Anomalous Phase Transition Research Articles

Anomalous correlation-induced dynamical phase transitions

The nonanalyticity of the Loschmidt echo at critical times in quantum quenched systems is termed as the dynamical quantum phase transition, extending the notion of quantum criticality to a nonequilibrium scenario. In this paper, we establish a new paradigm of dynamical phase transitions driven by a sudden change in the internal spatial correlations of the disorder potential in a low-dimensional disordered system. The quench dynamics between prequenched pure and postquenched random system Hamiltonian reveals an anomalous dynamical quantum phase transition triggered by an infinite disorder correlation in the modulation potential. The physical origin of the anomalous phenomenon is associated with the overlap between the two distinctly different extended states. Furthermore, we explore the quench dynamics between the prequenched random and postquenched pure system Hamiltonian. Interestingly, the quenched system undergoes dynamical quantum phase transitions for the prequench white-noise potential in the thermodynamic limit. In addition, the quench dynamics also shows a clear signature of the delocalization phase transition in the correlated Anderson model.

Kinetically-decoupled electrical and structural phase transitions in VO2

Vanadium dioxide (VO2) has drawn significant attention for its near room temperature insulator to metal transition and associated structural phase transition. The underlying Physics behind the temperature induced insulator to metal and concomitant structural phase transition in VO2 is yet to be fully understood. We have investigated the kinetics of the above phase transition behaviors of VO2 with the help of resistivity measurements and Raman spectroscopy. Resistance thermal hysteresis scaling and relaxation measurements across the temperature induced insulator to metal transition reveal the unusual behaviour of this first-order phase transition, whereas Raman relaxation measurements show that the temperature induced structural phase transition in VO2 follows usual behaviour and is consistent with mean field prediction. At higher temperature sweeping rates decoupling of insulator to metal transition and structural phase transition have been confirmed. The observed anomalous first order phase transition behavior in VO2 is attributed to the unconventional quasi particle dynamics, i.e. significantly lowered electronic thermal conductivity across insulator to metal transition, which is confirmed by ultrafast optical pump-probe time domain thermoreflectance measurements.

Tunable anomalous valley Hall effect and magnetic phase transition in MHfN2Cl2 (M = V, Cr) bimetallic nitrogen halide monolayers

Transition metal nitrogen halides (TMNHs) are environmentally friendly and widely studied van der Waals two-dimension (2D) materials. However, there are still few 2D TMNHs with magnetic properties that have been synthesized, which greatly limits the further applications of them in spintronics and valleytronics. Here, we substitute Hf atoms by magnetic elements V and Cr in β-type TMNHs Hf2N2Cl2, which evolved into ferromagnetic half-metals and ferrovalley semiconductors MHfN2Cl2 (M = V, Cr). Meanwhile, the valley splitting (VS) properties and magnetic properties can be effectively regulated by modulating the strong correlation effect of transition metals and applying biaxial strain. VS in VHfN2Cl2 increases linearly with the increasing strain and the U value; however, VS is robust to the strain and decreases linearly with the increasing U value in CrHfN2Cl2, and the maximum VS reaches to 175 and 62 meV for the two monolayers. CrHfN2Cl2 remains robustly ferromagnetic under different strain and U values, while there is magnetic phase transition in VHfN2Cl2 from ferromagnetic to antiferromagnetic, accompanied by a half-metal-to-semiconductor transition. The Curie temperatures of VHfN2Cl2 and CrHfN2Cl2 can be increased by a maximum of 2.5 and 2.36 times under modulation. This opens different ideas for the study of bimetallic TMNHs in spintronics and valleytronics.

An anomalous ferroelastic phase transition arising from an unusual cis-/anti-conformational reversal of polar organic cations.

Hybrid ferroelastics have attracted increasing attention for their potential application as mechanical switches. The sporadically documented anomalous ferroelastic phase transitions, i.e., ferroelasticity that appears at a high-temperature phase rather than a low-temperature phase, are of particular interest but are not well understood at the molecular level. By judiciously choosing a polar and flexible organic cation (Me2NH(CH2)2Br+) with cis-/anti- conformations as an A-site component, we obtained two new polar hybrid ferroelastics, A2[MBr6] (M = Te for 1 and Sn for 2). These materials undergo distinct thermal-induced ferroelastic phase transitions. The larger [TeBr6]2- anions anchor the adjacent organic cations well and essentially endow 1 with a conventional ferroelastic transition (P21 → Pm21n) arising from a common order-disorder transition of organic cations without conformational changes. Moreover, the smaller [SnBr6]2- anions can interact with the adjacent organic cations in energetically similar sets of intermolecular interactions, enabling 2 to undergo an anomalous ferroelastic phase transition (P212121 → P21) arising from an unusual cis-/anti-conformational reversal of organic cations. These two instances demonstrate the importance of the delicate balance of intermolecular interactions for inducing anomalous ferroelastic phase transitions. The findings here provide important insights for seeking new multifunctional ferroelastic materials.

