Showing papers on "Phase transition published in 2002"
TL;DR: This work observes a quantum phase transition in a Bose–Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential, and can induce reversible changes between the two ground states of the system.
Abstract: For a system at a temperature of absolute zero, all thermal fluctuations are frozen out, while quantum fluctuations prevail. These microscopic quantum fluctuations can induce a macroscopic phase transition in the ground state of a many-body system when the relative strength of two competing energy terms is varied across a critical value. Here we observe such a quantum phase transition in a Bose-Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential. As the potential depth of the lattice is increased, a transition is observed from a superfluid to a Mott insulator phase. In the superfluid phase, each atom is spread out over the entire lattice, with long-range phase coherence. But in the insulating phase, exact numbers of atoms are localized at individual lattice sites, with no phase coherence across the lattice; this phase is characterized by a gap in the excitation spectrum. We can induce reversible changes between the two ground states of the system.
4,467 citations
TL;DR: The discovery of a large magnetic entropy change is reported in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature, attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.
Abstract: Magnetic refrigeration techniques based on the magnetocaloric effect (MCE) have recently been demonstrated as a promising alternative to conventional vapour-cycle refrigeration1. In a material displaying the MCE, the alignment of randomly oriented magnetic moments by an external magnetic field results in heating. This heat can then be removed from the MCE material to the ambient atmosphere by heat transfer. If the magnetic field is subsequently turned off, the magnetic moments randomize again, which leads to cooling of the material below the ambient temperature. Here we report the discovery of a large magnetic entropy change in MnFeP0.45As0.55, a material that has a Curie temperature of about 300 K and which allows magnetic refrigeration at room temperature. The magnetic entropy changes reach values of 14.5 J K-1 kg-1 and 18 J K-1 kg-1 for field changes of 2 T and 5 T, respectively. The so-called giant-MCE material Gd5Ge2Si2 (ref. 2) displays similar entropy changes, but can only be used below room temperature. The refrigerant capacity of our material is also significantly greater than that of Gd (ref. 3). The large entropy change is attributed to a field-induced first-order phase transition enhancing the effect of the applied magnetic field.
2,272 citations
TL;DR: In this paper, the authors discuss the entanglement near a quantum phase transition by analyzing the properties of the concurrence for a class of exactly solvable models in one dimension.
Abstract: In this Letter we discuss the entanglement near a quantum phase transition by analyzing the properties of the concurrence for a class of exactly solvable models in one dimension. We find that entanglement can be classified in the framework of scaling theory. Further, we reveal a profound difference between classical correlations and the non-local quantum correlation, entanglement: the correlation length diverges at the phase transition, whereas entanglement in general remains short ranged.
1,175 citations
TL;DR: In this article, a new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid.
1,121 citations
TL;DR: Important advances have been made, for example, with new imaging techniques that allow direct observation of individual colloidal particles undergoing phase transitions, revealing some of the secrets of the complex pathways involved.
Abstract: Colloids display intriguing transitions between gas, liquid, solid and liquid crystalline phases. Such phase transitions are ubiquitous in nature and have been studied for decades. However, the predictions of phase diagrams are not always realized; systems often become undercooled, supersaturated, or trapped in gel-like states. In many cases the end products strongly depend on the starting position in the phase diagram and discrepancies between predictions and actual observations are due to the intricacies of the dynamics of phase transitions. Colloid science aims to understand the underlying mechanisms of these transitions. Important advances have been made, for example, with new imaging techniques that allow direct observation of individual colloidal particles undergoing phase transitions, revealing some of the secrets of the complex pathways involved.
902 citations
TL;DR: In this paper, a car-following model is proposed to investigate the bunching transition and bus delay in traffic flow and pedestrian flow, and detailed results obtained mainly from the microscopic car following models are presented.
