Minimum fluctuations in nanostructures

The properties of the Bose gas in traps have been experimentally and theoretically investigated. The main results of these investigations were discussed in L. Pitaevskii’s review. In this study, we consider excitations of low-lying levels in a disk-shaped magnetic trap. In contrast to the macrostructure, the excitation spectrum in the traps is a set of quasi-Bogolyubov modes with the gaps, which can be interpreted as a discrete breathing mode spectrum.     

具有无规分布陷阱点阵上的连续时间无规行走

用连续时间无规行走(CTRW)理论处理陷阱控制的无序点阵上的无规行走问题,首次导出行走者可有自发衰变及受陷态具有有限寿命情形下,行走者存活几率P(t)满足的方程。对一种广泛使用的等待时间分布密度ψ(t)=ααt^-(1-α)exp(-αt^α)0<α≤1,在受陷态寿命无限长情况下,给出适用于任意陷阱浓度和任意时间的P(t)的级数解。结合实验事实和Ngai的低能激发理论,指出同时考虑动力学关联和结构无序对解释实际过程的必要性。并提出包括可由Ngai低能激发理论描写的动力学关联在内的连续时间无规行走理论,其物理图象与目前的CTRW理论有根本不同。 关键词：     

Observation of a 500 meV collective mode in La2-xSrxCuO4 and Nd2CuO4 using resonant inelastic X-ray scattering

Utilizing resonant inelastic x-ray scattering, we report a previously unobserved mode in the excitation spectrum of La2-xSrxCuO4 and Nd2CuO4 at 500 meV. The mode is peaked around the (pi, 0) point in reciprocal space and is observed to soften, and broaden, away from this point. Samples with x=0, 0.01, 0.05, and 0.17 were studied. The new mode is found to be rapidly suppressed with increasing Sr content and is absent at x=0.17, where it is replaced by a continuum of excitations. This mode is only observed when the incident x-ray polarization is normal to the CuO planes.     

Haftstellenerzeugung und Leuchtmechanismus bei den Wolframat-Phosphoren

Thermoluminescence investigations of several tungstate and molybdate phosphors, excited by UV-, cathode- und X-rays, show that cathode- and X-rays are able to produce electron traps in the centres. Thus, after irradiation an amplification of the UV-light sum can be observed, and the form of the glow curves differs considerably after the various excitations. Theoretical conceptions about the trap production are confirmed quantitatively by measuring the variation of the light sum with irradiation time at various kinds of excitation. However, the produced traps influence the simple exponential decay after UV-excitation and lead to the appearance of a second exponential relation in the decay curve. These decay measurements can also be verified by theoretical considerations about the kinetics of possible transitions. It is supposed that the traps, which can be healed by annealing, are situated in the electron configuration of the tungstate complex; a model for the luminescence centre is discussed.     

Spin texture and magnetoroton excitations at nu=1/3

Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3.     

Quantum enhancement of higher-order phononlike excitations of a Bose-Einstein condensate

In a Bose-Einstein condensate, the excitation of a Bogoliubov phonon with low momentum (e.g., by a two-photon Bragg process) is strongly suppressed due to destructive interference between two indistinguishable excitation pathways. Here we show that scattering of this sound excitation into a double-momentum mode is strongly enhanced due to constructive interference. This enhancement yields an inherent amplification of second-order sound excitations of the condensate, as we confirm experimentally. We further show that due to parity considerations, this effect is extended to higher-order excitations.     

Higgs type excitations in cold atom systems

Higgs type excitations are the excitations which give mass to particles. The Higgs type excitations has a critical role both in particle physics and condensed matter physics. In particle physics, the suspected Higgs boson has been found by the Large Hadron Collider (LHC) in 2012. In condensed matter physics, the Higgs type excitations relate to order phase of the system. In this review, we present an overview of recent studies on the Higgs type excitations both in non-interacting and interacting cold atom systems. First, in non-interacting cold atom system, by synthesizing artificial non-Abelian gauge potential, we demonstrate that when a non-Abelian gauge potential is reduced to Abelian potential, the Abelian part constructs spin-orbit coupling, and the non-Abelian part emerges Higgs excitations. Secondly, the Higgs excitations which are the reputed Higgs amplitude mode in interacting cold atom system are discussed. We review the theoretical model and the experimental detection of Higgs amplitude mode in two dimensional superfluid. The observation of both Higgs type excitations in real experiments are also discussed.     

Real-time Ginzburg-Landau theory for bosons in optical lattices

Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for the Bose-Hubbard model which describes the real-time dynamics of the complex order parameter field. Analyzing the excitations in the vicinity of the quantum phase transitions it turns out that particle/hole dispersions in the Mott phase map continuously onto corresponding amplitude/phase excitations in the superfluid phase. Furthermore, in the superfluid phase we find a sound mode, which is in accordance with recent Bragg spectroscopy measurements in the Bogoliubov regime, as well as an additional gapped mode, which seems to have been detected via lattice modulation.     

Rydberg excitations in Bose-Einstein condensates in quasi-one-dimensional potentials and optical lattices

We experimentally realize Rydberg excitations in Bose-Einstein condensates of rubidium atoms loaded into quasi-one-dimensional traps and in optical lattices. Our results for condensates expanded to different sizes in the one-dimensional trap agree well with the intuitive picture of a chain of Rydberg excitations. We also find that the Rydberg excitations in the optical lattice do not destroy the phase coherence of the condensate, and our results in that system agree with the picture of localized collective Rydberg excitations including nearest-neighbor blockade.     

