Ruderman-Kittel interaction between Si in URuSi

Kambe, Shinsaku; Hattori, Taisuke; Tokunaga, Yo; Sakai, Hironori; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*

Journal of Physics; Conference Series, 969(1), p.012033_1 - 012033_6, 2018/03

https://doi.org/10.1088/1742-6596/969/1/012033

High quality URuSi enriched in Si isotope, which is an NMR nucleus, by 52% was prepared. Since the natural abundance ratio of Si isotope is about 4%, the accumulated measurement time can be shortened to about one hundredth by this concentration. Results of the Si-NMR linewidth of hidden ordered phase using this single crystal sample have already been reported. In this report, we will report more detailed analysis on the magnetic field, temperature and angle of this line width We also discuss the possibility of distribution of magnetic susceptibility in two-fold symmetry by RKKY model.

dependence of nuclear spin-echo decay at low temperatures in YbRhSi

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Hattori, Taisuke; Lapertot, G.*; Matsuda, Tatsuma*; Knebel, G.*; Flouquet, J.*; Walstedt, R. E.*

Physical Review B, 95(19), p.195121_1 - 195121_8, 2017/05

AA2017-0083.pdf:0.74MB

https://doi.org/10.1103/PhysRevB.95.195121

The authors report Si nuclear spin-echo oscillations and decay measurements on a single crystal of YbRhSi. These quantities are found to be independent from 300 K down to 20 K, showing, however, a strong dependence below 20 K. These results indicate that electronic states near the Fermi level are modified at low temperatures. The observed spin-echo oscillations can be interpreted with the Ruderman-Kittel and pseudo-dipolar interactions between nearest-neighbor Si nuclei driven by conduction electron scattering at the Fermi surface. Possible modifications to the Fermi surface at low temperatures are discussed.

Dilute RKKY model for NMR line broadening in the hidden-order state of URuSi

Walstedt, R. E.*; Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori

Physical Review B, 93(4), p.045122_1 - 045122_8, 2016/01

https://doi.org/10.1103/PhysRevB.93.045122

A well-known analytic model for Lorentzian broadening of metallic NMR lines by dilute localized magnetic centers embedded in a lattice has been applied to the case of the twofold-symmetry magnetism in URuSi. The observed Lorentzian spectra are accounted for with a simple formula giving the Si NMR linewidth in terms of the susceptibility of the magnetic broadening centers and a Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling parameter.

Distributed twofold ordering in URuSi

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Walstedt, R. E.*

Physical Review B, 91(3), p.035111_1 - 035111_8, 2015/01

https://doi.org/10.1103/PhysRevB.91.035111

In previous Si NMR basal-plane field rotation measurements, a modest breaking of the fourfold symmetry was suggested in the hidden-order state of URuSi. Here, the angular dependence of the Si NMR linewidth is analyzed in detail, indicating the occurrence of a distribution of twofold local fields at the Si sites even in a high-quality single crystal. The relation between sample quality and the occurrence of effects having twofold symmetry is discussed.

Self-radiation effects and glassy nature of magnetic transition in AmO revealed by O-NMR

Tokunaga, Yo; Nishi, Tsuyoshi; Nakada, Masami; Ito, Akinori*; Sakai, Hironori; Kambe, Shinsaku; Homma, Yoshiya*; Honda, Fuminori*; Aoki, Dai*; Walstedt, R. E.*

Physical Review B, 89(21), p.214416_1 - 214416_8, 2014/06

https://doi.org/10.1103/PhysRevB.89.214416

The magnetic phase transition near K in AmO has been investigated microscopically by means of O NMR. To avoid complexities arising from sample aging associated with the alpha decay of Am, all measurements have been performed within 40 days after sample synthesis. Even during such a short period, however, a rapid change of NMR line shape has been observed at 1.5 K, suggesting that the ground state of AmO is very sensitive to disorder. We have also confirmed the loss of O NMR signal intensity over a wide temperature range below , and more than half of oxygen nuclei are undetectable at 1.5 K. This behavior reveals the persistence of slow and distributed spin fluctuations down to temperatures well below . In the paramagnetic state, strong NMR line broadening and spatially inhomogeneous spin fluctuations have been observed. The results are all indicative of short-range, spin-glass-like character for the magnetic transition in this system.

