Search

Chromatin is a polymer complex of DNA and proteins that regulates gene expression. The three-dimensional structure and organization of chromatin controls DNA transcription and replication. High-throughput chromatin conformation capture techniques generate Hi-C maps that can provide insight into the 3D structure of chromatin. Hi-C maps can be represented as a symmetric matrix where each element represents the average contact probability or number of contacts between two chromatin loci. Previous studies have detected topologically associating domains (TADs), or self-interacting regions in Hi-C maps within which the contact probability is greater than that outside the region. Many algorithms have been developed to identify TADs within Hi-C maps. However, most TAD identification algorithms are unable to identify nested or overlapping TADs and for a given Hi-C map there is significant variation in the location and number of TADs identified by different methods. We develop a novel method, KerTAD, using a kernel-based technique from computer vision and image processing that is able to accurately identify nested and overlapping TADs. We benchmark this method against state-of-the-art TAD identification methods on both synthetic and experimental data sets. We find that KerTAD consistently has higher true positive rates (TPR) and lower false discovery rates (FDR) than all tested methods for both synthetic and manually annotated experimental Hi-C maps. The TPR for KerTAD is also largely insensitive to increasing noise and sparsity, in contrast to the other methods. We also find that KerTAD is consistent in the number and size of TADs identified across replicate experimental Hi-C maps for several organisms. KerTAD will improve automated TAD identification and enable researchers to better correlate changes in TADs to biological phenomena, such as enhancer-promoter interactions and disease states., Comment: 23 pages, 10 figures

The temperature dependence of the manganese magnetic moment and the spin-lattice relaxation rate measured by the muon spin relaxation technique in the magnetically ordered phase of the chiral intermetallic cubic MnSi system are both explained in terms of helimagnon excitations of a localized spin model. The two free parameters characterizing the helimagnon dispersion relation are determined. A combined analysis of the two data sets cannot be achieved using the self-consistent renormalization theory of spin fluctuations which assumes the magnetism of MnSi to arise uniquely from electronic bands. As a result of this work, MnSi is proposed to be a dual electronic system composed of localized and itinerant magnetic electrons. Finally we note that the analysis framework can be applied to other helimagnets such as the magnetoelectric compound Cu2OSeO3., Comment: 12 pages, 6 figures

High-quality single crystals of NdFeAsO$_{0.65}$F$_{0.35}$ (the transition temperature $T_{\rm c} \simeq 30.6$~K) were studied in zero-field (ZF) and transverse-field (TF) muon-spin rotation/relaxation ($\mu$SR) experiments. An upturn in muon-spin depolarization rate at $T\lesssim 3$~K was observed in ZF-$\mu$SR measurements and it was associated with the onset of ordering of Nd electronic moments. Measurements of the magnetic field penetration depth ($\lambda$) were performed in the TF geometry. By applying the external magnetic field $B_{\rm ex}$ parallel to the crystallographic $c$-axis ($B_{\rm ex}\| c$) and parallel to the $ab$-plane ($B_{\rm ex}\| ab$), the temperature dependencies of the in-plane component ($\lambda_{ab}^{-2}$) and the combination of the in-plane and the out of plane components ($\lambda_{ab,c}^{-2}$) of the superfluid density were determined, respectively. The out-of-plane superfluid density component ($\lambda_{c}^{-2}$) was further obtained by combining the results of $B_{\rm ex} \| c$ and $B_{\rm ex} \| {ab}$ set of experiments. The temperature dependencies of $\lambda_{ab}^{-2}$, $\lambda_{ab,c}^{-2}$, and $\lambda_{c}^{-2}$ were analyzed within the framework of a self-consistent two-gap model despite of using the traditional $\alpha$-model. Interband coupling was taken into account, instead of assuming it to be zero as it stated in the $\alpha$-model. A relatively small value of the interband coupling constant $\Lambda_{12} \simeq 0.01$ was obtained, thus indicating that the energy bands in NdFeAsO$_{0.65}$F$_{0.35}$ are only weakly coupled. In spite of their small magnitude, the coupling between the bands leads to the single value of the superconducting transition temperature $T_{\rm c}$., Comment: 10 pages, 8 figures

Muon spin rotation (muSR) spectra recorded for manganese silicide MnSi and interpreted in terms of a quantitative analysis constrained by symmetry arguments were recently published. The magnetic structures of MnSi in zero-field at low temperature and in the conical phase near the magnetic phase transition were shown to substantially deviate from the expected helical and conical structures. Here, we present material backing the previous results obtained in zero-field. First, from simulations of the field distributions experienced by the muons as a function of relevant parameters we confirm the uniqueness of the initial interpretation and illustrate the remarkable complementarity of neutron scattering and muSR for the MnSi magnetic structure determination. Second we present the result of a muSR experiment performed on MnSi crystallites grown in a Zn-flux and compare it with the previous data recorded with a crystal obtained from Czochralski pulling. We find the magnetic structure for the two types of crystals to be identical within experimental uncertainties. We finally address the question of a possible muon-induced effect by presenting transverse field muSR spectra recorded in a wide range of temperature and field intensity. The field distribution parameters perfectly scale with the macroscopic magnetization, ruling out a muon-induced effect., Comment: 9 pages, 5 figures