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. At filling factors close to nu=3 we observe two decoupled modes of edge excitations, one of which is related to the innermost compressible strip and is identified as an interedge magnetoplasmon mode. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.     

Zero sound mode in normal liquid 3He

Inelastic x-ray scattering has been utilized to study the elementary excitations of normal liquid 3He at the temperature T=1.10+/-0.05 K and saturated vapor pressure in the wave vector range 0.15相似文献   

A new exact solution and corresponding localized excitations of the ()-dimensional mKdV equation

In this Letter, we show that the new (2+1)-dimensional mKdV equation possesses Painlevé property. Then, starting from the standard truncated Laurent expansion and the direct variable separation approach, a new exact solution with two lower dimensional arbitrary functions is obtained. Some high-dimensional localized excitations of the physical quantity u are constructed. These localized excitations have abundant structures at x-axis and y-axis such as dromions, peakons, loop-solitons, compactons which depend on corresponding functions.     

Dynamical properties of the Haldane chain with bond disorder

By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at δ_∆ ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δ_c ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These “spins” can form the weakly coupled longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0.     

Condensates in annuli: dimensionality of the variance

Static and dynamic properties of Bose-Einstein condensates in annular traps are investigated by solving the many-boson Schrödinger equation numerically accurately using the multiconfigurational time-dependent Hartree for bosons method. We concentrate on weakly-interacting bosons exhibiting low depletion. Analysis of the mean-field position variance, which accounts for the shape of the density only, and the many-body position variance, which incorporates a tiny amount of excitations through the reduced two-particle density matrix, shows that the former behaves essentially as a quasi-one-dimensional quantity whereas the latter as a two-dimensional quantity. This brings another dimension to the physics of bosons in ring-shaped traps.     

Superinelastic electron transfer: electron trapping in H2O ice via the N-2((2)Pi(g)) resonance

We present measurements on the trapping of 0-3 eV electrons in H2O ice films covered with a submonolayer of N2 molecules. At the energy of the N-2((2)Pi(g)) shape resonance, the absolute cross section for electron trapping in ice is approximately 5.5 x 10(-16) cm(2), similar to that for vibrational excitations of gaseous N2 via the resonance. This result, indicating that nearly all electrons from autoionization of N-2((2)Pi(g)) are transferred to electron traps in ice, is explained by superinelastic electron transfer from N-2((2)Pi(g)) into preexisting traps in polar ice, leaving N2 in high vibrational excited states.     

Spin correlations near the surface of a three-dimensional Heisenberg antiferromagnet

Nearest-neighbor spin correlations are considered near the surface of a semi-infinite spin- Heisenberg antiferromagnet on a simple cubic lattice. In the spin-wave approximation, the excitation spectrum of this model involves bulk modes – standing spin waves and a quasi-two-dimensional mode of surface spin waves. These latter excitations eject the bulk excitations from the surface region thus dividing the antiferromagnet into two parts with different excitations. As a result absolute values of the spin correlations near the surface exceed the bulk value. In the surface region, the pattern of spin correlations resembles the comb structure recently obtained for the two-dimensional case.     

Dynamics of excitations in a one-dimensional bose liquid

We show that the dynamic structure factor of a one-dimensional Bose liquid has a power-law singularity defining the main mode of collective excitations. Using the Lieb-Liniger model, we evaluate the corresponding exponent as a function of the wave vector and the interaction strength.     

Elementary excitations of quantum critical (2+1)-dimensional antiferromagnets

It has been proposed that there are degrees of freedom intrinsic to quantum critical points that can contribute to quantum critical physics. We point out that this conclusion is quite general below the upper critical dimension. We show that in (2+1)D antiferromagnets Skyrmion excitations are stable at criticality and identify them as the critical excitations. We find exact solutions composed of Skyrmion and anti-Skyrmion superpositions, which we call topolons. We include the topolons in the partition function and renormalize by integrating out small size topolons and short wavelength spin waves. We obtain a correlation length exponent nu=0.690 666 and anomalous dimension eta=0.0166.     

Low-lying magnetic and electric dipole strength distribution in the <Superscript>176</Superscript>Hf nucleus

In this study the QRPA approach with the rotational and translational invariant Hamiltonians has been carried out to describe magnetic and electric dipole excitations in ¹⁷⁶Hf . Calculations show that the ¹⁷⁶Hf nucleus demonstrates a very rich B(M1) strength structure and in some aspects nicely confirm the experimental data. It has been shown that the main part of spin-1 states, observed at 2-4MeV in ¹⁷⁶Hf , may be attributed to have a M1 character and may be interpreted as the main fragments of the scissors mode. The agreement between the calculated mean excitation energies as well as the summed B(M1) values of the scissors mode excitations and the available experimental data is quite good. The constructive interference between the orbit and the spin part of M1 strength has been found to be below 3.5MeV. The calculations indicate the presence of a few prominent negative-parity states in the 2-4MeV energy interval. This suggests that the supposition of the experiment “all stronger K = 1 low-lying dipole excitations were of magnetic character” cannot be generalized.     

Neutral fermion excitations in the Moore-Read state at filling factor ν = 5/2

We present evidence supporting the weakly paired Moore-Read phase in the half-filled second Landau level, focusing on some of the qualitative features of its excitations. Based on numerical studies, we show that systems with odd particle number at the flux N(?)=2N-3 can be interpreted as a neutral fermion mode of one unpaired fermion, which is gapped. The mode is found to have two distinct minima, providing a signature that could be observed by photoluminescence. In the presence of two quasiparticles the same neutral fermion excitation is shown to be gapless, confirming expectations for non-abelian statistics of the Ising model with degenerate fusion channels 1 and ψ.