arXiv subjects

P. C. Ho

Publications and source records attributed to P. C. Ho.

4 recordsLinked to original sources

arXiv2019

Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: superconductivity and magnetism in Pr-rich alloys

The Pr-rich end of the alloy series Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ has been studied using muon spin rotation and relaxation. The end compound PrOs$_4$Sb$_{12}$ is an unconventional heavy-fermion superconductor, which exhibits a spontaneous magnetic field in the superconducting phase associated with broken time-reversal symmetry. No spontaneous field is observed in the Nd-doped alloys for x $>$ 0.05. The superfluid density is insensitive to Nd concentration, and no Nd$^{3+}$ static magnetism is found down to the lowest temperatures of measurement. Together with the slow suppression of the superconducting transition temperature with Nd doping, these results suggest anomalously weak coupling between Nd spins and conduction-band states.

cond-mat.supr-con↗

arXiv2009

Collapse of the hyperfine magnetic field at the Ru site in ferromagnetic rare earth intermetallics

The Mössbauer Effect(ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, $B_{hyperfine}$, at the ME active site. This is the case in the ruthenates, where the temperature dependence of $B_{hyperfine}$ at $^{99}$Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu$_2$ and HoRu$_2$. Specific heat, magnetization, magnetic susceptibility, Mössbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 82.3 and 15.3 K, respectively. Despite the ferromagnetic order of the rare earth moments in both systems, there is no evidence of a correspondingly large $B_{hyperfine}$ in the Mössbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out {\it ab initio} calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, $B_{hyperfine}$ is very small at those sites. This occurs because the 4$d$ Ru electrons form broad conduction bands rather than localized moments. These 4$d$ conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare earth moments.

cond-mat.str-el↗

arXiv2008

The filled skutterudite CeOs$_{4}$As$_{12}$: a hybridization gap semiconductor

X-ray diffraction, electrical resistivity, magnetization, specific heat, and thermoelectric power measurements are presented for single crystals of the new filled skutterudite compound {\CeOsAs}, which reveal phenomena that are associated with f - electron - conduction electron hybridization. Valence fluctuations or Kondo behavior dominates the physics down to $T$ $\sim$ 135 K. The correlated electron behavior is manifested at low temperatures as a hybridization gap insulating state. The small energy gap $Δ$$_1$/k$_B$ $\sim$ 73 K, taken from fits to electrical resistivity data, correlates with the evolution of a weakly magnetic or nonmagnetic ground state, which is evident in the magnetization data below a coherence temperature $T$$_{coh}$ $\sim$ 45 K. Additionally, the low temperature electronic specific heat coefficient is small, $γ$ $\sim$ 19 mJ/mol K$^2$. Some results for the nonmagnetic analogue compound {\LaOsAs} are also presented for comparison purposes.

cond-mat.str-el↗

arXiv2007

Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

Electrical resistivity $ρ$, specific heat C, and magnetic susceptibility $χ$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $ρ$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $χ$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.

cond-mat.str-el↗