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Lighta??Controlled Ferromagnetism in Porphyrin Functionalized Ultrathin FeS Nanosheets
摘要： The intrinsically weak photomagnetic interaction makes it difficult to realize effectively light-controlled magnetic structure transformation. Here unprecedented light-induced switching of magnetism is reported in porphyrin functionalized ultrathin FeS nanosheets. Contrary to the antiferromagnetic (AFM) bulk, the troilite FeS nanosheets demonstrate a ferromagnetic (FM) behavior due to superficial symmetry breaking. Under light irradiation, a large number of photo-generated carriers take part in a singlet-to-triplet conversion through intersystem crossing of tetra(4-carboxyphenyle)porphyrin molecules decorated on the nanosheets. The generated triplet carriers make spin flips occur at FeS surface, finally leading to a magnetic structure transition from FM to AFM configuration. The findings not only shed new light on steering arrangement of spin electrons but also open up almost unlimited possibilities for spintronics and optical detection of spin-dependent physiological reactions.
关键词： structural phase transition,spin flip,light-controlled ferromagnetism
更新于2025-09-23 15:21:01
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revealed by high-energy x-ray diffraction
摘要： We explore the evolution of the structural phase transition of (Sr, Ca)3Ir4Sn13, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature T ? against pressure, which extrapolates to zero at a critical pressure of ≈1.79(4) GPa. The temperature evolution of the superlattice Bragg peak in Ca3Ir4Sn13 reveals a drastic decrease of the intensity and an increase of the linewidth when T → 0 K and p → pc. Such anomaly is likely associated with the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of (Sr, Ca)3Ir4Sn13 thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors.
关键词： high-energy x-ray diffraction,structural phase transition,superconductivity,quantum criticality,quantum fluctuations
更新于2025-09-23 15:19:57
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Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI <sub/>3</sub> (M = Pb, Sn)
摘要： The structural phase transition, ferroelectric polarization, and electric properties have been investigated for photovoltaic films CsMI3 (M = Pb, Sn) epitaxially grown along (001) direction based on the density functional theory. The calculated results indicate that the phase diagrams of two epitaxial CsPbI3 and CsSnI3 films are almost identical, except critical transition strains varying slightly. The epitaxial tensile strains induce two ferroelectric phases Pmc21, and Pmn21, while the compressive strains drive two paraelectric phases P212121, P21212. The larger compressive strain enhances the ferroelectric instability in these two films, eventually rendering them another ferroelectric state Pc. Whether CsPbI3 or CsSnI3, the total polarization of Pmn21 phase comes from the main contribution of B-position cations (Pb or Sn), whereas, for Pmc21 phase, the main contributor is the I ion. Moreover, the epitaxial strain effects on antiferrodistortive vector, polarization and band gap of CsMI3 (M = Pb, Sn) are further discussed. Unusual electronic properties under epitaxial strains are also revealed and interpreted.
关键词： structural phase transition,electric properties,photovoltaic films,ferroelectric polarization,epitaxial strain,density functional theory,CsMI3
更新于2025-09-19 17:13:59
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Barkhausen effect in the first order structural phase transition in type-II Weyl semimetal MoTe <sub/>2</sub>
摘要： We report the first observation of the non-magnetic Barkhausen effect in van der Waals layered crystals, specifically, during transitions between the Td and 1T′ phases in type-II Weyl semimetal MoTe2. Thinning down the MoTe2 crystal from bulk material to about 25 nm results in a drastic strengthening of the hysteresis in the phase transition, with the difference in critical temperature increasing from ~40 K to more than 300 K. The Barkhausen effect appears for thin samples and the temperature range of the Barkhausen zone grows approximately linearly with reducing sample thickness, pointing to a surface origin of the phase pinning effects. The distribution of the Barkhausen jumps shows a power law behavior, with its critical exponent α = 1.27, in good agreement with existing scaling theory. Temperature-dependent Raman spectroscopy on MoTe2 crystals of various thicknesses shows results consistent with our transport measurements.
