Hidden magnetism uncovered in a charge ordered bilayer kagome material ScV6Sn6

Charge ordered kagome lattices have been demonstrated to be intriguing platforms for studying the intertwining of topology, correlation, and magnetism. The recently discovered charge ordered kagome material ScV6Sn6 does not feature a magnetic groundstate or excitations, thus it is often regarded as a conventional paramagnet. Here, using advanced muon-spin rotation spectroscopy, we uncover an unexpected hidden magnetism of the charge order. We observe an enhancement of the internal field width sensed by the muon ensemble, which takes place within the charge ordered state. More importantly, the muon spin relaxation rate below the charge ordering temperature is substantially enhanced by applying an external magnetic field. Taken together with the hidden magnetism found in AV3Sb5 (A = K, Rb, Cs) and FeGe kagome systems, our results suggest ubiqitous time-reversal symmetry-breaking in charge ordered kagome lattices.

Local spectroscopic evidence for a nodeless magnetic kagome superconductor CeRu2

We report muon spin rotation (µSR) experiments on the microscopic properties of superconductivity and magnetism in the kagome superconductor CeRu₂withTc≃5 K. From the measurements of the temperature-dependent magnetic penetration depthλ, the superconducting order parameter exhibits nodeless pairing, which fits best to an anisotropics-wave gap symmetry. We further show that theTc/λ^-2ratio is comparable to that of unconventional superconductors. Furthermore, the powerful combination of zero-field (ZF)-µSR and high-fieldµSR has been used to uncover magnetic responses across three characteristic temperatures, identified asT1∗≃110 K,T2∗≃65 K, andT3∗≃40 K. Our experiments classify CeRu₂as an exceedingly rare nodeless magnetic kagome superconductor.

Tunable anomalous Hall conductivity through volume-wise magnetic competition in a topological kagome magnet

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, we explore magnetic correlations in the kagome magnet Co3Sn2S2. Using muon spin-rotation, we present evidence for competing magnetic orders in the kagome lattice of this compound. Our results show that while the sample exhibits an out-of-plane ferromagnetic ground state, an in-plane antiferromagnetic state appears at temperatures above 90 K, eventually attaining a volume fraction of 80% around 170 K, before reaching a non-magnetic state. Strikingly, the reduction of the anomalous Hall conductivity (AHC) above 90 K linearly follows the disappearance of the volume fraction of the ferromagnetic state. We further show that the competition of these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure. Our results taken together suggest the thermal and quantum tuning of Berry curvature induced AHC via external tuning of magnetic order.

Unconventional scaling of the superfluid density with the critical temperature in transition metal dichalcogenides

We report on muon spin rotation experiments probing the magnetic penetration depth λ(T) in the layered superconductors in 2H-NbSe₂ and 4H-NbSe₂. The current results, along with our earlier findings on 1T'-MoTe₂ (Guguchia et al.), demonstrate that the superfluid density scales linearly with T _c in the three transition metal dichalcogenide superconductors. Upon increasing pressure, we observe a substantial increase of the superfluid density in 2H-NbSe₂, which we find to correlate with T _c. The correlation deviates from the abovementioned linear trend. A similar deviation from the Uemura line was also observed in previous pressure studies of optimally doped cuprates. This correlation between the superfluid density and T _c is considered a hallmark feature of unconventional superconductivity. Here, we show that this correlation is an intrinsic property of the superconductivity in transition metal dichalcogenides, whereas the ratio T _c/T _F is approximately a factor of 20 lower than the ratio observed in hole-doped cuprates. We, furthermore, find that the values of the superconducting gaps are insensitive to the suppression of the charge density wave state.

Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSe_{1-x}S_{x}

We report muon spin rotation and magnetization measurements under pressure on Fe_{1+δ}Se_{1-x}S_{x} with x≈0.11. Above p≈0.6  GPa we find a 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_{c}(p). The maximum of T_{c} corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of T_{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≥0.2.

