Energy Of Conduction Electrons Research Articles

The influence of thermal cycling on the activation energy of conduction electrons and filament temperature in Pt/NiOx/Pt ReRAMs

We investigate the electrical and thermal conduction properties of low- (ON) and high-resistance (OFF) states in Pt/NiOx/Pt based unipolar ReRAM devices during cooling and warming cycles between 300 and 180 K. The conduction electron-trap activation energy was found to decrease upon warming. Although thermal cycling did not significantly affect the average resistance-temperature coefficient of the Pt diffused conductive filaments in the system, the ON-state resistance fluctuations increase at high temperatures, indicating that ambient temperature significantly affects the sizes of the formed filaments. The mechanism behind these thermally activated changes is discussed.

A review of the Kondo insulator materials class of strongly correlated electron systems: Selected systems and anomalous behavior

Studies of strongly correlated electron systems have been at the forefront of research in condensed matter physics ever since the discovery of the co-existence of strong Pauli-paramagnetism and superconductivity in the archetypal heavy-fermion compound CeCu2Si2 in 1979. The construct of correlated electron physics typifies the behavior of thermal and electronic properties of a material when the Coulomb interaction between conduction electrons exceeds the electron kinetic energy at a given thermal energy and redefines in remarkable ways our understanding of the behavior of a metal near its ground state. While correlated electron behavior has by now been demonstrated in a variety of different types of materials, Kondo systems in particular are arguably the most intensively studied among these. The Kondo interaction is used to describe the effect that a spin-magnetic ion has on its environment when immersed in the conduction electron sea of a metal. The localized spin of the Kondo ion polarizes nearby conduction electrons to form a so-called Kondo cloud, which acts to screen and magnetically (partially) neutralize the localized spin. In Kondo systems, the low-temperature behavior is prone to the formation of heavy fermions, which is the term given to quasiparticle excitations that define the emergence of effective electron masses that can be up to three orders of magnitude greater than that of a free electron. The Kondo effect presents itself in three guises: first, the single-ion Kondo state which is found in a metal having only a small amount of magnetic ions dissolved into it; second, the incoherent Kondo state in materials where there is a Kondo ion in every crystallographic unit cell of the material, but the Kondo ions remain incoherent or uncoupled from each other; and third, the coherent Kondo lattice state which manifests itself toward low temperatures where the interaction between Kondo ions becomes comparable to the thermal energy of conduction electrons that mediate magnetic exchange between Kondo ions. In a small number of cases, the outcome of a material condensing into the Kondo state turns out to be the peculiar formation of a very narrow energy band gap at the metallic Fermi energy. Such a band gap has significant consequences in practically all of the physical properties of a material that stem from the behavior of conduction electrons in proximity of the Fermi energy. This is most readily seen in electrical resistivity, heat capacity, and magnetic susceptibility. The band gapping gives cause to the term Kondo insulator (also referred to as Kondo semimetal or heavy-fermion semiconductor) that is used to describe this exceptional variety of Kondo systems. The term Kondo insulator is in general use although most Kondo insulators have a small but finite electrical conduction in the low-temperature limit where Kondo screening may be accomplished to its full extent. While the Kondo lattice ground state is exemplified by a very high density of electronic states at the Fermi energy, Kondo insulators, on the other hand, have, by virtue of narrow band gapping, a low density of electronic states. It remains a counter-intuitive observation, therefore, that despite their low density of states, Kondo insulators have curiously strong spin polarization energy scales and accompanying high values of their Kondo temperature, being the defining quantity which acts as an organizing principle in their temperature-dependent physical properties. In this article, we review the fundamentals of the Kondo insulating state, and we discuss the theoretical principles of what is presently understood about the formation of a Kondo insulator. The experimental results of a selected number of examples that have gained prominence in this class of materials are compared to each other in order to seek out similarities that may help deepen our understanding of the Kondo insulating state.

Microstructure and Conduction Electron Quantum Properties of Small Diamond Cubic α-Sn Nanocrystals Embedded in Cubic Boron Nitride Crystals.

