appears in the low energy region, which is an out-of-phase oscillation mode of the superconducting phases. In Ref.14 a theory for the Josephson effect in superconducting hetero junctions made of a single-gap superconductor and a two-gap one is formulated. In such Josephson junctions, because two kinds of gauge-invariant phase differences can be defined, there are two phase oscillation modes, i.e., the in-phase mode and the out-of-phase one, which correspond, respectively, to the Josephson-plasma and the Josephson-Leggett (JL) mode. In this paper we construct a theory for the MQT in superconducting hetero junctions,...

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Effective action approach to the Leggett's mode in two-band superconductors

Cited by 95 publications

References 25 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

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

Macroscopic quantum tunneling in multigap superconducting Josephson junctions: Enhancement of escape rate via quantum fluctuations of the Josephson-Leggett mode

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