Speculative execution is an optimization technique that has been part of CPUs for over a decade. It predicts the outcome and target of branch instructions to avoid stalling the execution pipeline. However, until recently, the security implications of speculative code execution have not been studied. In this paper, we investigate a special type of branch predictor that is responsible for predicting return addresses. To the best of our knowledge, we are the first to study return address predictors and their consequences for the security of modern software. In our work, we show how return stack buffers (RSBs), the core unit of return address predictors, can be used to trigger misspeculations. Based on this knowledge, we propose two new attack variants using RSBs that give attackers similar capabilities as the documented Spectre attacks. We show how local attackers can gain arbitrary speculative code execution across processes, e.g., to leak passwords another user enters on a shared system. Our evaluation showed that the recent Spectre countermeasures deployed in operating systems can also cover such RSB-based cross-process attacks. Yet we then demonstrate that attackers can trigger misspeculation in JIT environments in order to leak arbitrary memory content of browser processes. Reading outside the sandboxed memory region with JIT-compiled code is still possible with 80\% accuracy on average., Comment: Updating to the cam-ready version and adding reference to the original paper

Whenever modern CPUs encounter a conditional branch for which the condition cannot be evaluated yet, they predict the likely branch target and speculatively execute code. Such pipelining is key to optimizing runtime performance and is incorporated in CPUs for more than 15 years. In this paper, to the best of our knowledge, we are the first to study the inner workings and the security implications of such speculative execution. We revisit the assumption that speculatively executed code leaves no traces in case it is not committed. We reveal several measurable side effects that allow adversaries to enumerate mapped memory pages and to read arbitrary memory---all using only speculated code that was never fully executed. To demonstrate the practicality of such attacks, we show how a user-space adversary can probe for kernel pages to reliably break kernel-level ASLR in Linux in under three seconds and reduce the Windows 10 KASLR entropy by 18~bits in less than a second.

Magnetic systems with spins sitting on a lattice of corner sharing regular tetrahedra have been particularly prolific for the discovery of new magnetic states for the last two decades. The pyrochlore compounds have offered the playground for these studies, while little attention has been comparatively devoted to other compounds where the rare earth R occupies the same sub-lattice, e.g. the spinel chalcogenides CdR2X4 (X = S, Se). Here we report measurements performed on powder samples of this series with R = Yb using specific heat, magnetic susceptibility, neutron diffraction and muon-spin-relaxation measurements. The two compounds are found to be magnetically similar. They long-range order into structures described by the \Gamma_5 irreducible representation. The magnitude of the magnetic moment at low temperature is 0.77 (1) and 0.62 (1) mu_B for X = S and Se, respectively. Persistent spin dynamics is present in the ordered states. The spontaneous field at the muon site is anomalously small, suggesting magnetic moment fragmentation. A double spin-flip tunneling relaxation mechanism is suggested in the cooperative paramagnetic state up to 10 K. The magnetic space groups into which magnetic moments of systems of corner-sharing regular tetrahedra order are provided for a number of insulating compounds characterized by null propagation wavevectors., Comment: 11 pages, 14 figures, 2 tables, among which a list of the magnetic space groups of frustrated magnets on the pyrochlore lattice with null propagation wavevectors

In the light of recent results obtained for the prototype helimagnet MnSi we examine the possible magnetic structures of compounds of the same family, consistent with the crystal symmetries when the magnetic propagation vector is parallel to the [001] axis. The analysis of a published muon spin rotation spectrum recorded in MnGe [Phys. Rev. B 93, 174405 (2016)] shows no deviation from the canonical helimagnetic structure, unlike in MnSi. This qualitative difference calls for further theoretical works on chiral magnets., Comment: 7 pages, 3 figures

In the temperature-magnetic field phase diagram, the binary metallic compound MnSi exhibits three magnetic phases below Tc ~ 29 K. An unconventional helicoidal phase is observed in zero field. At moderate field intensity a conical phase sets in. Near Tc, in an intermediate field range, a skyrmion lattice phase appears. Here we show the magnetic structure in the conical phase to strongly depend on the field direction and to deviate substantially from a conventional conical structure., Comment: 5 pages, 4 figures

The insulating pyrochlore compound Nd2Sn2O7 has been shown to undergo a second order magnetic phase transition at Tc ~ 0.91 K to a noncoplanar all-in--all-out magnetic structure of the Nd3+ magnetic moments. An anomalously slow paramagnetic spin dynamics has been evidenced from neutron backscattering and muon spin relaxation (muSR). In the case of muSR this has been revealed through the strong effect of a 50 mT longitudinal field on the spin-lattice relaxation rate. Here, motivated by a recent successful work performed for Yb2Ti2O7 and Yb2Sn2O7, analyzing the shape of the muSR longitudinal polarization function, we substantiate the existence of extremely slow paramagnetic spin dynamics in the microsecond time range for Nd2Sn2O7. Between 1.7 and 7 K, this time scale is temperature independent. This suggests a double spin-flip tunneling relaxation mechanism to be at play, probably involving spin substructures such as tetrahedra. Unexpectedly, the standard deviation of the field distribution at the muon site increases as the system is cooled. This exotic spin dynamics is in sharp contrast with the dynamics above 100 K which is driven by the Orbach relaxation mechanism involving single Nd3+ magnetic moments., Comment: 7 pages, 6 figures

Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here, we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a <111> axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a <111> axis, thus preserving the overall helical structure., Comment: 10 pages, 4 figures

Pressure, together with temperature and magnetic field, is an important thermodynamical parameter in physics. Investigating the response of a compound or of a material to pressure allows to elucidate ground states, investigate their interplay and interactions and determine microscopic parameters. Pressure tuning is used to establish phase diagrams, study phase transitions and identify critical points. Muon spin rotation/relaxation (muSR) is now a standard technique making increasing significant contribution in condensed matter physics, material science research and other fields. In this review, we will discuss specific requirements and challenges to perform muSR experiments under pressure, introduce the high-pressure muon facility at the Paul Scherrer Institute (PSI, Switzerland) and present selected results obtained by combining the sensitivity of the muSR technique with pressure., Comment: Submitted to High Pressure Research. 26 pages, 17 Figures

We report a positive muon spin relaxation and rotation (\muSR) study of the quantum spin ice materials Yb2Ti2O7 and Yb2Sn2O7 focusing on the low field response. In agreement with earlier reports, data recorded in small longitudinal fields evidence anomalously slow spin dynamics in the microsecond range below the temperature T_c at which the specific heat displays an intense peak, namely T_c = 0.24 K and 0.15 K, respectively, for the two systems. We found that slow dynamics extends above T_c up to at least 0.7 K for both compounds. The conventional dynamical Gaussian Kubo-Toyabe model describes the \muSR spectra recorded above T_c. At lower temperatures a published analytical extension of the Gaussian Kubo-Toyabe model provides a good description, consistent with the existence of short-range magnetic correlations. While the physical response of the two systems is qualitatively the same, Yb2Ti2O7 exhibits a much larger local magnetic susceptibility than Yb2Sn2O7 below T_c. Considering previously reported ac susceptibility, neutron scattering and \muSR results, we suggest the existence of anomalously slow spin dynamics to be a common physical property of pyrochlore magnetic materials. The possibility of molecular spin substructures to be associated to the slow dynamics and therefore the short-range correlations is mentioned. The slow spin dynamics observed under field does not exclude the presence of much faster dynamics detected in extremely low or zero field., Comment: 11 pages, 10 figures

The superconducting pairing state of LaPt$_{4}$Ge$_{12}$ is studied by measuring the magnetic penetration depth $\lambda(T,B)$ and the superfluid density $\rho_s(T)$ using a tunnel-diode-oscillator (TDO)-based method and by transverse field muon-spin rotation ($\mu$SR) spectroscopy. $\lambda(T)$ follows an exponential-type temperature dependence at $T\ll T_{c}$, but its zero-temperature value $\lambda(0)$ increases linearly with magnetic field. Detailed analyses demonstrate that both $\lambda(T)$ and the corresponding $\rho_{s}(T)$, measured in the Meissner state by the TDO method are well described by a two-gap $\gamma$ model with gap sizes of $\Delta_1(0)=1.31k_{B}T_c$ and $\Delta_2(0)=1.80k_{B}T_c$ and a very weak interband coupling. In contrast, $\rho_s(T)$, derived from the $\mu \rm{SR}$ data taken in a small field, can be fitted by a single-gap BCS model with a gap close to $\Delta_2(0)$. We conclude that LaPt$_{4}$Ge$_{12}$ is a marginal two-gap superconductor and the small gap $\Delta_1$ seems to be destroyed by a small magnetic field. In comparison, in PrPt$_4$Ge$_{12}$ the $4f$-electrons may enhance the interband coupling and, therefore, give rise to more robust multiband superconductivity., Comment: 5 pages, 4 figures

Whenever a compound exhibits a spontaneous muSR oscillation, long-range magnetic ordering is usually inferred. Here we show that some caution is required. The coherence length needs not to be large for a spontaneous muon spin precession to be observed. Establishing the incommensurate nature of a magnetic structure, solely based on muSR measurements, may not be reliable. The absence of a spontaneous muon precession at low temperature does not mean that the system under investigation does not display long-range magnetic ordering. The relaxation measured in zero and longitudinal field in the quasi-static limit is usually analyzed in the framework of the strong-collision model, the static polarization function being taken to be the famous Kubo-Toyabe function. This might not be satisfactory if short-range correlation effects are strong. Here we propose a method based on the maximum entropy concept and reverse Monte Carlo technique which gives results consistent with those obtained in 2013 by analytical means for the considered example., Comment: To appear in the proceedings of the 13th International Conference on Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland, 1-6 June 2014

The field distribution in the vortex lattice of a pure niobium single crystal with an external field applied along a three-fold axis has been investigated by the transverse-field muon-spin-rotation (TF-$\mu$SR) technique over a wide range of temperatures and fields. The experimental data have been analyzed with the Delrieu's solution for the form factor supplemented by phenomenological formulas for the parameters. This has enabled us to experimentally establish the temperatures and fields for the Delrieu's, Ginzburg-Landau's, and Klein's regions of the vortex lattice. Using the numerical solution of the quasiclassical Eilenberger's equation the experimental results have been reasonably understood. They should apply to all clean BCS superconductors. The analytical Delrieu's model supplemented by phenomenological formulas for its parameters is found to be reliable for analyzing TF-$\mu$SR experimental data for a substantial part of the mixed phase. The Abrikosov's limit is contained in it., Comment: 12 pages, 15 figures

