27AI NMR Study of Np‐ Based Superconductor Nppd5A:2
We力 a veわ vesfrgared a newry dlscο vered lVp― based
わea1/y fermわ n sυ ρercο ndυ cror rvpPd5ハ r2by means οr2ζ ハ′Arν R Oυ rArν R dara ρrOyFde eydence rOr d̲wave symmerry:strongly sυ ggesls めarοrめ e cOο ρer ρa′ rs Iわ rs resυ ′5r‐ elecrrOn sρ ゎ rltrcrtra″ οns cο υtt ρlay an′mρ οrranf rOleヵめe sypercOndυ c″ vrfy or7vpPd5ハ 12f7′

丁he actinide compOunds with 5f electrons occupy a

special position in research on condensed matter physics
丁he reason forthis is that 5f electrons in actinides behave as

though they are near the boundary between localized anditinerant character The electronic properties of theseactinides are often characterized by a so‐ ca‖ ed heavy
fermion state at low temperatures A recent discovery of
considerable interest was that of superconductivity in theheavy fermion compound PuCoGa5 in 2002, where thesuperconduclng(SC)transllon temperature Tc was found tobe 185 K Fo‖ owing that discovery, in 2007 the first Np‐
based, heavy fermion superconductor NpPd5A12 WaS
discovered with the relatively high Tc=4 9 K by D Aokietal

1[2]NpPd5A12 haS a tetragonal crystal structure as shown inthe insetto Fig 2 The physical properties ofthe SC state in

NpPd5A12 are interesting, e g strong Pauli paramagneticeffect,first― order SC transition,and so on Recently,we haveinvestigated the superconductivity in NpPd5A12 uSing theNMR technique

10T(K)

Fig 2 丁emperature dependence of 1/71 Solid line shovvs
calculation of 1/71 Black dotted, red solid and red brokenlines show calculated 1/71 using fu‖ , ‖ne‐ node and pOint‐
node gaps,respectively lnset shows the crystal structure ofNpPd5A12

Figure l shows a variety of symmetries for Cooper pairs
in a superconductor S‐ wave symmetry forthe Cooper pairs
is compOsed of an isotropic orbital form and a singlet spinstate. On the other hand, p‐ and d‐ wave symmetries are

the coherence peak strongly indicates the occurrence of ananisotropic(non S‐ Wave)SC state tthe black solid line is acharacterized by anisotropic orbital forms vvith triplet(p)andline calculated assuming a line― nodeinthe SC gap From thesinglet(d)Spin states, respectively in the figure, we also
show the posslble origin for the attractive force within a
Cooper pair.

たBTc=6 4 ofthe SC gap has been obtained,vvhich indicates

NMR ls a powerfultoolforinvesugaung the symmetry of
Cooper pairs The orbital form of the Cooper pairs can bebest fit to the experimental data,a relatively large value 2△ o/strong coup‖ ng superconductivity On the other hand,fromthe decrease of the Knight shrt be10w Tc(not ShOWn),wehave confirmed a singlet spin state in NpPd5A12

丁herefore,

wave

determined by measuring the temperature dependence ofour 1/Tl and Knight shift results strongly indicate d‐

the nuclear spin― lattlce relaxation rate 1/71 below Tc 1/71

superconductivity in NpPd5A12

reflects the density of states near the Fermi leve1 0n themagnetic fluctuations of the 5f‐ electron spins plays animportant role in the superconduc‖ vtty of NpPd5A12 11l Weother hand, the spin state of the Cooper pairs can be

丁his suggests that thedetermined by measuring the Knight shift The Knight shiftis

are currently investigating the characteristics of the magnetic

associated with a localfield induced by the electron spins atfluctuations in the norrnal statea nuclear site

Fig 2 shows the temperature dependence of 1/Tl throughthe SC transtion 1/71 shows a sharp drop lust be10w Tc
vvithoutthe coherence peak(dOtted line in Fig 2)charaCteristicof a conventional s‐ wave superconductor tthe absence ofReferences11]H ChudO H Sakal,Y Tokunaga,S Kambe,D Aoki、 Y
Homma,Y Shiokawa、 Y Haga,S lkeda.T D Matsuda,YOnukl, and H Yasuoka. 」 Phys Soc Jpn 77, 083702(2008)

Symmetry ofρ wavethe Cooper pa rs

d waveN Tateiwa S lkeda.YHomma,H Sakal Y Shiokawa,E Yamamoto A Nakamura
R Settal, and Y Onuki、 」 Phys Soc Jpn 76, 063701(2007)

orbnalfOrm of
the Cooper pairs[2]D Aoki、 Y Haga、 T D Matsuda、{1lli::〕 ￨Key WOrds
Heavy― ferlnlon Superconductor,Transuranium Compound

盆 1地spln state of

the Cooper pairsSpin t‖ pletSpin singlet
Candidate fo「 the oHginofthe atlracuve 10rcePhonon

Spin singlet

Ferromagnet c Antferromagnetc
f uctuat ons

f uctuations

Contact toHiroyuki Chudo(Advanced Science Research Center,」 apan
Atomic Energy Agency(」 AEA))e‐

mall:chudo hiroyuki@laea 90 ip

Yoshiya Homma(Radiochemistry of Metals Division)
Fig l variety of symrnetries forthe Cooper pairs The+and―show the sign ofthe wave function

KINKEN Reseo「 ch Hi9hi9his 2009e―

maili yhomma@imrtohoku acip