Condensation Energy Research Articles

A system for probing Casimir energy corrections to the condensation energy

In this article, we present a nanoelectromechanical system (NEMS) designed to detect changes in the Casimir energy. The Casimir effect is a result of the appearance of quantum fluctuations in an electromagnetic vacuum. Previous experiments have used nano- or microscale parallel plate capacitors to detect the Casimir force by measuring the small attractive force these fluctuations exert between the two surfaces. In this new set of experiments, we aim to directly detect the shifts in the Casimir energy in a vacuum due to the presence of the metallic parallel plates, one of which is a superconductor. A change in the Casimir energy of this configuration is predicted to shift the superconducting transition temperature (Tc) because of the interaction between it and the superconducting condensation energy. In our experiment, we take a superconducting film, carefully measure its transition temperature, bring a conducting plate close to the film, create a Casimir cavity, and then measure the transition temperature again. The expected shifts are smaller than the normal shifts one sees in cycling superconducting films to cryogenic temperatures, so using a NEMS resonator in situ is the only practical way to obtain accurate, reproducible data. Using a thin Pb film and opposing Au surface, we observe no shift in Tc >12 µK down to a minimum spacing of ~70 nm at zero applied magnetic field.

Cleaner production of freshwater using multi-effect tubular solar still

Tubular solar still is a promising technique for freshwater cleaner production. However, the main reason lowering its productivity is the heat lost from the tube surface to the surrounding atmosphere during the condensation process. The present study introduces a techno-economical feasibility study and evaluation of using multi-effect tubular solar still to introduce a clear vision for stakeholders in the desalination market in Saudi Arabia. The heat lost by the first-effect is utilized in the second-effect to evaporate more saline water which then condensates on the inner surface of the outer tube of the second-effect and so on. Minimum condensation energy is subjected to the last effect causing considerable lower heat loss to the surrounding. Major findings of the present study showed a great opportunity for the enhancement of the double and triple-effect active tubular solar still performance more than that of the higher effects. The proposed device is expected to increase the freshwater productivity by 60.5%, 97.8% and 122.4% for double, triple and quadruple-effect TSS, respectively. The optimum number of effects is the double and the triple-effect due to having the lower cost ($0.007) of water production per liter.

Condensation Energy in a Superconductor for All Temperatures

An exact analytical expression for the condensation energy $$E_{\text{cond}} \left( T \right)$$ of a phonon-driven superconductor for all absolute temperatures $$T$$ and for any coupling strength is introduced so as to calculate the Helmholtz free energy difference $$F_{s} \left( T \right) - F_{n} \left( T \right)$$ between superconducting $$\left( s \right)$$ and normal $$\left( n \right)$$ states. This is achieved via a boson–fermion ternary gas theory—called the generalized Bose–Einstein condensation (GBEC) theory—which includes two-hole Cooper pairs, two-electron ones as well as single, free/unbound electrons. The GBEC formalism turns out to be quite useful in dealing with nonzero $$T$$ values of $$E_{\text{cond}} \left( T \right)$$ and reproduces several well-known experimental results. An expression for the condensation energy per atom is also calculated and applied to aluminum and niobium, and both results are compared with experimental data.

Polariton condensate trapping by parametric pair scattering

Spatially confined, trapped polariton condensates have been shown to exhibit strong stochastic on-site spin polarization and in longer polariton condensate chains, distance controlled ferromagnetic and antiferromagnetic spin couplings. Until now, little is known, on how such polariton condensates spatially separated from their exciton reservoirs are trapped and formed. Here, we investigate the properties and formation dynamics of two main families of polariton condensates, those overlapping with the pump reservoir and those in confined geometries, under pulsed nonresonant excitation. The observed reduction in polariton condensation threshold and energy blueshift in trapped case is attributed to exciton reservoir-condensate spatial separation, whereas time-resolved photoluminescence measurements, reveal distinct relaxation and condensate formation dynamics with pair parametric scattering process being the dominant relaxation mechanism in trapped geometry.

