Emergence of classical structures from the quantum vacuum
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
SEARCH · Engineering Papers
Results for “Quantum 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.
Terahertz-Driven Local Dipolar Correlation in a Quantum Paraelectric
Light-induced ferroelectricity in quantum paraelectrics is a new avenue of achieving dynamic stabilization of hidden orders in quantum materials. In this Letter, we explore the possibility of driving a transient ferroelectric phase in the quantum paraelectric KTaO 3 via intense terahertz excitation of the soft mode. We observe a long-lived relaxation in the terahertz-driven second harmonic generation (SHG) signal that lasts up to 20 ps at 10 K, which may be attributed to light-induced ferroelectricity. Through analyzing the terahertz-induced coherent soft-mode oscillation and finding its hardening with fluence well described by a single-well potential, we demonstrate that intense terahertz pulses up to 500 kV=cm cannot drive a global ferroelectric phase in KTaO 3 . Instead, we find the unusual long-lived relaxation of the SHG signal comes from a terahertz-driven moderate dipolar correlation between the defect-induced local polar structures. We discuss the impact of our findings on current investigations of the terahertz-induced ferroelectric phase in quantum paraelectrics.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Diffeomorphism-invariant lattice actions
We present a lattice-discretization procedure which is based on the simplicial lattice preserves diffeomorphism invariance. The presented procedure is the straightforward generalization for the procedure used for discretization of the spinor gravity [7]. As a stable way to guarantee the removing of the lattice regularization, i.e. the continuum limit, for lattice diffeomorphism invariant theories, we propose to tune the system to point of the phase transition. We expect that the Einstein gravitation is achieved at this point.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation
In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Phase diagrams of orientational transitions in absorbing nematic liquid crystals
A theory of orientational transitions in nematic liquid crystals (NLCs), which employs the expansion of optical torques acting on the NLC director with respect to the rotation angle, has been developed for NLCs with additives of conformationally active compounds under the action of optical and low-frequency electric and magnetic fields. Phase diagrams of NLCs are constructed as a function of the intensity and polarization of the light field, the strength of low-frequency electric field, and a parameter that characterizes the feedback between the rotation of the NLC director and optical torque. Conditions for the occurrence of first- and second-order transitions are determined. The proposed theory agrees with available experimental data.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Krylov complexity in mixed phase space
We investigate the Krylov complexity of thermofield double states in systems with mixed phase space, uncovering a direct correlation with the Brody distribution, which interpolates between Poisson and Wigner statistics. Our analysis spans two-dimensional random matrix models featuring (I) GOE-Poisson and (II) GUE-Poisson transitions and extends to higher-dimensional cases, including a stringy matrix model (GOE-Poisson) and the mass-deformed SYK model (GUE-Poisson). Krylov complexity consistently emerges as a reliable marker of quantum chaos, displaying a characteristic peak in the chaotic regime that gradually diminishes as the Brody parameter approaches zero, signaling a shift toward integrability. These results establish Krylov complexity as a powerful diagnostic of quantum chaos and highlight its interplay with eigenvalue statistics in mixed phase systems.
chaos & nonlinear dynamics↗
Photoinduced Melting of V 4 O 7 Correlated State
The compound V 4 O 7 is one of the Magnéli phase (V n O 2n - 1 , n = 3, 4, …, 9) correlated vanadium oxides with distinct intriguing electronic and structural properties. The possibility to manipulate the phase state of V 4 O 7 on an ultrafast time scale by light makes this material promising for potential applications in photonics, optoelectronics, quantum, and neuromorphic circuit design. In this work, the ultrafast spectroscopy of V 4 O 7 reveals the second-order nature of the photoinduced insulator-to-metal transition, emphasizing electronic and lattice contributions. The findings reveal the influence of the laser excitation level and temperature on these dynamics, providing a comprehensive understanding of V 4 O 7 structural changes and response to external stimuli. The phenomenological model based on the Landau–Ginzburg formalism provides a robust framework for explaining the photoinduced transition dynamics, showing a detailed picture of the light interaction with the electronic and lattice subsystems. This integrated approach significantly enhances the understanding of V 4 O 7 complex behavior upon photoexcitation, opening new possibilities for developing new optoelectronic devices and noninvasive optical control of the phase transition pathways in vanadates.
