Effective field theory for bound state reflection

Elastic quantum bound-state reflection from a hard-wall boundary provides direct information regarding the structure and compressibility of quantum bound states. We discuss elastic quantum bound-state reflection and derive a general theory for elastic reflection of shallow dimers from hard-wall surfaces using effective field theory. We show that there is a small expansion parameter for analytic calculations of the reflection scattering length. We present a calculation up to second order in the effective Hamiltonian in one, two, and three dimensions. We also provide numerical lattice results for all three cases as a comparison with our effective field theory results. Finally, we provide an analysis of the compressibility of the alpha particle confined to a cubic lattice with vanishing Dirichlet boundaries.     

Temperature dependence of infrared spectra

A simple form of cell for the study of infrared absorption spectra at low and high temperatures is described. Preliminary results of a study of the temperature-phase dependence of fluorobenzene and m-toluic acid spectra are reported.     

Temperature dependence of diffuse field phase

Diffuse fields, which have scattered from microstructure or reflected from walls so much as to prohibit conventional analyses, are usually examined by means of the time evolution of their ultrasonic spectral energy density. The phase information is usually discarded as resisting analysis. The phase, while unpredictable is, however, robust; according to theory it remains constant if source and receiver are not disturbed. Nevertheless, in practice we do observe slow drifts of phase over time scales of minutes. Here we examine the hypothesis that the phase drifts are due to temperature fluctuations. Temperature changes on cooling from 40 degrees C to room temperature were monitored and compared with changes in diffuse field phase. It was found that the reverberant ultrasonic field in a 7 cm aluminum block evolves with temperature in a manner that is in accord with published data on the temperature dependence of the ultrasonic velocities. Our 1 MHz transient source gives rise to a complex waveform that is observed to undergo an almost pure dilation. The precision with which this shift can be measured approaches 20 ns. This is remarkable when compared with the 100 ms travel time of the signal. Thus the temperature dependence of elastic wave speed is measured with a precision limited by the precision of one's thermometer. The signal is also found to suffer some distortion which, it is suggested, is related to the different rates of change of longitudinal and shear speeds. The corresponding prediction for the degree of distortion is found to be in accord with measurements.     

Temperature dependence of infrared reflectance spectra of InN

To investigate both the optical and electrical properties of InN, we have measured the infrared reflectance spectra of InN thin films and performed the fitting analyses of the infrared spectra to obtain not only phonon frequencies and the damping factors but also the carrier concentration of InN. In this paper, we extend the aim of those analyses to the electron mobility and demonstrate that the temperature dependence of the electron mobility can be discussed using the infrared reflectance spectra analyses.     

Negative power spectra in quantum field theory

We consider the spatial power spectra associated with fluctuations of quadratic operators in field theory, such as quantum stress tensor components. We show that the power spectrum can be negative, in contrast to most fluctuation phenomena where the Wiener-Khinchin theorem requires a positive power spectrum. We show why the usual argument for positivity fails in this case, and discuss the physical interpretation of negative power spectra. Possible applications to cosmology are discussed.     

Temperature dependence of luminescence time-resolved spectra from quartz

Pulsed optical stimulation of luminescence has been used to study the thermal dependence of luminescence lifetimes in quartz over the temperature range 20–200°C. Time-resolved spectra for lifetime analysis were recorded from samples of quartz over a dynamic range of 64 μs following stimulation of luminescence by pulsed 525 nm green light emitting diodes (LEDs) using an 11 μs pulse and 12% duty cycle. It has been demonstrated that an increase in measurement temperature generally leads to a decrease in lifetimes from about 30 μs at 20°C to about 7 μs at 200°C. The form of the decrease is influenced by the initial optical or thermal pre-treatment of samples.     

Temperature dependence of high field transport in ZnS

High field transport process in ZnS in the temperature range of (10–500) K was simulated by help of Monte Carlo method. The band structure of ZnS is described by analytical fitting of real band structure. Phonon scattering, spatial charge scattering, and impact ionization process are included in the simulation. The phonon scattering rates at different temperatures are calculated and compared. The transient acceleration time of electrons in ZnS is found to be temperature-independent. We attribute this result to the compensation of two opposite factors in ZnS. Average energy of electrons decreases with temperature.     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性. 关键词： 场发射 纳米金刚石 尺度效应 热载流子     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性.     

The entropy bound for local quantum field theory

We investigate the entropy bound for local quantum field theory in this Letter. Both the bosonic and fermionic fields confined to an asymptotically flat space–time are examined. By imposing the non-gravitational collapse condition, we find both of them are limited by the same entropy bound A3/4$A^{3/4}$, where A is the boundary area of the region where the quantum fields are contained in. The gap between this entropy bound and the holographic entropy has been verified.     

