Quantum critical fluctuations in a transverse-field Ising magnet.

CoNb2O6is a model system for a spin-1/2 one-dimensional (1D) transverse-field Ising magnet (TFIM) with a rather low three-dimensional (3D) Néel ordering temperature atTN=2.95K. We studied CoNb2O6using ultrasound measurements down to 0.3 K in transverse magnetic fields applied along thebdirection. Upon entering the 3D ordered state, we observe pronounced anomalies in the transverse acoustic modec66. In particular, from 1.3 to 1.5 K and around 4.7 T, this mode reveals an almost diverging softening, which is considerably reduced at lower and higher magnetic fields. We interpret this as an influence of quantum critical fluctuations emerging from the quantum critical point (QCP) of the 1D Ising spin chains at about 4.75 T, which lies below the QCP of the 3D ordering at about 5.4 T. This is clear experimental evidence of the predicted generic phase diagram for a TFIM with superimposed 3D ordering.

Ultrasound measurement technique for the single-turn-coil magnets.

Ultrasound is a powerful means to study numerous phenomena of condensed-matter physics as acoustic waves couple strongly to structural, magnetic, orbital, and charge degrees of freedom. In this paper, we present such a technique combined with single-turn coils (STCs) that generate magnetic fields beyond 100 T with the typical pulse duration of 6 µs. As a benchmark of this technique, the ultrasound results for MnCr2S4, Cu6[Si6O18]·6H2O, and liquid oxygen are shown. The resolution for the relative sound-velocity change in the STC is estimated as Δv/v ∼ 10-3, which is sufficient to study various field-induced phase transitions and critical phenomena.

Neurotrophin-mediated neuroprotection of hippocampal neurons following traumatic brain injury is not associated with acute recovery of hippocampal function.

Traumatic brain injury (TBI) causes selective hippocampal cell death which is believed to be associated with the cognitive impairment observed in both clinical and experimental settings. The endogenous neurotrophin-4/5 (NT-4/5), a TrkB ligand, has been shown to be neuroprotective for vulnerable CA3 pyramidal neurons after experimental brain injury. In this study, infusion of recombinant NT-4/5 increased survival of CA2/3 pyramidal neurons to 71% after lateral fluid percussion brain injury in rats, compared with 55% in vehicle-treated controls. The functional outcome of this NT-4/5-mediated neuroprotection was examined using three hippocampal-dependent behavioral tests. Injury-induced impairment was evident in all three tests, but interestingly, there was no treatment-related improvement in any of these measures. Similarly, injury-induced decreased excitability in the Schaffer collaterals was not affected by NT-4/5 treatment. We propose that a deeper understanding of the factors that link neuronal survival to recovery of function will be important for future studies of potentially therapeutic agents.