Abstract: Traffic flow is a kind of many-body system of strongly interacting vehicles. Traffic jams are a typical signature of the complex behaviour of vehicular traffic. Various models are presented to understand the rich variety of physical phenomena exhibited by traffic. Analytical and numerical techniques are applied to study these models. Particularly, we present detailed results obtained mainly from the microscopic car-following models. A typical phenomenon is the dynamical jamming transition from the free traffic (FT) at low density to the congested traffic at high density. The jamming transition exhibits the phase diagram similar to a conventional gas-liquid phase transition: the FT and congested traffic correspond to the gas and liquid phases, respectively. The dynamical transition is described by the time-dependent Ginzburg-Landau equation for the phase transition. The jamming transition curve is given by the spinodal line. The metastability exists in the region between the spinodal and phase separation lines. The jams in the congested traffic reveal various density waves. Some of these density waves show typical nonlinear waves such as soliton, triangular shock and kink. The density waves are described by the nonlinear wave equations: the Korteweg-de-Vries (KdV) equation, the Burgers equation and the Modified KdV equation. Subjects like the traffic flow such as bus-route system and pedestrian flow are touched as well. The bus-route system with many buses exhibits the bunching transition where buses bunch together with proceeding ahead. Such dynamic models as the car-following model are proposed to investigate the bunching transition and bus delay. A recurrent bus exhibits the dynamical transition between the delay and schedule-time phases. The delay transition is described in terms of the nonlinear map. The pedestrian flow also reveals the jamming transition from the free flow at low density to the clogging at high density. Some models are presented to study the pedestrian flow. When the clogging occurs, the pedestrian flow shows the scaling behaviour.
880 citations
TL;DR: While the density and solid-liquid phase transition properties are similar for both series, the new RTILs present a considerably lower viscosity and an increased ability to dissolve HgCl(2) and LaCl(3) (up to 16 times higher).
Abstract: A new series [CnOm mim][X] of imidazolium cation-based room temperature ionic liquids (RTILs), with ether and alcohol functional groups on the alkyl side-chain has been prepared. Some physical properties of these RTILs were measured, namely solubility in common solvents, viscosity and density. The solubility of LiCl, HgCl2 and LaCl3 in room temperature ionic liquids was also determined. The features of the solid–liquid phase transition were analysed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. These properties were compared with those reported for the 1-n-alkyl-3-methylimidazolium [Cn mim][X] series. While the density and solid–liquid phase transition properties are similar for both series, the new RTILs present a considerably lower viscosity and an increased ability to dissolve HgCl2 and LaCl3 (up to 16 times higher).
504 citations
TL;DR: In this article, the bulk modulus and phase transition pressures of various high-pressure polymorphs have been derived from the Hartree-Fock theory at various pressures, and the calculated bulk moduli are within 10% of the most reliable experimental results.
Abstract: First-principles calculations of the crystal structures, bulk moduli, and relative stabilities of seven known and hypothetical ${\mathrm{TiO}}_{2}$ polymorphs (anatase, rutile, columbite, baddeleyite, cotunnite, pyrite, and fluorite structures) have been carried out with the all-electron linear combination of atomic orbitals (LCAO) and pseudopotential planewave (PW) methods. The anatase versus rutile relative phase stability at 0 K and zero pressure has been investigated using high-quality basis sets and carefully controlled computational parameters. From the optimal crystal structures obtained with the Hartree-Fock theory at various pressures, the bulk modulus and phase transition pressures of various high-pressure polymorphs have been derived at the athermal limit. In most cases, the calculated unit cell data agree to within 2% of the corresponding experimental determination. Complete predicted structural data (unit cell constants and fractional atomic coordinates) are presented for the baddeleyite and pyrite forms. The calculated bulk moduli are within 10% of the most reliable experimental results. Both the all-electron LCAO and pseudopotential PW methods predict anatase to be more stable than rutile at 0 K and ambient pressure. The computed anatase-columbite, rutile-columbite, columbite-baddeleyite, and baddeleyite-cotunnite phase transitions appear in the same order as observed in experiments, and the transition pressures agree semiquantitatively with those measured. The pyrite and fluorite structures are predicted to be less stable than other polymorphs at pressures below 70 GPa in agreement with experiments. Finally, the elastic properties, compressibilities and phase transformations of the various polymorphs are discussed in terms of simple models based on the behavior of the constituent Ti-O polyhedra under compression.
488 citations
TL;DR: In this paper, the stability and evolution of ferroelectric domain structures in thin films are studied and Elastic solutions are derived for both elastically anisotropic and isotropic thin films with arbitrary domain structures, subject to mixed stress-free and constraint boundary conditions.