Holographic entropy bound and local quantum field theory

I show how the holographic entropy bound can be derived from elementary flat-spacetime quantum field theory when the total energy of Fock states is constrained gravitationally. This energy constraint makes the Fock space dimension (whose logarithm is the maximum entropy) finite for both bosons and fermions. Despite the elementary nature of my analysis, it results in an upper limit on entropy in remarkable agreement with the holographic bound, and also provides a microscopic deviation of a more general entropy bound recently introduced by Gour.     

Temperature dependence of the anisotropy parameter of the LiFeAs upper critical field in the two-band Ginzburg-Landau theory

An analytical formula is obtained for the temperature dependence of the anisotropy parameter of the upper critical field of a two-band superconductor in the context of the generalized Ginzburg-Landau theory for layered superconductors. The theoretical results are compared with the experimental data for new superconductor LiFeAs.     

Temperature dependence of electric field gradient in TbCoO3

The temperature dependence of the electric field gradient (efg) in TbCoO₃ perovskite was measured by perturbed angular correlation (PAC) technique using ¹¹¹Cd and¹⁸¹Ta nuclear probes. The radioactive parent nuclei ¹¹¹In and ¹⁸¹Hf were introduced into the compound through a chemical process during sample preparation. The electric quadrupole interactions at ¹¹¹Cd show two different sites, assigned to probe substituting Tb and Co atoms. The temperature dependence of quadrupole frequencies show sharp discontinuities which have been interpreted as thermally activated spin state transitions from low-spin ground state configuration to the intermediate-spin state and from intermediate-spin to high-spin state of Co^3?+? ion. For ¹⁸¹Ta only one interaction was observed, which was assigned to probe at Co site. Indication of a Jahn–Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out. No magnetic order was observed till 77 K.     

Tachyon bound state in Yang-Mills theory and instability of the vacuum

Existence of the tachyon bound state in a Yang-Mills system is discussed using the ladder approximation for the BS equation. Due to the attractive force between two massless gauge fields in the group singlet channel a tachyon pole is formed for whatever small coupling constant. The normal vacuum is expected to be unstable with respect to the condensation of this tachyon field.     

Temperature dependence of indirect-exciton luminescence in in-plane magnetic field

We report on a magneto-luminescence on a double quantum well subject to an in-plane magnetic field. The attention is paid to the properties of interwell excitons, which are indirect in the real space and which become indirect in the reciprocal space as well when a finite in-plane magnetic field is applied. Such indirect exciton states become optically inactive unless some relaxation mechanisms of their momentum appear. The experiment is carried out on a sample where, as reported previously, the radiative recombination of indirect excitons is possible due to their localization or via collisions with structural defects. The experimental data presented here, measured at various temperatures, favour the latter mechanism which is less sensitive to the system temperature in comparison with the former one.     

Temperature dependence of photoluminescence spectra in n-type modulation-doped quantum dot arrays

Temperature dependence of photoluminescence (PL) spectra of an electrostatically prepared modulation-doped quantum dot array is investigated. We report a strong temperature dependence of the enhanced PL near the Fermi energy between 0.4 and 4.2 K under a negative bias condition, where an interconnected quantum dot array is formed. This strong temperature dependence suggests that the Fermi-surface-mediated many-body interaction between a photo-created hole and the electron-gas plays an important role in the observed enhanced PL near the Fermi energy.     

Temperature dependence of aluminum nitride reflectance spectra in vacuum ultraviolet region

Temperature dependence of optical reflectance spectra in vacuum ultraviolet region for aluminum nitride has been measured on high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition is observed at photon energy around 7.7 eV. With decreasing temperature, the energy position of the dominant structure in the reflectance spectra shifts towards higher energy. The experimental data has been fitted to the Bose-Einstein expression and the obtained parameter related to the strength of the electron-phonon interactions is much smaller than that for the peak at 6.2 eV, suggesting that the higher-lying interband transition energy decreases more slowly with increasing temperature in aluminum nitride (AlN).     

A variational approach to bound states in quantum field theory

We consider here in a toy model an approach to bound state problem in a nonperturbative manner using equal time algebra for the interacting field operators. The potential is replaced by offshell bosonic quanta inside the bound state of nonrelativistic particles. The bosonic dressing is determined through energy minimisation, and mass renormalisation is carried out in a nonperturbative manner. Since the interaction is through a scalar field, it does not include spin effects. The model however nicely incorporates an intuitive picture of hadronic bound states in which the gluon fields dress the quarks providing the binding between them and also simulate the gluonic content of hadrons in deep inelastic collisions.