The antiferromagnetic (AFM) phase transition temperature T_N of EuTiO_3 has been studied as a function of pressure p. The data reveal a nonlinear dependence of T_N on p with T_N increasing with increasing pressure. The exchange interactions exhibit an analogous dependence on p as T_N (if the absolute value of the nearest neighbor interaction is considered) and there is evidence that the AFM transition is robust with increasing pressure. The corresponding Weiss temperature {\Theta}_W remains anomalous since it always exhibits positive values. The data are analyzed within the Bloch power law model and provide excellent agreement with experiment., Comment: 9 pages, 4 figures article was selected for inclusion in IOPselect

Polarized negative muons were used to study the behaviour of the boron acceptor centre in synthetic diamond produced by the chemical vapour deposition (CVD) method. The negative muon substitutes one of the electrons in a carbon atom, and this muonic atom imitates the boron acceptor impurity in diamond. The temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of 20 - 330 K in a transverse magnetic field of 14 kOe. For the first time a negative shift of the muon spin precession was observed in diamond. It is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor. The magnetic measurements showed that the magnetic susceptibility of the CVD sample was close to that of the purest natural diamond., Comment: 8 pages, 3 figures

We present the results of high-field magnetization and muon-spin relaxation measurements on the coordination polymer CuF_2(H_2O)_2(pyrazine) in pressures up to 22.5 kbar. We observe a transition from a quasi-two-dimensional to a quasi-one-dimensional antiferromagnetic phase at 9.1 kbar, driven by a rotation of the Jahn-Teller axis. Long-range antiferromagnetic ordering is seen in both regimes, as well as a phase separation in the critical pressure region. The magnetic dimensionality switching as pressure is increased is accompanied by a halving of the primary magnetic exchange energy J and a fivefold decrease in the ordering temperature T_N. J decreases gradually with pressure in the two-dimensional phase, and then increases in the one-dimensional regime. We relate both effects to the changes in the crystal structure with applied pressure., Comment: 5 pages, 3 figures, supplemental material included

Magnetization and muon spin rotation experiments were performed in La_(2-x)Ba_xCuO_4 (x = 1/8) as a function of hydrostatic pressure up to p = 2.2 GPa. It was found that the magnetic volume fraction of the static stripe phase strongly decreases linearly with pressure, while the superconducting volume fraction increases by the same amount. This demonstrates competition between bulk superconductivity and static magnetic order in the stripe phase of La_1.875Ba_0.125CuO_4 and that these phenomena occur in mutually exclusive spatial regions. The present results also reveal that the static spin-stripe phase still exists at pressures, where the long-range low-temperature tetragonal (LTT) structure is completely suppressed. This indicates that the long-range LTT structure is not necessary for stabilizing the static spin order in La_1.875Ba_0.125CuO_4., Comment: 12 pages, 4 figures

We investigated the Abrikosov vortex lattice (VL) of a pure Niobium single crystal with the muon spin rotation (\mu SR) technique. Analysis of the \mu SR data in the framework of the BCS-Gor'kov theory allowed us to determine microscopic parameters and the limitations of the theory. With decreasing temperature the field variation around the vortex cores deviates substantially from the predictions of the Ginzburg-Landau theory and adopts a pronounced conical shape. This is evidence of partial diffraction of Cooper pairs on the VL predicted by Delrieu for clean superconductors., Comment: 9 pages, 6 figures

We review the magnetic form factor deduced by Delrieu from the Gorkov's equation for a Bardeen-Cooper-Schrieffer (BCS) type-II superconductor near its Bc2 phase boundary, i.e. when its magnetization is small. A numerical study of the form factor, field map, and field distribution follows. The characteristics of the transition from the low-temperature BCS to the high-temperature Ginzburg-Landau vortex lattices is studied. The exotic shape of the component field distribution and the form factor at low temperature and as a function of the external field intensity are discussed. Our numerical work should be helpful for the analysing of small angle neutron scattering and muon spin rotation vortex-lattice data recorded for BCS superconductors and maybe other superconductors in the clean limit., Comment: A mistake for the form factor normalization was made in our original draft. In this version Eqs.: (25), (31), (32), (35), (D5), (D6), and (E4) are corrected by including the missing factor 1/4\pi. Second sentence of Sec. VII referring to Eq. (E4) was also corrected

In the tetragonal heavy fermion system CeCoIn5 the unconventional superconducting state is probed by means of muon spin rotation. The pressure dependence (0-1 GPa) of the basal-plane magnetic penetration depth (\lambda_a), the penetration depth anisotropy (\gamma=\lambda_c/\lambda_a) and the temperature dependence of 1/\lambda_i^2 (i=a,c) were studied in single crystals. A strong decrease of \lambda_a with pressure was observed, while \gamma and \lambda_i^2(0)/\lambda_i^2(T) are pressure independent. A linear relationship between 1/\lambda_a^2(270 mK) and Tc was also found. The large decrease of \lambda_a with pressure is the signature of an increase of the number of superconducting quasiparticles by a factor of about 2., Comment: 5 pages, 6 figures. To appear in PRL

