A single crystal high-temperature pyrochlore antiferromagnet

We report the magnetic characterization of the frustrated transition metal pyrochlore NaCaCo$_2$F$_7$. This material has high spin Co$^{2+}$ in CoF$_6$ octahedra in a pyrochlore lattice, and disordered non-magnetic Na and Ca on the large-atom sites in the structure. Large crystals grown by the floating zone method were studied. The magnetic susceptibility is isotropic, the Co moment is larger than the spin-only value, and in spite of the large Curie Weiss theta (-140 K), freezing of the spin system, as characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until around 2.4 K. This yields a frustration index of f = $-\theta_{CW}$/$T_f$ $\approx$ 56, an indication that the system is highly frustrated. The observed entropy loss at the freezing transition is low, indicating that magnetic entropy remains present in the system at 0.6 K. The compound may be the realization of a frustrated pyrochlore antiferromagnet with weak bond disorder. The high magnetic interaction strength, strong frustration, and the availability of large single crystals makes NaCaCo$_2$F$_7$ an interesting alternative to rare earth oxide pyrochlores for the study of geometric magnetic frustration in pyrochlore lattices.Comment: Submitted to PRL; 14 pages, 4 figures, 2 table

The Link Between Aggregate and Micro Productivity Growth: Evidence from Retail Trade

Understanding the nature and magnitude of resource reallocation, particularly as it relates to productivity growth, is important both because it affects how we model and interpret aggregate productivity dynamics, and also because market structure and institutions may affect the reallocation's magnitude and efficiency. Most evidence to date on the connection between reallocation and productivity dynamics for the U.S. and other countries comes from a single industry: manufacturing. Building upon a unique establishment-level data set of U.S. retail trade businesses, we provide some of the first evidence on the connection between reallocation and productivity dynamics in a non-manufacturing sector. Retail trade is a particularly appropriate subject for such a study since this large industry lies at the heart of many recent technological advances, such as E-commerce and advanced inventory controls. Our results show that virtually all of the productivity growth in the U.S. retail trade sector over the 1990s is accounted for by more productive entering establishments displacing much less productive exiting establishments. Interestingly, much of the between-establishment reallocation is a within, rather than between-firm phenomenon.

Novel photon detectors

The paper reviews recent progress in photodetectors, discussing vacuum-based detectors, semiconductor sensors, and gas-based detectors. The emphasis in this review is on the detection of low light levels, enhanced timing resolution, and spectral range of photon detectors, as well as the development of photosensors for extreme conditions, for operation in cryogenic and high radiation-level environments

The Belle II Upgrade Program

The Belle II detector at the SuperKEKB accelerator complex is covering a wide range of exciting physics topics. To achieve the project's research goals, a substantial increase of the data sample to 50~ab$^{-1}$ is needed, and for that, the luminosity has to reach the ambitious goal of $6 \times 10^{35}$ cm$^{-2}$ s$^{-1}$. The progress towards the design luminosity is accompanied by research and development of the accelerator, detector components, operation methods, as well as their upgrades. In the present contribution, we will discuss the status and plans of the project, timescales for upgrades, their motivations, and opportunities, an overview of upgrade options, and finish with an outlook and perspectives