Estimation of Cooper pair density and its relation to the critical current density in Y(Ca)BCO high-Tc cuprate superconductors

Hole concentration (p) in the CuO2 plane largely controls all the electronic properties in the normal and superconducting states of high-Tc cuprates. The critical current density, Jc, is no exception. Previous hole content dependent studies have demonstrated the role of intrinsic depairing current density in determining the observed critical current density in copper oxide superconductors. The intrinsic pinning energy depends directly on the superconducting condensation energy which determines the magnitude of the depairing critical current density. Superconducting condensation energy is proportional to the Cooper pair density (superpair density) and depends strongly on the hole concentration within the CuO2 plane. We have calculated the Cooper pair density, ρs, of YBCO (Y123), a typical hole doped cuprate, as a function of p, in this study. A triangular pseudogap, pinned at the Fermi level, in the quasiparticle spectral density has been considered. The low-temperature zero-field critical current density of a number of high quality Y(Ca)BCO thin films over wide range of compositions and hole concentrations have been explored. The normalized values of the superpair density and the experimental critical current density exhibit a clear correspondence as the in-plane hole content is varied. This systematic behavior provides us with strong evidence that the critical current density of hole doped cuprates is primarily dependent on the superpair density, which in turn depends on the magnitude of the pseudogap energy. The agreement between the estimated p-dependent superpair density and the previously experimentally determined superfluid density of Y(Ca)BCO is quite good.

Application of BP Neural Network for Pre-Dehumidification Time Prediction of Capillary Ceiling Radiant Cooling Panel Air Conditioning System

Pre-dehumidifying the room is generally needed before the capillary ceiling radiant cooling panel (CCRCP) air condition system is turned on. Accurate pre- dehumidification time is critical for condensation prevention and energy usage. The pre- dehumidification time, which is related to multiple variables with complicated correlation relationship, is difficult to be calculated by conventional methods. Therefore, BP neural network is considered to be applied to predict the pre-dehumidification time. In this study, a dynamic model of CCRCP + displacement ventilation air conditioning system was built to simulate the pre-dehumidification process in TRANSYS. And then BP neural network was established, it takes the indoor and outdoor temperature and humidity conditions at 7:00 in every morning as the influencing factors and predict the optimal pre-dehumidification time for each day. The results show that the mean square error (MSE) of the BP neural network training process is 1.90958×10−4, the correlation coefficient R between the training data and the sample data reaches 0.99906, and the correlation coefficient R between the predicted data and the sample data reaches 0.99897. The BP neural network can reflect the intrinsic relationship between optimal pre-dehumidification time and input variables, and has high accuracy in predicting optimal pre-dehumidification time of CCRCP air conditioning system.

Nonlinear structure formation in Bound Dark Energy

We study nonlinear structure formation in the Bound Dark Energy model (BDE), where dark energy (DE) corresponds to a light scalar meson particle ϕ dynamically formed at a condensation energy scale Λc. The evolution of this dark-energy meson is determined by the potential V(ϕ)=Λc4+2/3ϕ−2/3, with a distinguishing phenomenology from other quintessence scenarios. Particularly, the expansion rate of the universe is affected not only at late times, but also when the condensation of ϕ occurs, which in linear theory leads to an enhancement (with respect to standard ΛCDM) of matter perturbations on small scales. We study how much of this signature is still present at late times as well as the properties of dark matter halos in the nonlinear regime through N-body simulations. Our results show that nonlinear corrections wash out this feature from the matter power spectrum even before DE becomes dominant. There is, however, a small but clear suppression of the BDE spectrum of 2% today on the largest scales due to the distinct late-time dynamics of DE. The differences on the clustering power between BDE and ΛCDM are reflected in the halo mass function, where small halos are more abundant in BDE as opposed to large heavy structures, whose formation is delayed because of the expansion history of the universe. This result is well captured by the semi-analytical Sheth-Tormen formula. However, despite these differences, the halo concentration parameter is essentially the same in both models, which suggest that clustering inside the halos decouple from the general expansion once the halos form.

Ab initio study of superconductivity and inhomogeneity in a Hg-based cuprate superconductor

Understanding physics of high-${T}_{c}$ cuprate superconductors remains one of the important problems in materials science. Though a number of diverse theories argue about the superconductivity and competing orders, ab initio and quantitative understanding is lacking. Here, we reproduce the experimental phase diagram of ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+y}$ by solving its ab initio low-energy effective Hamiltonian without adjustable parameters. It shows a superconducting phase in a wide range of hole density $\ensuremath{\delta}$, and its competition with charge period-4 plus spin period-8 stripe order near $\ensuremath{\delta}\ensuremath{\sim}0.1$, in agreement with experimental results including recent x-ray scattering. Then a crucial role of off-site interactions in stabilizing the superconductivity is elucidated with emphasis on charge fluctuations. It also clarifies the condensation energy mainly contributed from the on-site Coulomb interaction. The present achievement will enable deeper, predictable understanding on open issues of the high-${T}_{c}$ superconducting mechanism and promote ab initio studies on strongly correlated electrons beyond parametrized model studies.

