We present DARKNESS (the DARK-speckle Near-infrared Energy-resolving Superconducting Spectrophotometer), the first of several planned integral field spectrographs to use optical/near-infrared Microwave Kinetic Inductance Detectors (MKIDs) for high-contrast imaging. The photon counting and simultaneous low-resolution spectroscopy provided by MKIDs will enable real-time speckle control techniques and post-processing speckle suppression at framerates capable of resolving the atmospheric speckles that currently limit high-contrast imaging from the ground. DARKNESS is now operational behind the PALM-3000 extreme adaptive optics system and the Stellar Double Coronagraph at Palomar Observatory. Here we describe the motivation, design, and characterization of the instrument, early on-sky results, and future prospects.

The Collider Detector at Fermilab (CDF) pursues a broad physics program at Fermilab's Tevatron collider. Between Run II commissioning in early 2001 and the end of operations in September 2011, the Tevatron delivered 12 fb −1 of integrated luminosity of pp collisions at √ s = 1.96 TeV. The physics at CDF includes precise measurements of the masses of the top quark and W boson, measurement of CP violation and B s mixing, and searches for Higgs bosons and new physics signatures, all of which require heavy flavor tagging with large charged particle tracking acceptance. To realize these goals, in 2001 CDF installed eight layers of silicon microstrip detectors around its interaction region. These detectors were designed for 2-5 years of operation, radiation doses up to 2 Mrad (0.02 Gy), and were expected to be replaced in 2004. The sensors were not replaced, and the Tevatron run was extended for several years beyond its design, exposing the sensors and electronics to much higher radiation doses than anticipated. In this paper we describe the operational challenges encountered over the past 10 years of running the CDF silicon detectors, the preventive measures undertaken, and the improvements made along the way to ensure their optimal performance for collecting high quality physics data. In addition, we describe the quantities and methods used to monitor radiation damage in the sensors for optimal performance and summarize the detector performance quantities important to CDF's physics program, including vertex resolution, heavy flavor tagging, and silicon vertex trigger performance.

The development of the Skipper-charge-coupled devices (Skipper-CCDs) has been a major technological breakthrough for sensing very weak ionizing particles. The sensor allows to reach the ultimate sensitivity of silicon material as a charge signal sensor by unambiguous determination of the charge signal collected by each cell or pixel, even for single electron-hole pair ionization. Extensive use of the technology was limited by the lack of specific equipment to operate the sensor at the ultimate performance. A simple, single-board Skipper-CCD controller designed by the authors is presented and aimed for the operation of the detector in high sensitivity scientific applications. Our article describes the main components and functionality of the so-called low threshold acquisition controller together with experimental results when connected to a Skipper-CCD sensor. Measurements show unprecedented deep subelectron noise of 0.039 e − rms ∕pix by nondestructively measuring the charge 5000 times in each pixel.

Experimentally we establish the quantitative phase diagram of 1/4-filled β ′′ -(BEDT-TTF)2SF5RSO3 with a tendency towards charge order. Comprehensive optical, transport and susceptibility measurements reveal the insulating nature and magnetic properties of the chargeordered ground state. Going from R =CHF via CH2CF2 and CHFCF2 towards CH2, a finite charge disproportionation appears and grows up to 2δ = 0.5e, as evidenced by charge-sensitive molecular vibrations. This is accompanied by an increase of electronic correlation strength, i.e. the inter-site Coulomb repulsion V becomes more pronounced in relation to the bandwidth W . The broadband electronic excitations and their anisotropy unveil a distinct charge pattern for R =CH2 (checkerboard-type) as compared to the other compounds (stripe-like). Our results validate theoretical predictions for 1/4-filled systems, substantiating the importance of charge fluctuations for unconventional superconductivity at the verge between metal and insulator.

The Mott insulator β ′ -EtMe3Sb[Pd(dmit)2]2 belongs to a class of charge transfer solids with highly-frustrated triangular lattice of S = 1/2 molecular dimers and a quantum-spin-liquid ground state. Our experimental and ab initio theoretical studies show the fingerprints of strong correlations and disorder, important role of cation-dimer bonding in charge redistribution, no sign of intra-and inter-dimer dipoles, and the decisive van der Waals contribution to inter-dimer interactions and the ground state structure. The latter consists of quasi-degenerate electronic states related to the different configurations of cation moieties which permit two different equally probable orientations. Upon reducing the temperature, the low-energy excitations slow down, indicating glassy signatures as the cation motion freezes out. PACS numbers:Quantum spin liquid (QSL), a highly correlated fluctuating quantum spin state, is a long-standing intriguing phenomenon in physics [1,2]. It is expected to appear in geometrically frustrated systems when strong quantum fluctuations suppress the long-range magnetic order. Recently the QSL has been realized in materials with frustrated lattices at the insulating side of Mott transition [3]. Because of this exciting discovery considerable efforts have been devoted to the studies of organic Mott insulators -charge transfer crystalline solids in which electrons are strongly correlated and confined to two dimensions. They form layers with triangular structures of molecular pairs-dimers with an odd number of electrons separated by non-conducting inorganic moities. Three organic Mott systems with different degrees of correlationsexhibit an anomalous electrodynamic response below 60 K [4-8], while at very low temperatures the magnetic and thermodynamic response exhibits unconventional behavior ascribed to the QSL ground state [9][10][11]. The full understanding of the nature of QSL is missing primarily because frustrated triangular lattices on their own are unable to destroy the long-range magnetic order [12]. It was suggested that an additional, exotic spin-dipolar coupling in the presence of geometrical frustration would suffice to induce quantum fluctuations and suppress magnetic ordering, however its experimental confirmation is still lacking [13][14][15][16][17]. The mechanism of dipolar-spin coupling relies on the Coulomb interactions within the sublattice of molecular dimers only, thereby completely neglecting the role of inorganic moieties to which the molecular sublattice is strongly hydrogen-bonded. For κ-CuCN and κ-AgCN the decisive role of cation-anion hydrogen bonding is revealed by the experimental results combined with ab initio numerical calculations. This points to a significant anion-driven renormalization of the electronic properties due to disorder by cyanide isomorphism [7,8]. Notably, despite the fact that single crystals of these two BEDT-TTF materials are nominally pure, the variable-range hopping, relaxor dielectric response and anomalous terahertz response are observed wit...