We report on a study of the superconducting properties for a series of polycrystalline BaPt(4-x)Au(x)Ge12 filled skutterudite compounds for x = 0, 0.5, 0.75, and 1. Muon spin rotation (muSR) spectroscopy as well as magnetization, specific heat, and electrical resistivity measurements were performed. The magnetic penetration depth \lambda, the coherence length \xi, and the Ginzburg-Landau parameter \kappa are evaluated. The temperature dependence of the superfluid density is well described by an s-wave superconducting gap and this classical scenario is supported by the field-independent \lambda. The gap-to-Tc ratio \Delta/kTc increases with the Au content from 1.70 for x = 0 to 2.1(1) for x = 1. By combining muSR, magnetization, and specific heat data, we find that BaPt(4-x)Au(x)Ge12 compounds are in between the dirty and clean limits with mean free paths of the carriers l ~ \xi. Interestingly, resistivity data for BaPt4Ge12 indicate a much higher upper critical field, which is probably due to defects or impurities close to the surface of the crystallites., Comment: 11 pages, 10 figures

The effect of pressure on the copper and praseodymium magnetic order in the system Nd(1-x)$Pr(x)Ba2Cu3$O7 with x=0.3, 0.5, 0.7, and 1 was investigated by means of the muon spin rotation (muSR) technique. It was found that the effect of pressure on the Neel temperatures of both copper and praseodymium is positive for the whole range of Pr concentrations (0.3

The superfluid density and superconducting gaps of superconducting RbFe_{2}As_{2} have been determined as a function of temperature, magnetic field and hydrostatic pressure by susceptibility and muon-spin spectroscopy measurements. From the data, fundamental microscopic parameters of the superconducting state like the London penetration depth \lambda, the gap values \Delta, the upper critical field B_{c2}, and the Ginzburg-Landau parameter \kappa have been obtained. In accordance with earlier measurements the ratio of the superfluid density n_{s} \propto \lambda^{-2} to the superconducting transition temperature T_{c}=2.52(2) K at ambient pressure is found to be much larger in the strongly hole-overdoped RbFe_{2}As_2 than in high-T_{c} Fe-based and other unconventional superconductors. As a function of pressure T_{c} strongly decreases with a rate of dT_{c}/dp = -1.32 K/GPa, i.e. it is reduced by 52 % at p = 1 GPa. The temperature dependence of n_{s} is best described by a two gap s-wave model with both superconducting gaps being decreased by hydrostatic pressure until smaller gap completely disappears at p = 1 GPa., Comment: 5 figures. 1 Table

The magnetic properties of Fe1.03Te under hydrostatic pressure up to p ~ 5.7 GPa were investigated by means of muon spin rotation, dc magnetization, and neutron depolarization measurements. With increasing pressure the antiferromagnetic ordering temperature TN decreases continuously from 70 K at ambient pressure towards higher pressures. Surprisingly, the commensurate antiferromagnetic order of FeTe enters a region of incommensurate and dynamical magnetic order before at p ~ 1.7 GPa the system turns ferromagnetic. The ferromagnetic ordering temperature TC increases with increasing pressure.

The magnetic phase diagram of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ was investigated by means of magnetization and muon-spin rotation studies as a function of chemical (isovalent substitution of As by P) and hydrostatic pressure. The magnetic phase diagrams of the magnetic ordering of the Eu and Fe spins with respect to P content and hydrostatic pressure are determined and discussed. The present investigations reveal that the magnetic coupling between the Eu and the Fe sublattices strongly depends on chemical and hydrostatic pressure. It is found that chemical and hydrostatic pressure have a similar effect on the Eu and Fe magnetic order., Comment: 11 pages, 10 figures

The magneto-electric (ME) coupling on spin-wave resonances in single-crystal Cu2OSeO3 was studied by a novel technique using electron spin resonance combined with electric field modulation. An external electric field E induces a magnetic field component \mu_0 H^i = \gamma E along the applied magnetic field H with \gamma=0.7(1) \mu T/(V/mm) at 10 K. We found that ME coupling strength \gamma is temperature dependent and highly anisotropic. \gamma(T) nearly follows that of spin susceptibility J(T) and rapidly decreases above the Curie temperature Tc. The ratio \gamma/J monotonically decreases with increasing temperature without an anomaly at Tc., Comment: to appear in Phys. Rev. Lett

We report a comprehensive experimental and theoretical study of the quasi-one-dimensional quantum magnet CuNCN. Based on magnetization measurements above room temperature as well as muon spin rotation and electron spin resonance measurements, we unequivocally establish the localized Cu+2-based magnetism and the magnetic transition around 70 K, both controversially discussed in the previous literature. Thermodynamic data conform to the uniform-spin-chain model with a nearest-neighbor intrachain coupling of about 2300 K, in remarkable agreement with the microscopic magnetic model based on density functional theory band-structure calculations. Using exact diagonalization and the coupled-cluster method, we derive a collinear antiferromagnetic order with a strongly reduced ordered moment of about 0.4 mu_B, indicating strong quantum fluctuations inherent to this quasi-one-dimensional spin system. We re-analyze the available neutron-scattering data, and conclude that they are not sufficient to resolve or disprove the magnetic order in CuNCN. By contrast, spectroscopic techniques indeed show signatures of long-range magnetic order below 70 K, yet with a rather broad distribution of internal field probed by implanted muons. We contemplate the possible structural origin of this effect and emphasize peculiar features of the microstructure studied with synchrotron powder x-ray diffraction., Comment: 17 pages, 17 figures, 1 table

