Quantum Statistical Theory Research Articles

Gate-tunabe gap of heated monolayer graphene on substrates

Temperature effect of energy gap is researched in the presence of the homogeneous magnetic field based on the electrons/holes - surface optical phonons coupling induced by different polar substrates under monolayer graphene. The quantum statistical theory and LLP variational method are used to calculate the energy gap of monolayer graphene on the polar substrate. We found that substrate-induced gap can be tunable in the landau energy level by controlling the temperature T, confinement strength parameter g, polarization strength η of substrate. The energy gap matches with the recent experimental data. These conclusions obtained highlight the vital role of polaron effect in deciding substrate-induced gap and provide a promising way to increase the substrate-induced gap of monolayer graphene.

Effects of temperature and magnetic field on the ground state binding energy of the strong coupling magneto-polaron in an RbCl asymmetrical semi-exponential quantum well

The ground state binding energy (E[Formula: see text]) and the mean number of LO phonons (N) of the strong-coupling magneto-polaron (SCMP) in an asymmetrical semi-exponential quantum well (ASEQW) are studied theoretically. Temperature (T) effects on E[Formula: see text] and N are acquired with the quantum statistics theory (QST). By using the Lee-Low-Pines unitary transformation (LLPUT) and linear combination operation method (LCOM), the variations of E[Formula: see text] and N with T and [Formula: see text] of magnetic field are discussed. The investigated results indicate that both T and [Formula: see text] have great influence on E[Formula: see text] and N of LO phonons.

Vibrational frequency and ground state energy of the strong-coupled- magnetopolaron in a RbCl asymmetrical semi-exponential quantum well at finite temperature

The vibrational frequency (VF) and the ground state energy (GSE) of the strongly coupled -magnetopolaron in an asymmetrical semi-exponential quantum well (ASEQW) are researched theoretically. By employing the linear combination operator and LLP unitary transformation methods and quantum statistics theory (QST), the variations of the VF and the GSE with the temperature and the cyclotron frequency of magnetic field (CFMF) are calculated. The results indicate that both the temperature and the cyclotron frequency have great effects on the VF and the GSE.

The ground state energy of the polaron: An asymmetrical semi-exponential polar slab

In this work, the influence of the temperature (T) and RbCl asymmetrical semi-exponential confinement potential on intermediate coupling polaron in a polar slab was studied by applying the Lee-Low-Pines (LLP) unitary transformation and linear combination operation methods, based on the quantum statistical theory. We have derived the ground state energy (E0) and the mean phonon number (N). According to the obtained results, E0 increases with increasing T and parameter [Formula: see text], whereas it is a decaying function with raising parameter U0.

Exotic quantum statistics and thermodynamics from a number-conserving theory of Majorana fermions

We propose a closed form for the statistical distribution of non-interacting Majorana fermions at low temperature. Majorana particles often appear in the contemporary many-body literature in the Kitaev, Fu–Kane, or Sachdev–Ye–Kitaev models, where the Majorana condition of self-conjugacy immediately results in non-conserved particle number, non-trivial braiding statistics, and the absence of a non-interacting limit. We deviate from this description and instead consider a gas of non-interacting, spin-1/2 Majorana fermions that obey the spin-statistics theorem via imposing a condensed matter analog of momentum conservation. This allows us to build a quantum statistical theory of the Majorana system in the low temperature, low density limit without the need to account for strong fluctuations in the particle number. A combinatorial analysis leads to a configurational entropy which deviates from the fermionic result with an increasing number of available microstates. A number-conserving Majorana distribution function is derived which shows signatures of a sharply-defined Fermi surface at finite temperatures. Such a distribution is then re-derived from a microscopic model in the form of a modified Kitaev chain with a bosonic pair interaction. The thermodynamics of this free Majorana system is found to be nearly identical to that of a free Fermi gas, except now distinguished by a two-fold ground state degeneracy and, subsequently, a residual entropy at zero temperature. Despite clear differences with the anyonic or Sachdev–Ye–Kitaev models, we nevertheless find surprising agreement between our theory and experimental signatures of Majorana excitations in several materials. Experimental realization of our exactly solvable model is also discussed in the realm of astrophysical and high-energy phenomena.

Anharmonicity in elastic constants and extended x-ray-absorption fine structure cumulants

We have investigated temperature dependence of the elastic constants and higher-order EXAFS (extended x-ray-absorption fine structure) cumulant moments, both of which originate from vibrational anharmonicity. We focus our attention on how the third- or fourth-order anharmonicity contributes to these physical quantities. Although it may be believed that the fourth-order anharmonicity should dominantly contribute to the fourth-order EXAFS cumulant through the first-order quantum statistical perturbation theory, it is consequently found that the experimental fourth-order EXAFS cumulant observed in fcc Ni, Cu, and stainless steel 316 are described mainly by the third-order anharmonicity through the second-order perturbation. In case of the elastic constants, such a situation is more prominent, and the contribution of the fourth-order anharmonicity is negligibly small for the estimation of temperature dependence of the elastic constants. We have also observed significant lattice strains on Cr and Mo in stainless steel 316 through the Fe, Ni, Cr, and Mo K-edge EXAFS measurements: a compressive lattice strain on Cr associated with larger thermal fluctuations and a more significant compressive lattice strain on Mo without enhanced thermal fluctuation. Such a characteristic dissimilarity may be caused by the differences in the atomic weights and the cohesive energies between Cr and Mo. Moreover, we have performed path-integral effective classical potential and classical Monte-Carlo simulations to describe the bulk moduli of the Invar and Elinvar alloys that show noticeable anomalies due to the so-called Invar effect. Appropriate temperature dependence of the bulk moduli is successfully obtained for the Invar, Elinvar, and stainless steel 304 and 316 alloys as well as elemental fcc Cu and Ni metals.