关键词： Barkhausen effect,2D materials,MoTe2,structural phase transition
更新于2025-09-11 14:15:04
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A Scanning Tunneling Microscopy Study of Monolayer and Bilayer Transition-Metal Dichalcogenides Grown by Molecular-Beam Epitaxy
摘要： This review presents an account of some recent scanning tunneling microscopy and spectroscopy (STM/S) studies of monolayer and bilayer transition-metal dichalcogenide (TMD) films grown by molecular-beam epitaxy (MBE). In addition to some intrinsic properties revealed by STM/S, defects such as inversion domain boundaries and point defects, their properties and induced effects, are presented. More specifically, the quantum confinement and moiré potential effects, charge state transition, quasi-particle interference and structural phase transition as revealed by STM/S are described.
关键词： transition-metal dichalcogenides,quantum confinement,structural phase transition,molecular-beam epitaxy,moiré potential,quasi-particle interference,scanning tunneling microscopy,charge state transition
更新于2025-09-09 09:28:46
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Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites
摘要： Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed.
关键词： structural phase transition,negative thermal expansion,perovskite,scandium trifluoride,antiferrodistortive phase transition,quantum phase transition,structural negative thermal expansion
更新于2025-09-04 15:30:14
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Local insight into the La-induced structural phase transition in multiferroic BiFeO3 ceramics by X-ray absorption fine structure spectroscopy
摘要： Substitution of bismuth by rare-earth (RE) ions is of great technological importance to develop room-temperature BiFeO3-based multiferroic materials. Despite this interest, many fundamental properties and the structure-property correlations of RE-doped BiFeO3 remain poorly understood. Here we report a systematical experimental and theoretical exploration on the structural phase transition in Bi1-xLaxFeO3 (0 ≤ x ≤ 0.2) ceramics. By using x-ray absorption fine structure spectroscopy, we for the first time show that the La3+ dopants in fact substitute the Bi site of a secondary nanosized particles with orthorhombic Pbam symmetry instead of the long-believed parental rhombohedral R3c phase at all La3+ doping concentrations (0.001 ≤ x ≤ 0.2). This finding is further supported by complementary studies of transmission electron microscopy and thermodynamic preference, and it casts serious challenges on the prevailing assumption of La substitution on the Bi3+ site in R3c structure when x ≤ 0.1 as well as the previously proposed origin of enhanced functional properties based on morphotropic phase boundary. This new insight may ignite a revival on exploring the underlying multiferroic mechanisms in BiFeO3-based materials and facilitate the bottom-up design of novel multifunctional devices.
关键词： XAFS,BiFeO3,structural phase transition,La doping,multiferroic materials
更新于2025-09-04 15:30:14
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Structural and Optical Properties of Cs2AgBiBr6 Double Perovskite.
摘要： We present a comprehensive study of the relationship between the crystal structure and optoelectronic properties of the double perovskite Cs2AgBiBr6, which has emerged as a promising candidate for photovoltaic. Based on single-crystal/powder X-ray diffraction and neutron powder diffraction, we have revealed the presence of a structural phase transition at Ts ～122K between the room-temperature cubic structure (space group F mˉ3m) and a new low-temperature tetragonal structure (I4/m). From reflectivity measurements we found that the peak exciton energy Eex ≈ 2.85 eV near the direct gap shifts proportionally to the tetragonal strain, which is consistent with the Eex being primarily controlled by a rotational degree of freedom of the crystal structure, thus by the angle Bi-Br-Ag. We observed the time-resolved photoluminescence kinetics and we found that, among the relaxation channels, a fast one is mainly present in the tetragonal phase, suggesting that its origin may lie in the formation of tetragonal twin domains.
关键词： optoelectronic properties,structural phase transition,double perovskite,photovoltaic,Cs2AgBiBr6
更新于2025-09-04 15:30:14