36 MATERIALS SCIENCE↗
Y-doped La{sub 0.7}Ca{sub 0.3}MnO{sub 3} manganites exhibiting a large magnetocaloric effect and the crossover of first-order and second-order phase transitions
We prepared orthorhombic La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} samples (x = 0, 0.04, 0.06, and 0.08) by conventional solid-state reaction and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field measurements, M(T, H). The experimental results revealed that an x increase in La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} reduced the ferromagnetic-paramagnetic transition temperature (T{sub C}) from 260 K (for x = 0) to ∼126 K (for x = 0.08). Around the T{sub C}, maximum magnetic-entropy changes for a magnetic-field variation interval H = 50 kOe are about 10.7, 8.5, 7.4, and 5.8 J·kg{sup −1}·K{sup −1} for x = 0, 0.04, 0.06, and 0.08, respectively, corresponding to refrigerant capacities RC = 250–280 J·kg{sup −1}. These values are comparable to those of some conventional MC materials, revealing the applicability of La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} in magnetic refrigeration. Using the Arrott method and scaling hypothesis as analyzing high-field M(H, T) data, and the universal-curve construction of the magnetic entropy change, we found a magnetic-phase separation. While the samples x = 0−0.06 exhibit a first-order magnetic phase transition, x = 0.08 exhibits the crossover of the first-to-second-order phase transformation (with its critical-exponent values close to those expected for the tricritical mean-field theory) and has the presence of ferromagnetic clusters even above the T{sub C}. Such the variations in the magnetism and MC effect are related to the changes in structural parameters caused by the Y substitution for La because Y doping does not change the concentration ratio of Mn{sup 3+}/Mn{sup 4+}.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Excitons in coupled type-II double quantum wells under electric and magnetic fields: InAs/AlSb/GaSb
We calculate the wave functions and the energy levels of an exciton in double quantum wells under electric (F) and magnetic (B) fields along the growth axis. The result is employed to study the energy levels, the binding energy, and the boundary on the F–B plane of the phase between the indirect exciton ground state and the semiconductor ground state for several typical structures of the type-II quasi-two-dimensional quantum wells such as InAs/AlSb/GaSb. The inter-well inter-band radiative transition rates are calculated for exciton creation and recombination. We find that the rates are modulated over several orders of magnitude by the electric and magnetic fields.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Harnessing interpretable and unsupervised machine learning to address big data from modern X-ray diffraction
The information content of crystalline materials becomes astronomical when collective electronic behavior and their fluctuations are taken into account. In the past decade, improvements in source brightness and detector technology at modern X-ray facilities have allowed a dramatically increased fraction of this information to be captured. Now, the primary challenge is to understand and discover scientific principles from big datasets when a comprehensive analysis is beyond human reach. We report the development of an unsupervised machine learning approach, X-ray diffraction (XRD) temperature clustering (X-TEC), that can automatically extract charge density wave order parameters and detect intraunit cell ordering and its fluctuations from a series of high-volume X-ray diffraction measurements taken at multiple temperatures. We benchmark X-TEC with diffraction data on a quasi-skutterudite family of materials, (Ca x Sr 1–x ) 3 Rh 4 Sn 13 , where a quantum critical point is observed as a function of Ca concentration. We apply X-TEC to XRD data on the pyrochlore metal, Cd 2 Re 2 O 7 , to investigate its two much-debated structural phase transitions and uncover the Goldstone mode accompanying them. We demonstrate how unprecedented atomic-scale knowledge can be gained when human researchers connect the X-TEC results to physical principles. Specifically, we extract from the X-TEC–revealed selection rules that the Cd and Re displacements are approximately equal in amplitude but out of phase. This discovery reveals a previously unknown involvement of 5d 2 Re, supporting the idea of an electronic origin to the structural order. Our approach can radically transform XRD experiments by allowing in operando data analysis and enabling researchers to refine experiments by discovering interesting regions of phase space on the fly.
36 MATERIALS SCIENCE↗
Anyon superconductivity from topological criticality in a Hofstadter–Hubbard model
We argue that the combination of strong repulsive interactions and high magnetic fields can generate electron pairing and superconductivity. Inspired by the large lattice constants of moiré materials, which make large flux per unit cell accessible at laboratory fields, we study the triangular lattice Hofstadter-Hubbard model at one-quarter flux quantum per plaquette, where previous literature has argued that a chiral spin liquid separates a weak-coupling integer quantum Hall phase and a strong-coupling topologically trivial antiferromagnetic insulator at a density of one electron per site. We argue that topological superconductivity emerges upon doping in the vicinity of the integer quantum Hall to chiral spin liquid transition. We employ exact diagonalization and density matrix renormalization group methods to examine this theoretical scenario and find that electronic pairing indeed occurs on both sides of criticality over a remarkably broad range of interaction strengths. On the chiral spin liquid side, our results provide a concrete model realization of the long-hypothesized mechanism of anyon superconductivity. Our study thus establishes a beyond-Bardeen-Cooper-Schrieffer route to electron pairing in a well-controlled limit, relying crucially on the interplay between electron correlations and band topology.
