arXiv subjects

S. Holenstein

Publications and source records attributed to S. Holenstein.

7 recordsLinked to original sources

arXiv2019

Muon spin rotation measurements on RbEuFe$_{4}$As$_{4}$ under pressure

We report muon spin rotation and magnetization measurements on the magnetic superconductor RbEuFe$_{4}$As$_{4}$ under hydrostatic pressures up to 3.8 GPa. At ambient pressure, RbEuFe$_{4}$As$_{4}$ exhibits a superconducting transition at $T_{c} \approx$ 36.5 K and a magnetic transition at $T_{m} \approx$ 15 K below which the magnetic and the superconducting order coexist. With increasing pressure, $T_{c}$ decreases while $T_{m}$ and the ordered Eu magnetic moment increase. In contrast to iron-based superconductors with ordering Fe moments, the size of the ordered Eu moment is not proportional to $T_{m}$. The muon spin rotation signal is dominated by the magnetic response impeding the determination of the superconducting properties.

cond-mat.supr-con↗

arXiv2019

Coupled Magnetic and Superconducting Transitions in Sr$_{2}$VO$_{3}$FeAs Under Pressure

We report muon spin rotation ($μ$SR) and magnetization measurements on superconducting Sr$_{2}$VO$_{3}$FeAs under pressure. At ambient pressure, Sr$_{2}$VO$_{3}$FeAs undergoes an antiferromagnetic transition of the V moments at $T_{N}$ and becomes superconducting at $T_{c}<T_{N}$. As a function of pressure, $T_{N}$ initially decreases while $T_{c}$ increases. Surprisingly, once $T_{N}\approx T_{c}$ at 0.6~GPa, $T_{N}$ reverses its trend and increases together with $T_{c}$ suggesting that the static V magnetism is a prerequisite for superconductivity. We explain this cooperative coupling by a possible localization of the V 3$d$ states below the magnetic transition which enables the nesting of the Fermi surface necessary for superconductivity.

cond-mat.supr-con↗

arXiv2019

Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSe$_\mathrm{1\text{-}x}$S$_\mathrm{x}$

We report muon spin rotation ($μ$SR) and magnetization measurements under pressure on Fe$_{1+δ}$Se$_\mathrm{1\text{-}x}$S$_\mathrm{x}$ with x $\approx 0.11$.Above $p\approx0.6$ GPa we find microscopic coexistence of superconductivity with an extended dome of long range magnetic order that spans a pressure range between previously reported separated magnetic phases. The magnetism initially competes on an atomic scale with the coexisting superconductivity leading to a local maximum and minimum of the superconducting $T_\mathrm{c}(p)$. The maximum of $T_\mathrm{c}$ corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of $T_\mathrm{c}(p)$ for a series of single crystals with x up to 0.14 roughly extrapolates to a putative magnetic and superconducting state at ambient pressure for x $\geq0.2$.

cond-mat.supr-con↗

arXiv2019

Observation of a charge-neutral muon-polaron complex in antiferromagnetic Cr$_2$O$_3$

We report a comprehensive muon spin rotation ($μ$SR) study of the prototypical magnetoelectric antiferromagnet Cr$_2$O$_3$. We find the positively charged muon ($μ^+$) occupies several distinct interstitial sites, and displays a rich dynamic behavior involving local hopping, thermally activated site transitions and the formation of a charge-neutral complex composed of a muon and an electron polaron. The discovery of such a complex has implications for the interpretation of $μ$SR spectra in a wide range of magnetic oxides, and opens a route to study the dopant characteristics of interstitial hydrogen impurities in such materials. We address implications arising from implanting a $μ^+$ into a linear magnetoelectric, and discuss the challenges of observing a local magnetoelectric effect generated by the charge of the muon.

cond-mat.mtrl-sci↗

arXiv2018

Pressure effects on the electronic properties of the undoped superconductor ThFeAsN

The recently synthesized ThFeAsN iron-pnictide superconductor exhibits a $T_c$ of 30 K, the highest of the 1111-type series in absence of chemical doping. To understand how pressure affects its electronic properties, we carried out microscopic investigations up to 3 GPa via magnetization, nuclear magnetic resonance, and muon-spin rotation experiments. The temperature dependence of the ${}^{75}$As Knight shift, the spin-lattice relaxation rates, and the magnetic penetration depth suggest a multi-band $s^{\pm}$-wave gap symmetry in the dirty limit, while the gap-to-$T_c$ ratio $Δ/k_\mathrm{B}T_c$ hints at a strong-coupling scenario. Pressure modulates the geometrical parameters, thus reducing $T_c$, as well as $T_m$, the temperature where magnetic-relaxation rates are maximized, both at the same rate of approximately -1.1 K/GPa. This decrease of $T_c$ with pressure is consistent with band-structure calculations, which relate it to the deformation of the Fe 3$d_{z^2}$ orbitals.

cond-mat.supr-con↗

arXiv2017

Magnetic order and spin dynamics in the helical magnetic system Fe$_3$PO$_4$O$_3$

The 3$d$-electronic spin dynamics and the magnetic order in Fe$_3$PO$_4$O$_3$ were investigated by muon spin rotation and relaxation ($μ$SR) and $^{57}$Fe Mössbauer spectroscopy. Zero-field (ZF)-$μ$SR and $^{57}$Fe Mössbauer studies confirm static long range magnetic ordering below $T_{\mathrm{N}}$ $\approx$ 164\,K. Both transverse-field (TF) and ZF-$μ$SR results evidence 100\% magnetic volume fraction in the ordered state. The ZF-$μ$SR time spectra can be best described by a Bessel function, which is consistent with the helical magnetic structure proposed by neutron scattering experiments. The Mössbauer spectra are described in detail by considering the specific angular distribution of the local hyperfine field $B_{\mathrm{hyp}}$ with respect to the local electric field gradient. The $μ$SR spin-lattice relaxation rate exhibits two peaks: One at the magnetic ordering temperature related to critical magnetic fluctuations and another peak at 35\,K signaling the presence of a secondary low energy scale in Fe$_3$PO$_4$O$_3$.

cond-mat.str-el↗

arXiv2016

Coexistence of low moment magnetism and superconductivity in tetragonal FeS and suppression of $T_\mathrm{c}$ under pressure

We report local probe ($μ$SR) measurements on the recently discovered tetragonal FeS superconductor which has been predicted to be electronically very similar to superconducting FeSe. Most remarkably, we find that low moment ($10^{-2}-10^{-3}μ_\mathrm{B})$ disordered magnetism with a transition temperature of $T_\mathrm{N}\approx 20$ K microscopically coexists with bulk superconductivity below $T_\mathrm{c}=4.3(1)$ K. From transverse field $μ$SR we obtain an in-plane penetration depth $λ_\mathrm{ab}(0)=223(2)$ nm for FeS. The temperature dependence of the corresponding superfluid density $λ_\mathrm{ab}^{-2}(T)$ indicates a fully gapped superconducting state and is consistent with a two gap s-wave model. Additionally, we find that the superconducting $T_\mathrm{c}$ of FeS continuously decreases for hydrostatic pressures up to 2.2 GPa.

cond-mat.supr-con↗