Magnetism in semiconducting molybdenum dichalcogenides

Transition metal dichalcogenides (TMDs) are interesting for understanding the fundamental physics of two-dimensional (2D) materials as well as for applications to many emerging technologies, including spin electronics. Here, we report the discovery of long-range magnetic order below T _M = 40 and 100 K in bulk semiconducting TMDs 2H-MoTe₂ and 2H-MoSe₂, respectively, by means of muon spin rotation (μSR), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The μSR measurements show the presence of large and homogeneous internal magnetic fields at low temperatures in both compounds indicative of long-range magnetic order. DFT calculations show that this magnetism is promoted by the presence of defects in the crystal. The STM measurements show that the vast majority of defects in these materials are metal vacancies and chalcogen-metal antisites, which are randomly distributed in the lattice at the subpercent level. DFT indicates that the antisite defects are magnetic with a magnetic moment in the range of 0.9 to 2.8 μ_B. Further, we find that the magnetic order stabilized in 2H-MoTe₂ and 2H-MoSe₂ is highly sensitive to hydrostatic pressure. These observations establish 2H-MoTe₂ and 2H-MoSe₂ as a new class of magnetic semiconductors and open a path to studying the interplay of 2D physics and magnetism in these interesting semiconductors.

Breakdown of Magnetic Order in the Pressurized Kitaev Iridate β-Li_{2}IrO_{3}

Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate β-Li_{2}IrO_{3} is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Néel temperature of β-Li_{2}IrO_{3} increases with the slope of 0.9  K/GPa upon initial compression, but the reduction in the polarization field H_{c} reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Γ under pressure.

Complementary Response of Static Spin-Stripe Order and Superconductivity to Nonmagnetic Impurities in Cuprates

We report muon-spin rotation and neutron-scattering experiments on nonmagnetic Zn impurity effects on the static spin-stripe order and superconductivity of the La214 cuprates. Remarkably, it was found that, for samples with hole doping x≈1/8, the spin-stripe ordering temperature T_{so} decreases linearly with Zn doping y and disappears at y≈4%, demonstrating a high sensitivity of static spin-stripe order to impurities within a CuO_{2} plane. Moreover, T_{so} is suppressed by Zn in the same manner as the superconducting transition temperature T_{c} for samples near optimal hole doping. This surprisingly similar sensitivity suggests that the spin-stripe order is dependent on intertwining with superconducting correlations.

Magnetic states of MnP: muon-spin rotation studies

Muon-spin rotation data collected at ambient pressure (p) and at p  =  2.42 GPa in MnP were analyzed to check their consistency with various low- and high-pressure magnetic structures reported in the literature. Our analysis confirms that in MnP the low-temperature and low-pressure helimagnetic phase is characterised by an increased value of the average magnetic moment compared to the high-temperature ferromagnetic phase. An elliptical double-helical structure with a propagation vector [Formula: see text], an a-axis moment elongated by approximately 18% and an additional tilt of the rotation plane towards c-direction by [Formula: see text]-8° leads to a good agreement between the theory and the experiment. The analysis of the high-pressure μSR data reveals that the new magnetic order appearing for pressures exceeding 1.5 GPa can not be described by keeping the propagation vector [Formula: see text]. Even the extreme case-decoupling the double-helical structure into four individual helices-remains inconsistent with the experiment. It is shown that the high-pressure magnetic phase which is a precursor of superconductivity is an incommensurate helical state with [Formula: see text].

Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.

Negative oxygen isotope effect on the static spin stripe order in superconducting La(2-x)Ba(x)CuO(4) (x=1/8) observed by muon-spin rotation

Large negative oxygen-isotope (^{16}O and ^{18}O) effects (OIEs) on the static spin-stripe-ordering temperature T_{so} and the magnetic volume fraction V_{m} were observed in La_{2-x}Ba_{x}CuO_{4}(x=1/8) by means of muon-spin-rotation experiments. The corresponding OIE exponents were found to be α_{T_{so}}=-0.57(6) and α_{V_{m}}=-0.71(9), which are sign reversed to α_{T_{c}}=0.46(6) measured for the superconducting transition temperature T_{c}. This indicates that the electron-lattice interaction is involved in the stripe formation and plays an important role in the competition between bulk superconductivity and static stripe order in the cuprates.

Superconductivity in a new layered bismuth oxyselenide: LaO(0.5)F(0.5)BiSe₂

We report superconductivity at T(c) ≈ 2.6 K in a new layered bismuth oxyselenide LaO(0.5)F(0.5)BiSe2 with the ZrCuSiAs-type structure composed of alternating superconducting BiSe2 and blocking LaO layers. The superconducting properties of LaO(0.5)F(0.5)BiSe2 were investigated by means of dc magnetization, resistivity and muon-spin rotation experiments, revealing the appearance of bulk superconductivity with a rather large superconducting volume fraction of ≈ 70% at 1.8 K.

