Ultrasonic Investigation on a Cage Structure Compound PrTi<sub>2</sub>Al<sub>20</sub>

Koseki, Minoru; Nakanishi, Y.; Deto, Kazuhisa; Koseki, Gen; Kashiwazaki, Reiko; Shichinomiya, Fumitaka; Nakamura, Mitsuteru; Yoshizawa, Michito; Sakai, Akihito; Nakatsuji, Satoru

doi:10.1143/jpsjs.80sa.sa049

Cited by 40 publications

(45 citation statements)

References 18 publications

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“…18) It also clarified that the quadrupolar phase has a ferro-type uniform order of the quadrupolar moment O 0 2 , consistent with the ferro-type intersite coupling found in the ultrasonic measurements, 19) and the absence of internal magnetic field confirmed by recent SR measurements. 20) Hybridization effects between the quadrupolar moments and conduction electrons are inferred from the magnetic properties above the ordering temperatures, such as the ÀT 1=2 dependence of the susceptibility and T 2 dependence of the resistivity.…”

supporting

confidence: 76%

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀

2012

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The cubic compound PrTi 2 Al 20 is a quadrupolar Kondo lattice system that exhibits quadrupolar ordering due to the non-Kramers À 3 ground doublet and has strong hybridization between 4f and conduction electrons. Our study using high-purity single crystals reveals that PrTi 2 Al 20 exhibits type-II superconductivity at T c ¼ 200 mK in the nonmagnetic ferroquadrupolar state. The superconducting critical temperature and field phase diagram indicates clean limit superconductivity with moderately enhanced effective mass of m Ã =m 0 $ 16. Orbital degree of freedom in strongly correlated electron systems leads to rich variety of nontrivial phenomena, such as colossal magnetoresistance, orbital ordering, 1) and spinorbital disordered states.2) In particular, for the study of topical subjects of d-electron systems including hightemperature superconductivity and frustrated magnetism, orbital arrangement has been found to provide an important basis to understand the underlying electronic and spin structures. This is because of the strong coupling between orbital, spin and charge degrees of freedom, which, on the other hand, makes it hard to study purely orbital-driven effects.Interestingly, however, f -electron systems may provide a rare example of nonmagnetic ground states that have mainly orbital degree of freedom known as quadrupolar moments, i.e., irreducible tensor operators of the total angular momentum J.3) In particular, cubic Pr and U based compounds with 4f 2 configuration are known to sometimes exhibit a nonmagnetic ground state with the À 3 quadrupolar degree of freedom. In comparison with the uranium compounds, Pr based materials have been found to exhibit rich variety of electronic ground state due to quadrupole moments, such as ferro-and antiferroquadrupolar states, e.g., in PrPtBi and PrPb 3 , [4][5][6] and superconductivity in a quadrupolar phase in PrIr 2 Zn 20 . 7,8) Moreover, for these nonmagnetic states, the hybridization between the 4f and conduction electrons is expected to lead to two competing interactions. One is the indirect RKKY type intersite coupling between quadrupole moments, which may sometimes induce incommensurate modulated structure as observed in PrPb 3 .6) The other is the two-channel (quadrupolar) Kondo effect that quenches the orbital degrees of freedom and stabilize an anomalous metallic state. [9][10][11] For Ce and Yb based compounds described as Kondo lattice systems, it is known that the competition between the Kondo effect and RKKY interaction gives rise to quantum criticality and related phenomena such as unconventional superconductivity and non-Fermi liquid behavior. In analogy, novel quantum criticality and exotic superconductivity might arise as a result of the competition between the quadrupolar Kondo effect and RKKY interaction.In the search for the novel screening effects, pioneer works on the cubic 4f 2 À 3 systems PrInAg 2 and PrMg 3 have found that these compounds do not exhibit any long-range order 12,13) and suggested a nonmagnetic heavy fermion state due to the qu...