Experimental Investigation on Airflow and Water Production in the Integrated Rooftop Solar Thermal System

Abstract Solar chimney is a passive renewable technology, adopted and followed widely for the application of room ventilation and power production. It requires a wide space for operation. Hence, an effective heat transfer mechanism is required within the available space to improve the performance. The solar chimney is integrated with a solar still using an external condenser to effectively utilize the energy released during the condensation of water vapor in the external condenser. The external condenser acts as an additional heat source besides the solar collector in the solar chimney. The experiments were conducted with the solar chimney of heights 1 m and 2 m, by considering the effects of an external condenser in both summer and winter. Heat transfer studies on the external condenser are also made to determine the effectiveness and the number of transfer units. The temperature and mass flow rate of vapor in the still are the influential parameters on the effectiveness of the external condenser. The condensation energy released from the external condenser increased the daily average air velocity by 14.9% and 22.4% in summer and winter, respectively. However, the overall solar chimney efficiency was improved by 37.1% in summer and 14.5% in winter for the integrated system with the chimney of height 2 m.

Pseudogap transition within the superconducting phase in the three-band Hubbard model

The onset of the pseudogap in high-$T_c$ superconducting cuprates (HTSC) is marked by the $T^*$ line in the doping-temperature phase diagram, which ends at a point $p^*$ at zero temperature within the superconducting dome. Although various theoretical and experimental studies indicate a competition between the pseudogap and superconductivity, there is no general consensus on the effects of the pseudogap within the superconducting phase. We use cluster dynamical mean field theory on a three-band Hubbard model for the HTSC to study the superconducting phase at $T=0$, obtained when doping the charge-transfer insulator, for several values of $U$. We observe a first-order transition within the superconducting phase, which separates the underdoped and overdoped solutions. The transition to the underdoped solution is marked by a discontinuous increase in the spectral gap, and on further underdoping the spectral gap increases while the superconducting order parameter decreases. We conclude that this is due to the onset of the pseudogap in the underdoped region, which contributes to the increasing spectral gap; this is further consistent with the appearance of a pole in the normal component of the self-energy, in the antinodal region, in the underdoped solution. This is accompanied by a change in the source of the condensation energy from potential energy, in the overdoped region, to kinetic energy in the underdoped region. Further, we also observe that the $d$-wave node vanishes smoothly within the superconducting phase at low values of hole doping, within the underdoped region. We see this as a manifestation of Mott physics operating at very low doping. Various aspects of the results and their implications are discussed.

Superconducting size effect in thin films under electric field: Mean-field self-consistent model

We consider effects of an externally applied electrostatic field on superconductivity, self-consistently within a BCS mean field model, for a clean 3D metal thin film. The electrostatic change in superconducting condensation energy scales as $\mu^{-1}$ close to subband edges as a function of the Fermi energy $\mu$, and follows 3D scaling $\mu^{-2}$ away from them. We discuss nonlinearities beyond gate effect, and contrast results to recent experiments.

Superconductivity at the Pressure-Induced Ferromagnetic Critical Region in UCoGe

The phase separation of the ferromagnetic (FM) and paramagnetic (PM) phases in the superconducting (SC) state of UCoGe at the FM critical region was investigated using $^{59}$Co nuclear quadrupole resonance (NQR) technique by taking advantage of its site-selective feature. The NQR measurements revealed that the first-order quantum phase transition occurs between the FM and the PM states. The nuclear spin-lattice relaxation rate $1/T_1$ exhibited a clear drop at the SC state in the PM phase, whereas it was not detected in the FM phase, which indicates that the superconductivity in the FM phase becomes weaker at the FM critical region due to the presence of the PM SC state. This result suggests that the SC condensation energy of the PM SC state is equal or larger than that of the FM SC state in this region. The pressure-temperature phase diagram of UCoGe was modified by taking the results from this study into account.

Revisiting Oxidation Scanning Probe Lithography of Graphene: Balance of Water Condensation Energy and Electrostatic Energy

We present a study on oxidation scanning probe lithography (o-SPL) of chemical vapor deposition grown graphene conducted under a pulsed voltage bias (Vbias) with millisecond rise time. It is found ...

