Perovskite solar cells with record power conversion efficiency are fabricated by alloying both hybrid and fully inorganic compounds. While the basic electronic properties of the hybrid perovskites ...are now well understood, key electronic parameters for solar cell performance, such as the exciton binding energy of fully inorganic perovskites, are still unknown. By performing magneto-transmission measurements, we determine with high accuracy the exciton binding energy and reduced mass of fully inorganic CsPbX3 perovskites (X = I, Br, and an alloy of these). The well-behaved (continuous) evolution of the band gap with temperature in the range of 4–270 K suggests that fully inorganic perovskites do not undergo structural phase transitions like their hybrid counterparts. The experimentally determined dielectric constants indicate that at low temperature, when the motion of the organic cation is frozen, the dielectric screening mechanism is essentially the same for both hybrid and inorganic perovskites and is dominated by the relative motion of atoms within the lead halide cage.
Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory ...experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154.
The generation of astrophysically relevant jets, from magnetically collimated, laser-produced plasmas, is investigated through three-dimensional, magnetohydrodynamic simulations. We show that for ...laser intensities I∼10(12)-10(14) W cm(-2), a magnetic field in excess of ∼0.1 MG, can collimate the plasma plume into a prolate cavity bounded by a shock envelope with a standing conical shock at its tip, which recollimates the flow into a supermagnetosonic jet beam. This mechanism is equivalent to astrophysical models of hydrodynamic inertial collimation, where an isotropic wind is focused into a jet by a confining circumstellar toruslike envelope. The results suggest an alternative mechanism for a large-scale magnetic field to produce jets from wide-angle winds.
We investigate the formation of a laser-produced magnetized jet under conditions of a varying mass ejection rate and a varying divergence of the ejected plasma flow. This is done by irradiating a ...solid target placed in a 20 T magnetic field with, first, a collinear precursor laser pulse (10^{12} W/cm^{2}) and, then, a main pulse (10^{13} W/cm^{2}) arriving 9-19 ns later. Varying the time delay between the two pulses is found to control the divergence of the expanding plasma, which is shown to increase the strength of and heating in the conical shock that is responsible for jet collimation. These results show that plasma collimation due to shocks against a strong magnetic field can lead to stable, astrophysically relevant jets that are sustained over time scales 100 times the laser pulse duration (i.e., >70 ns), even in the case of strong variability at the source.
In this work, we perform a comparative study of the magnetization behavior of four series of compounds R 2 Fe 14 B and their hydrides R 2 Fe 14 BH 5.5 , and the compositions (Nd 0.5 R 0.5 ) 2 Fe 14 B ...and their hydrides (Nd<inline-formula> <tex-math notation="LaTeX">_{0.5}\text{R}^\prime _{0.5})_{2} </tex-math></inline-formula>Fe 14 BH 5.5 with R and <inline-formula> <tex-math notation="LaTeX">\text{R}^\prime = </tex-math></inline-formula> Ho, Er, and Tm. The magnetization is measured in pulsed magnetic fields up to 58 T and in megagauss fields up to 135 T at 5 K. The first and second critical fields of the field-induced transitions, <inline-formula> <tex-math notation="LaTeX">H_{c1} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">H_{c2} </tex-math></inline-formula> were estimated analytically and the results were verified against experimental data. We find that hydrogenation of R 2 Fe 14 B and (Nd<inline-formula> <tex-math notation="LaTeX">_{0.5}\text{R}^\prime _{0.5})_{2} </tex-math></inline-formula>Fe 14 B reduces drastically the <inline-formula> <tex-math notation="LaTeX">H_{c1} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">H_{c2} </tex-math></inline-formula> values and, as a consequence, the intersublattice R-Fe exchange interaction parameter <inline-formula> <tex-math notation="LaTeX">\lambda </tex-math></inline-formula>.
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In this paper, we describe in detail the BMV (
Biréfringence Magnétique du Vide
) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a ...very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives.
Near-infrared magneto-optical spectroscopy of single-walled carbon nanotubes reveals two absorption peaks with an equal strength at high magnetic fields (>55 T). We show that the peak separation is ...determined by the Aharonov-Bohm phase due to the tube-threading magnetic flux, which breaks the time-reversal symmetry and lifts the valley degeneracy. This field-induced symmetry breaking thus overcomes the Coulomb-induced intervalley mixing which is predicted to make the lowest exciton state optically inactive (or dark).
In antiferromagnets, the interplay of spin frustration and spin-lattice coupling has been extensively studied as the source of complex spin patterns and exotic magnetism. Here, we demonstrate that, ...although neglected in the past, the spin-lattice coupling is essential to ferrimagnetic spinels as well. We performed ultrahigh-field magnetization measurements up to 110 T on a Yafet-Kittel ferrimagnetic spinel, MnCr2S4, which was complemented by measurements of magnetostriction and sound velocities up to 60 T. Classical Monte Carlo calculations were performed to identify the complex high-field spin structures. Our minimal model incorporating spin-lattice coupling accounts for the experimental results and corroborates the complete phase diagram, including two new high-field phase transitions at 75 and 85 T. Magnetoelastic coupling induces striking effects: An extremely robust magnetization plateau is embedded between two unconventional spin-asymmetric phases. Ferrimagnetic spinels provide a new platform to study asymmetric and multiferroic phases stabilized by spin-lattice coupling.
We report that the local Ising anisotropy in pyrochlore oxides-the crucial requirement for realizing the spin-ice state-can be broken by means of high magnetic fields. For the case of the ...well-established classical spin-ice compound Ho2Ti2O7 the magnetization exceeds the angle-dependent saturation value of the Ising limit using ultrahigh fields up to 120 T. However, even under such extreme magnetic fields full saturation cannot be achieved. Crystal-electric-field calculations reveal that a level crossing for two of the four ion positions leads to magnetization steps at 55 and 100 T. In addition, we show that by using a field sweep rate in the range of the spin-relaxation time the dynamics of the spin system can be probed. Exclusively at 25 ns/T, a new peak of the susceptibility appears around 2 T. We argue, this signals the crossover between spin-ice and polarized correlations.
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