Critical speeding-up near the monopole liquid-gas transition in magnetoelectric spin-ice

Competing interactions in the so-called spin-ice compounds stabilize a frustrated ground-state with finite zero-point entropy and, interestingly, emergent magnetic monopole excitations. The properties of these monopoles are at the focus of recent research with particular emphasis on their quantum dynamics. It is predicted that each monopole also possesses an electric dipole moment, which allows to investigate their dynamics via the dielectric function \epsilon(\nu). Here, we report on broadband spectroscopic measurements of \epsilon(\nu) in Dy2Ti2O7 down to temperatures of 200mK with a specific focus on the critical endpoint present for a magnetic field along the crystallographic [111] direction. Clear critical signatures are revealed in the dielectric response when, similarly as in the liquid-gas transition, the density of monopoles changes in a critical manner. Surprisingly, the dielectric relaxation time \tau\ exhibits a critical speeding-up with a significant enhancement of 1/\tau\ as the temperature is lowered towards the critical temperature. Besides demonstrating the magnetoelectric character of the emergent monopole excitations, our results reveal unique critical dynamics near the monopole condensation transition.Comment: Changes: Data shown and discussed as function of internal field H and flux density B, Figs.3&4 rearranged, references adde

Ferroelectric order versus metallicity in Sr1−x_{1-x}Cax_xTiO3−δ_{3-\delta} (x=0.009x=0.009)

We report on a thermal-expansion study of the ferroelectric phase transition in insulating Sr$_{1-x}$Ca$_x$TiO$_3$ ($x=0.009$) and its evolution upon increasing charge-carrier concentration up to $n\simeq 60 \times 10^{19}$cm$^{-3}$. Although electric polarization is screened by mobile charge carriers, we find clear signatures of the ferroelectric phase transition in the thermal-expansion coefficient $\alpha$ of the weakly doped metallic samples. Upon increasing $n$, the transition temperature $T_\mathrm{C}(n)$ and the magnitude of the anomalies in $\alpha$ rapidly decrease up to a threshold carrier density $n^\star$ above which broadened anomalies remain present. There is no indication for a sign change of $\alpha$ as is expected for a pressure-dependent quantum phase transition with $n$ as the control parameter. Thus, the ferroelectriclike transition is either continuously fading away or it transforms to another low-temperature phase above $n^\star$, but this change hardly affects the temperature-dependent $\alpha(T)$ data.Comment: 6 pages, 3 figure

Designing Polar and Magnetic Oxides: Zn2FeTaO6 - in Search of Multiferroics

Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB′O6 family with unusually small cations at the A-site and a d0 electron configuration ion at B′-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm2 along the c-axis was obtained from point charge model calculations. Zn2Fe3+Ta5+O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component

Designing Polar and Magnetic Oxides: Zn2FeTaO6 - in Search of Multiferroics

Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB′O6 family with unusually small cations at the A-site and a d0 electron configuration ion at B′-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm2 along the c-axis was obtained from point charge model calculations. Zn2Fe3+Ta5+O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component

Polar and Magnetic Mn2FeMO6 (M = Nb, Ta) with LiNbO3-type Structure - High Pressure Synthesis

Polar oxides are of much interest in materials science and engineering. Their symmetry-dependent properties such as ferroelectricity/multiferroics, piezoelectricity, pyroelectricity, and second-order harmonic generation (SHG) effect are important for technological applications. However, polar crystal design and synthesis is challenging, because multiple effects, such as steric or dipole-dipole interactions, typically combine to form non-polar structures; so the number of known polar materials, especially polar magnetoelectric materials, is still severely restricted. Therefore, it is necessary for the material science community to develop new strategies to create these materials

Magnetostriction-polarization coupling in multiferroic Mn2MnWO6

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (T N = 58 K) and high spontaneous polarization (~ 63.3 μC·cm−2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens

Albuminuria Testing in Hypertension and Diabetes:An Individual-Participant Data Meta-Analysis in a Global Consortium

Albuminuria is an under-recognized component of chronic kidney disease definition, staging, and prognosis. Guidelines, particularly for hypertension, conflict on recommendations for urine albumin-to-creatinine ratio (ACR) measurement. Separately among 1 344 594 adults with diabetes and 2 334 461 nondiabetic adults with hypertension from the chronic kidney disease Prognosis Consortium, we assessed ACR testing, estimated the prevalence and incidence of ACR ≥30 mg/g and developed risk models for ACR ≥30 mg/g. The ACR screening rate (cohort range) was 35.1% (12.3%-74.5%) in diabetes and 4.1% (1.3%-20.7%) in hypertension. Screening was largely unrelated to the predicted risk of prevalent albuminuria. The median prevalence of ACR ≥30 mg/g across cohorts was 32.1% in diabetes and 21.8% in hypertension. Higher systolic blood pressure was associated with a higher prevalence of albuminuria (odds ratio [95% CI] per 20 mm Hg in diabetes, 1.50 [1.42-1.60]; in hypertension, 1.36 [1.28-1.45]). The ratio of undetected (due to lack of screening) to detected ACR ≥30 mg/g was estimated at 1.8 in diabetes and 19.5 in hypertension. Among those with ACR/g, the median 5-year incidence of ACR ≥30 mg/g across cohorts was 23.9% in diabetes and 21.7% in hypertension. Incident albuminuria was associated with initiation of renin-angiotensin-aldosterone system inhibitors (incidence-rate ratio [95% CI], diabetes 3.09 [2.71-3.53]; hypertension 2.87 [2.29-3.59]). In conclusion, despite similar risk of albuminuria to those with diabetes, ACR screening in patients with hypertension was low. Our findings suggest that regular albuminuria screening should be emphasized to enable early detection of chronic kidney disease and initiation of treatment with cardiovascular and renal benefits

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Observation of chiral solitons in LiCuVO4

Quantum spin liquids represent a magnetic ground state arising in the presence of strong quantum fluctuations that preclude ordering down to zero temperature and leave clear fingerprints in the excitation spectra. While theory bears a variety of possible quantum spin liquid phases their experimental realization is still scarce. Here, we report experimental evidence for chiral solitons in the S = 1/2 spin chain compound LiCuVO4 from measurements of the complex permittivity epsilon* in the GHz range. In zero magnetic field our results show short-lived thermally activated chiral fluctuations above the multiferroic phase transition at T-N = 2.4 K. In epsilon* these fluctuations are seen as the slowing down of a relaxation with a critical dynamical exponent nu(xi)z approximate to 1.3 in agreement with mean-field predictions. When using a magnetic field to suppress T-N towards 0 K the influence of quantum fluctuations increases until the thermally activated fluctuations vanish and only an excitation can be observed in the dielectric response in close proximity to the phase transition below 400 mK. From direct measurements we find this excitation's energy gap as E-SE approximate to 14.1 mu eV, which is in agreement with a nearly gapless chiral soliton that has been proposed for LiCuVO4 based on quantum spin liquid theory. Quantum spin liquids describe a system where any type of long-range or local ordering is absent even at absolute zero but despite prominent theoretical studies definitive experimental evidence of such a system is difficult to obtain. Here, by analysing the complex permittivity of LiCuVO4 the authors find evidence of chiral solitons suggesting the presence of a quantum spin liquid state