78 research outputs found
Two-gap superconductivity in MoGa and its evolution upon the V substitution
Zero-field and transverse-field muon spin rotation/relaxation (SR)
experiments were undertaken in order to elucidate microscopic properties of a
strongly-coupled superconductor MoGa with K.
The upper critical field extracted from the transverse-field SR data
exhibits significant reduction with respect to the data from thermodynamic
measurements indicating the coexistence of two independent length scales in the
superconducting state. Accordingly, the temperature-dependent magnetic
penetration depth of MoGa is described using the model, in which
two s-wave superconducting gaps are assumed. The V for Mo substitution in the
parent compound leads to the complete suppression of one superconducting gap,
and MoVGa is well described within the single s-wave gap scenario.
The reduction in the superfluid density and the evolution of the
low-temperature resistivity upon the V substitution indicate the emergence of a
competing state in MoVGa that may be responsible for the closure
of one of the superconducting gaps
Tuning the structural instability of SrTiO_3 by Eu doping: The phase diagram of Sr_1-xEu_xTiO_3
The phase diagram of Sr_1-xEu_xTiO_3 is determined experimentally by electron
paramagnetic resonance and resistivity measurements and analyzed theoretically
within the self-consistent phonon approximation as a function of x
([0.03-1.0]). The transition temperature of the structural instability of the
system increases nonlinearly to higher temperatures with increasing x. This is
interpreted theoretically by a substantial alteration in the dynamics caused by
a change in the double-well potential from broad and shallow to narrow and
deep.Comment: 15 pages, 5 figure
Penetration depth and gap structure in the antiperovskite oxide superconductor SrSnO revealed by SR
We report a SR study on the antiperovskite oxide superconductor
SrSnO. With transverse-field SR, we observed the increase of the
muon relaxation rate upon cooling below the superconducting transition
temperature K, evidencing bulk superconductivity. The
exponential temperature dependence of the relaxation rate at low
temperatures suggests a fully gapped superconducting state. We evaluated the
zero-temperature penetration depth to be
around 320-1020 nm. Such a large value is consistent with the picture of a
doped Dirac semimetal. Moreover, we revealed that the ratio
is larger than those of ordinary
superconductors and is comparable to those of unconventional superconductors.
The relatively high for small carrier density may hint at an
unconventional pairing mechanism beyond the ordinary phonon-mediated pairing.
In addition, zero-field SR did not provide evidence of broken
time-reversal symmetry in the superconducting state. These features are
consistent with the theoretically proposed topological superconducting state in
SrSnO, as well as with -wave superconductivity.Comment: 9 pages, 9 figures, to be published in Physical Review
Short-range magnetic interactions and spin-glass behavior in the quasi-2D nickelate Pr4Ni3O8
The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of
three stacked square-planar NiO2 planes, in a similar way to the well-known
cuprate superconductors. The mixed-valent nature of Ni and its metallic
properties makes it a candidate for potentially unconventional
superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of
Pr4Ni3O10 in 10 percent hydrogen gas, and report on measurements of
powder-neutron diffraction, magnetization and muon-spin rotation (uSR). We find
that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic
memory effect in the temperature range from 2 to 300 K and a freezing
temperature T_s ~ 68 K. Moreover, the analysis of uSR spectra indicates two
magnetic processes characterized by remarkably different relaxation rates: a
slowly-relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions,
and a fast-relaxing signal, whose relaxation rate increases substantially below
~ 70 K which can be ascribed to the presence of short-range correlated regions.
