Heavy-Fermion Superconductivity in the Quadrupole Ordered State ofPrV2Al20

Abstract

PrV2Al20 is a rare example of a heavy fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc = 50 mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy fermion character of the superconductivity is evident from the specific heat jump of ∆C/T ∼ 0.3 J/mol K 2 and the effective mass m * /m0 ∼ 140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ = 0.75 K and T * = 0.65 K associated with quadrupole and octapole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T 3 dependence, indicating the gapless mode associated with the quadrupole and/or octapole order. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.PACS numbers: 74.70. Tx, 75.25.Dk, 72.15.Qm 4f electron systems exhibit a large variety of nontrivial ground states by tuning the hybridization between localized 4f and conduction (c−) electrons. Especially, emergence of exotic superconductivity (SC) with a large effective mass from unconventional quantum criticality has attracted much attention [1][2][3][4][5]. While most of the examples have been reported at the border of magnetism [6,7], similarly exotic states of matter may be found in the vicinity of quantum phase transition associated with different degrees of freedom of f -electrons, such as electrical quadrupole (orbital) and valence. In particular, experimental exploration of the quadrupolar instability is important since few studies on the associated quantum criticality has been made to date.For the exploration, the simplest example could be found in materials that carry no magnetic but quadrupole moments. Such a nonmagnetic ground state is known as the Γ 3 doublet in the cubic crystalline electric field (CEF) of a f 2 configuration. Intensive studies have revealed various interesting states in the cubic Γ 3 doublet systems, in particular in Pr-based intermetallic compounds [8][9][10][11][12]. However, Pr-based cubic Γ 3 doublet systems usually have well-localized quadrupole moments, and thus until quite recently there have been no study on the quadrupolar instability by tuning the c-f hybridization.PrT r 2 Al 20 (T r = Ti, V) has been reported as a rare example of cubic Γ 3 -doublet based Kondo lattice systems where one may tune the hybridization strength between quadrupole moments and conduction electrons by chemical substitution and by pressure [13,14]. These materials have the nonmagnetic Γ 3 CEF ground state with the well separated excited state at ∆ CEF ∼ 60 K (Ti) and 40 K (V), as confirmed by various experiments [13,15,16], and * Electronic address: satoru@issp.u-tokyo.ac.jp exhibit the respective ferro-and antiferro-quadrupole ordering at T Q = 2.0 K (Ti) and 0.6 K (...

Emergent spin-valley-orbital physics by spontaneous parity breaking

“…Although our model is a skeleton model and further sophistication is necessary to compare with the experiments, we believe that our analyses dig out the new essential features of the spin-charge-orbital coupled systems, which are possibly explored in monolayer M XX 3 . Moreover, similar interesting physics is expected also in other centrosymmetric lattices with local asymmetry like the zig-zag chain and diamond lattice, which are found in several f -electron compounds, such as UGe 2 [46,47,48], URhGe [49,50,51], UCoGe [52,53,54], LnM 2 Al 10 (Ln = Ce, Nd, Gd, Dy, Ho, Er, M = Fe, Ru, Os) [55,56,57,58,59,60,61,62], RT 2 X 20 (R = Pr, La, Yb, U, T = Fe, Co, Ti, V, Nb, Ru, Rh, Ir, X = Al, Zn) [63,64,65,66,67,68,69,70,71,72,73,74], and β-YbAlB 4 [75,76,77,78]. Further efforts from both theoretical and experimental sides are highly desired for such exploration.…”

Perturbation on hyperfine-enhancedPr141nuclear spin dynamics associated with antiferroquadrupolar order inPrV2Al20Ito1, Higemoto2, Sakai3 et al. 2015Phys. Rev. B8030View full textAdd to dashboardCite

“…This strongly suggests that the order parameter is a time-reversal-even multipole, supporting the AFQ order scenario from a microscopic point of view. Note that a T xyz -type magnetic octupole is also active in the Γ 3 subspace [7]. Our results suggest that T xyz octupolar order is unlikely in our samples.…”

“…Herein, we first establish the nonmagnetic nature of the primary order parameter in PrV 2 Al 20 from the µSR point of view using its high sensitivity to local magnetic fields. This provides a strong justification for the AFQ order and AFQ quantum criticality at ambient pressure [5,7,16]. Next, we show that the muon spin-lattice relaxation rate (1/T 1,µ ) exhibits a step-like change at around T Q , which can be attributed to the perturbation on the strength of electronmediated 141 Pr nuclear spin interactions.…”

“…Various novel phenomena related to Γ 3g quadrupoles, such as incommensurate quadrupolar order, multi-channel Kondo effects, quadrupolar quantum criticality, and consequent heavy fermion superconductivity, have been intensively studied [1][2][3][4][5][6][7]. However, experimental techniques to probe quadrupolar properties are still quite limited.…”

Large positive correlation between the effective electron mass and the multipolar fluctuation in the heavy-fermion metal Ce1 − x La x B6

“…Therefore, Ce 1−x La x B 6 can be regarded as a model system to study rather general features of multipolar phases and superexchange interactions between multipolar moments. [31][32][33] Furthermore, recent discoveries of superconductivity (SC) near quadrupolar quantum critical point (QCP) 10,11 strongly motivate researchers to investigate one of unresolved problems about the relation between the substitution-tuned multipolar QCP and proximate competing order parameters, including SC that occurs on the La-rich side in Ce 1−x La x B 6 . 34 By convention for naming primary order parameters, the spin/pseudospin (orbital) paramagnetic (PM) phase, the AFQ phase, the AFM phase, and the AFO phase are referred to as phases I, II, III, and IV, respectively.…”