Lateral diffusion of lipids in the DMPG membrane across the anomalous melting regime: effects of NaCl.

The anionic dimyristoyl phosphatidylglycerol (DMPG) membrane in solvents with a low ionic strength is known to exhibit an unusually wide melting regime between the gel and fluid phase characterized by various anomalous macroscopic characteristics, such as low turbidity and high electrical conductivity and viscosity. A recent neutron spin echo study [Kelley, E. G. et al., Struct. Dyn., 7 (2020) 054704] revealed that during the extended melting phase transition the DMPG membrane becomes softer and exhibits faster collective bending fluctuation compared to the higher temperature fluid phase. In contrast, in the present work, using incoherent quasielastic neutron scattering through the anomalous phase transition regime we find that single-particle lateral and internal lipid motions in the DMPG membrane show regular temperature dependence, with no enhanced dynamics evident in the anomalous melting regime. Further, we find that incorporation of NaCl in DMPG suppresses the anomalous extended melting regime, concurrently enhancing the single-particle lipid dynamics, both the lateral diffusivity and (to a lesser extent) the internal lipid motion. This seems rather counterintuitive and in variance with the dynamic suppression effect exerted by a salt on a zwitterionic membrane. However, since incorporation of a salt in anionic DMPG leads to enhanced cooperativity, the disrupted cooperativity in the salt-free DMPG is associated with the baseline lipid dynamics that is suppressed to begin with, whereas addition of salt partially restores the cooperativity, thus enhancing lipid dynamics compared to the salt-free baseline DMPG membrane state. These results provide new insights into the ion-membrane interaction and divulge a correlation between microscopic dynamics and the structure of the lipid bilayer.

Anomalous Phase Transition, Polarization Switching, and Relaxation in a Novel Composite Consisting of Dimethylammonium Aluminum Sulfate Hexahydrate and Oxidized Multiwalled Carbon Nanotubes

A novel ferroelectric composite consisting of dimethylammonium aluminum sulfate hexahydrate (CH3)2NH2Al(SO4)2·6H2O and oxidized multiwalled carbon nanotubes was developed to investigate its dielectric relaxation, phase transition, and ferroelectric switching behaviors. Experimental methods combined with theoretical analyses were employed. The results showed that the filler of oxidized multiwalled carbon nanotubes caused the freezing of domain-wall motion in (CH3)2NH2Al(SO4)2·6H2O at 98.2 K, leading to a decrease in dielectric constant, dielectric loss, and the polarization. In addition, an increase in dielectric permittivity and dielectric loss was found at higher temperatures. The role of hydroxyl groups incorporated in the carbon nanotubes after its oxidation was responsible for the obtained anomalies.

Metal-Insulator Transition Detection of Vanadium Dioxide Thin Films by Visible Light Reflection.

Vanadium dioxide (VO2)-based thin films have received considerable attention in recent years due to their superior performance in creating next-generation color-rendering materials. The near-room-temperature metal-insulator transition of VO2 promises the advantage of active color tuning in the visible wavelength range. Although various results of dynamic color generation combined with plasmonic nanostructures are currently being investigated, so far, very few studies have addressed the visible-light optical performance of pure VO2 thin films prepared on conventional substrates. This article shows in detail the phase-transition behavior of VO2 thin films in the visible wavelength range of 400-750 nm prepared on glass with subsequent annealing at temperatures of 350, 400, 450, and 500 °C. The results show an anomalous phase transition reducing the overall RGB reflectivity correlated with the crystallization behavior of the VO2 phase and scattering effect. The sample annealed at 350 °C shows the smallest phase transition at 47 °C, correlating with a crystallite size of 7 nm. The blue band reflectivity anomaly after annealing at 450 °C was considered an effect of the secondary reflection. The results of this research could play a huge role in the production of active-switching photonic devices, color-managed reflectors, and temperature indicators.

Unraveling Anomalous Dielectric Phase Transition in Few-Layered 2H/1T MoS2 Nanosheets

In the present work, highly crystalline molybdenum disulfide (MoS2) nanosheets were grown by a simple and cost-effective hydrothermal route. An anomalous structural phase transition in MoS2 nanoshe...