Hubbard model↗
Delocalization Transition of a Disordered Axion Insulator
The axion insulator is a higher-order topological insulator protected by inversion symmetry. We show that, under quenched disorder respecting inversion symmetry on average, the topology of the axion insulator stays robust, and an intermediate metallic phase in which states are delocalized is unavoidable at the transition from an axion insulator to a trivial insulator. We derive this conclusion from general arguments, from classical percolation theory, and from the numerical study of a 3D quantum network model simulating a disordered axion insulator through a layer construction. We find the localization length critical exponent near the delocalization transition to be ν = 1.42 ± 0.12. We further show that this delocalization transition is stable even to weak breaking of the average inversion symmetry, up to a critical strength. Finally, we also quantitatively map our quantum network model to an effective Hamiltonian and we find its low-energy k ∙ p expansion.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Exciton condensation in quantum Hall bilayers at total filling ν T = 5
We introduce the coupled quantum Hall bilayers each at half-filled first excited Landau levels with varying the layer distance. Based on numerical exact diagonalization on torus, we identify two distinct phases separated by a critical layer distance dc. From dc to infinite layer distance, the topological phase is smoothly connected to a direct tensor product of two Moore-Read states, while the interlayer coherence emerges at d < dc characterizedby the xy easy-plane ferromagnetic energy spectra, gapless pseudospin excitations and the finite exciton super-fluid stiffness, corresponding to the exciton superfluid state. More interestingly, the results of the ground state fidelity, the evolution of energy spectra, and the superfluid stiffness indicate a possible continuous transition.Theoretically it can be interpreted as a topological phase transition which simultaneously changes the topology of ground state and breaks symmetry, providing a fascinating example of transitions beyond Landau paradigm.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A multiscale coupled finite-element and phase-field framework to modeling stressed grain growth in polycrystalline thin films
A previously-developed finite-deformation- and crystal-elasticity-based constitutive theory for stressed grain growth in cubic polycrystalline bodies has been augmented to include a description of excess surface energy and grain-growth stagnation mechanisms through the use of surface effect state variables in a thermodynamically-consistent manner. The constitutive theory was also implemented into a multiscale coupled finite-element and phase-field computational framework. With the material parameters in the constitutive theory suitably calibrated, our three-dimensional numerical simulations show that the constitutive model is able to accurately predict the experimentally-determined evolution of crystallographic texture and grain size statistics in polycrystalline copper thin films deposited on polyimide substrate and annealed at high-homologous temperatures. In particular, our numerical analyses show that the broad texture transition observed in the annealing experiments of polycrystalline thin films is caused by grain growth stagnation mechanisms. - Graphical abstract: - Highlights: • Developing a theory for stressed grain growth in polycrystalline thin films. • Implementation into a multiscale coupled finite-element and phase-field framework. • Quantitative reproduction of the experimental grain growth data by simulations. • Revealing the cause of texture transition to be due to the stagnation mechanisms.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
High mobility organic field-effect transistor based on water-soluble deoxyribonucleic acid via spray coating
High mobility organic field-effect transistors (OFETs) by inserting water-soluble deoxyribonucleic acid (DNA) buffer layer between electrodes and pentacene film through spray coating process were fabricated. Compared with the OFETs incorporated with DNA in the conventional organic solvents of ethanol and methanol: water mixture, the water-soluble DNA based OFET exhibited an over four folds enhancement of field-effect mobility from 0.035 to 0.153 cm{sup 2}/Vs. By characterizing the surface morphology and the crystalline structure of pentacene active layer through atomic force microscope and X-ray diffraction, it was found that the adoption of water solvent in DNA solution, which played a key role in enhancing the field-effect mobility, was ascribed to both the elimination of the irreversible organic solvent-induced bulk-like phase transition of pentacene film and the diminution of a majority of charge trapping at interfaces in OFETs.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Practical uncertainty reduction and quantification in shock physics measurements
We report the development of a simple error analysis sampling method for identifying intersections and inflection points to reduce total uncertainty in experimental data. This technique was used to reduce uncertainties in sound speed measurements by 80% over conventional methods. Here, we focused on its impact on a previously published set of Mo sound speed data and possible implications for phase transition and geophysical studies. However, this technique's application can be extended to a wide range of experimental data.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Temperature dependence of equilibrium separation and lattice parameters of nematic boojum-colloids
We report experimental studies on the temperature dependence of equilibrium separation of a pair of nematic boojum colloids. The interparticle separation is linearly proportional to the elastic anisotropy and the orientation angle with respect to the rubbing direction. The latter result is in agreement with the recent prediction of computer simulations. We prepared two-dimensional colloidal crystals assisted by a laser tweezer and measured the temperature dependence of the lattice parameters. We observe a structural transition in boojum colloidal crystal across the N-SmA transition. The structural transition is mediated by the transformation of boojum defects into focal conic lines across the phase transition. The hexagonal close pack structure of the colloidal crystal in the SmA phase could be useful for designing photonic crystal.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Optical pump-terahertz probe analysis of long-lived d-electrons and relaxation to self-trapped exciton states in MnO
The dynamics of photoexcited electrons in various excited d-states was investigated in a transition metal oxide MnO by tunable optical pump-terahertz probe measurements. Photoexcited electrons in the lowest excited d-state showed the longest relaxation time among the three excited d-states that are accessible in MnO at room temperature. The relaxation rate in the lowest excited d-state showed a drastic increase below the Neel temperature T{sub N} = 120 K in MnO. We conclude that this increase is caused by the appearance of a decay channel related to magnetic-excitation-assisted photoluminescence from self-trapped exciton (STE) states. The opening of relaxation channels to the STE states in an antiferromagnetic phase suggests that it may be possible to control photocarrier lifetime by magnetic order in transition metal oxides.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