Magnetization in superconducting films.
Magnetization in superconducting films as magnetic field function studied for influence of thickness and temperature on phase transition
Di Castro, C.↗
SEARCH · Engineering Papers
Results for “superconducting phase transition”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Study of high temperature oxide superconductors
Experimental studies are reported whose results indicate that proper processing procedures are critical to the formation of high-temperature copper oxide superconductors. Superconducting 123 films can be fabricated using the green 211 phase as a substrate. The transition temperature and transition width characteristics of these films are better than those obtained when other oxide compounds are used as substrates. A compact or single-crystal 211 phase will be desirable as a substrate for high-quality thin films. A new high T(c) copper oxide compound with nonrare earth elements was prepared using high-temperature processing. A YBa2Cu3O7-Ag composite with improved electrical conductivity was also prepared.
Wu, M. K.↗
Spectroscopic fingerprint of charge order melting driven by quantum fluctuations in a cuprate
Copper oxide high-T C superconductors possess a number of exotic orders that coexist with or are proximal to superconductivity. Quantum fluctuations associated with these orders may account for the unusual characteristics of the normal state, and possibly affect the superconductivity. Yet, spectroscopic evidence for such quantum fluctuations remains elusive. Here in this paper, we use resonant inelastic X-ray scattering to reveal spectroscopic evidence of fluctuations associated with a charge order in nearly optimally doped Bi 2 Sr 2 CaCu 2 O 8+δ . In the superconducting state, while the quasielastic charge order signal decreases with temperature, the interplay between charge order fluctuations and bond-stretching phonons in the form of a Fano-like interference increases, an observation that is incompatible with expectations for competing orders. Invoking general principles, we argue that this behaviour reflects the properties of a dissipative system near an order–disorder quantum critical point, where the dissipation varies with the opening of the pseudogap and superconducting gap at low temperatures, leading to the proliferation of quantum critical fluctuations, which melt charge order.
36 MATERIALS SCIENCE↗
Dynamical cluster approximation study of electron localization in the extended Hubbard model
We perform a detailed study of the phase transitions and mechanisms of electron localization in the extended Hubbard model using the dynamical cluster approximation on a 2×2 cluster. We explore the interplay of charge order and Mott physics. We find that a nearest-neighbor Coulomb interaction V causes “screening” effects close to the Mott phase transition, pushing the phase boundary to larger values of U. We also demonstrate the different effects of V on correlations in metallic and insulating regimes, and document the different correlation aspects of charge order and Mott states.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Possible quadrupole-order-driven commensurate-incommensurate phase transition in B20 CoGe
For this study, the B20-type cobalt germanide CoGe was investigated by measuring the specific heat, resistivity, and 59 Co nuclear magnetic resonance (NMR). We observed a phase transition at T Q = 13.7 K, evidenced by a very narrow peak of the specific heat and sharp changes of the nuclear spin-spin (T 2 –1 ) and spin-lattice ( T 1 – 1 ) relaxation rates. The fact that the entropy release is extremely small and the Knight shift is almost independent of temperature down to low temperatures as anticipated in a paramagnetic metal indicates that the T Q transition is of nonmagnetic origin. In addition, we detected a crossover scale T 0 ~ 30 K below which the resistivity and the NMR linewidth increase, and T 1 –1 is progressively distributed in space, that is, a static and dynamical spatial inhomogeneity develops. While the order parameter for the T Q transition remains an open question, a group-theoretical analysis suggests that the finite electric quadrupole density arising from the low local site symmetry at cobalt sites could drive the crystal symmetry lowering from the P2 1 3 symmetry that is commensurate to the R3 symmetry with an incommensurate wave vector, which fairly well accounts for the T Q transition. The quadrupole-order-driven commensurate-incommensurate phase transition may be another remarkable phenomenon arising from the structural chirality inherent in the noncentrosymmetric B20 family.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Anisotropic magnetocaloric effect and critical behavior in CrCl 3
We report anisotropic magnetocaloric effect and magnetic critical behavior in the van der Waals crystal CrCl 3 . The maximum magnetic entropy change $-ΔS^{max}_M ~ 14.6 J kg -1 K -1 and the relative cooling power RCP ~ 340.3 J kg -1 near T c with a magnetic field change of 5 T are much larger when compared to CrI 3 or CrBr 3 . The rescaled ΔS M (T, H) curves collapse onto a universal curve, confirming the second-order ferromagnetic transition. Finally, further critical behavior analysis around T c presents a set of critical exponents β = 0.28 (1) with T c = 19.4 (2) K, γ = 0.89 (1) with T c = 18.95 (8) K, and δ = 4.6 (1) at T c = 19 K , which are close to those of the theoretical tricritical mean-field model.