Evidence of a structural phase transition in the triangular-lattice compound CuIr2Te4

Synthesized $\mathrm{Cu}{\mathrm{Ir}}_{2}{({\mathrm{Te}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x})}_{4}$ samples were comprehensively characterized using various techniques. At ambient pressure, $\mathrm{Cu}{\mathrm{Ir}}_{2}{\mathrm{Te}}_{4}$ undergoes an anomalous phase transition at ${T}_{s}\ensuremath{\sim}250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ with a large thermal hysteresis of $\mathrm{\ensuremath{\Delta}}{T}_{s} \ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and a superconducting transition at ${T}_{c}\ensuremath{\sim}3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ during magnetization and electrical-resistivity measurements. We determined this transition to be a first-order structural phase transition from high-temperature hexagonal ($P\overline{3}m1$) to low-temperature triclinic ($P\overline{1}$) symmetry. Both external physical pressure and chemical doping largely enhance ${T}_{s}$ and $\mathrm{\ensuremath{\Delta}}{T}_{s}$ and suppress ${T}_{c}$, thereby indicating a strong correlation between ${T}_{s}$ and ${T}_{c}$. Critically, no superlattice is observed below ${T}_{s}$ as per the electron-diffraction examinations. Thus, the anomalous phase transition at ${T}_{s}$, which exhibits a large thermal hysteresis in resistivity and magnetization measurements, is structural rather than a charge-density-wave formation.

Influence of carbonization on phase transition and electrical conductivity of ferroelectric composite with Rochelle salt inclusion

The present study is devoted to clarifying effects of carbonization toward cellulose nanoparticles that are pre-carbonized at different temperatures of 240, 250, 340 and 400 °C on the phase transition and conductive properties of nanocomposites with Rochelle salt. Fourier-transform infrared spectroscopy (FTIR) technique was employed to investigate the changes in functional groups during carbonization process. The results indicated that the influence of carbonized cellulose component on properties of Rochelle salt volume part in the composite was negligible, but significant at the interfaces between Rochelle salt and surrounding cellulose. The elevated carbonization temperatures resulted in the reduction of phase transition temperatures and increase in conductivity. The weakness of Rochelle salt/cellulose interaction caused by carbonized cellulose and the formation of carbon clusters in the composite were considered as the main reasons for anomalous phase transition and high electrical conductivity, respectively.

New Polymorphism for Ba3Zn2(BO3)3F with Two Polymorphs Exhibiting Anomalous Phase Transition

AbstractA new polymorph of Ba3Zn2(BO3)3F, α‐Ba3Zn2(BO3)3F, was synthesized and its structure was determined by single crystal X‐ray diffraction. The two polymorphous phases of Ba3Zn2(BO3)3F are referred to as α‐ and β‐Ba3Zn2(BO3)3F according to their synthesis temperature from low to high. Both structures exhibit a similar three‐dimensional (3D) framework, while the two‐dimensional (2D) 2∞[Zn2B2O7] layers in their structures show different configurations and feature diverse topological structures. Interestingly, an anomalous phase transition, that is, the high‐temperature β‐phase having a higher density, was observed and further confirmed by detailed structural analyses, which shows that the unusual density evolution mainly originates from the different configurations of 2∞[Zn2B2O7] layers. Moreover, the phase transformation was characterized by powder X‐ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses.

Enhanced dynamics in the anomalous melting regime of DMPG lipid membranes.

Like many soft materials, lipids undergo a melting transition associated with a significant increase in their dynamics. At temperatures below the main melting transition (Tm), all molecular and collective dynamics are suppressed, while above Tm the alkyl tail motions, lipid diffusivity, and collective membrane undulations are at least an order of magnitude faster. Here we study the collective dynamics of dimyristoylphosphatidylglycerol (DMPG, di 14:0 PG) using neutron spin echo spectroscopy throughout its anomalous phase transition that occurs over a 12 °C–20° C wide temperature window. Our results reveal that the membranes are softer and more dynamic during the phase transition than at higher temperatures corresponding to the fluid phase and provide direct experimental evidence for the predicted increase in membrane fluctuations during lipid melting. These results provide new insights into the nanoscale lipid membrane dynamics during the melting transition and demonstrate how these dynamics are coupled to changes in the membrane structure.