We report on muon spin rotation studies of the noncentrosymmetric heavy fermion antiferromagnet CeRhSi$_3$. A drastic and monotonic suppression of the internal fields, at the lowest measured temperature, was observed upon an increase of external pressure. Our data suggest that the ordered moments are gradually quenched with increasing pressure, in a manner different from the pressure dependence of the N\'eel temperature. At $\unit{23.6}{kbar}$, the ordered magnetic moments are fully suppressed via a second-order phase transition, and $T_{\rm{N}}$ is zero. Thus, we directly observed the quantum critical point at $\unit{23.6}{kbar}$ hidden inside the superconducting phase of CeRhSi$_3$.

The pressure dependence of the magnetic penetration depth in polycrystalline samples of YBa2Cu3Ox with different oxygen concentrations x = 6.45, 6.6, 6.8, and 6.98 was studied by muon spin rotation (muSR). The pressure dependence of the superfluid density (p_s) as a function of the superconducting transition temperature Tc is found to deviate from the usual Uemura line. The ratio (dTc/dP)/(dp_s/dP) is factor of 2 smaller than that of the Uemura relation. In underdoped samples, the zero temperature superconducting gap and the BCS ratio both increase with increasing external hydrostatic pressure, implying an increase of the coupling strength with pressure. The relation between the pressure effect and the oxygen isotope effect on the magnetic penetration depth is also discussed. In order to analyze reliably the muSR spectra of samples with strong magnetic moments in a pressure cell, a special model was developed and applied., Comment: 10 pages, 9 figures

Measurements of the magnetic penetration depth (lambda) in the Fe-based superconductor Ba_(1-x)Rb_xFe_2As_2 (x=0.3, 0.35, 0.4) were carried out using the muon-spin rotation muSR technique. The temperature dependence of lambda is well described by a two-gap s+s-wave scenario with a small gap Delta_1 = 1 - 3 mev and a large gap Delta_2 = 7 - 9 mev. By combining the present data with those obtained for RbFe_2As_2 a decrease of the BCS ratio 2Delta_2/(k_B)(T_c) with increasing Rb content x is observed. On the other hand, the BCS ratio 2Delta_1/(k_B)(T_c) is almost independent of x. In addition, the contribution of Delta_1 to the superfluid density is found to increase with x. These results are discussed in the light of the suppression of interband processes upon hole doping., Comment: 7 pages, 6 figures

A detailed zero and transverse field (ZF&TF) muon spin rotation (muSR) investigation of magnetism and the magneto-electric coupling in Cu2OSeO3 is reported. An internal magnetic field B_int(T=0) = 85.37(25) mT was found, in agreement with a ferrimagnetic state below Tc = 57.0(1) K. The temperature dependence of the magnetic order parameter is well described by the relation B_int = B(0)(1-(T/Tc)^2)^b with an effective exponent b = 0.39(1) which is close to the critical exponent B ~ 1/3 for a three dimensional (3D) magnetic system. Just above Tc the muon relaxation rate follows the power low \lambda (T)\propto (T/Tc - 1)^\omega with \omega = 1.06(9), which is characteristic for 3D ferromagnets. Measurements of B_int(T) with and without an applied electrostatic field E = 1.66 x 10^5 V/m suggest a possible electric field effect of magnitude \Delta Bv = Bv(0 V)-Bv(500 V) = - 0.4(4) mT., Comment: 7 pages, 5 figures

A combination of x-ray diffraction, magnetization, and 75As nuclear magnetic resonance (NMR) experiments were performed on single-crystal EuFe1.9Co0.1As2. The strength of the hyperfine interaction between the 75As nuclei and the Eu^(2+) 4f states suggests a strong coupling between the Eu^(2+) moments and the Fe1.9Co0.1As2 layers. Such a strong interlayer coupling may be due to an indirect exchange interaction between the localized Eu^(2+) 4f moments, mediated by the Fe 3d conduction electrons. Magnetic susceptibility as well as 75As-NMR measurements reveal a decrease of the SDW transition temperature to T_SDW = 120 K as a result of Co doping. A change of the slope in the temperature dependence of the NMR frequency of the 75As lower-satellite line was observed at 225 K. At the same temperature also a change of the satellite line shape was found. These changes of the NMR spectra may be caused by the formation of a nematic phase below 225 K in EuFe1.9Co0.1As2., Comment: 8 pages, 7 figures

Zero and longitudinal field muon spin rotation (muSR) experiments were performed on the superconductors PrPt4Ge12 and LaPt4Ge12. In PrPt4Ge12 below Tc a spontaneous magnetization with a temperature variation resembling that of the superfluid density appears. This observation implies time-reversal symmetry (TRS) breaking in PrPt4Ge12 below Tc = 7.9 K. This remarkably high Tc for an anomalous superconductor and the weak and gradual change of Tc and of the related specific heat anomaly upon La substitution in La_(1-x)Pr_xPt_4Ge_(12) suggests that the TRS breaking is due to orbital degrees of freedom of the Cooper pairs., Comment: To appear in Phys. Rev. B. 5 pages, 3 figures