446 citations
TL;DR: The cubic-tetragonal phase transition of CH 3 NH 3 PbI 3 was investigated by single crystal X-ray diffractometry as discussed by the authors, where the crystal structure was refined at five temperatures in the teragonal phase.
Abstract: The cubic–tetragonal phase transition of CH 3 NH 3 PbI 3 was investigated by single crystal X-ray diffractometry. The crystal structure was refined at five temperatures in the teragonal phase. The PbI 6 octahedron rorates around the c -axis alternatively to construct the SrTiO 3 -type tetragonal structure. A methylammonium ion is partially orderd; 24 disordered states in the cubic phase are reduced to 8. With decreasing temperature, the rotation angle of the octahedron increases monotonically, which indicates it is an order parameter of the cubic-tetragonal transition.
TL;DR: A new assay to quantify the phase transition behavior of SRPs at the solid–water interface is presented, and it is shown that stimuli-responsive surfaces can be created by the immobilization of an elastin-like polypeptide (ELP), a thermally responsive biopolymer, on a glass surface.
Abstract: Surfaces modified with stimuli-responsive polymers (SRPs) dynamically alter their physico-chemical properties in response to changes in their environmental conditions. The triggered control of interfacial properties provided by immobilized SRPs at the solid–water interface has application in the design of biomaterials, regenerable biosensors, and microfluidic bioanalytical devices. In this article, we briefly summarize recent research in this area, followed by two recent examples of research from our laboratory on stimuli-responsive surfaces. First, we present a new assay to quantify the phase transition behavior of SRPs at the solid–water interface. This assay, which is based on the distance-dependent colorimetric properties of gold nanoparticles, provides a technically simple and convenient method to determine the effect of different variables on the lower critical solution temperature (LCST) behavior of SRPs at the solid–water interface. Second, we show that stimuli-responsive surfaces can be created by the immobilization of an elastin-like polypeptide (ELP), a thermally responsive biopolymer, on a glass surface. We exploit the phase transition of the ELP at a surface to reversibly address an ELP fusion protein to a surface. This method, which we term thermodynamically reversible addressing of proteins (TRAP), enables the reversible, spatio-temporal modulation of protein binding at the solid-liquid interface, and will enable the realization of new bioanalytical applications.
TL;DR: In this article, a theory of the magnetic field driven (semi)metal-insulator phase transition is developed for planar systems with a low density of carriers and a linear (i.e., relativisticlike) dispersion relation for low-energy quasiparticles.
Abstract: A theory of the magnetic field driven (semi)metal-insulator phase transition is developed for planar systems with a low density of carriers and a linear (i.e., relativisticlike) dispersion relation for low-energy quasiparticles. The general structure of the phase diagram of the theory with respect to the coupling constant, the chemical potential, and the temperature is derived in two cases, with and without an external magnetic field. The conductivity and resistivity as functions of temperature and magnetic field are studied in detail. An exact relation for the value of the ``offset'' magnetic field ${B}_{c},$ determining the threshold for the realization of the phase transition at zero temperature, is established. The theory is applied to the description of a recently observed phase transition induced by a magnetic field in highly oriented pyrolytic graphite.
TL;DR: In this article, the authors describe an atomic physics experiment that can provide critical insight into the origin of high-temperature superconductivity in cuprates, using standing wave light.
Abstract: Fermionic atoms confined in a potential created by standing wave light can undergo a phase transition to a superfluid state at a dramatically increased transition temperature Depending upon carefully controlled parameters, a transition to a superfluid state of Cooper pairs, antiferromagnetic states or d-wave pairing states can be induced and probed under realistic experimental conditions We describe an atomic physics experiment that can provide critical insight into the origin of high-temperature superconductivity in cuprates
TL;DR: By including fluctuation contributions to the free energy similar to that considered by Nozières and Schmitt-Rink, the character of the superfluid phase transition continuously changes from the BCS-type to the BEC-type, as the threshold of the quasimolecular band is lowered.
Abstract: We discuss the BCS-BEC crossover in a degenerate Fermi gas of two hyperfine states interacting close to a Feshbach resonance. We show that, by including fluctuation contributions to the free energy similar to that considered by Nozieres and Schmitt-Rink, the character of the superfluid phase transition continuously changes from the BCS-type to the BEC-type, as the threshold of the quasimolecular band is lowered. In the BEC regime, the superfluid phase transition is interpreted in terms of molecules associated with both the Feshbach resonance and Cooper pairing.
