arXiv subjects

B. Schmidt

Publications and source records attributed to B. Schmidt.

At least 73 records · Page 4Linked to original sources

arXiv2019

Putative spin-nematic phase in BaCdVO(PO$_{4}$)$_{2}$

We report neutron scattering and AC magnetic susceptibility measurements of the 2D spin-1/2 frustrated magnet BaCdVO(PO$_{4}$)$_{2}$. At temperatures well below $T_{\sf N}\approx 1K$, we show that only 34 % of the spin moment orders in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and comparison to published $μ$sr measurements indicates that the remaining 66 % is fluctuating. This demonstrates the presence of strong frustration, associated with competing ferromagnetic and antiferromagnetic interactions, and points to a subtle ordering mechanism driven by magnon interactions. On applying magnetic field, we find that at $T=0.1$ K the magnetic order vanishes at 3.8 T, whereas magnetic saturation is reached only above 4.5 T. We argue that the putative high-field phase is a realization of the long-sought bond-spin-nematic state.

cond-mat.str-el↗

arXiv2019

Magneto-structural properties of the layered quasi-2D triangular-lattice antiferromagnets Cs$_2$CuCl$_{4-x}$Br$_x$ for ${x}$ = 0,1,2 and 4

We present a study of the magnetic susceptibility $χ_{mol}$ under variable hydrostatic pressure on single crystals of Cs$_2$CuCl$_{4-x}$Br$_x$. This includes the border compounds \textit{x} = 0 and 4, known as good realizations of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as well as the isostructural stoichiometric systems Cs$_2$CuCl$_{3}$Br$_1$ and Cs$_2$CuCl$_{2}$Br$_2$. For the determination of the exchange coupling constants $J$ and $J^{\prime}$, $χ_{mol}$ data were fitted by a $J-J^{\prime}$ model \cite{Schmidt2015}. Its application, validated for the border compounds, yields a degree of frustration $J^{\prime}$/$J$ = 0.47 for Cs$_2$CuCl$_3$Br$_1$ and $J^{\prime}$/$J$ $\simeq$ 0.63 - 0.78 for Cs$_2$CuCl$_2$Br$_2$, making these systems particular interesting representatives of this family. From the evolution of the magnetic susceptibility under pressure up to about 0.4\,GPa, the maximum pressure applied, two observations were made for all the compounds investigated here. First, we find that the overall energy scale, given by $J_c = (J^2$ + $J^{\prime 2}$)$^{1/2}$, increases under pressure, whereas the ratio $J^{\prime}$/$J$ remains unchanged in this pressure range. These experimental observations are in accordance with the results of DFT calculations performed for these materials. Secondly, for the magnetoelastic coupling constants, extraordinarily small values are obtained. We assign these observations to a structural peculiarity of this class of materials.

cond-mat.str-el↗

arXiv2019

Specific Heat Study of 1D and 2D Excitations in the Layered Frustrated Quantum Antiferromagnets Cs$_2$CuCl$_{4-x}$Br$_x$

We report an experimental and theoretical study of the low-temperature specific heat $C$ and magnetic susceptibility $χ$ of the layered anisotropic triangular-lattice spin-1/2 Heisenberg antiferromagnets Cs$_2$CuCl$_{4-x}$Br$_x$ with $x$ = 0, 1, 2, and 4. We find that the ratio $J'/J$ of the exchange couplings ranges from 0.32 to $\approx 0.78$, implying a change (crossover or quantum phase transition) in the materials' magnetic properties from one-dimensional (1D) behavior for $J'/J < 0.6$ to two-dimensional (2D) behavior for $J'/J \approx 0.78$ behavior. For $J'/J < 0.6$, realized for $x$ = 0, 1, and 4, we find a magnetic contribution to the low-temperature specific heat, $C_{\rm m} \propto T$, consistent with spinon excitations in 1D spin-1/2 Heisenberg antiferromagnets. Remarkably, for $x$ = 2, where $J'/J \approx 0.78$ implies a 2D magnatic character, we also observe $C_{\rm m} \propto T$. This finding, which contrasts the prediction of $C_{\rm m} \propto T^2$ made by standard spin-wave theories, shows that Fermi-like statistics also plays a significant role for the magnetic excitations in frustrated spin-1/2 2D antiferromagnets.