Cooper pairing of incoherent electrons: An electron-phonon version of the Sachdev-Ye-Kitaev model

We introduce and solve a model of interacting electrons and phonons that is a natural generalization of the Sachdev-Ye-Kitaev-model and that becomes superconducting at low temperatures. In the normal state two Non-Fermi liquid fixed points with distinct universal exponents emerge. At weak coupling superconductivity prevents the onset of low-temperature quantum criticality, reminiscent of the behavior in several heavy-electron and iron-based materials. At strong coupling, pairing of highly incoherent fermions sets in deep in the Non-Fermi liquid regime, a behavior qualitatively similar to that in underdoped cuprate superconductors. The pairing of incoherent time-reversal partners is protected by a mechanism similar to Anderson's theorem for disordered superconductors. The superconducting ground state is characterized by coherent quasiparticle excitations and higher-order bound states thereof, revealing that it is no longer an ideal gas of Cooper pairs, but a strongly coupled pair fluid. The normal-state incoherency primarily acts to suppress the weight of the superconducting coherence peak and reduce the condensation energy. Based on this we expect strong superconducting fluctuations, in particular at strong coupling.

Molecular modeling and computational study of the chiral-dependent structures and properties of self-assembling diphenylalanine peptide nanotubes.

The structure and properties of diphenylalanine (FF) peptide nanotubes (PNT) based on phenylalanine were investigated by various molecular modeling methods. The main approach employed semi-empirical quantum-chemical methods (PM3 and AM1). Ab initio, density functional theory methods and molecular mechanical approaches were also used. Both model structures and structures extracted from experimental crystallographic databases obtained by X-ray methods were examined. A comparison of optimized model structures and structures obtained by natural self-assembly revealed important differences depending on chirality: D and L. In both the cases, the effect of chirality on the results of self-assembly of FF PNT was established: PNT based on the D-FF has large condensation energy E0 in the transverse direction, and form thicker and shorter PNT bundles than those based on L-FF. A topological difference was established: model PNT were optimized into structures consisting of rings, while naturally self-assembled PNT consisted of helical turns. The latter nanotubes differed from the original L-FF and D-FF and formed helix structures of different chirality signs in accordance with the alternation rule of chirality due to macromolecule hierarchy. A topological transition between ring and helix turn PNT structures is discussed: self-assembled natural helix structures are favorable and their energy is lower by a value of the order of one to several eV.

Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures

Recent theoretical and experimental work has demonstrated how the superconducting critical temperature ($T_c$) can be modified by rotating the magnetization of a single homogeneous ferromagnet proximity-coupled to the superconducting layer. This occurs when the superconductor and ferromagnet are separated by a thin heavy normal metal that provides an enhanced interfacial Rashba spin-orbit interaction. We consider the reciprocal effect: magnetization reorientation driven by the superconducting phase transition. We solve the tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and find that the relative angle between the spin-orbit field and the magnetization gives rise to a contribution in the free energy even in the normal state due to band-structure effects. For temperatures below $T_c$, superconductivity gives rise to a competing contribution. By lowering the temperature, in addition to reorientation of the favored magnetization direction from in-plane to out-of-plane, a $\pi/4$ in-plane rotation for thicker ferromagnetic layers is possible. Furthermore, computation of $T_c$ of the structure in the ballistic limit shows a dependence on the in-plane orientation of the magnetization, in contrast to our previous result on the diffusive limit. This finding is relevant with respect to thin-film heterostructures since these are likely to be in the ballistic regime of transport. Finally, we discuss the experimental feasibility of observing the magnetic anisotropy induced by the superconducting transition when other magnetic anisotropies, such as the shape anisotropy for a ferromagnetic film, are taken into account. Our work suggests that the superconducting condensation energy in principle can trigger a reorientation of the magnetization of a thin-film ferromagnet upon lowering the temperature below $T_c$, in particular for ferromagnets with weak magnetic anisotropies.

Chiral Peculiar Properties of Self-Organization of Diphenylalanine Peptide Nanotubes: Modeling Of Structure and Properties