Two-dimensional superfluid density in an alkali metal-organic solvent intercalated iron selenide superconductor Li(C5H5N)0.2Fe2Se2

We report the low-temperature electronic and magnetic properties of the alkali metal-organic solvent intercalated iron selenide superconductor Li(C5H5N)0.2Fe2Se2 using muon-spin-spectroscopy measurements. The zero-field muon spin relaxation (μSR) results indicate that nearly half of the sample is magnetically ordered and spatially phase separated from the superconducting region. The transverse-field μSR results reveal that the superfluid density of Li(C5H5N)0.2Fe2Se2 is two dimensional in nature. The temperature dependence of the penetration depth λ(T) can be explained using a two-gap s-wave model. This implies that, despite the 2D nature of the superfluid density, the symmetry of the superconducting gap remains unaltered to the parent compound FeSe.

Direct observation of the quantum critical point in heavy fermion CeRhSi3

We report on muon spin rotation studies of the noncentrosymmetric heavy fermion antiferromagnet CeRhSi3. 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 Néel temperature. At 23.6 kbar, the ordered magnetic moments are fully suppressed via a second-order phase transition, and T(N) is zero. Thus, we directly observed the quantum critical point at 23.6 kbar hidden inside the superconducting phase of CeRhSi3.

Gemcitabine (G) and cisplatin (C) as first-line treatment of metastatic breast cancer (MBC): Results of phase II trial

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Background: G has been studied in combination with a variety of agents known to be active in cancer. G has a mild toxicity profile. GC is active in various advanced tumors. Splitting of C dose (D 1 + d8) is better tolerated and can be a good alternative to once a cycle in pts with advanced breast cancer. This phase II trial evaluates G (1000 mg/m2) C (35 mg/ m2) d1+8 repeated every 21 d in the 1st-line treatment of metastatic breast cancer (MBC). The primary objective of the study was to determine the objective tumor response rate (ORR) of 1st-line GC in patients with metastatic breast cancer.The one-stage design tested the null hypothesis that the true response rate for this population should be equal to 50% for efficacy. Overall survival (OS), time to progression (TTP) and toxicity were evaluated.

Methods: 70 female MBC pts with the median age of 49.8 ys (range 29.6-80.0) were enrolled. Tumor assessment was performed every other cycle by standard criteria including CT or MRI. 67 pts received a total of 310 cycles GC, out of these 54 pts were evaluable for efficacy.

Results: Complete and partial responses were observed in 7/54 (13.0%) and 19/54 (35.2%) evaluable pts, respectively with an overall response of 48.2%. Disease stabilization was noticed in 19/54 (35.2%) pts. Progression was observed in 5/54 (9.3%) pts. TTP was 33.9 weeks (95% CI, 23.9-48.0). OS was 84.0 weeks (95% CI, 58.6-119.3). 1-year overall survival rate was 68.4% (95% CI, 53.6-79.3%). Hematological toxicity G4 was neutropenia in 14.9% (10/67), and no G4 thrombocytopenia. Hypotension G4 (1.5%) was the only severe non-hematological toxicity.

Conclusions: GC in the first-line treatment of MBC, demonstrated a substantial overall response rate and had a good toxicity profile. GC is a suitable option for first-line MBC in selected pts.

Coexistence of magnetism and superconductivity in the iron-based compound Cs0.8(FeSe0.98)2

We report on muon-spin rotation and relaxation (μSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs(0.8)(FeSe(0.98))(2). Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T(c)=29.6(2)  K, the μSR data indicate that the system is magnetic below T(N)=478.5(3)  K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs(0.8)(FeSe(0.98))(2) a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed T(N) is the highest reported to date for a magnetic superconductor.

Synthesis and crystal growth of Cs(0.8)(FeSe(0.98))(2): a new iron-based superconductor with T(c) = 27 K

We report on the synthesis of large single crystals of a new FeSe layer superconductor Cs(0.8)(FeSe(0.98))(2). X-ray powder diffraction, neutron powder diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs(0.8)(FeSe(0.98))(2) with those of the recently discovered potassium intercalated system K(x)Fe(2)Se(2). The new compound, Cs(0.8)(FeSe(0.98))(2), shows a slightly lower superconducting transition temperature (T(c) = 27.4 K) in comparison to 29.5 in (K(0.8)(FeSe(0.98))(2)). The volume of the crystal unit cell increases by replacing K by Cs-the c parameter grows from 14.1353(13) to 15.2846(11) Å. For the alkali metal intercalated layered compounds known so far, (K(0.8)Fe(2)Se(2) and Cs(0.8)(FeSe(0.98))(2)), the T(c) dependence on the anion height (distance between Fe layers and Se layers) was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se(1 - x)Ch(x)), where Ch = Te, S.