TL;DR: In this article, shape stabilized phase change materials (PCMs) were made by combining paraffin with a thermoplastic elastomer poly(styrene-butadiene-styrene), which can keep the same shape in a solid state.
TL;DR: In this article, it was shown that BiMnO 3 is ferromagnetic with a T C of 105 K and ferroelectric with a Curie temperature of around 450 K.
TL;DR: In this paper, size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica were observed in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.
Abstract: We have observed size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica. The ${\mathrm{VO}}_{2}$ nanoprecipitates are produced by the stoichiometric coimplantation of vanadium and oxygen and subsequent thermal processing. The observed size dependence in the transition temperature and hysteresis loops of the semiconductor-to-metal phase transition in ${\mathrm{VO}}_{2}$ is described in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.
TL;DR: In this article, a body-centered-cubic ordered structure in a Ni-Ga-Fe system has been developed for ferromagnetic shape memory alloys, which exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase.
Abstract: Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni–Ga–Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20–22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L21 structure at about 970 K during cooling, and the degree of the L21 order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The ductility of these alloys is improved by introducing of a small amount of a γ-phase solid solution. Consequently, we can conclude that the present alloys are promising for ferromagnetic shape memory alloys.
TL;DR: In this article, the influence of Nb doping on the TiO2 anatase-to-rutile phase transition was studied using combined transmission electron microscopy, Raman spectroscopy, x-ray diffraction and selected area electron diffraction analysis.
Abstract: We study the influence of Nb doping on the TiO2 anatase-to-rutile phase transition, using combined transmission electron microscopy, Raman spectroscopy, x-ray diffraction and selected area electron diffraction analysis. This approach enabled anatase-to-rutile phase transition hindering to be clearly observed for low Nb-doped TiO2 samples. Moreover, there was clear grain growth inhibition in the samples containing Nb. The use of high resolution transmission electron microscopy with our samples provides an innovative perspective compared with previous research on this issue. Our analysis shows that niobium is segregated from the anatase structure before and during the phase transformation, leading to the formation of NbO nanoclusters on the surface of the TiO2 rutile nanoparticles.
TL;DR: In this paper, high-resolution neutron powder diffraction and single crystal measurements on the ferromagnetic shape memory compound Ni2MnGa have been carried out, which enabled the sequence of transformations which take place when the unstressed, stoichiometric compound is cooled from 400 to 20 K to be established.
Abstract: High resolution neutron powder diffraction and single crystal measurements on the ferromagnetic shape memory compound Ni2MnGa have been carried out. They enabled the sequence of transformations which take place when the unstressed, stoichiometric compound is cooled from 400 to 20 K to be established. For the first time the crystallographic structure of each of the phases which occur has been determined. At 400 K the compound has the cubic L21 structure, and orders ferromagnetically at TC ≈ 365 K. On cooling below ~ 260 K a super-structure, characterized by tripling of the repeat in one of the 110cubic directions, forms. This phase, known as the pre-martensitic phase, persists down to the structural phase transition at TM ≈ 200 K and can be described by an orthorhombic unit cell with lattice parameters aortho = 1/√2acubic, bortho = 3/√2acubic, cortho = acubic and space group Pnnm. Below TM the compound has a related orthorhombic super-cell with bortho ≈ 7/√2acubic, which can be described within the same space group. The new modulation appears abruptly at TM and remains stable down to at least 20 K.
TL;DR: In this article, the authors report dielectric data on six different plastic crystalline materials, namely 1-cyanoadamantane, adamantanone, pentachloronitrobenzene, cyclohexanol, ethanol, and meta-carborane, covering a frequency range of up to 14 decades and up to 20 GHz.