cond-mat.str-el↗

arXiv2019

A tunable plasma-based energy dechirper

A tunable plasma-based energy dechirper has been developed at FLASHForward to remove the correlated energy spread of a 681~MeV electron bunch. Through the interaction of the bunch with wakefields excited in plasma the projected energy spread was reduced from a FWHM of 1.31$\%$ to 0.33$\%$ without reducing the stability of the incoming beam. The experimental results for variable plasma density are in good agreement with analytic predictions and three-dimensional simulations. The proof-of-principle dechirping strength of $1.8$~GeV/mm/m significantly exceeds those demonstrated for competing state-of-the-art techniques and may be key to future plasma wakefield-based free-electron lasers and high energy physics facilities, where large intrinsic chirps need to be removed.

physics.plasm-ph↗

arXiv2018

The CUORE cryostat

The Cryogenic Underground Observatory for Rare Events (CUORE) is a bolometric experiment for neutrinoless double-beta decay in $^{130}$Te search, currently taking data at the underground facility of Laboratori Nazionali del Gran Sasso (LNGS). The CUORE cryostat successfully cooled down a mass of about 1 ton at $\sim$7\,mK, delivering an uniform and constant base temperature. This result marks a fundamental milestone in low temperature detectors techniques, opening the path for future ton-scale bolometric experiments searching for rare events. In this paper we present the CUORE cryogenic infrastructure, briefly describing its critical subsystems.

physics.ins-det↗

arXiv2018

Study of Rare Nuclear Processes with CUORE

TeO2 bolometers have been used for many years to search for neutrinoless double beta decay in 130-Te. CUORE, a tonne-scale TeO2 detector array, recently published the most sensitive limit on the half-life, $T_{1/2}^{0ν} > 1.5 \times 10^{25}\,$yr, which corresponds to an upper bound of $140-400$~meV on the effective Majorana mass of the neutrino. While it makes CUORE a world-leading experiment looking for neutrinoless double beta decay, it is not the only study that CUORE will contribute to in the field of nuclear and particle physics. As already done over the years with many small-scale experiments, CUORE will investigate both rare decays (such as the two-neutrino double beta decay of 130-Te and the hypothesized electron capture in 123-Te), and rare processes (e.g., dark matter and axion interactions). This paper describes some of the achievements of past experiments that used TeO2 bolometers, and perspectives for CUORE.

nucl-ex↗

arXiv2017

Controlling $T_c$ of Iridium films using interfacial proximity effects

High precision calorimetry using superconducting transition edge sensors requires the use of superconducting films with a suitable $T_c$, depending on the application. To advance high-precision macrocalorimetry, we require low-$T_c$ films that are easy to fabricate. A simple and effective way to suppress $T_c$ of superconducting Iridium through the proximity effect is demonstrated by using Ir/Pt bilayers as well as Au/Ir/Au trilayers. While Ir/Au films fabricated by applying heat to the substrate during Ir deposition have been used in the past for superconducting sensors, we present results of $T_c$ suppression on Iridium by deposition at room temperature in Au/Ir/Au trilayers and Ir/Pt bilayers in the range of $\sim$20-100~mK. Measurements of the relative impedance between the Ir/Pt bilayers and Au/Ir/Au trilayers fabricated show factor of $\sim$10 higher values in the Ir/Pt case. These new films could play a key role in the development of scalable superconducting transition edge sensors that require low-$T_c$ films to minimize heat capacity and maximize energy resolution, while keeping high-yield fabrication methods.

physics.ins-det↗

arXiv2017

Search for Neutrinoless $β^{+}\hspace{-0.2em}EC$ Decay of $^{120}$Te with CUORE-0

