Expanded quantum vortex liquid regimes in the electron nematic superconductors FeSe1-xSx and FeSe1-xTex

The quantum vortex liquid (QVL) is an intriguing state of type-II superconductors in which intense quantum fluctuations of the superconducting (SC) order parameter destroy the Abrikosov lattice even at very low temperatures. Such a state has only rarely been observed, however, and remains poorly understood. One of the key questions is the precise origin of such intense quantum fluctuations and the role of nearby non-SC phases or quantum critical points in amplifying these effects. Here we report a high-field magnetotransport study of FeSe_1-xS_x and FeSe_1-xTe_x which show a broad QVL regime both within and beyond their respective electron nematic phases. A clear correlation is found between the extent of the QVL and the strength of the superconductivity. This comparative study enables us to identify the essential elements that promote the QVL regime in unconventional superconductors and to demonstrate that the QVL regime itself is most extended wherever superconductivity is weakest.

Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe

We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field μ_{0}H_{c2}^{ab} shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ_{0}H^{*}≈24  T well below μ_{0}H_{c2}^{ab}, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.

Emergence of a real-space symmetry axis in the magnetoresistance of the one-dimensional conductor Li0.9Mo6O17

We report on an emerging symmetry axis in the magnetoresistance of bulk single crystals of quasi-one-dimensional Li_0.9Mo₆O₁₇ below T _min = 25 K, the temperature at which the electrical resistivity experiences a minimum. Detailed angle-dependent magnetoresistance sweeps reveal that this symmetry axis is induced by the development of a negative magnetoresistance, which is suppressed only for magnetic fields oriented along the poles of the MoO₆ octahedra that form the conducting chains. We show that this unusual negative magnetoresistance is consistent with the melting of dark excitons, composed of previously omitted orbitals within the t _2g manifold that order below T _min. The unveiled symmetry axis in directional magnetic fields not only provides evidence for the crystallization of these dark excitons but also sheds new light on the long-standing mystery of the metal-insulator transition in Li_0.9Mo₆O₁₇.

A tale of two metals: contrasting criticalities in the pnictides and hole-doped cuprates

The iron-based high temperature superconductors share a number of similarities with their copper-based counterparts, such as reduced dimensionality, proximity to states of competing order, and a critical role for 3d electron orbitals. Their respective temperature-doping phase diagrams also contain certain commonalities that have led to claims that the metallic and superconducting (SC) properties of both families are governed by their proximity to a quantum critical point (QCP) located inside the SC dome. In this review, we critically examine these claims and highlight significant differences in the bulk physical properties of both systems. While there is now a large body of evidence supporting the presence of a (magnetic) QCP in the iron pnictides, the situation in the cuprates is much less apparent, at least for the end point of the pseudogap phase. We argue that the opening of the normal state pseudogap in cuprates, so often tied to a putative QCP, arises from a momentum-dependent breakdown of quasiparticle coherence that sets in at much higher doping levels but which is driven by the proximity to the Mott insulating state at half filling. Finally, we present a new scenario for the cuprates in which this loss of quasiparticle integrity and its evolution with momentum, temperature and doping plays a key role in shaping the resultant phase diagram.

Simultaneous loss of interlayer coherence and long-range magnetism in quasi-two-dimensional PdCrO2

In many layered metals, coherent propagation of electronic excitations is often confined to the highly conducting planes. While strong electron correlations and/or proximity to an ordered phase are believed to be the drivers of this electron confinement, it is still not known what triggers the loss of interlayer coherence in a number of layered systems with strong magnetic fluctuations, such as cuprates. Here, we show that a definitive signature of interlayer coherence in the metallic-layered triangular antiferromagnet PdCrO₂ vanishes at the Néel transition temperature. Comparison with the relevant energy scales and with the isostructural non-magnetic PdCoO₂ reveals that the interlayer incoherence is driven by the growth of short-range magnetic fluctuations. This establishes a connection between long-range order and interlayer coherence in PdCrO₂ and suggests that in many other low-dimensional conductors, incoherent interlayer transport also arises from the strong interaction between the (tunnelling) electrons and fluctuations of some underlying order.

Incoherent transport is an important feature of many anisotropic quantum materials but often its origin is not well understood. Here, the authors show that in a layered quantum magnet, incoherence is driven by the interaction of electrons with spin fluctuations after the melting of magnetic order.