The structure and properties of diphenylalanine peptide nanotubes based on phenylalanine were investigated by various molecular modeling methods. The main approaches were semi-empirical quantum-chemical methods (PM3 and AM1), and molecular mechanical ones. Both the model structures and the structures extracted from their experimental crystallographic databases obtained by X-ray methods were examined. A comparison of optimized model structures and structures obtained by naturally-occurring self-assembly showed their important differences depending on D- and L-chirality. In both the cases, the effect of chirality on the results of self-assembly of diphenylalanine peptide nanotubes was established: peptide nanotubes based on the D-diphenylalanine (D-FF) has high condensation energy E0 in transverse direction and forms thicker and shorter peptide nanotubes bundles, than that based on L-diphenylalanine (L-FF). A topological difference was established: model peptide nanotubes were optimized into structures consisting of rings, while naturally self-assembled peptide nanotubes consisted of helical coils. The latter were different for the original L-FF and D-FF. They formed helix structures in which the chirality sign changes as the level of the macromolecule hierarchy raises. Total energy of the optimal distances between two units are deeper for L-FF (–1.014 eV) then for D-FF (–0.607 eV) for ring models, while for helix coil are approximately the same and have for L-FF (–6.18 eV) and for D-FF (–6.22 eV) by PM3 method; for molecular mechanical methods energy changes are of the order of 2–3 eV for both the cases. A topological transition between a ring and a helix coil of peptide nanotube structures is discussed: self-assembled natural helix structures are more stable and favourable, they have lower energy in optimal configuration as compared with ring models by a value of the order of 1 eV for molecular mechanical methods and 5 eV for PM3 method.

Magnetic vortex lattices in finite isospin chiral perturbation theory

We study finite isospin chiral perturbation theory (χPT) in a uniform external magnetic field and find the condensation energy of magnetic vortex lattices using the method of successive approximations (originally used by Abrikosov) near the upper critical point beyond which the system is in the normal vacuum phase. The difference between standard Ginzburg–Landau (GL) theory (or equivalently the Abelian Higgs model) and χPT arises due to the presence of additional momentum-dependent (derivative) interactions in χPT and the presence of electromagnetically neutral pions that interact with the charged pions via strong interactions but do not couple directly to the external magnetic field. We find that while the vortex lattice structure is hexagonal similar to vortices in GL theory, the condensation energy (relative to the normal vacuum state in a uniform, external magnetic field) is smaller (larger in magnitude) due to the presence of derivative interactions. Furthermore, we establish that neutral pions do not condense in the vortex lattice near the upper critical field.

Magnetic vortices in the Abelian Higgs model with derivative interactions

We study the properties of a single magnetic vortex and magnetic vortex lattices in a generalization of the Abelian Higgs model containing the simplest derivative interaction that preserves the [Formula: see text] gauge symmetry of the original model. The paper is motivated by the study of finite isospin chiral perturbation theory in a uniform, external magnetic field: since pions are Goldstone bosons of QCD (due to chiral symmetry breaking by the QCD vacuum), they interact through momentum-dependent terms. We find the asymptotic properties of single vortex solutions and compare them to the well-known solutions of the standard Abelian Higgs model. Furthermore, we study the vortex lattice solutions near the upper critical field using the method of “successive approximations,” which was originally used by Abrikosov in his seminal paper on type-II superconductors. We find the vortex lattice structure, which remains hexagonal as in the standard Abelian Higgs model, and condensation energy of the vortex lattices relative to the normal vacuum (in a uniform magnetic field).

Theoretical and Observational Constraints of Bound Dark Energy with Precision Cosmological Data.

We present a dark energy (DE) model as a natural extension of the standard model of particle physics where the lightest bound state, a scalar particle ϕ, corresponds to DE. The potential V=Λ_{c}^{4+2/3}ϕ^{-2/3} is dynamically formed at the condensation energy scale Λ_{c} and scale factor a_{c}. Our DE model has excellent agreement with current cosmological data improving the fit of baryon acoustic oscillation (BAO) measurements, specially designed to determine the dynamics of DE, from (χ^{2})_{BAO}^{ΛCDM}=7.115 in the standard cold dark matter model with a cosmological constant (ΛCDM) model to (χ^{2})_{BAO}^{BDE}=5.609, a difference of Δχ_{BAO}^{2}=1.5 and a likelihood ratio of 2.1. We obtain an exact constraint a_{c}Λ_{c}/eV=1.0939×10^{-4} and a theoretical prediction on Λ_{c}=34_{-11}^{+16} eV, consistent with the best fit Λ_{c}=44.08±0.27 eV, while in the standard ΛCDM there is no understanding of the value of the cosmological constant Λ. Remarkably, our model prediction on a_{c}Λ_{c} has a relative difference of only 0.2% with the best fit value if we allow a_{c} and Λ_{c} to vary independently. Unlike a cosmological constant Λ, our DE model predicts the amount of DE and leaves detectable cosmological imprints at different times and scales at a background and perturbation level.