We have performed a search for neutrinoless $β^{+}\hspace{-0.2em}EC$ decay of $^{120}$Te using the final CUORE-0 data release. We describe a new analysis method for the simultaneous fit of signatures with different event topology, and of data subsets with different signal efficiency, obtaining a limit on the half-life of the decay of $T_{1/2}>1.6\cdot10^{21}$ yr at $90\%$ CI. Combining this with results from Cuoricino, a predecessor experiment, we obtain the strongest limit to date, corresponding to $T_{1/2}>2.7\cdot10^{21}$ yr at $90\%$ CI.

nucl-ex↗

arXiv2017

HATS-43b, HATS-44b, HATS-45b, and HATS-46b: Four Short Period Transiting Giant Planets in the Neptune-Jupiter Mass Range

We report the discovery of four short period extrasolar planets transiting moderately bright stars from photometric measurements of the HATSouth network coupled to additional spectroscopic and photometric follow-up observations. While the planet masses range from 0.26 to 0.90 M$_J$, the radii are all approximately a Jupiter radii, resulting in a wide range of bulk densities. The orbital period of the planets range from 2.7d to 4.7d, with HATS-43b having an orbit that appears to be marginally non-circular (e= 0.173$\pm$0.089). HATS-44 is notable for a high metallicity ([Fe/H]= 0.320$\pm$0.071). The host stars spectral types range from late F to early K, and all of them are moderately bright (13.3<V<14.4), allowing the execution of future detailed follow-up observations. HATS-43b and HATS-46b, with expected transmission signals of 2350 ppm and 1500 ppm, respectively, are particularly well suited targets for atmospheric characterisation via transmission spectroscopy.

astro-ph.EP↗

arXiv2017

Performance of the EDELWEISS-III experiment for direct dark matter searches

We present the results of measurements demonstrating the efficiency of the EDELWEISS-III array of cryogenic germanium detectors for direct dark matter searches. The experimental setup and the FID (Fully Inter-Digitized) detector array is described, as well as the efficiency of the double measurement of heat and ionization signals in background rejection. For the whole set of 24 FID detectors used for coincidence studies, the baseline resolutions for the fiducial ionization energy are mainly below 0.7 keV$_{ee}$ (FHWM) whereas the baseline resolutions for heat energies are mainly below 1.5 keV$_{ee}$ (FWHM). The response to nuclear recoils as well as the very good discrimination capability of the FID design has been measured with an AmBe source. The surface $β$- and $α$-decay rejection power of $R_{\rm surf} < 4 \times 10^{-5}$ per $α$ at 90% C.L. has been determined with a $^{210}$Pb source, the rejection of bulk $γ$-ray events has been demonstrated using $γ$-calibrations with $^{133}$Ba sources leading to a value of $R_{γ{\rm -mis-fid}} < 2.5 \times 10^{-6}$ at 90% C.L.. The current levels of natural radioactivity measured in the detector array are shown as the rate of single $γ$ background. The fiducial volume fraction of the FID detectors has been measured to a weighted average value of $(74.6 \pm 0.4)\%$ using the cosmogenic activation of the $^{65}$Zn and $^{68,71}$Ge isotopes. The stability and uniformity of the detector response is also discussed. The achieved resolutions, thresholds and background levels of the upgraded EDELWEISS-III detectors in their setup are thus well suited to the direct search of WIMP dark matter over a large mass range.

physics.ins-det↗

arXiv2016

Improved EDELWEISS-III sensitivity for low-mass WIMPs using a profile likelihood approach

We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range $m_χ\in [4, 30]\,\mathrm{GeV}/c^2$ with the EDELWEISS-III experiment. A 2D profile likelihood analysis is performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from $γ$- and $β$-radiation, recoils from $^{206}$Pb and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on Boosted Decision Trees (BDT). For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90% C.L. exclusion limit set for WIMPs with $m_χ= 4\,\mathrm{GeV/}c^2$ is $1.6 \times 10^{-39}\,\mathrm{cm^2}$, which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above $15\,\mathrm{GeV/}c^2$ the exclusion limits found with both analyses are in good agreement.