Observation of anomalous phase transition and band gap shrinkage in zinc germanate nanorods

This work reports the high temperature anomalous phase transition with high dielectric constant and low band gap in pure zinc germanate (Zn2GeO4) nanorods. Crystal structure of Zn2GeO4 nanorods were analyzed by X-ray powder diffraction and Raman studies. Electron microscopy reveals that nanorods have average diameter and length of 30 nm and 100 nm, respectively. UV–ViS study indicates low band gap of 3.96 eV. The observed dielectric constant is 40 times higher than bulk Zn2GeO4. High dielectric constant of ~772 and phase transition was observed around 400 °C. In the low and high temperature range, activation energy were ~0.33 and 1.34 eV. High dielectric constant and shrinkage in bang gap with temperature phase transition of Zn2GeO4 nanorods makes it the potential candidate for nano-optoelectronic and nanodevices applications in near future.

Surface depletion field in 2D perovskite microplates: Structural phase transition, quantum confinement and Stark effect

Surface depletion field would introduce the depletion region near surface and thus could significantly alter the optical, electronic and optoelectronic properties of the materials, especially low-dimensional materials. Two-dimensional (2D) organic—inorganic hybrid perovskites with van der Waals bonds in the out-of-plane direction are expected to have less influence from the surface depletion field; nevertheless, studies on this remain elusive. Here we report on how the surface depletion field affects the structural phase transition, quantum confinement and Stark effect in 2D (BA)2PbI4 perovskite microplates by the thickness-, temperature- and power-dependent photoluminescence (PL) spectroscopy. Power dependent PL studies suggest that high-temperature phase (HTP) and low-temperature phase (LTP) can coexist in a wider temperature range depending on the thickness of the 2D perovskite microplates. With the decrease of the microplate thickness, the structural phase transition temperature first gradually decreases and then increases below 25 nm, in striking contrast to the conventional size dependent structural phase transition. Based on the thickness evolution of the emission peaks for both high-temperature phase and low-temperature phase, the anomalous size dependent phase transition could probably be ascribed to the surface depletion field and the surface energy difference between polymorphs. This explanation was further supported by the temperature dependent PL studies of the suspended microplates and encapsulated microplates with graphene and boron nitride flakes. Along with the thickness dependent phase transition, the emission energies of free excitons for both HTP and LTP with thickness can be ascribed to the surface depletion induced confinement and Stark effect.

Topological Phase Transition Driven by Infinitesimal Instability: Majorana Fermions in Non-Hermitian Spintronics.

Quantum phase transitions are intriguing and fundamental cooperative phenomena in physics. Analyzing a superconducting nanowire with spin-dependent non-Hermitian hopping, we discover a topological quantum phase transition driven by infinitesimal cascade instability. The anomalous phase transition is complementary to the universal non-Bloch wave behavior of non-Hermitian systems. We show that an infinite small magnetic field drastically suppresses the non-Hermitian skin effect, inducing a topological phase with Majorana boundary states. Furthermore, by identifying the bulk topological invariant, we establish the non-Hermitian bulk-boundary correspondence that does not have a Hermitian counterpart. We also discuss an experimental realization of the system by using the spin-current injection to a quantum wire.

Softening of DMPG Lipid Membranes along the Anomalous Gel-Fluid Transition

Phosphatidylglycerols are an anionic phospholipid found in mitochondrial membranes as a precursor to cardiolipin and are a major component of the cytoplasmic membrane of bacteria. The phase behavior of these lipids not only depends on the hydrocarbon tail length, but also is highly sensitive to the pH and ionic strength of the surrounding solution. In particular, the phase behavior of dimyristoylphosphatidylglycerol (DMPG) with saturated 14 carbon tails is highly unusual. The calorimetric profile shows several broad peaks that span 20 degrees and sharpen with increasing buffer ionic strength. Here we use neutron spin echo spectroscopy (NSE) to study the nanoscale membrane fluctuations along the anomalous phase transition in DMPG vesicle solutions as a function of buffer ionic strength. Our results show that the membrane dynamics are enhanced during the melting transition, which we quantify as a decrease in the bending modulus. The results provide direct experimental evidence for the increase in fluctuations needed to form the holey or perforated bilayer structures proposed in other works. Our results provide new insights into the nanoscale membrane dynamics during the melting transition and demonstrate how these dynamics are necessary for changes in the bilayer structure.

Syntheses, structures, anomalous phase transition and optical properties of two new polymorphic α- and β-LiMoPO6.