Anomalies in the Fermi surface and band dispersion of quasi-one-dimensional CuO chains in the high-temperature superconductor YBa2Cu4O8

We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this latter effect [energy scale (∼40 meV), temperature dependence, and behavior with Zn-doping] are identical to those of the bosonic mode observed in CuO2 planes of high-temperature superconductors, indicating they have a common origin.

Magnetic excitations of Fe(1+y)Se(x)Te(1-x) in magnetic and superconductive phases

We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe(1.01)Se(0.50)Te(0.50) and non-superconducting Fe(1.10)Se(0.25)Te(0.75). We confirm the existence of a spin resonance in the superconducting phase of Fe(1.01)Se(0.50)Te(0.50), at an energy of 7 meV and a wavevector of (1/2, 1/2, 0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2, 1/2, 0) ± (0.18, - 0.18, 0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low energy magnetic excitation is also observed in Fe(1.10)Se(0.25)Te(0.75) close to the commensurate antiferromagnetic ordering wavevector (1/2 - δ, 0, 1/2), where δ≈0.03. The magnetic correlations in both samples are found to be quasi-two-dimensional in character and persist well above the magnetic (Fe(1.10)Se(0.25)Te(0.75)) and superconducting (Fe(1.01)Se(0.50)Te(0.50)) transition temperatures.

Evolution of two-gap behavior of the superconductor FeSe1-x

The superfluid density, rho{s}, of the iron chalcogenide superconductor, FeSe1-x, was studied as a function of pressure by means of muon-spin rotation. The analysis of rho{s}(T) within the two-gap scheme reveals that the effect on both, the transition temperature T{c} and rho{s}(0), is entirely determined by the band(s) where the large superconducting gap develops, while the band(s) with the small gap become practically unaffected.

Pressure induced static magnetic order in superconducting FeSe1-x

We report on a detailed investigation of the electronic phase diagram of FeSe1-x under pressures up to 1.4 GPa by means of ac magnetization and muon-spin rotation. At a pressure approximately 0.8 GPa the nonmagnetic and superconducting FeSe1-x enters a region where static magnetic order is realized above T{c} and bulk superconductivity coexists and competes on short length scales with the magnetic order below T{c}. For even higher pressures an enhancement of both the magnetic and the superconducting transition temperatures as well as of the corresponding order parameters is observed. These exceptional properties make FeSe1-x to be one of the most interesting superconducting systems investigated extensively at present.

Superfluid density and energy gap function of superconducting PrPt4Ge12

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 T3 dependence of the electronic specific heat indicate the presence of pointlike nodes in the superconducting energy gap. The gap and the specific heat are found to be well described by two models with point nodes, similar to results obtained for the unconventional heavy fermion skutterudite superconductor PrOs4Sb12.

Superconductivity and field-induced magnetism in SrFe_{1.75}Co_{0.25}As_{2}

Using muon-spin rotation, we studied the in-plane (lambda_{ab}) and the out of plane (lambda_{c}) magnetic field penetration depth in SrFe_{1.75}Co_{0.25}As_{2} (T_{c} approximately 13.3 K). The penetration depth anisotropy gamma_{lambda} = lambda_{c}/lambda_{ab} increases from gamma_{lambda} approximately 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.

Comparative study of the pressure effects on the magnetic penetration depth in electron- and hole-doped cuprate superconductors

The effect of pressure on the magnetic penetration depth λ was tested for the hole-doped superconductor YBa(2)Cu(3)O(7-δ) and in the electron-doped one Sr(0.9)La(0.1)CuO(2) by means of magnetization measurements. Whereas a large change of λ was found in YBa(2)Cu(3)O(7-δ), confirming the non-adiabatic character of the electron-phonon coupling in hole-doped superconductors, the same quantity is not affected by pressure in electron-doped Sr(0.9)La(0.1)CuO(2), suggesting a close similarity of the latter to conventional adiabatic Bardeen-Cooper-Schrieffer superconductors. The present results imply a remarkable difference between the electronic properties of hole-doped cuprates and electron-doped Sr(0.9)La(0.1)CuO(2), giving a strong contribution to the long debated asymmetric consequences of hole and electron doping in cuprate superconductors.

