Interface between heavy fermions and normal electrons investigated by spatially resolved nuclear magnetic resonance

Yamanaka, Takayoshi; Shimozawa, Masaaki; Endo, Ryota; Mizukami, Y.; Shishido, Hiroaki; Terashima, Takahito; Shibauchi, T.; Matsuda, Yuji; Ishida, Kenji

doi:10.1103/physrevb.92.241105

Cited by 18 publications

(31 citation statements)

References 25 publications

(24 reference statements)

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“…Thus, the model captures qualitative properties of these materials although a significantly simplified model is adopted. The suppression of magnetic fluctuation by the ASOC is a generic feature [16], and it has been confirmed by a NMR experiment in CeCoIn 5 superlattices [92]. A qualitatively same conclusion is obtained from noninteracting magnetic susceptibility (see Fig.…”

Section: Magnetic Fluctuationsupporting

confidence: 74%

Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

Ishizuka

Yanase

2018

Phys. Rev. B

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A microscopic calculation and symmetry argument reveal superconductivity in the vicinity of parity-violating magnetic order. In a crystal structure lacking local space inversion symmetry, an augmented cluster magnetic multipole order may break global inversion symmetry, and therefore it is classified into an odd-parity multipole order. We investigate unconventional superconductivity induced by an odd-parity magnetic multipole fluctuation in a two-dimensional two-sublattice Hubbard model motivated by Sr2IrO4. We find that even-parity superconductivity is more significantly suppressed by spin-orbit coupling than that in a globally noncentrosymmetric system. Consequently, two odd-parity superconducting states are stabilized by magnetic multipole fluctuations in a large spin-orbit coupling region. Both of them are identified as Z2 topological superconducting states. The obtained gap function of inter-sublattice pairing shows a gapped or nodal structure protected by nonsymmorphic symmetry. Our finding implies a family of odd-parity topological superconductors. Candidate materials are discussed.

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Section: Magnetic Fluctuationsupporting

confidence: 74%

Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

Ishizuka

Yanase

2018

Phys. Rev. B

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“…Moreover, the large Fermi velocity mismatch across the interface between heavy-fermion and nonmagnetic metal layers significantly reduces the transmission probability of heavy QPs [5]. In fact, it has been shown that the superconducting heavy QPs as well as the magnetic fluctuations are well confined within the 2D Ce-BLs, as revealed by recent studies of upper critical field and site-selective nuclear magnetic resonance [6,7]. Quantum fluctuations are expected to be more pronounced in reduced spatial , the effect of reduced dimensionality would be more prominent in the present superlattices based on the tetragonal CeRhIn 5 with lower T N .…”

mentioning

confidence: 88%

“…Here, in the n = 3 superlattice, the inversion symmetry is locally broken at the top and bottom layers of the CeRhIn 5 blocks in the immediate proximity to the YbRhIn 5 layers, whereas the symmetry is preserved in the middle layer [7,[9][10][11]. In the 5 absence of inversion symmetry, asymmetry of the potential in the direction perpendicular to In the presence of the local inversion symmetry breaking at the interfaces, the magnetic anisotropy is expected to be modified.…”

mentioning

confidence: 99%

“…Since the noncentrosymmetric interface layers occupy two thirds of the CeRhIn 5 layers in the n = 3 superlattice, the local inversion symmetry breaking at the interfaces, which results in the Rashba spin-orbit splitting of the Fermi surface, has a significant impact on the magnetic properties. In fact, it has been reported that local inversion symmetry breaking strongly affects the superconducting and magnetic properties in CeCoIn 5 /YbCoIn 5 superlattices, leading to the suppression of the Pauli paramagnetic pair breaking effect and magnetic fluctuations at the interface [7,[9][10][11].…”

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confidence: 99%

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Tuning the Magnetic Quantum Criticality of Artificial Kondo SuperlatticesCeRhIn5/YbRhIn5