Abstract: We report dielectric data on six different plastic crystalline materials, namely 1-cyanoadamantane, adamantanone, pentachloronitrobenzene, cyclo-hexanol, ethanol, and meta-carborane, covering a frequency range of up to 14 decades and up to 20 GHz. Information on phase transitions, the α-relaxation, and relaxation processes beyond the α-relaxation are provided. The α-relaxation shows clear non-Debye behavior and varying degrees of deviation from thermally activated behavior. Our results reveal a generally rather low fragility of plastic crystals. In some of the investigated materials evidence for Johari–Goldstein type β-relaxations is obtained. In addition, the question of the so-called excess wing of the α-relaxation peak is addressed in detail. In all cases, it is either absent or can be ascribed to a β-relaxation submerged under the α-peak. Overall, the present work provides a broad database on the dielectric behavior of plastic crystals, and may be taken as a review of the dynamic phenomena occurring in these materials, many of them being observed also in structural glass formers.
TL;DR: In this paper, the magnetocaloric properties of a variety of compounds, like Gd5(Si1−xGex)4 with x=0.576 and 0.5875, MnFeP1+xAsx with x between 0.25 and0.65, RTiGe with R=Tb, Dy, Ho, Er and Tm, Ni53Mn22Ga25, Mn5Si3, and Mn1.95Cr0.05Sb, were studied.
Abstract: We have studied the magnetocaloric properties of a variety of compounds, like Gd5(Si1−xGex)4 with x=0.576 and 0.5875, MnFeP1−xAsx with x between 0.25 and 0.65, RTiGe with R=Tb, Dy, Ho, Er and Tm, Ni53Mn22Ga25, Mn5Si3, and Mn1.95Cr0.05Sb. These compounds have in common that they exhibit either temperature- or field-induced first-order magnetic-phase transitions. Gd5(Si1−xGex)4 exhibits simultaneously a magnetic and a structural transition, which is accompanied by a huge magnetic-entropy change. A temperature-induced ferromagnetic (FM) to paramagnetic (PM) transition and a magnetic-field-induced PM to FM transition which are both of first order are observed in MnFeP1−xAsx compounds. Here the magnetic-phase transitions are not accompanied by structural transitions. Nevertheless, a large magnetic-entropy change, comparable with that in Gd5(Si1−xGex)4, is observed in the MnFeP1−xAsx compounds. In several of the RTiGe compounds, an applied magnetic field induces an antiferromagnetic (AF) to FM phase transition. Here, we observed a magnetic anisotropy dependence of the magnetic-entropy change. The Heusler alloy Ni53Mn22Ga25 exhibits a first-order martensitic transformation accompanied by a magnetic-phase transition around 220 K. The magnitude and the shape of the magnetic-entropy changes observed for this compound are quite different. Mn5Si3 compound exhibits two successive first-order magnetic-phase transitions and shows a different type of magnetocaloric effect (MCE). Mn1.95Cr0.05Sb exhibits an AF to FM phase transition and a negative MCE. The relationship between the magnetic-phase transitions and the MCE is discussed, based on the comparison of the observed MCEs and the exchange interactions in these materials.
TL;DR: In this article, phase relations in the natural pyrolitic mantle composition (KLB-1) around 670-km depth have been determined at 1600-2200°C by high-pressure experiments using multianvil apparatus.
Abstract: [1] Phase relations in the natural pyrolitic mantle composition (KLB-1) around 670-km depth have been determined at 1600–2200°C by high-pressure experiments using multianvil apparatus. A phase transition between majorite garnet and Al-bearing Mg-rich perovskite occurs at depths similar to the postspinel phase transition. The seismic discontinuity observed at this depth could be caused by a combination of both transitions. The majorite-perovskite transition boundary has a positive Clausius-Clapeyron slope (+0.0013 GPa/°C for majorite-out curve), in contrast to the negative slope of the postspinel phase boundary (−0.0028 GPa/°C). Both transition boundaries cross each other at 1700–1800°C. Below this temperature, formation of Mg-perovskite starts at the majorite-perovskite or akimotoite-perovskite transition coexisting with ringwoodite but is predominantly formed by the postspinel phase transition at higher pressures. On the other hand, the stability of majorite significantly expands relative to Mg-perovskite at higher temperatures. Majorite becomes a dominant postspinel phase, and a majority of Mg-perovskite is formed by the majorite-perovskite transition with a positive Clapeyron slope. Phase transition within high-temperature plumes (>1800°C at 670-km depth) assists their upwelling from the lower mantle through the 670-km boundary. The depth of the 670-km seismic discontinuity becomes much less temperature-sensitive and is greater in such a higher temperature region.