NMR study of in-plane twofold ordering in URuSi

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Matsuda, Tatsuma*; Haga, Yoshinori; Fisk, Z.; Walstedt, R. E.*

Physical Review Letters, 110(24), p.246406_1 - 246406_5, 2013/06

https://doi.org/10.1103/PhysRevLett.110.246406

We report Si NMR spectra and Knight shift measurements as a function of applied field orientation in the (001) basal plane of URuSi. Observed linewidth oscillations confirm the in-plane 2-fold ordered domain state observed in recent magnetic susceptibility measurements. Analysis of our linewidth data leads to the estimate for the 2-fold intrinsic (mono-domain) susceptibility anisotropy in the basal plane, a value times smaller than that obtained from recent susceptibility measurements.

T-dependent nuclear hyperfine coupling at the In site in CeIrIn

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Matsuda, Tatsuma; Haga, Yoshinori; Takeuchi, Tetsuya*; Onuki, Yoshichika*; Walstedt, R. E.*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA009_1 - SA009_3, 2011/07

http://jpsj.ipap.jp/link?JPSJS/80SA/SA009/

We report an In NMR study of a single-crystal sample of the heavy fermion superconductor CeIrIn. The observed non-linear variation of Knight Shift with static susceptibility in the normal state is consistent with the two-fluid (components) model of Nakatsuji et al, indicating that two individual contributions to static susceptibility exist. However, our results can also be understood in terms of a T-dependent hyperfine coupling, which accounts for the spin-lattice relaxation data naturally on the basis of a one-component dynamical susceptibility. In addition, the observed T-dependence of the hyperfine coupling is scaled to a density of states given by dynamical mean field theory (DMFT). We believe that this contrast between the static and dynamical properties is a crucial dual nature of the heavy fermion crossover, which related with the coherence between localized and itinerant excitations.

La substitution effect and hyperfine-enhanced Pr nuclear spin dynamics in PrPb; La NMR study in PrLaPb

Tokunaga, Yo; Sakai, Hironori; Chudo, Hiroyuki; Kambe, Shinsaku; Yasuoka, Hiroshi; Suzuki, Hiroyuki*; Walstedt, R. E.*; Homma, Yoshiya*; Aoki, Dai*; Shiokawa, Yoshinobu*

Physical Review B, 82(10), p.104401_1 - 104401_6, 2010/09

https://doi.org/10.1103/PhysRevB.82.104401

La NMR studies have been performed on PrPb substituted with 3% La. The temperature dependence of the local magnetic susceptibility around La ions has been extracted from the La Knight shift. These data show that the non-magnetic crystalline-electric-field (CEF) ground state (GS) is preserved even at the nearest neighboring Pr ions, although their CEF level scheme is slightly modified due to the La substitution. On the other hand, the temperature dependence of the nuclear spin-lattice relaxation rate is found to be well reproduced by assuming the same CEF level scheme over a wide temperature range. However, shows a strong upturn below 10 K, which is not expected from the non-magnetic CEF GS. We show that the low temperature anomaly can be quantitatively understood in terms of a cross-relaxation process between Pr and La nuclear spins.

Diagnosis of quantum criticality by nuclear spin-echo decay method

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Chudo, Hiroyuki; Walstedt, R. E.*

Physica Status Solidi (B), 247(3), p.520 - 524, 2010/03

https://doi.org/10.1002/pssb.200983063

In order to diagnose the quantum critical behaviour in heavy fermion systems, the Gaussian spin-spin relaxation time determined by NMR spin-echo decay measurements is found to be useful. Combined with the spin-lattice relaxation time , an exponent of quantity is predicted to be sensitive to the type of quantum criticality. In fact in heavy fermion USn near the quantum critical point, is found to be constant as expected for the -SDW magnetic instability.

Crossover from the quantum critical to overdamped regime in the heavy-fermion system USn

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Matsuda, Tatsuma; Haga, Yoshinori; Chudo, Hiroyuki; Walstedt, R. E.*

Physical Review Letters, 102(3), p.037208_1 - 037208_4, 2009/01

https://doi.org/10.1103/PhysRevLett.102.037208

We report measurements of the Sn nuclear spin echo decay rate in the heavy fermion compound USn. From , the magnetic spin-spin correlation length is found to vary as above 100 K, which is expected for a quantum critical regime at high temperatures. Combined with the spin-lattice relaxation rate , is found to be temperature independent in the heavy fermion state below 30 K. This indicates that the heavy fermion state of USn is categorized in the overdamped regime with a dynamical critical exponent . These observations are consistent with a spin density wave (SDW) magnetic instability at the quantum critical point.