et al. 2016

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The effects of reduced dimensions and the interfaces on antiferromagnetic quantum criticality are studied in epitaxial Kondo superlattices, with alternating n layers of heavy-fermion antiferromagnet CeRhIn 5 and 7 layers of normal metal YbRhIn 5 . As n is reduced, the Kondo coherence temperature is suppressed due to the reduction of effective Kondo screening. The Néel temperature is gradually suppressed as n decreases and the quasiparticle mass is strongly enhanced, implying dimensional control toward quantum criticality. Magnetotransport measurements reveal that a quantum critical point is reached for n = 3 superlattice by applying small magnetic fields. Remarkably, the anisotropy of the quantum critical field is opposite to the expectations from the magnetic susceptibility in bulk CeRhIn 5 , suggesting that the Rashba spin-orbit interaction arising from the inversion symmetry breaking at the interface plays a key role for tuning the quantum criticality in the two-dimensional Kondo lattice. 1In Kondo lattices consisting of a periodic array of localized spins which are coupled to conduction electrons, a very narrow conduction band is formed at sufficiently low temperatures through the Kondo effect [1]. Such systems are realized in intermetallic heavy-fermion metals, which contain a dense lattice of certain lanthanide (4f ) and actinide (5f ) ions. In particular, in Ce(4f )-based compounds, strong electron correlations strikingly enhance the quasiparticle (QP) effective mass to about 100 times or more of the bare electron mass, resulting in a heavy Fermi liquid state. In the strongly correlated electron systems, nonFermi liquid behavior, associated with the quantum fluctuations near a quantum critical point (QCP), a point at which a material undergoes a second-order transition from one phase to another at absolute zero temperature [2], has been one of the central issues. The heavy-fermion systems are particularly suitable for this study, because the ground state can be tuned readily by control parameters other than temperature, such as magnetic field, pressure, or chemical substitution [3]. As a result of the many-body effects within the narrow band in these heavy-fermion compounds, a plethora of fascinating properties have been reported in the vicinity of a QCP.Recently, a state-of-the-art molecular beam epitaxy (MBE) technique has been developed to fabricate an artificial Kondo superlattice, a superlattice with alternating layers of Ce-based heavy-fermion compounds and nonmagnetic conventional metals with a few atomic layers thick [4]. These artificially engineered materials provide a new platform to study the properties of two-dimensional (2D) Kondo lattices, in contrast to the three-dimensional bulk materials. In the previously studied CeCoIn 5 /YbCoIn 5 superlattices [4], where CeCoIn 5 is a heavy-fermion superconductor and YbCoIn 5 is a conventional metal, each Ce-block layer (BL) is magnetically decoupled from the others, since the Ruderman-Kittel-Kasuya-Yoshida interaction between the spatially se...

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“…Recent siteselective NMR spectroscopy experiments have also indicated that the local ISB affects the magnetic properties, leading to the suppression of AFM fluctuations. 37 Thus, the interfacial effect becomes a key element for understanding the electronic state in the CeCoIn 5 /YbCoIn 5 superlattices. The details of these experiments are given in the following subsections.…”

Section: Local Inversion Symmetry Breakingmentioning

confidence: 99%

From Kondo lattices to Kondo superlattices

et al. 2016

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Realization of new classes of ground states in strongly correlated electron systems continues to be a major issue in condensed matter physics. Heavy fermion materials, whose electronic structure is essentially three-dimensional, are one of the most suitable systems for obtaining novel electronic states because of their intriguing properties associated with many-body effects. Recently, a state-of-theart molecular beam epitaxy technique was developed to reduce the dimensionality of heavy electron systems by fabricating artificial superlattices that include heavy fermion compounds; this approach can produce a new type of electronic state in two-dimensional (2D) heavy fermion systems. In artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3, the magnetic order is suppressed by a reduction in the thickness of the CeIn3 layers. In addition, the 2D confinement of heavy fermions leads to enhancement of the effective electron mass and deviation from the standard Fermi liquid electronic properties, which are both associated with the dimensional tuning of quantum criticality. In the superconducting superlattices of the heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, signatures of superconductivity are observed even at the thickness of one unit-cell layer of CeCoIn5. The most remarkable feature of this 2D heavy fermion superconductor is that the thickness reduction of the CeCoIn5 layers changes the temperature and angular dependencies of the upper critical field significantly. This result is attributed to a substantial suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking at the interfaces of CeCoIn5 block layers. The importance of the inversion symmetry breaking in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy, which can resolve spectroscopic information from each layer separately, even within the same CeCoIn5 block layer. In addition, recent experiments involving CeCoIn5/YbCoIn5 superlattices have shown that the degree of the inversion symmetry breaking and, in turn, the Rashba splitting are controllable, offering the prospect of achieving even more fascinating superconducting states. Thus, these Kondo superlattices pave the way for the exploration of unconventional metallic and superconducting states. CONTENTS

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Interface between heavy fermions and normal electrons investigated by spatially resolved nuclear magnetic resonance

Cited by 18 publications

References 25 publications

Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

Odd-parity multipole fluctuation and unconventional superconductivity in locally noncentrosymmetric crystal

Tuning the Magnetic Quantum Criticality of Artificial Kondo SuperlatticesCeRhIn5/YbRhIn5

From Kondo lattices to Kondo superlattices

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