Two-gap superconductivity in Ba1-xKxFe2As2: a complementary study of the magnetic penetration depth by muon-spin rotation and angle-resolved photoemission

We investigate the magnetic penetration depth lambda in superconducting Ba1-xKxFe2As2 (Tc approximately 32 K) with muon-spin rotation (microSR) and angle-resolved photoemission (ARPES). Using microSR, we find the penetration-depth anisotropy gamma lambda=lambda c/lambda ab and the second-critical-field anisotropy gammaHc2 to show an opposite T evolution below Tc. This dichotomy resembles the situation in the two-gap superconductor MgB2. A two-gap scenario is also suggested by an inflection point in the in-plane penetration depth lambda ab around 7 K. The complementarity of microSR and ARPES allows us to pinpoint the values of the two gaps and to arrive to a remarkable agreement between the two techniques concerning the full T evolution of lambdaab. This provides further support for the described scenario and establishes ARPES as a tool to assess macroscopic properties of the superconducting condensate.

Three- to two-dimensional transition of the electronic structure in CaFe2As2: a parent compound for an iron arsenic high-temperature superconductor

We use angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of CaFe2As2-parent compound of a pnictide superconductor. We find that the structural and magnetic transition is accompanied by a three- to two-dimensional (3D-2D) crossover in the electronic structure. Above the transition temperature (T_{s}) Fermi surfaces around Gamma and X points are cylindrical and quasi 2D. Below T_{s}, the Gamma pocket forms a 3D ellipsoid, while the X pocket remains quasi 2D. This finding strongly suggests that low dimensionality plays an important role in understanding the superconducting mechanism in pnictides.

The electronic phase diagram of the LaO(1-x)F(x)FeAs superconductor

The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates, heavy fermions and organic superconductors. Here superconductivity is often found close to a quantum critical point where long-range antiferromagnetic order is gradually suppressed as a function of a control parameter, for example charge-carrier doping or pressure. It is believed that dynamic spin fluctuations associated with this quantum critical behaviour are crucial for the mechanism of superconductivity. Recently, high-temperature superconductivity has been discovered in iron pnictides, providing a new class of unconventional superconductors. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state and superconductivity is induced on charge-carrier doping. In this Letter the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mössbauer spectroscopy on the series LaO(1-x)F(x)FeAs. We find a discontinuous first-order-like change of the Néel temperature, the superconducting transition temperature and the respective order parameters. Our results strongly question the relevance of quantum critical behaviour in iron pnictides and prove a strong coupling of the structural orthorhombic distortion and the magnetic order both disappearing at the phase boundary to the superconducting state.

Comparison of different methods for analyzing μSR line shapes in the vortex state of type-II superconductors

A detailed analysis of muon-spin rotation (μSR) 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 for extracting parameters such as the magnetic penetration depth λ and the coherence length ξ from the experimental μSR spectra were investigated. The analysis of the simulated μSR spectra showed that at high magnetic fields there is a strong correlation between λ and ξ obtained for any value of the Ginzburg-Landau parameter κ = λ/ξ. The smaller the applied magnetic field, the smaller the possibility of finding the correct value of ξ. A simultaneous determination of λ and ξ without any restrictions is very problematic, regardless 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 λ is practically independent of ξ. The second-moment method frequently used to analyze μSR spectra by means of a multi-component Gaussian fit generally yields reliable values of λ over the whole range of applied fields [Formula: see text] (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 experiments on the vortex state in type-II superconductors.

Evidence for a competition between the superconducting state and the pseudogap state of (BiPb)2(SrLa)2CuO6+delta from muon spin rotation experiments

The in-plane magnetic penetration depth lambda ab in optimally doped (BiPb)2(SrLa)2CuO6+delta (OP Bi2201) was studied by means of muon-spin rotation. The measurements of lambda ab(-2)(T) are inconsistent with a simple model of a d-wave order parameter and a uniform quasiparticle weight around the Fermi surface. The data are well described assuming the angular gap symmetry obtained in ARPES experiments [Phys. Rev. Lett. 98, 267004 (2007)], which suggest that the superconducting gap in OP Bi2201 exists only in segments of the Fermi surface near the nodes. The remaining parts of the Fermi surface, which are strongly affected by the pseudogap state, do not contribute significantly to the superconducting condensate.