2-dimensional systems↗
Enhanced ferroelectric and piezoelectric properties of BCT-BZT at the morphotropic phase boundary driven by the coexistence of phases with different symmetries
The discovery of lead-free piezoelectric materials is crucial for future information and energy storage applications. Enhanced piezoelectric and other physical properties are commonly observed near the morphotropic phase boundary (MPB) composition of ferroelectric solid solutions. The (1 – x)Ba(Zr 0.2 Ti 0.8 )O 3 -x(Ba0.7Ca0.3)TiO 3 (BZT-xBCT) system exhibits a large electromechanical response around its MPB region at x = 0.5. Here, we report experimental and theoretical results of BZT-xBCT over a wide composition range (0.3 ≤ x ≤ 1.0). X-ray diffraction and Raman spectroscopy studies indicate a composition-induced structural phase transition from a rhombohedral (R3m) phase at x ≤ 0.4 to a tetragonal (P4mm) phase at x ≥ 0.6 through a multiphase coexistence region at 0.45 ≤ x ≤ 0.55 involving orthorhombic + tetragonal (Amm2 + P4mm) phases. First-principles calculations elucidate the phase competition in the coexistence region. The critical composition (x = 0.5) displays enhanced dielectric, ferroelectric, and piezoelectric properties, where notably d 33 ~ 320 pC/N. This paper provides clear evidence of Amm2+P4mm crystallographic phases in the MPB region, which is responsible for the improved functional properties.
MPB↗
First-order phase transition to a nonmagnetic ground state in nonsymmorphic NbCrP
Here, we report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with the P n m a space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ~30 % from that in the HT phase, suggesting that the phase transition is triggered by the electronic instability. The possible origin of the phase transition in NbCrP is discussed based on the electronic structure by comparing it with those in other nonsymmorphic compounds, RuP and RuAs.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Valence bond order in a honeycomb antiferromagnet coupled to quantum phonons
We use exact quantum Monte Carlo simulations to demonstrate that the Néel ground state of an antiferromagnetic SU(2) spin-1/2 Heisenberg model on the honeycomb lattice can be destroyed by a coupling to quantum phonons. Here, we find a clear first-order transition to a valence bond solid state with Kekulé order instead of a deconfined quantum critical point. However, quantum lattice fluctuations can drive the transition towards weakly first order, revealing a tunability of the transition by the retardation of the interaction. In contrast to the one-dimensional case, our phase diagram in the adiabatic regime is qualitatively different from the frustrated J 1 –J 2 model. Our results suggest that a coupling to bond phonons can induce Kekulé order in Dirac systems.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Pressure control of the spin reorientation transition in the rare-earth orthoferrite YbFeO 3
YbFeO 3 is exceptional among the rare-earth orthoferrites for having the lowest spin-reorientation transition (SRT) temperature, T SRT ≃8K, which makes it particularly appealing to examine the interplay between noncollinear magnetism of the Fe sublattice and quasi-one-dimensional XXZ effective S = 1/2 chains of Yb 3+ moments. Our paper focuses on the magnetic dynamics of YbFeO 3 using inelastic neutron scattering (INS), at temperatures below and above the SRT, under an applied hydrostatic pressure of 2 GPa, and in magnetic fields up to 4 T. The low-energy zero-field excitation spectrum at ambient pressure and temperatures below the SRT is dominated by a gapped magnon mode of the Yb subsystem at 0.84 meV with a dispersion only in the [00L] direction. Above T SRT , a continuum appears on top of the magnon mode because of temperature population of the magnon band, and the gap decreases to around 0.4 meV. The INS spectra in the magnetic field, both above and below T SRT , are characterized by two well-separated gapped modes. The SRT is clearly visible at low fields B < 1T, but it gradually disappears at higher magnetic fields. The hydrostatic pressure of p = 2GPa effectively reduces the transition width, ΔT SRT , and keeps the SRT at higher fields up to B≃3T. Here, we discuss the effect of the applied pressure in the frame of the modified mean-field theory and show that in the vicinity of the T SRT the pressure tunes the fourth-order anisotropy constant that effectively reduces the ΔT SRT .