Superradiance of Gravitational Waves and Relic Photons from Binary Black Holes and Neutron Stars

Type Ia supernova explosions and the merging of binary black holes and neutron stars are considered separate sources of pulsing in the Universe. Their transient signals and characteristic parameters are described using the Dicke superradiance model and quantum statistical theory. Estimates are given for the parameters of gravitational waves, the intensity of relic photons, the boson and Higgs fields, and binary black holes and neutron stars before and after merging.

Influences of temperature and Rashba spin-orbit interaction on oscillation period of bound polaron in quantum pseudodot

In the present work, we study the influences of the temperature and the Rashba spin-orbit interaction on the oscillation period of the bound polaron in the quantum pseudodot using the Lee-Low-Pines unitary transformation, the variational method of Pekar-type and the quantum statistical theory. We have derived the oscillation period of the bound polaron in the superposition state and reported the temperature dependences and the Rashba spin-orbit interaction effects of the oscillation period of polaron when the wave vector, the electron-LO phonon coupling, the Coulomb bound potential and the chemical potential take different values.

Temperature Effect on Vibration Frequency of the Strong-Coupling Polaron in RbCl Asymmetrical Semi-exponential Quantum Wells

We carried out the theoretical study of the influence of temperature on the polaron vibration frequency in the RbCl asymmetrical semi-exponential quantum wells by using the quantum statistical theory. The vibration frequency and the ground-state binding energy (GSBE) varying with the temperature and the Coulomb interaction are calculated by employing the Lee–Low–Pines transformation method combined with linear combination operation technique. We show that the vibration frequency and the GSBE will be enhanced with raising the temperature and the Coulomb repulsion interaction.

Phase transitions in the extended particle systems, Hagedorn temperature and fractal dimension of space, as a confinement phase transition order parameter

We consider a formal definition of New physics, fundamental constants of physics, formulation of the quantum statistical theory including extra integrals, monopole mechanism for hadronization in QCD, finite approximation of the zeta-function and fermion factorization of the bosonic statistical sum.

Resonant Electronic-Bridge Excitation of the ^{235}U Nuclear Transition in Ions with Chaotic Spectra.

Electronic-bridge excitation of the 76eV nuclear isomeric state in ^{235}U is shown to be strongly enhanced in the U^{7+} ion, potentially enabling laser excitation of this nucleus. This is because the electronic spectrum has a very high level density near the nuclear transition energy that ensures the resonance condition is fulfilled. We present a quantum statistical theory based on many-body quantum chaos to demonstrate that typical values for the electronic factor increase the probability of electronic bridge in ^{235}U^{7+} by many orders of magnitude. We also extract the nuclear matrix element by considering internal conversion from neutral uranium. The final electronic-bridge rate is comparable to the rate of the Yb^{+} octupole transition currently used in precision spectroscopy.

Temperature Effects on the First Excited State of the Polaron in an Asymmetric Quantum Pseudodot Under Magnetic Field

Using the variational method of the Pekar type, we investigate the first excited state energy of the polaron in an asymmetric quantum pseudodot under the magnetic field. Temperature effects on the polaron are calculated by employing the quantum statistical theory, and the influences of the chemical potential, the zero point of pseudo-harmonic potential (PHP), the cyclotron frequency, the electron–phonon coupling strength and the transverse and the longitudinal effective confinement lengths are taken into account. The results show that the first excited state energy decreases (increases) when the temperature is increased at lower (higher) temperature region. And it is an increasing function of the chemical potential, the zero point of PHP, the cyclotron frequency and the electron–phonon coupling strength. Simultaneously, it is a decreasing one of the transverse and the longitudinal effective confinement lengths.

Effect of hydrogen-like impurity on a qubit in quantum pseudodot at finite temperature

Influences of temperature on the qubit's properties in a quantum pseudodot (QPD) are studied by using the variational method of Pekar type (VMPT) and quantum statistics theory (QST). The formation of qubit requires two special conditions: One is the strong-coupling between the electron and the bulk longitudinal optical (LO) phonon, and the other is the hydrogen-like impurity (HLI) locating at the center of the QPD. So, we choose strong-coupling RbCl crystal as an example and calculate the electron probability density (EPD) and the oscillating period (OP) of the QPD qubit changing with the temperature and the Coulombic impurity potential (CIP).