The morphology, structure, composition, and conduction electron properties of quasi-spherical tin nanocrystals (NCs) of 2.5 nm average diameter, with unstrained, bulk-like α-Sn diamond cubic structure, observed in dark cubic boron nitride (cBN) crystallites, were determined by correlated analytical high-resolution scanning transmission electron microscopy and multifrequency electron spin resonance (ESR) investigations. The narrow Lorentzian ESR line with g = 2.0028 is attributed to the conduction ESR of the α-Sn NCs, consistent with the temperature- and frequency-independent small g-shift and intensity reduction under high temperature (950 °C) vacuum annealing when the α-Sn NCs are thermally dissolved in the host cBN crystallites. The ESR linewidth and line intensity vs temperature dependences recorded in the 20 to 295 K range are quantitatively described considering the presence of discrete, quantum confinement-induced conduction electron energy levels with ΔQC/k B = 125 K separation, close to the theoretical value for conductive α-Sn NCs of 2.5 nm in diameter. The observed properties are tentatively explained with the predicted nanosize induced band-gap opening and change of band ordering from bulk α-Sn to small unstrained α-Sn NCs, resulting in a topological phase transition that also explains the predominantly s-like character of the conduction band electron orbitals.

Long-Range Order in the Dislocation Structure of Martensite Crystals

Optimal estimation of the diffraction observations over the object reliably detects periodicity in the dislocation structure of martensitic transformation as an exhibition of its wave nature. The period along normal to the slip planes is comparable with the radius of dislocation loops in crystals. The measured degree of one-dimensional long-range order in the arrangement of the loops is close to the upper limit equal to unity. Subject to the theory of metals, the observed structure could be generated by quantum lattice vibrations, which actuate a jump-like phase transition. A simple explanation exists: after a sharp fall in temperature, the excess energy of conduction electrons causes the crystal to expand instantly with the transformation of translational symmetry. Internal shifts of the crystal lattice caused by electron-phonon interactions concurrently trigger the wave process of formation of thin martensitic plates in the surrounding matrix, which are observed in metallography. Based on an in-depth analysis of the dislocation structure of martensite crystals, a physically founded concept is advanced in which the martensitic transformation is a macroscopic quantum phenomenon connected with the symmetry properties of a crystal system in metals.

The Thermopower and Electron Mobility in Monophase Monocrystalline SmS in a Wide Temperature Range

Abstract—The results of thermopower studies in the temperature range 50 < T < 325 K of two SmS single crystals are presented. One of them contained a high-pressure (“gold”) phase on the surface and another one was without this phase, which was removed by etching in HCl solution. The features in the temperature dependence of the thermopower of the etched SmS sample were observed, that correlate with the features in the temperature dependence of the local activation energy of conduction electrons. The calculation of the Hall mobility of conduction electrons was carried out and it was shown that it varies slightly in the temperature range 60–300 K due to the presence of two dominant types of electron scattering in SmS—on acoustic phonons and on charged defects.

Direct observation of a Γ−X energy spectrum transition in narrow AlAs quantum wells

Spectra of magnetoplasma excitations have been investigated in a two-dimensional electron systems in AlAs quantum wells (QWs) of different widths. The magnetoplasma spectrum have been found to change profoundly when the quantum well width became thinner than $5.5$~nm, indicating a drastic change in the conduction electron energy spectrum. The transformation can be interpreted in terms of transition from the in-plane strongly anisotropic $X_x - X_y$ valley occupation to the out-of-plane isotropic $X_z$ valley in the QW plane. Strong enhancement of the cyclotron effective mass over the band value in narrow AlAs QWs is reported.

