Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>CeCoIn</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>

Park, W. K.; Sarrao, J. L.; Thompson, J. D.; Greene, L. H.

doi:10.1103/physrevlett.100.177001

Cited by 123 publications

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“…1e). However, measurements on all surfaces and on several samples reveal that this d-wave gap (with a magnitude of 535 ± 35 µV, consistent with that extracted from point contact data 18,19 ), is filled (40%) with low-energy excitations-a feature that cannot be explained by simple thermal broadening (determined to be 245 mK from measurements on a single-crystal Al sample, see Supplementary Section SII). The complex multiband structure of CeCoIn 5 could involve different gaps on different Fermi surface sheets, and there is the possibility that some remain ungapped even at temperatures well below T c (ref.…”

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confidence: 92%

Visualizing nodal heavy fermion superconductivity in CeCoIn5

et al. 2013

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Understanding the origin of superconductivity in strongly correlated electron systems continues to be at the forefront of the unsolved problems of physics 1 . Among the heavy f-electron systems, CeCoIn 5 is one of the most fascinating, as it shares many of the characteristics of correlated d-electron high-T c cuprate and pnictide superconductors 2-4 , including competition between antiferromagnetism and superconductivity 5 . Although there has been evidence for unconventional pairing in this compound 6-11 , high-resolution spectroscopic measurements of the superconducting state have been lacking. Previously, we have used high-resolution scanning tunnelling microscopy (STM) techniques to visualize the emergence of heavy fermion excitations in CeCoIn 5 and demonstrate the composite nature of these excitations well above T c (ref. 12). Here we extend these techniques to much lower temperatures to investigate how superconductivity develops within a strongly correlated band of composite excitations. We find the spectrum of heavy excitations to be strongly modified just before the onset of superconductivity by a suppression of the spectral weight near the Fermi energy (E F ), reminiscent of the pseudogap state 13,14 in the cuprates. By measuring the response of superconductivity to various perturbations, through both quasiparticle interference (QPI) and local pair-breaking experiments, we demonstrate the nodal d-wave character of superconducting pairing in CeCoIn 5 .CeCoIn 5 undergoes a superconducting transition at 2.3 K. Despite evidence of unconventional pairing, consensus on the mechanism of pairing and direct experimental verification of the order parameter symmetry are still lacking [6][7][8][9]11 . Moreover, experiments have suggested that superconductivity in this compound emerges from a state of unconventional quasiparticle excitations with a pseudogap phase similar to that found in underdoped high-T c cuprates [15][16][17] . Previously, we demonstrated that scanning tunnelling spectroscopic techniques can be used to directly visualize the emergence of heavy fermion excitations in CeCoIn 5 and their quantum critical nature 12 . Through these measurements, we also demonstrated the composite nature of heavy quasiparticles and showed their band formation as the f -electrons hybridize with the spd-electrons starting at 70 K, well above T c (ref. 12). This previous breakthrough, together with our recent development of high-resolution millikelvin STM, offers a unique opportunity to measure how superconductivity emerges in a heavy electron system. Figure 1 shows STM topographs of the two commonly observed atomically ordered surfaces of CeCoIn 5 produced after the cleaving of single crystals in situ in the ultra-high vacuum environment 1 Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA, 2 Condensed Matter and Magnet Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. † These authors contributed equally to this work. *e-mail: yazdani@pr...

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Visualizing nodal heavy fermion superconductivity in CeCoIn5

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“…6) The magnetic origin of the SC pairing is inferred from the d-wave (d x 2 −y 2 ) symmetry of the SC gap determined by thermal conductivity, specific heat, and conductance measurements. [7][8][9] In magnetic fields, the spin degrees of freedom are significantly coupled with the stability of the SC order; a strong Pauli paramagnetic effect gives rise to a first-order transition at the SC upper critical field H c2 below 0.7 K, 7,[10][11][12] and the SC phase coexistent with AFM spin modulation evolves just below H c2 at very low temperatures. [13][14][15][16][17][18] Furthermore, the existence of the AFM-QCP at ∼ H c2 is strongly suggested from the observations of the NFL behavior in the paramagnetic phase above H c2 , including the − ln T divergence in specific heat divided by temperature, the T -linear dependence in magnetization, and electrical resistivity.…”

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confidence: 99%

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

et al. 2016

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The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavyfermion compound CeCo 1−x Ni x In 5 is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature T c monotonically decreases from 2.3 K (x = 0) to 0.8 K (x = 0.20) with increasing x, and then the SC order disappears above x = 0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x = 0.25, characterized by the − ln T divergence in specific heat divided by temperature, C p /T , and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x = 0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn 5 , suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni-, Sn-, and Pt-substituted CeCoIn 5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In 5 and the other alloys, such as the rates of decrease in T c , dT c /dx, and specific heat jump at T c , d(∆C p /T c )/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.

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“…Remarkably, this challenge has been overcome in scanning tunneling microscopy measurements [4][5][6][7][8] as well as in the point contact spectroscopy. 9,10,14 Recent tunneling experiments have been convincingly able to trace the formation of the heavy quasiparticles. What is more, momentum and energy resolved tunneling spectra visualized not only the formation of the heavy quasiparticles, but also the formation of unconventional superconductivity in a prototypical Kondo lattice heavy-fermion superconductor CeCoIn 5 .…”

Section: Tunneling Into a Kondo Lattice: Overviewmentioning

confidence: 99%

Tunneling in Heavy-Fermion Junctions

Dzero

2014

J. Phys. Soc. Jpn.

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In this paper I review recent theoretical and experimental advances in understanding of tunneling processes between normal metals and metals containing electrons which occupy partially filled f -orbitals. In heavy-fermion materials the effective mass of the quasiparticles far exceeds the bare electron mass due to strong hybridization between conduction and f -orbital states. Kondo lattices form a class of heavy-fermion systems in which an average occupation number of f -electron states is close to an integer. Therefore, the tunneling into a Kondo lattice necessarily involves co-tunneling process of a tip electron into an f -electron state of a Kondo lattice. This co-tunneling process is manifested in the Fano-lineshape of differential conductance as a function of an applied voltage, which has been routinely observed in recent experiments on various Kondo lattice systems. To illustrate these ideas, I discuss the problem of the tunneling junction when the single particle states in the tip are also a product of hybridization between conduction and f -states, i.e. tunneling between two heavy-fermion materials.

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Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry inCeCoIn5

Cited by 123 publications

References 31 publications

Visualizing nodal heavy fermion superconductivity in CeCoIn5

Visualizing nodal heavy fermion superconductivity in CeCoIn5

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

Tunneling in Heavy-Fermion Junctions

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Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry inCeCoIn5

Cited by 123 publications

References 31 publications

Visualizing nodal heavy fermion superconductivity in CeCoIn5

Visualizing nodal heavy fermion superconductivity in CeCoIn5

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1−xNixIn5

Tunneling in Heavy-Fermion Junctions

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Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