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Register a new userFerromagnetic properties of SrRuO3 thin films deposited on the spin-triplet superconductor Sr2RuO4
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We report magnetic properties of epitaxial thin films of the itinerant ferromagnet SrRuO3 deposited on the cleaved ab surface of the spin-triplet superconductor Sr2RuO4. The films exhibit ferromagnetic transition near 160 K as in the bulk SrRuO3, although the films are under 1.7% compressive strain. The observed magnetization is even higher than that of the bulk SrRuO3. In addition, we newly found that the magnetization relaxation after field removal is strongly anisotropic: two relaxation processes are involved when magnetic domains are aligned along the ab-plane.
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We report the magnetic susceptibility and the magnetization under pressures up to 1.7GPa above the critical pressure, Pc ~ 1.5GPa, for H // a, b, c-axes in the novel spin triplet superconductor UTe2. The anisotropic magnetic susceptibility at low pressure with the easy magnetization a-axis changes to the quasi-isotropic behavior at high pressure, revealing a rapid suppression of the susceptibility for a-axis, and a gradual increase of the susceptibility for the b-axis. At 1.7GPa above Pc, magnetic anomalies are detected at T_MO ~ 3K and T_WMO ~ 10K. The former anomaly corresponds to long-range magnetic order, most likely antiferromagnetism, while the latter shows a broad anomaly, which is probably due to the development of short range order. The unusual decrease and increase of the susceptibility below T_WMO for H // a and b-axes, respectively, indicate the complex magnetic properties at low temperatures above Pc. This is related to the interplay between multiple fluctuations dominated by antiferromagnetism, ferroamgnetism, valence and Fermi surface instabilities.
Inelastic neutron scattering was used to study the low energy magnetic excitations of the ferromagnetic superconductor UGe$_{2}$. The ferromagnetic fluctuations are of Ising nature with a non-conserved magnetization and have an intermediate behavior between localized and itinerant magnetism.
The 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.
Spin-triplet superconductors are of extensive current interest because they can host topological state and Majorana ferimons important for quantum computation. The uranium based heavyfermion superconductor UTe$_2$ has been argued as a spin-triplet superconductor similar to UGe$_2$, URhGe, and UCoGe, where the superconducting phase is near (or coexists with) a ferromagnetic (FM) instability and spin-triplet electron pairing is driven by FM spin fluctuations. Here we use neutron scattering to show that although UTe$_2$ exhibits no static magnetic order down to 0.3 K, its magnetism is dominated by incommensurate spin fluctuations near antiferromagnetic (AF) ordering wave vector and extends to at least 2.6 meV. We are able to understand the dominant incommensurate spin fluctuations of UTe$_2$ in terms of its electronic structure calculated using a combined density functional and dynamic mean field theory.
At a temperature of roughly 1,K, ce{Sr2RuO4} undergoes a transition from a normal Fermi liquid to a superconducting phase. Even while the former is relatively simple and well understood, the superconducting state is not even after 25 years of study. More recently it has been found that critical temperatures can be enhanced by application of uniaxial strain, up to a critical strain, after which it falls off. In this work, we take an `instability approach and seek for divergences in susceptibilities. This provides an unbiased way to distinguish tendencies to competing ground states. We show that in the unstrained compound the singlet and triplet instabilities of the normal Fermi liquid phase are closely spaced. Under uniaxial strain electrons residing on all orbitals contributing to the Fermiology become more coherent while the electrons of Ru-$d_{xy}$ character become heavier and electrons of Ru-$d_{xz,yz}$ characters become lighter. In the process, Im,$chi(mathbf{q},omega)$ increases rapidly around the incommensurate vector $mathbf{q}{=}(0.3,0.3,0)2pi/a$ while it gets suppressed at all other commensurate vectors, in particular at $q{=}0$, which is essential for spin-triplet superconductivity. Thus the triplet superconducting instability remains the lagging instability of the system and the singlet instability enhances under strain, leading to a large energy-scale separation between these competing instabilities. At large strain an instability to a spin density wave overtakes the superconducting one. The analysis relies on a high-fidelity, emph{ab initio} description of the one-particle properties and two-particle susceptibilities, based on the Quasiparticle Self-Consistent emph{GW} approximation augmented by Dynamical Mean Field theory. This approach is described and its high fidelity confirmed by comparing to observed one- and two-particle properties.
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