Orbitally defined field-induced electronic state in a Kondo lattice

Lessux, G. G.*; Sakai, Hironori; Hattori, Taisuke*; Tokunaga, Yo; Kambe, Shinsaku; Kuhns, P. L.*; Reyes, A. P.*; Thompson, J. D.*; Pagliuso, P. G.*; Urbano, R. R.*

Physical Review B, 101(16), p.165111_1 - 165111_6, 2020/04

https://doi.org/10.1103/PhysRevB.101.165111

CeRhIn is a Kondo-lattice prototype in which a magnetic field 31T induces an abrupt Fermi-surface (FS) reconstruction and pronounced in-plane electrical transport anisotropy all within its antiferromagnetic state. Here we report low-temperature nuclear magnetic resonance (NMR) measurements revealing a pronounced decrease in the In formal Knight shift, without changes in crystal or magnetic structures, of CeRhIn at fields () spanning . We discuss the emergent state above in terms of a change in Ce's 4 orbitals that arises from field-induced evolution of crystal-electric field (CEF) energy levels. This change in orbital character enhances hybridization between the 4 and the conduction electrons that leads ultimately to an itinerant quantum-critical point at 50T.

High-field phase diagram of the heavy-fermion metal CeIn; Pulsed-field NMR study on single crystals up to 56 T

Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, M.*; Higa, Nonoka; et al.

Physical Review B, 99(8), p.085142_1 - 085142_5, 2019/02

https://doi.org/10.1103/PhysRevB.99.085142

The heavy-fermion antiferromagnet CeIn exhibits a field-induced anomaly associated with Fermi surface reconstruction at 45 T, well below the antiferromagnetic (AFM) critical field that exceeds 60 T. In order to explore the origin of this anomaly, we have measured In NMR spectra in pulsed magnetic fields up to 56 T using high-quality single crystals. To within experimental resolution, we do not detect any change in the NMR spectra that could suggest a modification in either the character of the hyperfine field or the electric field gradient at In sites through . This strongly suggests that the 45 T anomaly cannot be simply ascribed to a field-induced change in the magnetic structure of the AFM state.

Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field orientation-dependent Pt NMR

Tokunaga, Yo; Nakamura, Ai*; Aoki, Dai*; Shimizu, Yusei*; Homma, Yoshiya*; Honda, Fuminori*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku

Physical Review B, 98(1), p.014425_1 - 014425_5, 2018/07

https://doi.org/10.1103/PhysRevB.98.014425

Pt NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below TN = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes. Nuclear relaxation rate measurement revealed the development of the antiferro-magnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.

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.

Anisotropy of spin fluctuations in a tetragonal heavy fermion antiferromagnet CeRhAlSi

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ghimire, N. J.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Journal of Physics; Conference Series, 868(1), p.012012_1 - 012012_5, 2017/07

https://doi.org/10.1088/1742-6596/868/1/012012

Al NMR experiments have been performed using a single crystal of CeRhAlSi. In the paramagnetic state, Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which has a local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. The relaxation rates suggest that 4 electrons behave as local moments in the high temperatures. From the NMR spectral analyses, the antiferromagnetic structures are discussed.

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.

Interplay between quantum fluctuations and reentrant superconductivity with a highly enhanced upper critical field in URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, M.*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku; et al.

Physical Review B, 93(20), p.201112_1 - 201112_5, 2016/05

https://doi.org/10.1103/PhysRevB.93.201112

The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the () crystal plane. Our high-field Co NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the axis, while being unaffected by any field component along the axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

Incommensurate to commensurate antiferromagnetism in CeRhAlSi; An Al NMR study

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ghimire, N. J.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Physical Review B, 93(1), p.014402_1 - 014402_9, 2016/01

https://doi.org/10.1103/PhysRevB.93.014402

Al nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAlSi, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of =14 K and =9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below , but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between and . The spin-lattice relaxation rate suggests that the electrons behave as local moments at temperatures above .

Si NMR study on single crystalline URuSi

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

no journal, , 

Recently possible nematic order has been discussed with several experiments in so-called "hidden order" phase in URuSi. This makes the superconductivity in URuSi a new interesting system where we can investigate the relationship between nematicity and superconductivity. This is because the chiral superconductivity, which breaks the time-reversal symmetry, under nematic order is suggested theoretically to show peculiar behavior, and the supercoducting pairing function in URuSi is expected as the chiral -wave. Thus we have performed Si NMR measurements on a single crystalline URuSi sample with the Si isotope enriched to about 50%.

Isotopic enrichment of S to single crystals of uranium chalcogenide -US

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Pospisil, J.; Tateiwa, Naoyuki; Yamamoto, Etsuji; Haga, Yoshinori

no journal, , 

-US exhibits a large magnetoresistive effect but the mechanism is still identified. In order to investigate microscopically be means of nuclear magnetic resonance (NMR) technique, isotopic enrichment of NMR-active S has been performed. The physical properties on the single crystals will be discussed.