We conclude that the complex spin-freezing process in Pr4Ni3O8 is governed by
these multiple magnetic interactions. It is possible that the complex magnetism
in Pr4Ni3O8 is detrimental to the occurrence of superconductivity
Pressure driven magnetic order in Sr 1-x Ca x Co 2 P 2
The magnetic phase diagram of Sr1-xCaxCo2P2 as a function of hydrostatic pressure and temperature is investigated by means of high pressure muon spin rotation, relaxation and resonance (μ+SR). The weak pressure dependence for the x≠ 1 compounds suggests that the rich phase diagram of Sr1-xCaxCo2P2 as a function of x at ambient pressure may not solely be attributed to chemical pressure effects. The x= 1 compound on the other hand reveals a high pressure dependence, where the long range magnetic order is fully suppressed at pc 2≈ 9.8 kbar, which seem to be a first order transition. In addition, an intermediate phase consisting of magnetic domains is formed above pc 1≈ 8 kbar where they co-exist with a magnetically disordered state. These domains are likely to be ferromagnetic islands (FMI) and consist of an high- (FMI-1) and low-temperature (FMI-2) region, respectively, separated by a phase boundary at Ti≈ 20 K. This kind of co-existence is unusual and is originating from a coupling between lattice and magnetic degrees of freedoms
Competing spin-glass and spin-fluctuation states in NdPrNiO
Neodymium nickelates have attracted research interest due to their strongly correlated behavior and remarkable magnetic properties. More importantly, superconductivity has recently been confirmed in thin-film samples of Sr-doped NdNiO, bringing the layered rare earth nickel oxides into the research spotlight. In this report, we present results on a series of NdNiO analogs, NdPrNiO (x=0.1, 0.25, 1, 2, and 4) obtained by topotactic reduction, in which we observe systematic changes in the magnetic behavior. As the Nd content increases, the initially large spin-freezing region with magnetic frustration becomes smaller and gradually shifts to low temperatures, while the magnetic response gradually increases. The muon-spin spectroscopy measurements on NdNiO show that this phenomenon is likely due to the enhancement of spin fluctuations in NdPrNiO, which weakens the spin frustration behavior for high Nd contents and at low temperatures. These spin fluctuations can be caused by both Nd and Ni ions and could be one of the factors determining the occurrence of possible superconductivity
Competing spin-glass and spin-fluctuation states in NdxPr4-xNi3O8
Neodymium nickelates have attracted research interest due to their strongly
correlated behaviour and remarkable magnetic properties. More importantly,
superconductivity has recently been confirmed in thin-film samples of Sr-doped
NdNiO2, bringing the layered rare earth nickel oxides into the research
spotlight. In this report, we present results on a series of NdNiO2 analogues,
NdxPr4-xNi3O8 (x = 0.1, 0.25, 1, 2, and 4) obtained by topotactic reduction, in
which we observe systematic changes in the magnetic behaviour. As the Nd3+
content increases, the initially large spin-freezing region with magnetic
frustration becomes smaller and gradually shifts to low temperatures, while the
magnetic response gradually increases. The muon-spin spectroscopy measurements
on Nd4Ni3O8 show that this phenomenon is likely due to the enhancement of spin
fluctuations in NdxPr4-xNi3O8, which weakens the spin frustration behaviour for
high Nd3+ contents and at low temperatures. These spin fluctuations can be
caused by both Nd and Ni ions and could be one of the factors determining the
occurrence of possible superconductivity.Comment: 21 pages 10 figure
Time reversal invariant single gap superconductivity with upper critical field larger than Pauli limit in NbIrB
Recently, compounds with noncentrosymmetric crystal structure have attracted
much attention for providing a rich playground in search for unconventional
superconductivity. NbIrB is a new member to this class of materials
harboring superconductivity below ~K and very high upper
critical field that exceeds Pauli limit. Here we report on muon spin rotation
(SR) experiments probing the temperature and field dependence of effective
magnetic penetration depth in this compound. Our transverse-field -SR
results suggest a fully gaped -wave superconductvity. Further, the estimated
high value of upper critical field is also supplemented by high field transport
measurements. Remarkably, the ratio / obtained for
NbIrB (2) is comparable to those of unconventional
superconductors. Zero-field SR data reveals no significant change in the
muon spin relaxation rate above and below , evincing that
time-reversal symmetry is preserved in the superconducting state. The presented
results will stimulate theoretical investigations to obtain a microscopic
understanding of the origin of superconductivity with preserved time reversal
symmetry in this unique noncentrosymmetric system.Comment: 8 pages, 4 figures. arXiv admin note: text overlap with
arXiv:2101.0823
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