Field and temperature dependence of the superfluid density in LaFeAsO1-xFx superconductors: a muon spin relaxation study

We present zero field and transverse field muon spin relaxation experiments on the recently discovered Fe-based superconductor LaFeAsO1-xFx (x=0.075 and x=0.1). The temperature dependence of the deduced superfluid density is consistent with a BCS s-wave or a dirty d-wave gap function, while the field dependence strongly evidences unconventional superconductivity. We obtain the in-plane penetration depth of lambda ab(0)=254(2) nm for x=0.1 and lambda ab(0)=364(8) nm for x=0.075. Further evidence for unconventional superconductivity is provided by the ratio of Tc versus the superfluid density, which is close to the Uemura line of high-Tc cuprates.

Commensurate spin density wave in LaFeAsO: a local probe study

We present a detailed study on the magnetic order in the undoped mother compound LaFeAsO of the recently discovered Fe-based superconductor LaFeAsO1-xFx. In particular, we present local probe measurements of the magnetic properties of LaFeAsO by means of 57Fe Mössbauer spectroscopy and muon-spin relaxation in zero external field along with magnetization and resistivity studies. These experiments prove a commensurate static magnetic order with a strongly reduced ordered moment of 0.25(5)muB at the iron site below T(N)=138 K, well separated from a structural phase transition at T(S)=156 K. The temperature dependence of the sublattice magnetization is determined and compared to theory. Using a four-band spin density wave model both, the size of the order parameter and the quick saturation below T(N) are reproduced.

Oxygen isotope effects on the superconducting transition and magnetic states within the phase diagram of Y1-xPrxBa2Cu3O7-delta

The various phases observed in all cuprate superconductors [superconducting (SC), spin-glass (SG), and antiferromagnetic (AFM)] were investigated with respect to oxygen-isotope (16O/18O) effects, using here as a prototype system of cuprates Y1-xPrxBa2Cu3O7-delta. All phases exhibit an isotope effect which is strongest where the respective phase terminates. In addition, the isotope effects on the magnetic phases (SG and AFM) are sign reversed as compared to the one on the superconducting phase. In the coexistence regime of the SG and SC phase a two-component behavior is observed where the isotope induced decrease of the superfluid density leads to a corresponding enhancement in the SG related density.

Depth-dependent spin dynamics of canonical spin-glass films: a low-energy muon-spin-rotation study

We have performed depth dependent muon-spin-rotation and -relaxation studies of the dynamics of single layer films of AuFe and CuMn spin glasses as a function of thickness and of its behavior as a function of distance from the vacuum interface (5-70 nm). A significant reduction in the muon-spin relaxation rate as a function of temperature with respect to the bulk material is observed when the muons are stopped near (5-10 nm) the surface of the sample. A similar reduction is observed for the whole sample if the thickness is reduced to, e.g., 20 nm and less. This reflects an increased impurity spin dynamics (incomplete freezing) close to the surface although the freezing temperature is only modestly affected by the dimensional reduction.

Estimating the magnitude of trastuzumab effects within patient subgroups in the HERA trial

BACKGROUND

Trastuzumab (Herceptin(R)) improves disease-free survival (DFS) and overall survival for patients with human epidermal growth factor receptor 2 (HER2)-positive early breast cancer. We aimed to assess the magnitude of its clinical benefit for subpopulations defined by nodal and steroid hormone receptor status using data from the Herceptin Adjuvant (HERA) study.

PATIENTS AND METHODS

HERA is an international multicenter randomized trial comparing 1 or 2 years of trastuzumab treatment with observation after standard chemotherapy in women with HER2-positive breast cancer. In total, 1703 women randomized to 1-year trastuzumab and 1698 women randomized to observation were included in these analyses. Median follow-up was 23.5 months. The primary endpoint was DFS.

RESULTS

The overall hazard ratio (HR) for trastuzumab versus observation was 0.64 [95% confidence interval (CI) 0.54-0.76; P < 0.0001], ranging from 0.46 to 0.82 for subgroups. Estimated improvement in 3-year DFS in subgroups ranged from +11.3% to +0.6%. Patients with the best prognosis (those with node-negative disease and tumors 1.1-2.0 cm) had benefit similar to the overall cohort (HR 0.53, 95% CI 0.26-1.07; 3-year DFS improvement +4.6%, 95% CI -4.0% to 13.2%).