Comparison of equilibrium ohmic and nonequilibrium swarm models for monitoring conduction electron evolution in high‐altitude EMP calculations

AbstractAtmospheric electromagnetic pulse (EMP) events are important physical phenomena that occur through both man‐made and natural processes. Radiation‐induced currents and voltages in EMP can couple with electrical systems, such as those found in satellites, and cause significant damage. Due to the disruptive nature of EMP, it is important to accurately predict EMP evolution and propagation with computational models. CHAP‐LA (Compton High Altitude Pulse‐Los Alamos) is a state‐of‐the‐art EMP code that solves Maxwell s equations for gamma source‐induced electromagnetic fields in the atmosphere. In EMP, low‐energy, conduction electrons constitute a conduction current that limits the EMP by opposing the Compton current. CHAP‐LA calculates the conduction current using an equilibrium ohmic model. The equilibrium model works well at low altitudes, where the electron energy equilibration time is short compared to the rise time or duration of the EMP. At high altitudes, the equilibration time increases beyond the EMP rise time and the predicted equilibrium ionization rate becomes very large. The ohmic model predicts an unphysically large production of conduction electrons which prematurely and abruptly shorts the EMP in the simulation code. An electron swarm model, which implicitly accounts for the time evolution of the conduction electron energy distribution, can be used to overcome the limitations exhibited by the equilibrium ohmic model. We have developed and validated an electron swarm model previously in Pusateri et al. (2015). Here we demonstrate EMP damping behavior caused by the ohmic model at high altitudes and show improvements on high‐altitude, upward EMP modeling obtained by integrating a swarm model into CHAP‐LA.

Study of electrical resistivity of semiconductor SmS in the absence of a metallic phase on the surface

The temperature dependences of the electrical resistivity of samarium monosulfide single-crystal samples subjected to chemical treatment to remove a metallic phase from their surfaces have been measured in the range of 1.5–400 K at atmospheric pressure and at a pressure of 0.3 GPa. The temperature dependences of the activation energy of conduction electrons at these pressures and the piezoresistance coefficient of uniform compression have been calculated. It has been shown that the known model of the structure of the impurity-level spectrum in SmS remains partially valid at temperatures higher than 15 K. At lower temperatures, the existence of shallow donor centers in SmS and the hopping conduction over them should be taken into account.

Manifestation of size quantization on protrusions of a rough A3B5 semiconductor surface

Field-electron emission from submicron protrusions of a rough surface of A3B5 semiconductors, including InSb, InAs, and GaAs, has been experimentally investigated. It is shown that the observed peaks in differential tunnel I–V characteristics of the InSb and InAs semiconductor samples can be interpreted as a manifestation of the size quantization of the conduction electron energy spectrum. In GaAs, manifestation of the size quantization in differential tunnel I–V characteristics was not experimentally found. Using the experimental data, the characteristic size of a quantum object formed on protrusions of the rough InSb and InAs surface is determined.

Role of direct electron-phonon coupling across metal-semiconductor interfaces in thermal transport via molecular dynamics.

Motivated by significant interest in metal-semiconductor and metal-insulator interfaces and superlattices for energy conversion applications, we developed a molecular dynamics-based model that captures the thermal transport role of conduction electrons in metals and heat transport across these types of interface. Key features of our model, denoted eleDID (electronic version of dynamics with implicit degrees of freedom), are the natural description of interfaces and free surfaces and the ability to control the spatial extent of electron-phonon (e-ph) coupling. Non-local e-ph coupling enables the energy of conduction electrons to be transferred directly to the semiconductor/insulator phonons (as opposed to having to first couple to the phonons in the metal). We characterize the effect of the spatial e-ph coupling range on interface resistance by simulating heat transport through a metal-semiconductor interface to mimic the conditions of ultrafast laser heating experiments. Direct energy transfer from the conduction electrons to the semiconductor phonons not only decreases interfacial resistance but also increases the ballistic transport behavior in the semiconductor layer. These results provide new insight for experiments designed to characterize e-ph coupling and thermal transport at the metal-semiconductor/insulator interfaces.

