arXiv subjects

O. O. Bernal

Publications and source records attributed to O. O. Bernal.

44 records · Page 3Linked to original sources

arXiv2001

Susceptibility Inhomogeneity and Non-Fermi-Liquid Behavior in Ce(Ru_{0.5}Rh_{0.5})_2Si_2

Magnetic susceptibility and muon spin rotation (\muSR) experiments have been carried out to study the effect of structural disorder on the non-Fermi-liquid (NFL) behavior of the heavy-fermion alloy Ce(Ru_{0.5}Rh_{0.5})_2Si_2. Analysis of the bulk susceptibility in the framework of disorder-driven Griffiths-phase and Kondo-disorder models for NFL behavior yields relatively narrow distributions of characteristic spin fluctuation energies, in agreement with \muSR linewidths that give the inhomogeneous spread in susceptibility. \muSR and NMR data both indicate that disorder explains the "nearly NFL" behavior observed above \sim2 K, but does not dominate the NFL physics found at low temperatures and low magnetic fields.

cond-mat.str-el↗

arXiv2001

Slow Spin Dynamics in Non-Fermi-Liquid UCu_{5-x}Pd_x, x = 1.0 and 1.5

Low-temperature muon spin-lattice relaxation measurements in the non-Fermi-liquid heavy-fermion alloys UCu_{5-x}Pd_x, x = 1.0 and 1.5, indicate inhomogeneously distributed f-electron spin fluctuation rates, and exhibit a time-field scaling of the muon relaxation function indicative of long-lived spin correlations. In UCu_4Pd the scaling exponent γis small and temperature independent. In UCu_{3.5}Pd_{1.5} γvaries with temperature, increasing with decreasing temperature similar to spin-glass AgMn. This suggests that the spin-glass state found for x \gtrsim 2 in UCu_{5-x}Pd_x modifies the low-frequency spin dynamics in UCu_{3.5}Pd_{1.5}.

cond-mat.str-el↗

arXiv2001

Time-Reversal-Symmetry Violation and Coexistence of Superconducting and Magnetic Order in CeRh(1-x)Ir(x)In(5)

This paper has been withdrawn by the authors. We performed additional zero-field muon spin relaxation measurements in the superconducting state of CeIrIn$_5$ and found that the spontaneous fields reported previously below $T_c$ are not present. Thus, there is no evidence for a time-reversal-symmetry-violating superconducting order parameter. These new zero-field measurements, as well as new measurements of the penetration depth in this system, will be reported elsewhere. Our zero-field measurements in CeIr$_{0.5}$Rh$_{0.5}$In$_5$, reporting coexistence of superconductivity and magnetic order, are still valid.

cond-mat.str-el↗

arXiv2001

29-Si NMR and Hidden Order in URu2Si2

We present new 29-Si NMR spectra in URu2Si2 for varying temperature T, and external field H. On lowering T, the systematics of the low-field lineshape and width reveal an extra component (lambda) to the linewidth below T_N ~ 17 K not observed previously. We find that lambda is magnetic-field independent and dominates the low-field lineshape for all orientations of H with respect to the tetragonal c axis. The behavior of lambda indicates a direct relationship between the 29-Si spin and the transition at T_N, but it is inconsistent with a coupling of the nuclei to static antiferromagnetic order/disorder of the U-spin magnetization. This leads us to conjecture that lambda is due to a coupling of 29-Si to the system's hidden-order parameter. A possible coupling mechanism involving charge degrees of freedom and indirect nuclear spin/spin interactions is proposed. We also propose further experiments to test for the existence of this coupling mechanism.

cond-mat.str-el↗

arXiv2001

Glassy Spin Dynamics in Non-Fermi-Liquid UCu_{5-x}Pd_x, x = 1.0 and 1.5

Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCu_{5-x}Pd_x, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function Gbar(t) indicates strongly inhomogeneous spin fluctuations, and exhibits the scaling Gbar(t,H) = Gbar(t/H^γ) expected from glassy dynamics. At 0.05 K γ(x=1.0) = 0.35 \pm 0.1, but γ(x=1.5) = 0.7 \pm 0.1. This is in contrast to inelastic neutron scattering results, which yield γ= 0.33 for both concentrations. There is no sign of static magnetism \gtrsim 10^{-3} μ_B/U ion in either material above 0.05 K. Our results strongy suggest that both alloys are quantum spin glasses.

cond-mat.str-el↗

arXiv1999

NMR Detection of Temperature-Dependent Magnetic Inhomogeneities in URu2Si2

We present 29Si-NMR relaxation and spectral data in URu2Si2. Our echo-decay experiments detect slowly fluctuating magnetic field gradients. In addition, we find that the echo-decay shape (time dependence) varies with temperature T and its rate behaves critically near the Neel temperature TN, indicating a correlation between the gradient fluctuations and the transition to small-moment order. T-dependent broadening contributions become visible below 100 Kelvin and saturate somewhat above TN, remaining saturated at lower temperatures. Together, the line width and shift suggest partial lattice distortions below TN. We propose an intrinsic minority phase below $T_{\rm N}$ and compare our results with one of the current theoretical models.

cond-mat.str-el↗

arXiv1999

Similarity of slow stripe fluctations between Sr-doped cuprates and oxygen-doped nickelates

Stripe fluctuations in La2NiO4.17 have been studied by 139La NMR using the field and temperature dependence of the linewidth and relaxation rates. In the formation process of the stripes the NMR line intensity is maximal below 230K, starts to diminish around 140K, disappears around 50K and recovers at 4K. These results are shown to be consistent with, but completely complementary to neutron measurements, and to be generic for oxygen doped nickelates and underdoped cuprates.

cond-mat.supr-con↗

arXiv1998

Stripes in La2NiO4.17: charge and spin ordering according to NMR

Charge and spin ordering in La2NiO4.17 has been studied by 139La NMR using the field and temperature dependence of the linewidth and relaxation rates. The stripes are site centered and the domain spins freeze at ~ 180 K, followed by a second transition at ~ 50 K, where the spins on the domain walls freeze. Although consistent with the neutron measurements, the results are quantitatively different from the NMR results in a nickelate with quenched Sr disorder.

cond-mat.str-el↗