Left-handed color-sextet diquark in Kaon system

We investigate whether a color-sextet scalar diquark (${\bf H}_6$) coupling to the left-handed quarks contributes to the $\Delta S=2$ process. It is found that the box diagrams mediated by $W$ and ${\bf H}_6$ bosons have no contributions to $\Delta S=2$ when the limit of $m_t=0$ is used, and the flavor mixing matrices for diagonalizing quark mass matrices are introduced at the same time. When the heavy top-quark mass effects are taken into account, it is found that in addition to the $W-{\bf H}_6$ box diagrams significantly contributing to $\Delta S=2$, their effects can be as large as those from the ${\bf H}_6-{\bf H}_6$ box diagrams. Using the parameters that are constrained by the $K^0-\bar K^0$ mixing parameter $\Delta M_K$ and the Kaon indirect CP violation $\epsilon_K$, we find that the left-handed color-sextet diquark can lead to the Kaon direct CP violation being $Re(\epsilon'/\epsilon) \sim 0.4 \times 10^{-3}$. In the chosen scheme, although the diquark contribution to $K_L\to \pi^0 \nu \bar\nu$ is small, the branching ratio of $K^+ \to \pi^+ \nu \bar\nu$ can reach the current experimental upper bound.Comment: 22 pages, 6 figure

Proposal for the detection of magnetic monopoles in spin ice via nanoscale magnetometry

We present a proposal for applying nanoscale magnetometry to the search for magnetic monopoles in the spin ice materials holmium and dysprosium titanate. Employing Monte Carlo simulations of the dipolar spin ice model, we find that when cooled to below 1.5K these materials exhibit a sufficiently low monopole density to enable the direct observation of magnetic fields from individual monopoles. At these temperatures we demonstrate that noise spectroscopy can capture the intrinsic fluctuations associated with monopole dynamics, allowing one to isolate the qualitative e↵ects associated with both the Coulomb interaction between monopoles and the topological constraints implied by Dirac strings. We describe in detail three di↵erent nanoscale magnetometry platforms (muon spin rotation, nitrogen vacancy defects, and nanoSQUID arrays) that can be used to detect monopoles in these experiments, and analyze the advantages of each

Proposal for the detection of magnetic monopoles in spin ice via nanoscale magnetometry

We present a proposal for applying nanoscale magnetometry to the search for magnetic monopoles in the spin ice materials holmium and dysprosium titanate. Employing Monte Carlo simulations of the dipolar spin ice model, we find that when cooled to below 1.5K these materials exhibit a sufficiently low monopole density to enable the direct observation of magnetic fields from individual monopoles. At these temperatures we demonstrate that noise spectroscopy can capture the intrinsic fluctuations associated with monopole dynamics, allowing one to isolate the qualitative e↵ects associated with both the Coulomb interaction between monopoles and the topological constraints implied by Dirac strings. We describe in detail three di↵erent nanoscale magnetometry platforms (muon spin rotation, nitrogen vacancy defects, and nanoSQUID arrays) that can be used to detect monopoles in these experiments, and analyze the advantages of each

Observation of a crossover from nodal to gapped superconductivity in LuxZr1-xB12

We have determined the superconducting and magnetic properties of four samples of LuxZr1-xB12 (x=0.04, 0.07, 0.17, and 0.8) using muon spin rotation (μSR) and magnetometry measurements. We observed a strong magnetic signal in both the μSR and magnetometry data in one sample (x=0.07), likely caused by the formation of static moments of size ≈1μB due to a clustering effect of the Lu3+ ions. In all other samples, we find only a small magnetic signal in the μSR data thought to originate from boron nuclei in the B12 cages. The superconductivity is found to evolve with x, with a decrease in x resulting in an increase in critical temperature and a decrease of the penetration depth. Most remarkably, we find evidence for the formation of nodes in the superconducting gap for x≤0.17, providing a potential new example of an s-to-s+d-wave crossover in a superconductor

Observation of a crossover from nodal to gapped superconductivity in LuxZr1-xB12

We have determined the superconducting and magnetic properties of four samples of LuxZr1-xB12 (x=0.04, 0.07, 0.17, and 0.8) using muon spin rotation (μSR) and magnetometry measurements. We observed a strong magnetic signal in both the μSR and magnetometry data in one sample (x=0.07), likely caused by the formation of static moments of size ≈1μB due to a clustering effect of the Lu3+ ions. In all other samples, we find only a small magnetic signal in the μSR data thought to originate from boron nuclei in the B12 cages. The superconductivity is found to evolve with x, with a decrease in x resulting in an increase in critical temperature and a decrease of the penetration depth. Most remarkably, we find evidence for the formation of nodes in the superconducting gap for x≤0.17, providing a potential new example of an s-to-s+d-wave crossover in a superconductor

Robustness of superconducting properties to transition metal substitution and impurity phases in Fe1-xVxSe

We have performed transverse- and zero-field muon spin rotation/relaxation experiments, as well as magnetometry measurements, on samples of Fe1-xVxSe and their Li+NH3 intercalates Li0.6(NH2)0.2(NH3)0.8Fe1-xVxSe. We examine the low vanadium substitution regime: x=0.005, 0.01, and 0.02. The intercalation reaction significantly increases the critical temperature (Tc) and the superfluid stiffness for all x. The nonintercalated samples all exhibit Tc≈8.5 K while the intercalated samples all show an enhanced Tc>40 K. Vanadium substitution has a negligible effect on Tc, but seems to suppress the superfluid stiffness for the nonintercalated samples and weakly enhance it for the intercalated materials. The optimal substitution level for the intercalated samples is found to be x=0.01, with Tc≈41K and λab(0)≈0.18μm. The nonintercalated samples can be modeled with either a single d-wave superconducting gap or with an anisotropic gap function based on recent quasiparticle imaging experiments, whereas the intercalates display multigap nodal behavior which can be fitted using s+d- or d+d-wave models. Magnetism, likely from iron impurities, appears after the intercalation reaction and coexists and competes with the superconductivity. However, it appears that the superconductivity is remarkably robust to the impurity phase, providing an avenue to stably improve the superconducting properties of transition metal substituted FeSe

Exsolution of SrO during the topochemical conversion of LaSr3CoRuO8 to the oxyhydride LaSr3CoRuO4H4

Reaction of the n = 1 Ruddlesden-Popper oxide LaSr3CoRuO8 with CaH2 yields the oxyhydride phase LaSr3CoRuO4H4 via a topochemical anion exchange. Close inspection of the X-ray and neutron powder diffraction data in combination with HAADF-STEM images reveals that the nanoparticles of SrO are exsolved from the system during the reaction, with the change in cation stoichiometry accommodated by the inclusion of n > 1 (Co/Ru)nOn+1H2n "perovskite" layers into the Ruddlesden-Popper stacking sequence. This novel pseudotopochemical process offers a new route for the formation of n > 1 Ruddlesden-Popper structured materials. Magnetization data are consistent with a LaSr3Co+Ru2+O4H4 (Co+, d8, S = 1; Ru2+, d6, S = 0) oxidation/spin state combination. Neutron diffraction and μ+SR data show no evidence for long-range magnetic order down to 2 K, suggesting the diamagnetic Ru2+ centers impede the Co-Co magnetic-exchange interactions