CONCLUSIONS

Adjuvant trastuzumab therapy reduces the risk of relapse similarly across subgroups defined by nodal status and steroid hormone receptor status, even those at relatively low risk for relapse.

Multiple gap symmetries for the order parameter of cuprate superconductors from penetration depth measurements

The temperature dependence of the London penetration depth lambda was measured for an untwinned single crystal of YBa_{2}Cu_{3}O_{7-delta} along the three principal crystallographic directions (a, b, and c). Both in-plane components (lambda_{a};{-2} and lambda_{b};{-2}) show an inflection point in their temperature dependence which is absent in the component along the c direction (lambda_{c};{-2}). The data provide convincing evidence that the in-plane superconducting order parameter is a mixture of (s+d)-wave symmetry whereas it is mainly s wave along the c direction. In conjunction with previous results it is concluded that coupled s+d-order parameters are universal and intrinsic to cuprate superconductors.

Formation of hydrogen impurity States in silicon and insulators at low implantation energies

The formation of hydrogenlike muonium (Mu) has been studied as a function of implantation energy in intrinsic Si, thin films of condensed van der Waals gases (N2, Ne, Ar, Xe), fused and crystalline quartz, and sapphire. By varying the initial energy of positive muons (mu+) between 1 and 30 keV the number of electron-hole pairs generated in the ionization track of the mu+ can be tuned between a few and several thousand. The results show the strong suppression of the formation of those Mu states that depend on the availability of excess electrons. This indicates that the role of H-impurity states in determining electric properties of semiconductors and insulators depends on the way in which atomic H is introduced into the material.

Dual character of the electronic structure of YBa2Cu4O8: the conduction bands of CuO2 planes and CuO chains

We use microprobe angle-resolved photoemission spectroscopy (microARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. For the CuO2 planes, a two-dimensional (2D) electronic structure is observed and, in contrast to Bi2Sr2CaCu2O8+delta, the bilayer splitting is almost isotropic and 50% larger, which strongly suggests that bilayer splitting has no direct effect on the superconducting properties. In addition, the scattering rate for the bonding band is about 1.5 times stronger than the antibonding band and is independent of momentum. For the CuO chains, the electronic structure is quasi-one-dimensional and consists of a conduction and insulating band. Finally, we find that the conduction electrons are well confined within the planes and chains with a nontrivial hybridization.

Experimental evidence for two gaps in the high-temperature La1.83Sr0.17CuO4 superconductor

The in-plane magnetic field penetration depth (lambda(ab)) in single-crystal La1.83Sr0.17CuO4 was investigated by muon-spin rotation (muSR). The temperature dependence of lambda(ab)(-2) has an inflection point around 10-15 K, 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(0)H=0.02 T were found to be Delta(1)(d)(0)=8.2(1) meV and Delta(2)(s)(0)=1.57(8) meV.

Effect of pressure on the Ginzburg-Landau parameter kappa=lambda/xi in YB6

Measurements of the transition temperature Tc, the upper critical field Hc2, and the magnetic penetration depth lambda under hydrostatic pressure (up to approximately 9.2 kbar) in the YB6 superconductor were carried out. A pronounced and negative pressure effect (PE) on Tc and Hc2 with dTc/dp=-0.0547(4) K/kbar and micro0dHc2(0)/dp=-4.84(20) mT/kbar, and zero PE on lambda(0) were observed. The PE on the coherence length dxi(0)/dp=0.28(2) nm/kbar was calculated from the measured pressure dependence of Hc2(0). Together with the zero PE on the magnetic penetration depth lambda(0), our results imply that the Ginzburg-Landau parameter kappa(0)=xi(0)/lambda(0) depends on pressure and that pressure "softens" YB6, e.g., moves it to the type-I direction.

Coexistence and coupling of superconductivity and magnetism in thin film structures

Superconducting and magnetic order are usually mutually exclusive, and are found to coexist in relatively few materials. We have obtained direct evidence for a spin-density wave (SDW) coexisting with bulk superconductivity in a ferromagnetic-superconducting trilayer. In the superconducting state the amplitude of the SDW is enhanced and modeling the data also suggests a pi/2 phase shift of one component of the SDW, implying a profound coupling of these two forms of order.