astro-ph.CO↗

arXiv2016

Measurement of the cosmogenic activation of germanium detectors in EDELWEISS-III

We present a measurement of the cosmogenic activation in the germanium cryogenic detectors of the EDELWEISS III direct dark matter search experiment. The decay rates measured in detectors with different exposures to cosmic rays above ground are converted into production rates of different isotopes. The measured production rates in units of nuclei/kg/day are 82 $\pm$ 21 for $^3$H, 2.8 $\pm$ 0.6 for $^{49}$V, 4.6 $\pm$ 0.7 for $^{55}$Fe, and 106 $\pm$ 13 for $^{65}$Zn. These results are the most accurate for these isotopes. A lower limit on the production rate of $^{68}$Ge of 74 nuclei/kg/day is also presented. They are compared to model predictions present in literature and to estimates calculated with the ACTIVIA code.

astro-ph.CO↗

arXiv2016

The new SOXS instrument for the ESO NTT

SOXS (Son Of X-Shooter) will be a unique spectroscopic facility for the ESO-NTT 3.5-m telescope in La Silla (Chile), able to cover the optical/NIR band (350-1750 nm). The design foresees a high-efficiency spectrograph with a resolution-slit product of ~4,500, capable of simultaneously observing the complete spectral range 350 - 1750 nm with a good sensitivity, with light imaging capabilities in the visible band. This paper outlines the status of the project.

astro-ph.IM↗

arXiv2016

HATS-31b Through HATS-35b: Five Transiting Hot Jupiters Discovered by the HATSouth Survey

We report the discovery of five new transiting hot Jupiter planets discovered by the HATSouth survey: HATS-31b through HATS-35b. These planets orbit moderately bright stars with V magnitudes within the range 11.9-14.4mag while the planets span a range of masses 0.88-1.22MJ, and have somewhat inflated radii between 1.23-1.64RJ.These planets can be classified as typical hot Jupiters, with HATS-31b and HATS-35b being moderately inflated gas giant planets with radii of $1.64 \pm 0.22$ RJ and 1.464+0.069-0.044RJ, respectively, that can be used to constrain inflation mechanisms. All five systems present a higher Bayesian evidence for a fixed circular orbit model than for an eccentric orbit. The orbital periods range from $1.8209993 \pm 0.0000016$ day for HATS-35b) to $3.377960 \pm 0.000012$ day for HATS-31b. Additionally, HATS-35b orbits a relatively young F star with an age of $2.13 \pm 0.51$ Gyr. We discuss the analysis to derive the properties of these systems and compare them in the context of the sample of well characterized transiting hot Jupiters known to date.

astro-ph.EP↗

arXiv2016

HATS-19b, HATS-20b, HATS-21b: Three Transiting Hot-Saturns Discovered by the HATSouth Survey

We report the discovery by the HATSouth exoplanet survey of three hot-Saturn transiting exoplanets: HATS-19b, HATS-20b, and HATS-21b. The planet host HATS-19 is a slightly evolved V = 13.0 G0 star with [Fe/H] = 0.240, a mass of 1.303 Msun, and a radius of 1.75 Rsun. HATS-19b is in an eccentric orbit (e = 0.30) around this star with an orbital period of 4.5697 days and has a mass of 0.427 Mjup and a highly inflated radius of 1.66 Rjup. The planet HATS-20b has a Saturn-like mass and radius of 0.273 Mjup and 0.776 Rjup respectively. It orbits the V = 13.8 G9V star HATS-20 (Ms = 0.910 Msun; Rs = 0.892 Rsun) with a period of 3.7993 days. Finally, HATS-21 is a V = 12.2 G4V star with [Fe/H] = 0.300, a mass of 1.080 Msun, and a radius of 1.021 Rsun. Its accompanying planet HATS-21b has a 3.5544-day orbital period, a mass of 0.332 Mjup, and a moderately inflated radius of 1.123 Rjup. With the addition of these three very different planets to the growing sample of hot-Saturns, we re-examine the relations between the observed giant planet radii, stellar irradiation, and host metallicity. We find a significant positive correlation between planet equilibrium temperature and radius, and a weak negative correlation between host metallicity and radius. To assess the relative influence of various physical parameters on observed planet radii, we train and fit models using Random Forest regression. We find that for hot-Saturns (0.1 < Mp < 0.5 Mjup), the planetary mass and equilibrium temperature play dominant roles in determining radii. For hot-Jupiters (0.5 < Mp < 2.0 Mjup), the most important parameter is equilibrium temperature alone. Finally, for irradiated higher-mass planets (Mp > 2.0 Mjup), we find that equilibrium temperature dominates in influence, with smaller contributions from planet mass and host metallicity.