Interaction of protons in metallic hydrogen

The three-particle interaction of protons in metallic hydrogen has been investigated in detail for the first time. It has been shown that this interaction is determined by the third-order perturbation-theory term in the potential of the electron-proton interaction for the energy of conduction electrons in the field of protons. It has been shown that the three-particle interaction for the majority of configurations of protons is small compared to the effective pairwise interaction, but for some configurations, it significantly exceeds the latter. It follows from the calculations performed that the three-particle interaction tends to compress hydrogen to larger densities than those produced by the pairwise effective interaction. The maximum depth of the potential well for the three-particle interaction of protons corresponds to the location of protons on a common straight line, which can be interpreted as a tendency to the formation of a cubic lattice in the metallic state. The liquid-metal state of hydrogen can be stable at temperatures that significantly exceed room temperature. The three-particle interaction also favors the transition of hydrogen into an atomic state as an intermediate state between its molecular and metallic phases.

Quantum phase transitions into Kondo states in bilayer graphene

We study a magnetic impurity intercalated in bilayer graphene. A representative configuration generates a hybridization function with strong dependence on the conduction-electron energy, including a full gap with one hard and one soft edge. Shifts of the chemical potential via gating or doping drive the system between non-Kondo (free-moment) and Kondo-screened phases, with strong variation of the Kondo scale. Quantum phase transitions near the soft edge are of Kosterlitz-Thouless type, while others are first order. Near the hard edge, a bound-state singlet appears inside the gap; although of single-particle character, its signatures in scanning tunneling spectroscopy are very similar to those arising from a many-body Kondo resonance.

The negative electromagnetic attractive forces arising from kinetic energy of conduction electrons in double-layer metallic nanowire arrays

The coupled-nanowire plasmatic resonances and very strong negative electromagnetic force between the double-layer metallic nanowire arrays is investigated theoretically. The negative electromagnetic force indicates attractive interaction between the metallic nanowires with the air-gap cavity local resonance effect. Plasmon resonances lead to extremely large localized field, thereby resulting in large mutual coupling forces between the double-layer metallic nanowire arrays. The light coupling into metallic microcavity can stimulate collective electron oscillations of plasmatic resonance, and cause the contraction of the negative pressure in metallic cavity wall. The electromagnetic field of the plasmatic resonance mode is mainly localized inside the air-gap region between the two wires.

Volume effects and pressure effects on ferromagnetic superconductors

Thermal expansion of ferromagnetic superconductors below the superconducting transition temperature Tsc↑ of a majority spin conduction band is re-examined. In the previous study [J.Phys.Conf .Ser. 200 012056 (2010)] the volume differential of the kinetic energy of conduction electrons is constant. In this study, the volume differential of the kinetic energy of conduction electrons is inconstant, however. The superconducting gaps used in this study are like those of the thin film of A2 phase in liquid 3He. We find that the thermal expansion coefficient has the divergence at the superconducting transition temperatures. Thermodynamic Grüneisen's relation is satisfied. The pressure effects on the superconductors are also investigated. As an example, the pressure differential of the superconducting transition temperatures and that of the Curie temperature are studied. We find the analytical expression of the pressure differential of the superconducting transition temperatures and that of the Curie temperature.

The reexamination of thermal expansion of ferromagnetic superconductors and the pressure differential of its superconducting transition temperature-possible application to UGe2

The temperature dependence of thermal expansion of ferromagnetic superconductors below the superconducting transition temperature Tsc↑ of a majority spin conduction band is reexamined. In the previous study [to be published in J. M. Phys. B] the volume differential of the kinetic energy of conduction electrons is constant. However, in this study the volume differential of the kinetic energy of conduction electrons is inconstant. The superconducting gap of the majority spin conduction band used in this study has a line node. It is appropriate to UGe2. The pressure differential of its superconducting transition temperature is also investigated. We find that the thermal expansion coefficient has the divergence at the superconducting transition temperature. The thermodynamic Grüneisen's relation is satisfied.

