Andreev-reflection experiments on layered superconductors

Goll, G.

doi:10.1016/j.physb.2006.03.059

Cited by 7 publications

(5 citation statements)

References 34 publications

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“…In our PCS data on CeCoIn 5 , there are two prominent and common features that are not seen in other classes of superconductors: highly suppressed AR and background conductance asymmetry. It is noted that these features have also been observed in other reports on the PCS of heavyfermion superconductors [27,85,95,96].…”

Section: Conductance Asymmetrysupporting

confidence: 81%

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅

Park

Greene

2009

J. Phys.: Condens. Matter

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We review the current status of Andreev reflection spectroscopy on the heavy fermions, mostly focusing on the case of CeCoIn(5), a heavy-fermion superconductor with a critical temperature of 2.3 K. This is a well-established technique to investigate superconducting order parameters via measurements of the differential conductance from nanoscale metallic junctions. Andreev reflection is clearly observed in CeCoIn(5) as in other heavy-fermion superconductors. Considering the large mismatch in Fermi velocities, this observation seemingly appears to disagree with the Blonder-Tinkham-Klapwijk (BTK) theory. The measured Andreev signal is highly reduced to the order of maximum ∼13% compared to the theoretically predicted value (100%). The background conductance exhibits a systematic evolution in its asymmetry over a wide temperature range from above the heavy-fermion coherence temperature down to well below the superconducting transition temperature. Analysis of the conductance spectra using the extended BTK model provides a qualitative measure for the superconducting order parameter symmetry, which is determined to be the d(x(2)-y(2)) wave in CeCoIn(5). It is found that existing models do not quantitatively account for the data, which we attribute to the intrinsic properties of the heavy fermions. A substantial body of experimental data and extensive theoretical analysis point to the existence of two-fluid components in CeCoIn(5) and other heavy-fermion compounds. A phenomenological model is proposed employing a Fano interference effect between two conductance channels in order to explain both the conductance asymmetry and the reduced Andreev signal. This model appears plausible not only because it provides good fits to the data but also because it is highly likely that the electrical conduction occurs via two channels, one into the heavy-electron liquid and the other into the conduction electron continuum. Further experimental and theoretical investigations will shed new light on the mechanism of how the coherent heavy-electron liquid emerges out of the Kondo lattice, a prototypical strongly correlated electron system. Unresolved issues and future directions are also discussed.

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Section: Conductance Asymmetrysupporting

confidence: 81%

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅

Park

Greene

2009

J. Phys.: Condens. Matter

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show abstract

“…In our PCS data on CeCoIn 5 , there are two prominent and common features that are not seen in other class of superconductors: highly suppressed AR and background conductance asymmetry. It is noted that these features have also been observed in other reports on the PCS of heavy-fermion superconductors [27,85,95,96].…”

Section: Conductance Asymmetrysupporting

confidence: 81%

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn$_5$

Park,

Greene

2009

Preprint

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We review the current status of Andreev reflection spectroscopy on the heavy fermions, mostly focusing on the case of CeCoIn 5 , a heavy-fermion superconductor with a critical temperature of 2.3 K. This is a well-established technique to investigate superconducting order parameters via measurements of the differential conductance from nanoscale metallic junctions. Andreev reflection is clearly observed in CeCoIn 5 as in other heavy-fermion superconductors. Considering the large mismatch in Fermi velocities, this observation seemingly appears to disagree with the Blonder-Tinkham-Klapwijk (BTK) theory. The measured Andreev signal is highly reduced to the order of maximum ∼ 13% compared to the theoretically predicted value (100%). The background conductance exhibits a systematic evolution in its asymmetry over a wide temperature range from above the heavy fermion coherence temperature down to well below the superconducting transition temperature. Analysis of the conductance spectra using the extended BTK model provides a qualitative measure for the superconducting order parameter symmetry, which is determined to be d x 2 −y 2wave in CeCoIn 5 . It is found that existing models do not quantitatively account for the data, which we attribute to the intrinsic properties of the heavy fermions. A substantial body of experimental data and extensive theoretical analysis point to the existence of two fluid components in CeCoIn 5 and other heavy-fermion compounds. A phenomenological model is proposed employing a Fano interference effect between two conductance channels in order to explain both the conductance asymmetry and the reduced Andreev signal. This model appears plausible not only because it provides good fits to the data but also because it is highly likely that the electrical conduction occurs via two channels, one into the heavy electron liquid and the other into the conduction electron continuum. Further experimental and theoretical investigations will shed new light on the mechanism of how the coherent heavy-electron liquid emerges out of the Kondo lattice, a prototypical strongly correlated electron system. Unresolved issues and future directions are also discussed.

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“…However, there is no indication that fields as high as 9 T affect the conductance. 10,43 In Fig. 6 we show selected normal-state conductance fits for CeCoIn 5 at 5 and 20 K that were used to extract the model parameters shown in Fig.…”

Section: A Model Parameters In the Normal Statementioning

confidence: 99%

Point-contact spectroscopy in heavy-fermion superconductors

et al. 2010

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We develop a microscopic model to calculate point-contact spectra between a metallic tip and a superconducting heavy-fermion system. We apply our tunneling model to the heavy fermion CeCoIn 5 , both in the normal and superconducting states. In point contact and scanning tunneling spectroscopy many heavy-fermion materials, such as CeCoIn 5 , exhibit an asymmetric differential conductance, dI / dV, combined with a strongly suppressed Andreev reflection signal in the superconducting state. We argue that both features may be explained in terms of a multichannel tunneling model in the presence of localized states near the interface. We find that it is not sufficient to tunnel into two itinerant bands of light and heavy electrons to explain the Fano line shape of the differential conductance. Localized states in the bulk or near the interface are an essential component for quantum interference to occur when an electron tunnels from the metallic tip of the point contact into the heavy-fermion system.

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Andreev-reflection experiments on layered superconductors

Cited by 7 publications

References 34 publications

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn$_5$

Point-contact spectroscopy in heavy-fermion superconductors

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Andreev-reflection experiments on layered superconductors

Cited by 7 publications

References 34 publications

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn5

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn5

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn$_5$

Point-contact spectroscopy in heavy-fermion superconductors

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Product

Resources

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Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅

Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn₅