astro-ph.EP↗

arXiv2016

Signals induced by charge-trapping in EDELWEISS FID detectors: analytical modeling and applications

The EDELWEISS-III direct dark matter search experiment uses cryogenic HP-Ge detectors Fully covered with Inter-Digitized electrodes (FID). They are operated at low fields ($<1\;\mathrm{V/cm}$), and as a consequence charge-carrier trapping significantly affects both the ionization and heat energy measurements. This paper describes an analytical model of the signals induced by trapped charges in FID detectors based on the Shockley-Ramo theorem. It is used to demonstrate that veto electrodes, initially designed for the sole purpose of surface event rejection, can be used to provide a sensitivity to the depth of the energy deposits, characterize the trapping in the crystals, perform heat and ionization energy corrections and improve the ionization baseline resolutions. These procedures are applied successfully to actual data.

physics.ins-det↗

arXiv2016

HATS-25b through HATS-30b: A Half-dozen New Inflated Transiting Hot Jupiters from the HATSouth Survey

We report six new inflated hot Jupiters (HATS-25b through HATS-30b) discovered using the HATSouth global network of automated telescopes. The planets orbit stars with $V$ magnitudes in the range $\sim 12-14$ and have masses in the largely populated $0.5M_J-0.7M_J$ region of parameter space but span a wide variety of radii, from $1.17R_J$ to $1.75 R_J$. HATS-25b, HATS-28b, HATS-29b and HATS-30b are typical inflated hot Jupiters ($R_p = 1.17-1.26R_J$) orbiting G-type stars in short period ($P=3.2-4.6$ days) orbits. However, HATS-26b ($R_p = 1.75R_J$, $P = 3.3024$ days) and HATS-27b ($R_p=1.50R_J$, $P=4.6370$ days) stand out as highly inflated planets orbiting slightly evolved F stars just after and in the turn-off points, respectively, which are among the least dense hot Jupiters, with densities of $0.153$ g cm$^{-3}$ and $0.180$ g cm$^{-3}$, respectively. All the presented exoplanets but HATS-27b are good targets for future atmospheric characterization studies, while HATS-27b is a prime target for Rossiter-McLaughlin monitoring in order to determine its spin-orbit alignment given the brightness ($V = 12.8$) and stellar rotational velocity ($v \sin i \approx 9.3$ km/s) of the host star. These discoveries significantly increase the number of inflated hot Jupiters known, contributing to our understanding of the mechanism(s) responsible for hot Jupiter inflation.

astro-ph.EP↗

arXiv2016

Constraints on low-mass WIMPs from the EDELWEISS-III dark matter search

We present the results of a search for elastic scattering from galactic dark matter in the form of Weakly Interacting Massive Particles (WIMPs) in the 4-30 GeV/$c^2$ mass range. We make use of a 582 kg-day fiducial exposure from an array of 800 g Germanium bolometers equipped with a set of interleaved electrodes with full surface coverage. We searched specifically for $\sim 2.5-20$ keV nuclear recoils inside the detector fiducial volume. As an illustration the number of observed events in the search for 5 (resp. 20) GeV/$c^2$ WIMPs are 9 (resp. 4), compared to an expected background of 6.1 (resp. 1.4). A 90% CL limit of $4.3\times 10^{-40}$ cm$^2$ (resp. $9.4\times 10^{-44}$ cm$^2$) is set on the spin-independent WIMP-nucleon scattering cross-section for 5 (resp. 20) GeV/$c^2$ WIMPs. This result represents a 41-fold improvement with respect to the previous EDELWEISS-II low-mass WIMP search for 7 GeV/$c^2$ WIMPs. The derived constraint is in tension with hints of WIMP signals from some recent experiments, thus confirming results obtained with different detection techniques.

astro-ph.CO↗