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The emissions of Taylor cones from a wide range of ionic liquids (ILs) have been tested in vacuo in an attempt to identify what physical properties favor the purely ionic regime (PIR). This regime is well known in the case of Taylor cones of liquid metals. For nonmetallic liquids, it has been previously observed in conventional (capillary tube) electrospray sources at room temperature only for the room temperature molten salt (ionic liquid) EMI-BF4 (EMI=1-ethyl-3-methylimidazolium). A large number of other ILs and their mixtures have been studied here, most of which (but not all) are unable to reach the PIR at room temperature. Based on these results and additional theoretical considerations, strong support is assembled for the notion that the PIR is favored by ILs not only of high electrical conductivity but also of high surface tension. This hypothesis is confirmed by tests with three recently synthesized ILs, EMI-GaCl4, EMI-C(CN)3, and EMI-N(CN)2, all of which combine exceptional surface tension and electrical conductivity, and all of which reach the PIR at room temperature far more readily than EMI-BF4.

The response of Low Gain Avalanche Diodes (LGADs), which are a type of thin silicon detector with internal gain, to X-rays of energies between 6-70 keV was characterized at the SLAC light source (SSRL). The utilized beamline at SSRL was 11-2, with a nominal beam size of 3 cm x 0.5 cm, a repetition rate of 500 MHz, and very monochromatic. LGADs of different thicknesses and gain layer configurations were read out using fast amplification boards and digitized with a fast oscilloscope. Standard PiN devices were characterized as well. The devices' energy resolution and time resolution as a function of X-ray energy were measured. The charge collection and multiplication mechanism were simulated using TCAD Sentaurus, and the results were compared with the collected data., Comment: 18 pages, 18 figures

In the past years, it has been observed at several beam test campaigns that irradiated LGAD sensors break with a typical star shaped burn mark when operated at voltages much lower than those at which they were safely operated during laboratory tests. The study presented in this paper was designed to determine the safe operating voltage that these sensors can withstand. Many irradiated sensors from various producers were tested in two test beam facilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS High Granularity Timing Detector (HGTD) beam tests. The samples were placed in the beam and kept under bias over a long period of time in order to reach a high number of particles crossing each sensor. Both beam tests lead to a similar conclusion, that these destructive events begin to occur when the average electric field in the sensor becomes larger than 12 Volts per micrometre., Comment: Published version

This paper presents the design and characterisation of a front-end prototype ASIC for the ATLAS High Granularity Timing Detector, which is planned for the High-Luminosity phase of the LHC. This prototype, called ALTIROC1, consists of a 5$\times$5-pad matrix and contains the analog part of the single-channel readout (preamplifier, discriminator, two TDCs and SRAM). Two preamplifier architectures (transimpedance and voltage) were implemented and tested. The ASIC was characterised both alone and as a module when connected to a 5$\times$5-pad array of LGAD sensors. In calibration measurements, the ASIC operating alone was found to satisfy the technical requirements for the project, with similar performances for both preamplifier types. In particular, the jitter was found to be 15$\pm$1~ps (35$\pm$1~ps) for an injected charge of 10~fC (4~fC). A degradation in performance was observed when the ASIC was connected to the LGAD array. This is attributed to digital couplings at the entrance of the preamplifiers. When the ASIC is connected to the LGAD array, the lowest detectable charge increased from 1.5~fC to 3.4~fC. As a consequence, the jitter increased for an injected charge of 4~fC. Despite this increase, ALTIROC1 still satisfies the maximum jitter specification (below 65~ps) for the HGTD project. This coupling issue also affects the time over threshold measurements and the time-walk correction can only be performed with transimpedance preamplifiers. Beam test measurements with a pion beam at CERN were also undertaken to evaluate the performance of the module. The best time resolution obtained using only ALTIROC TDC data was 46.3$\pm$0.7~ps for a restricted time of arrival range where the coupling issue is minimized. The residual time-walk contribution is equal to 23~ps and is the dominant electronic noise contribution to the time resolution at 15~fC., Comment: 20 pages, 15 figures Second version submitted to JINST including minor changes applied to address journal's comments

To meet the timing resolution requirement of up-coming High Luminosity LHC (HL-LHC), a new detector based on the Low-Gain Avalanche Detector(LGAD), High-Granularity Timing Detector (HGTD), is under intensive research in ATLAS. Two types of IHEP-NDL LGADs(BV60 and BV170) for this update is being developed by Institute of High Energy Physics (IHEP) of Chinese Academic of Sciences (CAS) cooperated with Novel Device Laboratory (NDL) of Beijing Normal University and they are now under detailed study. These detectors are tested with $5GeV$ electron beam at DESY. A SiPM detector is chosen as a reference detector to get the timing resolution of LGADs. The fluctuation of time difference between LGAD and SiPM is extracted by fitting with a Gaussian function. Constant fraction discriminator (CFD) method is used to mitigate the effect of time walk. The timing resolution of $41 \pm 1 ps$ and $63 \pm 1 ps$ are obtained for BV60 and BV170 respectively.

We report on the results of a radiation campaign with neutrons and protons of Low Gain Avalanche Detectors (LGAD) produced by Hamamatsu (HPK) as prototypes for the High-Granularity Timing Detector (HGTD) in ATLAS. Sensors with an active thickness of 50~$\mu$m were irradiated in steps of roughly 2$\times$ up to a fluence of $3\times10^{15}~\mathrm{n_{eq}cm^{-2}}$. As a function of the fluence, the collected charge and time resolution of the irradiated sensors will be reported for operation at $-30^{\circ}$.