Muon-spin-rotation measurements of the penetration depth of the infinite-layer electron-doped Sr0.9La0.1CuO2 cuprate superconductor

Muon-spin-rotation (muSR) measurements of the in-plane penetration depth lambda(ab) have been performed in the infinite-layer electron-doped Sr0.9La0.1CuO2 high-T(c) superconductor (HTS). Absence of the magnetic rare-earth ions in this compound allowed us to measure for the first time the absolute value of lambda(ab)(0) in electron-doped HTSs using muSR. We found lambda(ab)(0)=116(2) nm. The zero-temperature depolarization rate sigma(0) proportional, variant 1/lambda(2)(ab)(0)=4.6(1) micros(-1) is more than 4 times higher than expected from the Uemura line. Therefore, this electron-doped HTS does not follow the Uemura relation found for hole-doped HTSs.

Evidence for charged critical behavior in the pyrochlore superconductor RbOs2O6

We analyze magnetic penetration depth (lambda) data of the recently discovered superconducting pyrochlore oxide RbOs(2)O(6). Our results strongly suggest that in RbOs(2)O(6) charged critical fluctuations dominate the temperature dependence of lambda near T(c). This is in contrast with the mean-field behavior observed in conventional superconductors and the uncharged critical behavior found in nearly optimally doped cuprate superconductors. However, this finding agrees with the theoretical predictions for charged criticality and the charged criticality observed in underdoped YBa(2)Cu(3)O(6.59).

Pressure effects on the transition temperature and the magnetic field penetration depth in the pyrochlore superconductor RbOs2O6

Magnetization measurements under hydrostatic pressure up to 8 kbar in the pyrochlore superconductor RbOs2O6 (T(c) approximately or equal 6.3 K at p=0) were carried out. A positive pressure effect on T(c) with dT(c)/dp=0.090(3) K/kbar was observed, whereas no pressure effect on the magnetic penetration depth lambda was detected. The pressure independent ratio 2 Delta(0)/k(B)T(c)=3.72(2) (Delta(0) is the superconducting gap at zero temperature) was found to be close to the BCS value 3.52. Magnetization and muon-spin rotation measurements of lambda(T) indicate that RbOs2O6 is an adiabatic s-wave BCS-type superconductor. The value of lambda extrapolated to zero temperature and ambient pressure was estimated to be 230(30) nm.

Direct observation of nonlocal effects in a superconductor

We have used the technique of low energy muon spin rotation to measure the local magnetic field profile B(z) beneath the surface of a lead film maintained in the Meissner state (z depth from the surface, z less, similar 200 nm). The data unambiguously show that B(z) clearly deviates from an exponential law and represent the first direct, model independent proof for a nonlocal response in a superconductor.

Direct observation of the oxygen isotope effect on the in-plane magnetic field penetration depth in optimally doped YBa2Cu3O7-delta

We report the first direct observation of the oxygen-isotope ((16)O/(18)O) effect on the in-plane penetration depth lambda(ab) in a nearly optimally doped YBa(2)Cu(3)O(7-delta) film using the novel low-energy muon-spin rotation technique. Spin-polarized low-energy muons are implanted in the film at a known depth z beneath the surface and process in the local magnetic field B(z). This feature allows us to measure directly the profile B(z) of the magnetic field inside the superconducting film in the Meissner state and to make a straightforward determination of lambda(ab). A substantial isotope shift Delta lambda(ab)/lambda(ab)=2.8(1.0)% at 4 K is observed, implying that the in-plane effective supercarrier mass m*(ab) is oxygen-isotope dependent with Delta m*(ab)/m*(ab)=5.5(2.0)%. These results are in good agreement with magnetization measurements on powder samples.

Observation of the conduction electron spin polarization in the Ag spacer of a Fe/Fg/Fe trilayer

The spatially oscillating electron spin polarization in the Ag spacer of a 4 nm Fe/20 nmAg/4 nm Fe(001) epitaxial trilayer has been determined by means of low energy muon spin rotation. It oscillates with the same period as the interlayer exchange coupling, but shows a much weaker attenuation at large distances x from the interface. The measured magnetization profile from the inner 14 nm of the spacer is described by an oscillating polarization decaying as x(-0.8(1)). This unusual behavior may arise from a full confinement of electron states within the spacer.