New polymorphous phases, α- and β-LiMoPO6, have been successfully synthesized by the high temperature solution technique and their structures have been determined by single crystal X-ray diffraction. α-LiMoPO6 crystallizes in the orthorhombic space group Pbcn (No. 60) with a = 12.1141(4) Å, b = 8.9251(3) Å and c = 8.7389(3) Å, while β-LiMoPO6 crystallizes in the monoclinic space group P21/c (No. 14) with a = 6.3441(3) Å, b = 7.5949(3) Å, c = 9.3430(4) Å and β = 94.546(4)°. Both structures exhibit a similar three-dimensional (3D) framework composed of MoO6 octahedra and PO4 tetrahedra. Interestingly, an anomalous phase transition, i.e. the high-temperature β-LiMoPO6 phase exhibiting larger density than the low-temperature α-LiMoPO6, has been observed. Detailed structural analyses show that the anomalous phase transition mainly originates from the 'straightened' effect of the zigzag [MoO3O3PO]∞ chains in their structures. Furthermore, the optical and thermal properties of two compounds are also reported.

Anomalous phase transition behavior in hydrothermal grown layered tellurene.

Recent studies have demonstrated that tellurene is a van der Waals (vdW) two-dimensional material with potential optoelectronic and thermoelectric applications as a result of its pseudo-one-dimensional structure and properties. Here, we report on the pressure induced anomalous phase transition of tellurium nanoribbons. The observation of clean phase transitions was made possible with high quality single crystalline Te nanoribbons that are synthesized by hydrothermal reaction growth. The results show that phase transition has a large pressure hysteresis and multiple competing phases: during compression, the phase transition is sudden and takes place from trigonal to orthorhombic phase at 6.5 GPa. Orthorhombic phase remains stable up to higher pressures (15 GPa). In contrast, phase transition is not sudden during decompression, but orthorhombic and trigonal phases co-exist between 6.9 to 3.4 GPa. Grüneisen parameter calculations further confirm the presence of co-existing phases and suggest hysteretic phase change behavior. Finally, orthorhombic to trigonal phase transition occurs at 3.4 GPa which means overall pressure hysteresis is around 3.1 GPa.

Charge transfer drives anomalous phase transition in ceria

Ceria has conventionally been thought to have a cubic fluorite structure with stable geometric and electronic properties over a wide temperature range. Here we report a reversible tetragonal (P42/nmc) to cubic (Fm-3m) phase transition in nanosized ceria, which triggers negative thermal expansion in the temperature range of −25 °C–75 °C. Local structure investigations using neutron pair distribution function and Raman scatterings reveal that the tetragonal phase involves a continuous displacement of O2− anions along the fourfold axis, while the first-principles calculations clearly show oxygen vacancies play a pivotal role in stabilizing the tetragonal ceria. Further experiments provide evidence of a charge transfer between oxygen vacancies and 4f orbitals in ceria, which is inferred to be the mechanism behind this anomalous phase transition.

Physicochemical characterization of 6-O-acyl trehalose fatty acid monoesters in desiccated system

The understanding of the basic physicochemical properties of trehalose lipid is indispensable to extending their availability. In this study, the hydrate crystal (Cr), the liquid crystalline (LC) phase and the glassy state formations of 6-O-acyl trehalose fatty acid monoester (TREn) were examined under in a desiccated system. TREn (n = 10, 12, 14, 16) formed monohydrate Cr and showed the hydrate Cr-glassy fluid lamellar LC (Lα) phase transition via dehydration in the heating process. Here, Lα phase for TRE10 and TRE12 was kinetically formed by the dehydration below the glass transition temperature (Tg). On the dehydration temperature (Tdeh), Tgs, and heat capacity changes (ΔCps) at these Tgs, no distinct effects by the difference of the acyl chain length were recognized, possibly because the core structure of containing sugar hydrate Cr or sugar moieties should be similar regardless of the acyl chain length. Besides, TRE10 having a relatively high hydrophilic/hydrophobic balance (HLB) afforded to form the cubic LC (Q) phase and the corresponding glassy phase, while TRE14 and TRE16 having low HLB afforded the Lα phase as well as the corresponding glassy phases above Tg. TRE12 having middle HLB afforded both LCs and the corresponding glassy phase by controlling the kinetics of LC-LC phase transition between Lα and Q phases. Furthermore, the anomalous reversible phase transition during both the heating and cooling processes was also ascertained in the glassy phase for TRE16, which was considered the phase transition between glassy Lα and glassy lamellar gel (Lβ) phase. It greatly empathizes the two-dimensional trehalose glass layer and fluid hydrocarbon chains in the TREn glassy phase. Thus, in this study, it was demonstrated that TREn as the simplest trehalose lipid exhibited the glassy formation performance as well as the hydrate Cr formation, which showed less chain length dependence, together with the LC formation and the phase transition between glassy Lα and glassy Lβ phase, which depended on chain length greatly.