Iron-chalcogenide single crystals with the nominal composition FeSe$_{0.5}$Te$_{0.5}$ and a transition temperature of $T_{c}\simeq14.6$ K were synthesized by the Bridgman method. The structural and anisotropic superconducting properties of those crystals were investigated by means of single crystal X-ray and neutron powder diffraction, SQUID and torque magnetometry, and muon-spin rotation. Room temperature neutron powder diffraction reveals that 95% of the crystal volume is of the same tetragonal structure as PbO. The structure refinement yields a stoichiometry of Fe_1.045Se_0.406Te_0.594. Additionally, a minor hexagonal Fe_7Se_8 impurity phase was identified. The magnetic penetration depth \lambda at zero temperature was found to be 491(8) nm in the ab-plane and 1320(14) nm along the c-axis. The zero-temperature value of the superfluid density \rho_s(0) \lambda^-2(0) obeys the empirical Uemura relation observed for various unconventional superconductors, including cuprates and iron-pnictides. The temperature dependences of both \lambda_ab and \lambda_c are well described by a two-gap s+s-wave model with the zero-temperature gap values of \Delta_S(0)=0.51(3) meV and \Delta_L(0)=2.61(9) meV for the small and the large gap, respectively. The magnetic penetration depth anisotropy parameter \gamma_\lambda(T)=\lambda_c(T)/\lambda_{ab}(T) increases with decreasing temperature, in agreement with \gamma_\lambda(T) observed in the iron-pnictide superconductors.

Using muon-spin rotation, we studied the in-plane (\lambda_ab) and the out of plane (\lambda_c) magnetic field penetration depth in SrFe_1.75Co_0.25As_2 (T_c=13.3 K). Both \lambda_ab(T) and \lambda_c(T) are consistent with the presence of two superconducting gaps with the gap to T_c ratios 2\Delta/k_BT_c=7.2 and 2.7. The penetration depth anisotropy \gamma_\lambda=\lambda_c/\lambda_ab increases from \gamma_\lambda=2.1 at T_c to 2.7 at 1.6 K. The mean internal field in the superconducting state increases with decreasing temperature, just opposite to the diamagnetic response seen in magnetization experiments. This unusual behavior suggests that the external field induces a magnetic order which is maintained throughout the whole sample volume., Comment: 4 pages, 3 figures

The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin rotation (muSR), specific heat, and electrical resistivity experiments. The continuous increase of the superfluid density with decreasing temperature and the dependence of the magnetic penetration depth \lambda on the magnetic field obtained by means of muSR, as well as the observation of a T^3 dependence of the electronic specific heat establish the presence of point-like nodes in the superconducting energy gap. The energy gap was found to be well described by \Delta =\Delta_0| k_x - ik_y| or \Delta = \Delta_0(1 - k_y^4) functional forms, similar to that obtained for another skutterudite superconductor, PrOs4Sb12. The gap to T_c ratios were estimated to be \Delta_0/k_BT_c = 2.68(5) and 2.29(5), respectively., Comment: 4 pages, 5 figures

The relaxation of Yb$^{3+}$ in YBa$_{2}$Cu$_{3}$O$_{x}$ ($6

A detailed analysis of muon-spin rotation ($\mu$SR) spectra in the vortex state of type-II superconductors using different theoretical models is presented. Analytical approximations of the London and Ginzburg-Landau (GL) models, as well as an exact solution of the GL model were used. The limits of the validity of these models and the reliability to extract parameters such as the magnetic penetration depth $\lambda$ and the coherence length $\xi$ from the experimental $\mu$SR spectra were investigated. The analysis of the simulated $\mu$SR spectra showed that at high magnetic fields there is a strong correlation between obtained $\lambda$ and $\xi$ for any value of the Ginzburg-Landau parameter $\kappa = \lambda/\xi$. The smaller the applied magnetic field is, the smaller is the possibility to find the correct value of $\xi$. A simultaneous determination of $\lambda$ and $\xi$ without any restrictions is very problematic, independent of the model used to describe the vortex state. It was found that for extreme type-II superconductors and low magnetic fields, the fitted value of $\lambda$ is practically independent of $\xi$. The second-moment method frequently used to analyze $\mu$SR spectra by means of a multi-component Gaussian fit, generally yields reliable values of $\lambda$ in the whole range of applied fields $ H_{c1} \ll H \lesssim H_{c2}$ ($H_{c1}$ and $H_{c2}$ are the first and second critical fields, respectively). These results are also relevant for the interpretation of small-angle neutron scattering (SANS) experiments of the vortex state in type-II superconductors., Comment: 17 pages, 19 figures

