8 research outputs found
Evolution of ferromagnetic and non-Fermi liquid state with doping:the case of Ru doped UCoGe
We have investigated the impact of Ru substitution for Co on the behavior of
the ferromagnetic superconductor UCoGe by performing x-ray diffraction,
magnetization, specific heat and electrical resistivity measurements on
polycrystalline samples of the
series (). The initial Ru substitution up to
leads to a simultaneous sharp increase of the Curie temperature and spontaneous
magnetization up to maximum values of and
per formula unit, respectively, whereas
superconductivity vanishes already for . Further increase of the
Ru content beyond leads to a precipitous decrease of both,
and towards a ferromagnetic quantum critical
point (QCP) at . Consequently the magnetic phase
diagram consists of a well-developed ferromagnetic dome. We discuss the
evolution of ferromagnetism with on the basis of band structure changes due
to varying 5-ligand hybridization. This scenario is supported by the results
of electronic structure calculations and consideration of the simplified
periodic Anderson model. The analysis of the temperature dependencies of the
electrical resistivity and heat capacity at low temperatures of the samples in
the vicinity of the QCP reveals a non-Fermi liquid behavior and assigns the
ferromagnetic quantum phase transition to be most likely of a continuous
Hertz-Millis type.Comment: accepted for publication in PR
Field-Induced Superconductivity near the Superconducting Critical Pressure in UTe2
We report the magnetoresistance in the novel spin-triplet superconductor UTe2
under pressure close to the critical pressure Pc, where the superconducting
phase terminates, for field along the three a, b and c-axes in the orthorhombic
structure. The superconducting phase for H // a-axis just below Pc shows a
field-reentrant behavior due to the competition with the emergence of magnetic
order at low fields. The upper critical field Hc2 for H // c-axis shows a
quasi-vertical increase in the H-T phase diagram just below Pc, indicating that
superconductivity is reinforced by the strong fluctuations which persist even
at high fields above 20T. Increasing pressure leads to the disappearance of
superconductivity at zero field with the emergence of magnetic order.
Surprisingly, field-induced superconductivity is observed at high fields, where
a spin-polarized state is realized due to the suppression of the magnetic
ordered phases; the spin-polarized state is favorable for superconductivity,
whereas the magnetic ordered phase at low field seems to be unfavorable. The
huge Hc2 in the spin-polarized state seems to imply a spin-triplet state.
Contrary to the a- and c-axes, no field-reinforcement of superconductivity
occurs for magnetic field along the b-axis. We compare the results with the
field-reentrant superconductivity above the metamagnetic field, Hm for the
field direction tilted by about 30 deg. from b to c-axis at ambient pressure as
well as the field-reentrant (-reinforced) superconductivity in ferromagnetic
superconductors, URhGe and UCoGe.Comment: 7 pages, 5 figures, submitted to J. Phys. Soc. Jp
Gradual localization of 5f states in orthorhombic UTX ferromagnets - polarized neutron diffraction study of Ru substituted UCoGe
We report on a microscopic study of the evolution of ferromagnetism in the Ru
substituted ferromagnetic superconductor (FM SC) UCoGe crystallizing in the
orthorhombic TiNiSi-type structure. For that purpose, two single crystals with
composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge have been prepared and
characterized by magnetization, AC susceptibility, specific heat and electrical
resistivity measurements. Both compounds have been found to order
ferromagnetically below TC = 6.5 K and 7.5 K, respectively, which is
considerably higher than the TC = 3 K of the parent compound UCoGe. The higher
values of TC are accompanied by enhanced values of the spontaneous moment
mspont. = 0.11 mB/f.u. and mspont. = 0.21 mB/f.u., respectively in comparison
to the tiny spontaneous moment of UCoGe (about 0.07mB/f.u.). No sign of
superconductivity was detected in either compound. The magnetic moments of the
samples were investigated on the microscopic scale using polarized neutron
diffraction (PND) and for UCo0.88Ru0.12Ge also by soft X-ray magnetic circular
dichroism (XMCD). The analysis of the PND results indicates that the observed
enhancement of ferromagnetism is mainly due to the growth of the orbital part
of the uranium 5f moment mL(U), reflecting a gradual localization of the 5f
electrons with Ru substitution. In addition, the parallel orientation of the U
and Co moments has been established in both substituted compounds. The results
are discussed and compared with related isostructural ferromagnetic UTX
compounds (T - transition metals, X - Si, Ge) in the context of a varying
degree of the 5f-ligand hybridization
On the crossing numbers of join products of and
The crossing number cr(G) of a graph G is the minimum number of edge crossings over all drawings of G in the plane. The main aim of the paper is to give the crossing number of the join product and for the wheel on five vertices, where and are the path and the cycle on n vertices, respectively. Yue et al. conjectured that the crossing number of is equal to , for all m,n ≥ 3, and where the Zarankiewicz’s number is defined for n ≥ 1. Recently, this conjecture was proved for by Klesc. We establish the validity of this conjecture for and we also offer a new conjecture for the crossing number of the join product for m ≥ 3 and n ≥ 2
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Research data supporting: "Quantum interference between quasi-2D Fermi surface sheets in UTe2" Weinberger, T.I. et al.
Supporting research data of quantum interference oscillations. Data were measured in the 41 T all-resistive magnet in NHMFL, Tallahassee, by the TDO technique, and in a 70 T coil in HLD, Dresden, by the PDO technique
Spin-Triplet Superconductivity in UTe2 and Ferromagnetic Superconductors
6 pages, 3 figures, accepted for publication in JPSJ Conference ProceedingsInternational audienceThe spin-triplet state is most likely realized in uranium ferromagnetic superconductors, UGe2, URhGe, UCoGe. The microscopic coexistence of ferromagnetism and superconductivity means that the Cooper pair should be realized under the strong internal field due the ferromagnetism, leading to the spin-triplet state with equal spin pairing. The field-reinforced superconductivity, which is observed in all three materials when the ferromagnetic fluctuations are enhanced, is one of the strong evidences for the spin-triplet superconductivity. We present here the results of a newly discovered spin-triplet superconductor, UTe2, and compare those with the results of ferromagnetic superconductors. Although no magnetic order is found in UTe2, there are similarities between UTe2 and ferromagnetic superconductors. For example, the huge upper critical field exceeding the Pauli limit and the field-reentrant superconductivity for H || b-axis are observed in UTe2, URhGe and UCoGe. We also show the specific heat results on UTe2 in different quality samples, focusing on the residual density of states in the superconducting phase