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confidence: 76%

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀

2012

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“…The specific heat feature at T Q broadens under applied magnetic field, suggesting that order is possibly ferroquadrupolar in nature [259]. This hypothesis was confirmed in ultrasound measurements of PrTi 2 Al 20 that directly probe the quadrupolar susceptibility [386]. CurieWeiss behavior is observed in χ(T ) data for T > 250 K, characterized by Θ CW -40 K and µ e f f 3.43 µ B /Pr [259].…”

Section: Superconductivity In Prt 2 X 20 Compoundsmentioning

confidence: 60%

Unconventional superconductivity in heavy-fermion compounds

White

Thompson

Maple

2015

Physica C: Superconductivity and its Applications

130

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Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion compounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. We conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.

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“…As for PrTi 2 Al 20 , it is suggested that the ordered state is ferro quadrupole. 6,14,28) We briefly discuss below properties of Γ 3 ferro quadrupole order.…”

Section: Ferro Quadrupole Ordermentioning

confidence: 99%

Antiferro Quadrupole Orders in Non-Kramers Doublet Systems

Hattori

Tsunetsugu

2014

J. Phys. Soc. Jpn.

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We investigate antiferro quadrupole orders in systems with non-Kramers doublet ground state with total angular momentum J = 4 in T d point group symmetry. We demonstrate that a pure O 2 2 antiferro quadrupole order is impossible in general crystalline-electric field potential and should be accompanied by ferro O 0 2 quadrupole moment. The temperature and magnetic-field phase diagram is obtained by mean-field approximation of intersite quadrupole interactions and the excitation spectrum is analyzed by "spin"-wave approximations. Gapless excitations emerge at the boader of antiferro O 2 2 quadrupole phases under magnetic field. Quadrupole susceptibilities in the antiferro quadrupole ordered state exhibit unusual singularity and especially the uniform quadrupole susceptibility diverges in addition to the staggered ones. These unusual singularities are also realized at the critical field along [111] direction. We also discuss recent experimental results in PrT 2X20 (T =Ir, Rh, Ti, V, and X=Zn, Al). IntroductionOrbital order appears in varieties of systems in condensed matter physics such as in d-and f -electron strongly correlated systems with orbital degrees of freedom.1, 2) Quadrupole orders are typical and most intensively studied cases. Such orbital orders can be in principle described by similar theoretical approaches as in spin systems. As is evident from the nature of orbital degrees of freedom, interactions have spatial anisotropies depending on what kinds of orbital is considered and the symmetry is in general not fully isotropic in the orbital space. These differ from the typical case of spin systems, where the spin anisotropy is zero or not so strong unless the spin-orbit interaction is very strong. Each orbital order possesses a unique property and exploring such uniqueness is an important issue of the condensed matter theories and experiments.Recently, Pr-based compounds PrT 2 X 20 (T =Ir,Rh,Ti,V, and X=Zn,Al), so-called 1-2-20 compounds, have attracted great attention.3-12) In these compounds, each Pr ion has (4f) 2 electron configuration. Its ground state under the crystalline electric field (CEF) is a non-Kramers doublet, 13) and this doublet couples with conduction electrons. This is a typical situation that the two-channel Kondo effects take place. Thus, it is expected that these compounds show exotic properties due to the two-channel Kondo effects.

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Ultrasonic Investigation on a Cage Structure Compound PrTi₂Al₂₀

Cited by 40 publications

References 18 publications

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀

Unconventional superconductivity in heavy-fermion compounds

Antiferro Quadrupole Orders in Non-Kramers Doublet Systems

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Ultrasonic Investigation on a Cage Structure Compound PrTi2Al20

Cited by 40 publications

References 18 publications

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi2Al20

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi2Al20

Unconventional superconductivity in heavy-fermion compounds

Antiferro Quadrupole Orders in Non-Kramers Doublet Systems

Contact Info

Product

Resources

About

Ultrasonic Investigation on a Cage Structure Compound PrTi₂Al₂₀

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀

Superconductivity in the Ferroquadrupolar State in the Quadrupolar Kondo Lattice PrTi₂Al₂₀