[Therapeutic protocols compared in the treatment of postmenopausal osteoporotic disease]

The authors have compared the results obtained using four main drugs (calcitonin, ipriflavone, transdermal estrogens, fluorine-calcium) actually employed for the treatment of post-menopausal osteoporosis, administered to four groups of fast loser patients (442) in natural (months mean 19.97 +/- 5.99) and surgical (months mean 16.94 +/- 4.29) menopause. After six months of treatment, the efficacy of therapy has been evaluated on the basis of BD (bone density) and osteoarticular pain changes. The BD results have been compared with those of 100 non-treated patients, in the same clinical conditions. The authors have noticed an increase in bone mass (from +0.47% to +1.59%) and a great improvement in osteoarticular pain with all therapeutical protocols used while in the control group there was a progressive decrease of BMC (-1.23%) and a worsening pain. Comparing the results obtained with different therapies, the difference of mean mineralometric gain is not particularly significant among several treatments; but this difference is very significant between treated and non-treated patients who have continued to lose bone mass. The collateral effects, observed during administration of different drugs, have been minimal and the suspension of therapy has been always associated to their disappearance. In the opinion of the authors the good results, achieved with different therapies, depend on the precocity of the treatment, but also on the fact that, in peri-menopausal period, their effect has been increased by the estrogens. Being osteoporosis a multifactorial pathology, a careful control of the risk factors is appropriate and needs to be enforced in order to carry out a precocious treatment with specific drugs on bone metabolism and try to balance the natural turnover with the loss of bone mass.

Electrophysiologic properties and nature of ventrolateral thalamic nucleus neurons reactive to converging inputs of paleo- and neocerebellar origin

Acute experiments were carried out in chloralose-anesthetized, curarized, and artificially ventilated cats to investigate the consistency and functional characteristics of converging cerebellar nuclear (fastigial, interpositus, dentate nuclei) inputs to single neurons of the ventrolateral thalamic nucleus, and the nature (thalamocortical relay or interneuronal) of its convergent neuronal population responsive to stimulation of the cerebellar nuclei. From unitary analysis of both extra- and juxtacellular recordings, we conclude that convergence of paleo- and neocerebellar impulses on thalamic ventrolateral neurons occurs widely, and that both excitatory (mono- and polysynaptic) and inhibitory (di- and polysynaptic) effects are induced on the same neurons by cerebellar nuclei stimulation; these effects concern about 40% of the thalamic ventrolateral neuronal population tested using the extracellular recording technique and about 75% of the ventrolateral nucleus neurons tested using the juxtacellular recording; activation of neocerebellar nuclear outputs generates mainly excitatory and excitatory-inhibitory response patterns, whereas activation of the paleocerebellar nuclear outputs evokes predominantly inhibitory and excitatory-inhibitory response patterns; the convergent paleo- neocerebellar neurons are found commonly in the more anterior ventrolateral nucleus stereotaxic planes; and from the results obtained by stimulation of the somatomotor cortical areas, a large proportion of the ventrolateral nucleus convergent units consists of thalamocortical relay cells. The results have implications for a possible integration between posture and voluntary movements at the level of the thalamic relay nucleus of the cerebellar-cortical pathway, and an interaction between central feedback and peripheral feedback in the programming, execution, and correction of voluntary movements.

[Convergence effects evoked in neurons of the thalamic ventrolateral (VL) nucleus by the stimulation of paleo- and neocerebellar nuclear efferents]

The functional characteristics of the cerebellar nuclear outputs (fastigial, F.; interpositus, I.; dentate, D. nuclei) convergence on single neurones of th ventrolateral (VL) thalamic nucleus were studied in chloralosed, curarized and artificially ventilated cats (pCO2 continuously monitored), by means of the usual electrophysiological stimulation and intracellular recording techniques. From the experimental results on 90 VL n. neurones, with the analysis of the evoked cerebellar nuclear outputs unitary responses, it is possible to conclude: a) 69% of the reactive VL n. units are convergence neurones (CN); b) 34% of the CN are reactive to stimulation of all three cerebellar nuclei, showing similar patterns, with predominantly excitatory effects when located in the dorso-medial VL n. region and opposite patterns (excitation and inhibition) when located in the ventro-lateral VL n. region; c) 30% of the CN are reactive to the F.n and I.n. stimulation, often with opposite patterns; d) 36% of the CN are reactive to the D.n.-F.n. and D.n.--I.n. stimulation, usually with similar patterns. From this evidence, the effects evoked by the D.n. stimulation on to VL n. neurones seem to potentiate the F.n. and I.n. actions, whereas teh convergent F.n.-I.n. inputs exert often opposite effects on the same neurone. The dorso-medial and the ventro--lateral VL n. regions also seem to receive different actions from the converging cerebellar nuclear outputs. All the results are functionally discussed in terms of a possible integration between posture and voluntary movements at the level of the thalamic relay nucleus of the cerebello-cortical pathway.

Growth of Yoshida ascites tumor in the rat after radiofrequency destruction of the tuberoinfundibular region of the hypothalamus

The mitotic index of Yoshida ascites tumor cells was significantly higher in rats that underwent tuberoinfundibular destruction than those lesioned in other regions of the hypothalamus or in the cerebral hemispheres or in sham-operated animals. Survival was shorter in the rats lesioned in the tubero-infundibular and posterior hypothalamic regions. The rise in the mitotic index of Yoshida ascites tumor cells is consistent with the results of previous work showing significantly increased cell proliferation in the normal tissues of animals lesioned in the tuberoinfundibular region.