Strong Light-Induced Negative Optical Pressure Arising from Kinetic Energy of Conduction Electrons in Plasmon-Type Cavities

We found that very strong negative optical pressure can be induced in plasmonic cavities by LC resonance. This interesting effect could be described qualitatively by a Lagrangian model which shows that the negative optical pressure is driven by the internal inductance and the kinetic energy of the conduction electrons. If the metal is replaced by perfect conductors, the optical pressure becomes much smaller and positive.

Influence of dose on particle size of colloidal silver nanoparticles synthesized by gamma radiation

Colloidal silver nanoparticles were synthesized by γ-irradiation-induced reduction method of an aqueous solution containing silver nitrate as a precursor in various concentrations between 7.40×10 −4 and 1.84×10 −3 M, polyvinyl pyrrolidone for capping colloidal nanoparticles, isopropanol as radical scavenger of hydroxyl radicals and deionised water as a solvent. The irradiations were carried out in a 60Co γ source chamber at doses up to 70 kGy. The optical absorption spectra were measured using UV–vis spectrophotometer and used to study the particle distribution and electronic structure of silver nanoparticles. As the radiation dose increases from 10 to 70 kGy, the absorption intensity increases with increasing dose. The absorption peak λ max blue shifted from 410 to 403 nm correspond to the increase of absorption conduction electron energy from 3.02 to 3.08 eV, indicating the particle size decreases with increasing dose. The particle size was determined by photon cross correlation spectroscopy and the results showed that the particle diameter decreases exponentially with the increase of dose. The transmission electron microscopy images were taken at doses of 20 and 60 kGy and the results confirmed that as the dose increases the diameter of colloidal silver nanoparticle decreases and the particle distribution increases.

Evidence for Dielectric (e–h) and Superconducting (e–e) Pairing in Cuprates

It is demonstrated that anomalous behavior of cuprates can be described in a natural way by the model with partial dielectrization of conduction electron energy spectra (EES). In such a model, near the Fermi surface (FS), there are formed the fours of charged particles (FCP) rather than independent electron–hole (e–h)- and electron–electron (e–e)-pairs. Since the bonding energies are the same for Cooper (e–e)- and dielectric (e–h)-pairs, then the temperature of SC transition Tc due to the Bose-condensation of FCP can be much more than the temperature of Bose-condensation of Cooper pairs only. The dielectric (e–h)-transition is connected with structural phase transformation in the cuprate system, formation of stripe structure, etc. The model successfully describes the presence of maximum at Tc(x)-curve, T-dependence of pseudogap (PG) and SC-gap, effect of nonmagnetic impurities to Tc, STM and ARPES spectra and other properties of cuprates.

Thermoelectric effect in layered conductors in a strong magnetic field

We have theoretically studied the thermoelectric effect in layered conductors with a quasi-two-dimensional electron energy spectrum of an arbitrary form in a quantizing magnetic field at low temperatures. Giant quantum oscillations of thermoelectric field versus the inverse magnetic field have been predicted, which will facilitate the experimental study of quantum oscillatory effects. Thermoelectric force in a layered conductor is shown to depend periodically upon the angle between the magnetic field direction and the normal to the layers. This orientation effect arises from the quasi-two-dimensional character of the charge carriers energy spectrum and is representative of layered conductors. Layered structures with sharply anisotropic metal type electrical conductivity have been intensively studied recently. The strong anisotropy of the kinetic coefficients of such conductors is attributed to the quasi-two-dimensional character of the energy spectrum for charge carriers. The dependence of the energy of conduction electrons on their momentum depends weakly on the momentum projection pz = pn along the normal n to the layers and can be represented in the form of a rapidly converging series

Helicoidal magnetic ordering in double exchange systems

We show that double exchange does not always favour the ferromagnetic spinstate. In transition metal oxides with strongly hybridized dp bands, the energy ofconduction electrons can be minimized by an incommensurate helicoidal ordering oflocal spins. This explains the magnetic order observed in the iron perovskitesSrFeO3 and CaFeO3. This homogeneous helicoidal state is stable against phase separation in a wide interval ofelectron concentrations.