Superconducting tunneling spectroscopy on epitaxial UPd2Al3 thin films

Jourdan, Martin; Huth, Michael; Hessert, J.; Adrian, H.

doi:10.1016/s0921-4526(96)00710-7

Cited by 14 publications

(5 citation statements)

References 5 publications

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“…A clear superconducting gap at 2D 3.8k B T c has been observed in a recent study of tunneling spectroscopy of a thin UPd 2 Al 3 film [13]. It is quite interesting that the temperature dependence of this gap, which is obviously a charge gap, is very similar to the one of the magnetic excitation gap observed in this study.…”

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confidence: 86%

Superconducting Energy Gap Observed in the Magnetic Excitation Spectra of a Heavy Fermion SuperconductorUPd2Al3

et al. 1998

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High resolution neutron scattering experiments have been carried out in order to study the interplay between magnetism and superconductivity in the heavy fermion superconductor UPd 2 Al 3 . We found direct evidence for a magnetic excitation gap associated with superconductivity. We observed 1% suppression of the antiferromagnetic Bragg intensities below the superconducting transition temperature T c 1.9 K. We also observed the increases of the spin wave excitation energy and its linewidth in the superconducting state. These results indicate a strong coupling between magnetism and superconductivity in this compound. [S0031-9007(98)06447-3] PACS numbers: 74.70.Tx, 74.20.Mn Anisotropic superconductivity in heavy fermion superconductors is one of the most exciting topics in the field of condensed matter physics. The most important issue for the heavy fermion superconductor is that quasiparticles with a heavy mass (m ‫ء‬ ϳ 10 2 m 0 ) are of an f-electron character, condensing into Cooper pairs. When we compare the phonon-mediated attractive interaction to the strong repulsive interaction among the f electrons, it is theoretically difficult for the former interaction to overcome the latter one [1]. To avoid a large overlap of the wave functions of the paired particles, the heavy fermion system would rather choose an anisotropic channel, like a p-wave spin triplet or a d-wave spin singlet state, to form Cooper pairs. In fact, the heavy fermion superconductor exhibits antiferromagnetic (AFM) ordering. Therefore the interplay of superconductivity with the coexisting AFM ordering is a key concept for the ground state properties [2].Very recently we have observed a magnetic excitation gap associated with superconductivity in UPd 2 Al 3 [3]. UPd 2 Al 3 is a typical heavy fermion superconductor with T c 2 K. It also exhibits antiferromagnetic ordering with a relatively large magnetic moment of 0.85m B ͞U below the Néel temperature T N 14.5 K [4,5]. It is, however, reported that the neutron inelastic scattering profile could be explained by the coupling model which reproduces the quasielastic scattering due to strong damping of the spin wave excitation by the conduction electrons [6]. Namely, no trace of the magnetic excitation gap was found, which is inconsistent with our previous study.We have continued studying neutron inelastic scattering experiments with much higher resolution and lower temperatures. The present paper indicates clear evidence for the superconducting energy gap appearing in the magnetic excitation spectra. We also present the neutron data to show the strong coupling of the magnetic and superconducting order parameters. Finally, we mention the influence of the superconductivity on the spin wave excitation.Neutron scattering experiments were carried out using a cold neutron triple-axis spectrometer LTAS installed at C2-1 beam port of research reactor JRR-3M in Japan Atomic Energy Research Institute. The collimation was 26 0 -70 0 -72 0 -72 0 . The constant-Q profiles were measured with a fixed final energ...

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confidence: 86%

Superconducting Energy Gap Observed in the Magnetic Excitation Spectra of a Heavy Fermion SuperconductorUPd2Al3

et al. 1998

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“…It mainly relies on the availability of epitaxial thin films. For selected materials efforts in this direction have been successful [7][8][9] and have eventually led to well characterized tunnel junctions [10][11][12] . For CeCoIn 5 , however, attempts by severals groups have so far not led to epitaxial growth [13][14][15] .…”

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confidence: 99%

Josephson effect in CeCoIn5microbridges as seen via quantum interferometry

2011

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A superconducting quantum interference device (SQUID) was prepared on a micron-sized single crystal using a selected growth domain of a thin film of CeCoIn5 grown by molecular beam epitaxy. SQUID voltage oscillations of good quality were obtained as well as interference effects stemming from the individual Josephson microbridges. The transport characteristics in the superconducting state exhibited several peculiarities which we ascribe to the periodic motion of vortices in the microbridges. The temperature dependence of the Josephson critical current shows good correspondence to the Ambegaokar-Baratoff relation, expected for the ideal Josephson junction. The results indicate a promising pathway to identify the type of order parameter in CeCoIn5 by means of phase-sensitive measurements on microbridges.

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“…The neutron scattering experiments [4][5][6], tunneling spectroscopy [7] and NMR data [8][9][10] show that the systems UM 2 Al 3 (M = Pd, Ni) are unconventional superconductors with node lines and very exotic pairing mechanism. The most important issue for the heavy fermion (HF) superconductors is that the quasi-particles with heavy masses (m * ∼ 10 2 m e ) bearing the f -electron character, condense into Cooper pairs.…”

Section: Introductionmentioning

confidence: 99%

Superconducting gap anomaly in heavy fermion systems

Rout

Ojha²,

Behera³

2008

Pramana - J Phys

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The heavy fermion system (HFS) is described by the periodic Anderson model (PAM), treating the Coulomb correlation between the f -electrons in the meanfield Hartree-Fock approximation. Superconductivity is introduced by a BCS-type pairing term among the conduction electrons. Within this approximation the equation for the superconducting gap is derived, which depends on the effective position of the energy level of the f -electrons relative to the Fermi level. The latter in turn depends on the occupation probability n f of the f -electrons. The gap equation is solved self-consistently with the equation for n f ; and their temperature dependences are studied for different positions of the bare f -electron energy level, with respect to the Fermi level. The dependence of the superconducting gap on the hybridization leads to a re-entrant behaviour with increasing strength. The induced pairing between the f -electrons and the pairing of mixed conduction and f -electrons due to hybridization are also determined. The temperature dependence of the hybridization parameter, which characterizes the number of electrons with mixed character and represents the number of heavy electrons is studied. This number is shown to be small. The quasi-particle density of states (DOS) shows the existence of a pseudo-gap due to superconductivity and the signature of a hybridization gap at the Fermi level. For the choice of the model parameters, the DOS shows that the HFS is a metal and undergoes a transition to the gap-less superconducting state.

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Superconducting tunneling spectroscopy on epitaxial UPd2Al3 thin films

Cited by 14 publications

References 5 publications

Superconducting Energy Gap Observed in the Magnetic Excitation Spectra of a Heavy Fermion SuperconductorUPd2Al3

Superconducting Energy Gap Observed in the Magnetic Excitation Spectra of a Heavy Fermion SuperconductorUPd2Al3

Josephson effect in CeCoIn5microbridges as seen via quantum interferometry

Superconducting gap anomaly in heavy fermion systems

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