We report temperature- and magnetic field-dependent bulk muon spin rotation measurements in a c-axis oriented superconductor CaC6 in the mixed state. Using both a simple second moment analysis and the more precise analytical Ginzburg-Landau model, we obtained a field independent in-plane magnetic penetration depth {\lambda}ab (0) = 72(3) nm. The temperature dependencies of the normalized muon spin relaxation rate and of the normalized superfluid density result to be identical, and both are well represented by the clean limit BCS model with 2\Delta/kB Tc = 3.6(1), suggesting that CaC6 is a fully gapped BCS superconductor in the clean limit regime., Comment: Accepted for publication in PRB

We report on measurements of the in-plane magnetic penetration depth \lambda_{ab} in the infinite-layer electron-doped high-temperature cuprate superconductor Sr_0.9La_0.1CuO_2 by means of muon-spin rotation. The observed temperature and magnetic field dependences of \lambda_{ab} are consistent with the presence of a substantial s-wave component in the superconducting order parameter in good agreement with the results of tunneling, specific heat, and small-angle neutron scattering experiments., Comment: 6 pages, 5 figures

The results of the muon-spin rotation experiments on BCS superconductors NbB_2+x (x = 0.2, 0.34) are reported. Both samples, studied in the present work, exhibit rather broad transitions to the superconducting state, suggesting a distribution of the volume fractions with different transition temperatures (T_c)'s. By taking these distributions into account, the dependence of the inverse squared zero-temperature magnetic penetration depth (\lambda_0^{-2}) on T_c was reconstructed for temperatures in the range 1.5K

Oxygen isotope (^{16}O/^{18}O) effects (OIE's) on the superconducting transition (T_c), the spin-glass ordering (T_g), and the antiferromagnetic ordering (T_N) temperatures were studied for Y_1-xPr_xBa_2Cu_3O_7-\delta as a function of Pr content (0.0\leq x \leq 1.0). The OIE on T_c increases with increasing x up to x\approx0.55, where superconductivity disappears. For decreasing x the OIE's on T_N and T_g increase down to x\approx 0.7 where antiferromagnetic order and down to x\approx0.3 where spin-glass behavior vanish, respectively. The OIE's on T_g and T_N are found to have {\it opposite signs} as compared to the OIE on T_c. All OIE's are suggested to arise from the isotope dependent mobility (kinetic energy) of the charge carriers., Comment: 5 pages, 3 figures, 1 table

The recent observation of an inflection point in the temperature dependence of the in-plane magnetic field dependence (lambda_ab) is investigated within a two-band model with coupled order parameters of different symmetries. While the dominant order parameter has d-wave symmetry, the smaller one is of s-wave symmetry. Superconductivity is robust in the d-wave channel and induced via interband interactions in the s-wave subsystem., Comment: 10 pages, 4 figures

The in-plane magnetic field penetration depth (\lambda_{ab}) in single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the muon-spin rotation (\muSR) technique. The temperature dependence of \lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and \Delta_2^s(0)=1.57(8)meV., Comment: 5 pages, 3 figures

Measurements of the magnetic field penetration depth $\lambda$ in the ternary boride superconductor Li$_2$Pd$_3$B ($T_c\simeq7.3$ K) have been carried out by means of muon-spin rotation ($\mu$SR). The absolute values of $\lambda$, the Ginzburg-Landau parameter $\kappa$, and the first $H_{c1}$ and the second $H_{c2}$ critical fields at T=0 obtained from $\mu$SR were found to be $\lambda(0)=252(2)$ nm, $\kappa(0)=27(1)$, $\mu_0H_{c1}(0)=9.5(1)$ mT, and $\mu_0H_{c2}(0)=3.66(8)$ T, respectively. The zero-temperature value of the superconducting gap $\Delta_0=$1.31(3) meV was found, corresponding to the ratio $2\Delta_0/k_BT_c=4.0(1)$. At low temperatures $\lambda(T)$ saturates and becomes constant below $T\simeq 0.2T_c$, in agreement with what is expected for s-wave BCS superconductors. Our results suggest that Li$_2$Pd$_3$B is a s-wave BCS superconductor with the only one isotropic energy gap., Comment: 6 pages, 7 figures

The basic formal and numerical aspects of different degree interpolated moving least-squares (IMLS) methods are studied using sixteen different combinations of coordinate system for fitting and weight functions. For the application we use six-dimensional potential energy surface (PES) of hydrogen peroxide, for which an analytic ("exact") potential is available in the literature. We systematically examine the effect of parameters in the weight function, the degree of the IMLS fit, and number of ab initio points. From these studies we discovered that the IMLS for almost all pairs of coordinate system show qualitatively similar behavior, however, the accuracy of the fits is noticeably different. We also found compact and accurate representations of potentials for presented degrees of IMLS., Comment: 32 pages, 9 figures, 3 tables

Measurements of the magnetic field penetration depth \lambda in the pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3 K) were carried out by means of the muon-spin-rotation (\muSR) technique. At low temperatures \lambda^{-2}(T) saturates and becomes constant below T\simeq 0.2T_c, in agreement with what is expected for weak-coupled s-wave BCS superconductors. The value of \lambda at T=0 was found to be in the range of 250 nm to 300 nm. \muSR and equilibrium magnetization measurements both reveal that at low temperatures $\lambda$ is almost (at the level of 10%) independent of the applied magnetic field. This result suggests that the superconducting energy gap in RbOs_2O_6 is isotropic., Comment: 8 pages, 9 figures