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Magnetic field induced phase transition in spinel GeNi 2 O 4
Cubic spinel GeNi 2 O 4 exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions (T N1 ≈ 12.1 and T N2 ≈ 11.4 K) with the absence of any structural transition. We have performed detailed heat capacity and magnetic measurements in different crystallographic orientations. A new magnetic phase in presence of magnetic field (H ≥ 4 T) along the [111] direction is revealed, which is not observed when the magnetic field is applied along the [100] and [110] directions. High field neutron powder diffraction measurements confirm such a change in magnetic phase, which could be ascribed to a spin reorientation in the presence of magnetic field. In conclusion, a strong magnetic anisotropy and competing magnetic interactions play a crucial role on the complex magnetic behavior in this cubic system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Frustrated mixed-spin ladders: Evidence for a bond-order wave phase between rung-singlet and Haldane phases
In frustrated spin ladders, the interplay of frustration and correlations leads to the familiar Haldane (H) and rung-singlet (RS) phases. The nature of the transition between these two phases is still under debate. In this paper we tackle this issue using tools of quantum information theory. We consider frustrated mixed-spin-(1, 1/2) ladders with antiferromagnetic leg, rung and diagonal couplings, and calculate various quantities, such as the entanglement entropy (EE), the Schmidt gap, and the level degeneracy of the entanglement spectrum (ES). We use two numerical techniques, the infinite time-evolving block decimation (iTEBD) and the density matrix renormalization group (DMRG). We demonstrate that there exists an intermediate phase in which the ES levels do not exhibit the characteristic degeneracies of the H and RS phases. To understand the underlying physics in this phase, here we investigate short-range spin correlations along legs, rungs and diagonals and show that in this intermediate phase long-wavelength modulations occur, akin to bond-order waves.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Elementary excitations of a system of one-dimensional chiral fermions with short-range interactions
Here, we study general features of the excitation spectrum of a system of one-dimensional chiral spinless fermions with short-range interactions. We show that the nature of the elementary excitations of such a system depends strongly on the nonlinearity of the underlying dispersion of the fermions. In the case of quadratic nonlinearity, the low-momentum excitations are essentially fermionic quasiparticles and quasiholes, whereas the high-momentum ones are classical harmonic waves and solitons. In the case of cubic nonlinearity, the nature of the elementary excitations does not depend on momentum and is determined by the strength of the interactions. At a certain critical value of the interaction strength, the excitation spectrum changes qualitatively, pointing to a dynamic phase transition in the system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Nature of the ferromagnetic-antiferromagnetic transition in Y 1- x La x TiO 3
In this work, we explore the magnetically ordered ground state of the isovalently substituted Mott insulator Y 1- x La x TiO 3 for x≤ 0.3 via single-crystal growth, magnetometry, neutron diffraction, x-ray magnetic circular dichroism, muon spin rotation, and small-angle neutron scattering (SANS). We find that the decrease in the magnetic transition temperature on approaching the ferromagnetic-antiferromagnetic phase boundary at the La concentration xc ≈ 0.3 is accompanied by a strong suppression of both bulk and local ordered magnetic moments, along with a volume wise separation into magnetically ordered and paramagnetic regions. The thermal phase transition does not show conventional second-order behavior since neither a clear signature of dynamic critical behavior nor a power-law divergence of the magnetic correlation length is found for the studied substitution range; this finding becomes increasingly obvious with increasing La substitution. We find no evidence for a spin-glass phase. Finally, from SANS and magnetometry measurements, we discern a crossover from easy-axis to easy-plane magnetocrystalline anisotropy with increasing La substitution. These results indicate complex changes in magnetic structure upon approaching the phase boundary.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Itinerant ferromagnetism in van der Waals Fe 5 – x Ge Te 2 crystals above room temperature