The High-Granularity Timing Detector is a detector proposed for the ATLAS Phase II upgrade. The detector, based on the Low-Gain Avalanche Detector (LGAD) technology will cover the pseudo-rapidity region of $2.4<|\eta|<4.0$ with two end caps on each side and a total area of 6.4 $m^2$. The timing performance can be improved by implanting an internal gain layer that can produce signal with a fast rising edge, which improve significantly the signal-to-noise ratio. The required average timing resolution per track for a minimum-ionising particle is 30 ps at the start and 50 ps at the end of the HL-LHC operation. This is achieved with several layers of LGAD. The innermost region of the detector would accumulate a 1 MeV-neutron equivalent fluence up to $2.5 \times 10^{15} cm^{-2}$ before being replaced during the scheduled shutdowns. The addition of this new detector is expected to play an important role in the mitigation of high pile-up at the HL-LHC. The layout and performance of the various versions of LGAD prototypes produced by Hamamatsu (HPK) have been studied by the ATLAS Collaboration. The breakdown voltages, depletion voltages, inter-pad gaps, collected charge as well as the time resolution have been measured and the production yield of large size sensors has been evaluated., Comment: 17 pages, 20 figures

The Widom line identifies the locus in the phase diagram where a supercritical gas crosses over from gas-like to a more liquid-like behavior. A similar transition exists in correlated electron liquids, where the interplay of Coulomb repulsion, bandwidth and temperature triggers between the Mott insulating state and an incoherent conduction regime. Here we explore the electrodynamic response of three organic quantum spin liquids with different degrees of effective correlation, where the absence of magnetic order enables unique insight into the nature of the genuine Mott state down to the most relevant low-temperature region. Combining optical spectroscopy with pressure-dependent dc transport and theoretical calculations, we succeeded to construct a phase diagram valid for all Mott insulators on a quantitative scale. In the vicinity of the low-temperature phase boundary, we discover metallic fluctuations within the Mott gap, exhibiting enhanced absorption upon cooling that is not present in antiferromagnetic Mott insulators. Our findings reveal the phase coexistence region and Pomeranchuk-like anomaly of the Mott transition, previously predicted but never observed., Comment: Supplementary information after Acknowledgements

The Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ forms a highly-frustrated triangular lattice of $S=1/2$ dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasi-degenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$., Comment: 5 pages, 6 figures, submitted to Physical Review B Rapid Communications

Pressure-temperature phase diagram of the organic Mott insulator $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, a model system of the spin liquid on triangular lattice, has been investigated by $^1$H NMR and resistivity measurements. The spin-liquid phase is persistent before the Mott transition to the metal or superconducting phase under pressure. At the Mott transition, the spin fluctuations are rapidly suppressed and the Fermi-liquid features are observed in the temperature dependence of the spin-lattice relaxation rate and resistivity. The characteristic curvature of Mott boundary in the phase diagram highlights a crucial effect of the spin frustration on the Mott transition., Comment: 4 pages, 5 figures

$^{1}$H NMR and static susceptibility measurements have been performed in an organic Mott insulator with nearly isotropic triangular lattice, $\kappa$-(BEDT-TTF)$_{2}$Cu$_{2}$(CN)$_{3}$, which is a model system of frustrated quantum spins. The static susceptibility is described by the spin $S$ = 1/2 antiferromagnetic triangular-lattice Heisenberg model with the exchange constant $J$ $\sim$ 250 K. Regardless of the large magnetic interactions, the $^{1}$H NMR spectra show no indication of long-range magnetic ordering down to 32 mK, which is four-orders of magnitude smaller than $J$. These results suggest that a quantum spin liquid state is realized in the close proximity of the superconducting state appearing under pressure., Comment: 4 pages, 4 figures

The incommensurate spin-density-wave (SDW) phase in (TMTTF)$_2$Br was investigated through transport measurements under pressure and magnetic fields parallel to the $c^{\ast}$ axis. For the incommensurate SDW phase of (TMTTF)$_2$Br stabilized above 0.5 GPa, the SDW transition temperature $T_{\rm SDW}$ increases with the applied magnetic field. The field dependence of $T_{\rm SDW}$ is described by a quadratic behavior and the coefficient of the quadratic term increases with increasing pressure. These results are consistent with the prediction of the mean-field theory based on the suppression of the SDW transition by two-dimensionality. From the relation between the coefficient of the quadratic term and $T_{\rm SDW}$ at zero magnetic field, we determined the role of electron correlation and two dimensionality in the SDW phase of (TMTTF)$_2$Br under pressure and found that the SDW transition in (TMTTF)$_2$Br can be well explained within the mean field theory by taking into account the reduction of the coupling constant $N(0)I$ by pressure., Comment: 5 pages, 5 figures

We report measurements of the de Haas-van Alphen (DHVA) effect and AC susceptibility in the layered organic superconductor $\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$. The amplitude of the DHVA oscillations is attenuated over a wide field range above the irreversibility line, B_irr(B), below which a rigid flux lattice is formed. Thus the DHVA effect provides a unique probe of the superconducting fluctuations at high fields in this material. We compare our measurements with other determinations of the superconducting phase diagram of $\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$., Comment: Submitted to Phys. Rev. B

We have studied polarized Raman spectra of (TMTSF)2PF6 single crystals in the wide spectral and temperature range using different laser energies. We observed and assigned 23 Raman active modes. The carbon C=C in-phase and out-of-phase stretching modes at 1464 cm-1 and 1602 cm-1 show strong electron-molecular-vibration coupling. The mode at about 1565 cm-1 is temperature independent below 50 K due to the methyl group motion freezing. For (TMTSF)2PF6 in the spin density wave phase for a temperature induced dimensionality 1D (quarter filled dimerized linear chain with correlated electrons) the spin gapless magnon spectra have been calculated. No evidence of spin-lattice coupling or spin-related modes is found in the Raman spectra in the spin density wave phase., Comment: 18 pages, 5 figures, Synthetic Metals, in press