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Journal Articles

Nanoscale heterogeneity induced by nonmagnetic Zn dopants in the quantum critical metal CeCoIn$$_5$$; $$^{115}$$In NQR/NMR and $$^{59}$$Co NMR study

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Thompson, J. D.*; Ramakrishna, S. K.*; Reyes, A. P.*; Suzuki, Kohei*; Oshima, Yoshiki*; et al.

Physical Review B, 104(8), p.085106_1 - 085106_12, 2021/08

 Times Cited Count:3 Percentile:25.71(Materials Science, Multidisciplinary)

Antiferromagnetism in a prototypical quantum critical metal CeCoIn$$_5$$ is known to be induced by slight substitutions of non-magnetic Zn atoms for In. In nominally 7% Zn substituted CeCoIn$$_5$$, an antiferromagnetic (AFM) state coexists with heavy fermion superconductivity. Heterogeneity of the electronic states is investigated in Zn doped CeCoIn$$_5$$ by means of nuclear quadrupole and magnetic resonances (NQR and NMR). Site-dependent NQR relaxation rates $$1/T_1$$ indicate that the AFM state is locally nucleated around Zn substituents in the matrix of a heavy fermion state, and percolates through the bulk at the AFM transition temperature $$T_{rm N}$$. At lower temperatures, an anisotropic superconducting (SC) gap below the SC transition temperature $$T_{rm c}$$, and the SC state permeates through the AFM regions via a SC proximity effect. Applying an external magnetic field induces a spin-flop transition near 5 T, reducing the volume of the AFM regions. Consequently, a short ranged inhomogeneous AFM state survives and coexists with a paramagnetic Fermi liquid state at high fields.

Journal Articles

$$^{33}$$S nuclear magnetic resonance spectra of uranium disulfide $$beta$$-US$$_2$$

Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Ramakrishna, S. K.*; Reyes, A. P.*; Rosa, P. F. S.*; Ronning, F.*; Thompson, J. D.*; Fisk, Z.*; et al.

JPS Conference Proceedings (Internet), 30, p.011169_1 - 011169_6, 2020/03

Uranium disulfide $$beta$$-US$$_2$$ showing a semimetal-to-semiconductor crossover has been investigated by the nuclear magnetic resonance (NMR) technique for $$^{33}$$S nuclei with the nuclear spin of $$I=3/2$$. Since the natural concentration 0.76% of NMR active $$^{33}$$S nuclei is too dilute, the isotopic enrichment to $$sim$$50% has been carried out for the single crystal growth. The $$^{33}$$S NMR spectra have been successfully obtained using a single crystal of $$beta$$-US$$_2$$ with external fields along the crystallographic $$c$$ axis. The S sites assignments have been made based on these NMR spectra.

Oral presentation

$$^{33}$$S NMR study in $$beta$$-US$$_2$$

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Ramakrishna, S. K.*; Reyes, A. P.*; Rosa, P. F. S.*; Ronning, F.*; Thompson, J. D.*; Bauer, E. D.*

no journal, , 

Uranium disulfide $$beta$$-US$$_2$$ is a paramagnetic semiconductor with a narrow band gap of 90 K at low temperatures, whereas above 80 K it is a semimetal with an extremely low density of carriers. Another characteristic feature in $$beta$$-US$$_2$$ is the strong response of the electrical resistivity to magnetic field. The magnetoresistance is similar to that of colossal magnetoresistance materials but very anisotropic. In order to clarify the microscopic spin dynamics in $$beta$$-US$$_2$$, nuclear magnetic resonance experiments have been performed. Since the natural concentration of $$^{33}$$S nuclei ($$I=frac{3}{2}$$) is only 0.76%, isotopic enrichment to 50% has been carried out. In the presentation, we would like to discuss about the microscopic magnetism in $$beta$$-US$$_2$$ to show the NMR results under high fields.

Oral presentation

NMR study of Zn- and Ni-substitution effect in heavy fermion superconductor CeCoIn$$_5$$

Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Ramakrishna, S. K.*; Reyes, A. P.*; Kotegawa, Hisashi*; To, Hideki*; et al.

no journal, , 

In heavy fermion superconductor CeCoIn$$_5$$, slight Zn substitutions for In atoms induce antiferromagnetism, while slight Ni substitutions for Co atoms suppress superconductivity. The both substituted CeCoIn$$_5$$ exhibit non- fermi-liquid behaviors near the phase boundaries which have been detected by magnetization and specific heat measurements. We have performed NMR experiments in these systems to investigate the microscopic effects by substituents. We will discuss about the spin fluctuations near the boundaries by NMR relaxation rates.

Oral presentation

Magnetism and electric conductivity in uranium disulfide $$beta$$-US$$_2$$

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Ramakrishna, S. K.*; Reyes, A. P.*; Rosa, P. F. S.*; Thompson, J. D.*; Ronning, F.*; Fisk, Z.*; Bauer, E. D.*

no journal, , 

To investigate the microscopic magnetism for $$beta$$-US$$_2$$, we have performed the nuclear magnetic resonance (NMR) experiments under high fields. Isotopic enrichment of $$^{33}$$S nuclei has been attempted to gain the NMR sensitivity. In this presentation, we will discuss about the relationship between the microscopic magnetism and electrical conductivity in $$beta$$-US$$_2$$.

Oral presentation

Heterogeneous electronic state by Zn-substitutions in heavy fermion superconductor CeCoIn$$_5$$

Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Ramakrishna, S. K.*; Reyes, A. P.*; Suzuki, Kohei*; Oshima, Yoshiki*; et al.

no journal, , 

Substitutions of In sites by Zn atoms in heavy fermion superconductor CeCoIn$$_5$$ is reported to induce an antiferromagnetic order by Yokoyama et al. in Ibaraki University. Near the critical region, non-Fermi-liquid behavior has been observed in magnetization and specific heat. We have performed NMR measurements to reveal the spin fluctuations near the critical region.

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