TL;DR: An anomalous behavior of the magnetization, magnetic susceptibility and specific heat, when P(k) is fat tailed, or, loosely speaking, when the fourth moment of the distribution diverges in infinite networks is observed.
Abstract: We find the exact critical temperature T(c) of the nearest-neighbor ferromagnetic Ising model on an "equilibrium" random graph with an arbitrary degree distribution P(k). We observe an anomalous behavior of the magnetization, magnetic susceptibility and specific heat, when P(k) is fat tailed, or, loosely speaking, when the fourth moment of the distribution diverges in infinite networks. When the second moment becomes divergent, T(c) approaches infinity, the phase transition is of infinite order, and size effect is anomalously strong.
TL;DR: In this paper, the doping dependence of the order of the ferromagnetic metal to paramagnetic insulator phase transition in La1-xCaxMnO3 was investigated.
Abstract: We report on the doping dependence of the order of the ferromagnetic metal to paramagnetic insulator phase transition in La1-xCaxMnO3. At x=0.33, magnetization and specific heat data show a first order transition, with an entropy change (2.3 J/mol K) accounted for by both volume expansion and the discontinuity of M approximately 1.7mu(B) via the Clausius-Clapeyron equation. At x=0.4, the data show a continuous transition with tricritical point exponents alpha=0.48+/-0.06, beta=0.25+/-0.03, gamma=1.03+/-0.05, and delta=5.0+/-0.8. This tricritical point separates first- (x 0.4) transitions.
TL;DR: In this article, a detailed analysis of the production of gravitational waves during an electroweak phase transition in different supersymmetric models where, contrary to the case of the Standard Model, the transition can be first order is presented.
TL;DR: The observation of magnetic superstructure in a magnetization plateau state of SrCu2(BO3)2, a frustrated quasi–two-dimensional quantum spin system, and the crystallization of itinerant triplets in the plateau phase within a large rhomboid unit cell shows oscillations of the spin polarization.
Abstract: We report the observation of magnetic superstructure in a magnetization plateau state of SrCu2(BO3)2, a frustrated quasi–two-dimensional quantum spin system. The Cu and B nuclear magnetic resonance (NMR) spectra at 35 millikelvin indicate an apparently discontinuous phase transition from uniform magnetization to a modulated superstructure near 27 tesla, above which a magnetization plateau at 1/8 of the full saturation has been observed. Comparison of the Cu NMR spectrum and the theoretical analysis of a Heisenberg spin model demonstrates the crystallization of itinerant triplets in the plateau phase within a large rhomboid unit cell (16 spins per layer) showing oscillations of the spin polarization. Thus, we are now in possession of an interesting model system to study a localization transition of strongly interacting quantum particles.
TL;DR: It is reported that, for a material in the pseudogap state, left-circularly polarized photons give a different photocurrent from right- Circularly polarization photons, which shows that time-reversal symmetry is spontaneously broken below T*, which therefore corresponds to a phase transition.
Abstract: A change in ‘symmetry’ is often observed when matter undergoes a phase transition—the symmetry is said to be spontaneously broken. The transition made by underdoped high-transition-temperature (high-Tc) superconductors is unusual, in that it is not a mean-field transition as seen in other superconductors. Rather, there is a region in the phase diagram above the superconducting transition temperature Tc (where phase coherence and superconductivity begin) but below a characteristic temperature T* where a ‘pseudogap’ appears in the spectrum of electronic excitations1,2. It is therefore important to establish if T* is just a cross-over temperature arising from fluctuations in the order parameter that will establish superconductivity at Tc (refs 3, 4), or if it marks a phase transition where symmetry is spontaneously broken5,6,7,8,9,10. Here we report that, for a material in the pseudogap state, left-circularly polarized photons give a different photocurrent from right-circularly polarized photons. This shows that time-reversal symmetry is spontaneously broken11 below T*, which therefore corresponds to a phase transition.
TL;DR: The superconducting phase transition in heavy fermion CeCoIn5 becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c).
Abstract: The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K in zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c). The change from second order at lower fields is reflected in strong sharpening of both specific heat and thermal expansion anomalies associated with the phase transition, a strong magnetocaloric effect, and a steplike change in the sample volume. This effect is due to Pauli limiting in a type-II superconductor, and was predicted theoretically in the mid-1960s.