The ground-state lifetime of polaron in a two-dimensional quantum pseudodot system

We study the ground-state lifetime (GSL) of polaron in a two-dimensional RbCl quantum pseudodot (QPD) system by using a variational method of Pekar type (PTVM) and the quantum statistical theory. Considering the polaron effect, we derive the dependent relations of the temperature, the electric field, the chemical potential (CP) of the two-dimensional electron gas (TDEG), the polaron radius (PR) and the zero point (ZP) of the pseudoharmonic potential (PHP) on the GSL of polaron. The calculated results show that the GSL $$\tau$$ of polaron will decrease when the CP $$V_{0}$$ of the TDEG, the electric field and the PR $$R_{p}$$ increase, but will increase while the ZP $$r_{0}$$ of the PHP, the ground-state energy (GSE) and the temperature parameter $$\gamma$$ become larger, respectively. That means that by changing the electric field, the temperature, the PR, the CP of the TDEG and the ZP of the PHP, one can adjust the GSL of polaron, which may offer new insight into studying many related applications in quantum computation (QC) and control of electron transition.

Temperature effects on state-energy levels and transition frequency of magnetopolaron in asymmetric two-dimensional Gaussian quantum wells

Influence of the magnetic field on the energy levels and the excitation energy (EE) between the two states of the magnetopolaron strongly coupled in asymmetric Gaussian quantum wells is examined by the variational method of Pekar type. Then, we discover the temperature and magnetic field effects on the energy levels and EE with quantum statistics theory. According to the results of the article, the energy levels and the EE are a function relationship with the temperature rising and magnetic field increasing.

Influences of the Temperature on the Ground State of the Coupling Polaron in an Asymmetric Quantum Pseudodot Under the External Magnetic Field

We studied that the influences of the temperature on the ground state energy of the coupling polaron in an asymmetric quantum pseudodot (QPD) under the external magnetic field by using the quantum statistical theory (QST) and the variational method of the Pekar-type (VMPT). And the relations between the ground state energy and the external magnetic field, the chemical potential of the two-dimensional electron gas, the pseudoharmonic potential (PHP) zero point, the coupling strength and the effective confinement lengths are discussed. The results of our study have shown that the ground state energy firstly declines and then rises as the temperature is increased from a low value. We also find that the ground state energy rises with the enhancing external magnetic field and the chemical potential of the two-dimensional electron gas. And the ground state energy declines firstly and then reinforces as the PHP zero point is enhanced. What’s more, the ground state energy is reductive function of the coupling strength and the effective confinement lengths.

Effects of Temperature on the Ground State Energy of the Strong Coupling Polaron in a RbCl Asymmetrical Semi-Exponential Quantum Well

In this article, temperature effects on strong coupling polaron in a RbCl asymmetrical semi-exponential quantum well (ASEQW) are studied by applying the quantum statistical theory (QST). Based on the well-known LLP unitary transformation and linear combination operation (LCO) methods, we have derived the ground state energy and the mean phonon number of strong coupling polaron in the ASEQW. According to the obtained results, ground state energy decreases with increasing temperature, whereas mean phonon number increases by increasing temperature. The ground state energy and mean phonon number are decaying functions with raising parameter $\sigma $ , whereas they are enhancing ones with lifting parameter $U_{0}$ .

Temperature and impurity effects on the vibrational frequency of the strongly-coupled polaron in asymmetrical semi-exponential RbCl quantum wells

Properties of the vibrational frequency (VF) and the ground state binding energy (GSBE) of the strong-coupled polaron in asymmetrical semi-exponential quantum wells (ASEQWs) with a hydrogen-like impurity (HLI) at the origin of coordinates are investigated. The temperature effects on the VF and the GSBE are taken into account by using the quantum statistics theory (QST). Based on the linear combination operation and LLP unitary transformation methods, the variations of the VF and the GSBE varying with the temperature and the strength of the Coulombic impurity potential (CIP) are discussed. We have found that the VF and the GSBE are increasing functions of the temperature and the CIP.

Temperature effects of the electron probability density on quantum pseudodot qubit

With variational method of Pekar type and quantum statistics theory, the temperature effects on electron probability density (EPD) of a strongly-coupling electron-LO-phonon (polaron) in RbCl material quantum pseudodots (QPDs) are studied. The qubit in the QPD system can be built by the two-level energy states. The EPD periodically oscillates in the special material QPD with a certain period as the electron is located in the superposition state of the ground and first excited states. The changing functions of EPD and the oscillating period with the system temperature and the chemical potential of the two-dimensional electron gas are found.

The Effects of Hydrogen-Like Impurity and Temperature on State Energies and Transition Frequency of Strong-Coupling Bound Polaron in an Asymmetric Gaussian Potential Quantum Well

In the present work, we study the ground state energy, the first excited state energy and the transition frequency (TF) between the two states of the strong-coupling impurity bound polaron in an asymmetric Gaussian potential quantum well (AGPQW) by using the variational method of the Pekar type. By employing quantum statistics theory, the temperature effect on the state energies (SEs) and the TF are also calculated with a hydrogen-like impurity at the coordinate origin of the AGPQW. According to the obtained results, we found that the SEs and the TF are increasing functions of the temperature, whereas they are decreasing ones of the Coulombic impurity potential.