Two-dimensional (2D) van der Waals (vdW) magnets have recently attracted increasing attention, as they provide a novel system for exploring 2D magnetism. However, intrinsic ferromagnetism in 2D systems has almost exclusively been observed at low temperatures, limiting their technological relevance. Fe N Ge Te 2 ( N = 3 , 4, and 5) systems are currently becoming the most attractive 2D vdW materials due to their relatively high Curie temperatures and large saturation magnetization. However, the nature of their complex yet intriguing magnetic behaviors is still unclear, in part due to the multiple inequivalent iron sites and iron vacancies. In this study, we show evolution of magnetic ordering transitions in Fe 5 – x Ge Te 2 with high Curie temperature and a strong saturation magnetization using photoemission electron microscopy and transport measurements. At 275 K, the ferromagnet transitions to a ferrimagnet, and below 110 K transitions to a state with glassy clusters. These are evidenced from temperature-dependent magnetic stripe domain evolution and anisotropic magnetoresistance measurements. Our findings show a clear magnetic ground state of Fe 5 – x Ge Te 2 at room temperature which signals that Fe 5 – x Ge Te 2 system is a very promising candidate for spintronic devices and provides a material design pathway to further increase the Curie temperature and saturation moments in vdW ferromagnets.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Synthesis of Mg2IrH5: A potential pathway to high-Tc hydride superconductivity at ambient pressure
Following long-standing predictions associated with hydrogen, high-temperature superconductivity has recently been observed in several hydride-based materials. Nevertheless, these high-Tc phases only exist at extremely high pressures, and achieving high transition temperatures at ambient pressure remains a major challenge. Recent predictions of the complex hydride Mg2IrH6 may help overcome this challenge with calculations of high-Tc superconductivity (65K
High-temperature superconductors↗
Magnetic and electronic phases of U 2 Rh 3 Si 5
We present a detailed study of the magnetic and electronic properties of U 2 Rh 3 Si 5 , a material that has been demonstrated to exhibit a first-order antiferromagnetic phase transition. From a high-magnetic-field study, together with extensive experiments in moderate fields, we establish the magnetic phase diagrams for all crystallographic directions. The possibility of an electronic phase in a narrow interval above the Néel temperature as a precursor of a magnetic phase is discussed.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Site-selective correlations in interacting flat-band quasicrystals
Model lattices such as the kagome and Lieb lattices have been widely investigated to elucidate the properties of interacting flat-band systems. While a quasicrystal does not have proper bands, the noninteracting density of states of several of them displays the typical signature of a flat band pinned at the Fermi level: a delta-function zero-energy peak. Here, we employ quantum Monte Carlo simulations to determine the effect of onsite repulsion on these quasicrystals. While global properties such as the antiferromagnetic structure factor and the specific heat behave similarly as in the case of periodic lattices undergoing a Mott transition, the behavior of the local density of states depends on the coordination number of the site. In particular, sites with the smallest coordination number, which give the dominant spectral-weight contribution to the zero-energy peak, are the ones most strongly impacted by the interaction. Besides establishing site-selective correlations in quasicrystals, our work also points to the importance of the real-space structure of flat bands in interacting systems.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