A nonlinear response of the BiSrCaCuO single crystal in the microwave region

Third-harmonic microwave radiation of the BiSrCaCuO superconducting single crystal was studied. Two modes of microwave field-sample interactions were observed. In a weak field, a strong increase in the intensity of radiation after switching on a constant magnetic field, a hysteresis between opposite scan directions, and different harmonic amplitudes depending on the conditions of cooling (in the presence or absence of a magnetic field) were observed. These observations can be described by the generalized Ginzburg-Landau functional taking into account higher spatial derivatives of the order parameter. At a high intensity of incident waves, a magnetic field almost did not influence third-harmonic radiation, and, accordingly, hysteresis was absent. This is likely to be evidence that, at high powers, third-harmonic radiation arises as a result of generation of vortices under the action of a high-frequency magnetic field.     

Dimensional crossover in cuprate superconductors

A central concern in understanding the mechanism for the occurrence of superconductivity in cuprates is the interaction driving the phase transition and their dimensionality. As physical systems near a phase transition have a marked dependence on dimensionality, this can be explored with symples where one of the physical dimensions is reduced and becomes comparable to the correlation length. Recently, it became possible to fabricate sufficiently thin cuprate slabs, revealing a fall ofT _c with reduced thickness, becoming pronounced for slabs a few unit cells thick. Related effects have been observed in the YBCO bulk compounds 123, 124 and 247. We analyze the experimental data by invoking finite size scaling and a Ginzburg-Landau treatment. The main conclusions include the following: the fall ofT _c with decreasing thickness corresponds to a dimensional crossover, revealing the three-dimensional nature of the interaction mediating superconductivity; there is a predominance of two-dimensional fluctuations and boundaries with reduced thickness; there are crossover phenomena reminiscent of⁴He films and thin slabs of conventional super-conductors.     

Dimensional crossover in the large-N limit

We consider dimensional crossover for anO(N) Landau-Ginzburg-Wilson model on ad-dimensional film geometry of thicknessL in the large-N limit. We calculate the full universal crossover scaling forms for the free energy and the equation of state. We compare the results obtained using environmentally friendly renormalization with those found using a direct, non-renormalization-group approach. A set of effective critical exponents are calculated and scaling laws for these exponents are shown to hold exactly, thereby yielding nontrivial relations between the various thermodynamic scaling functions.     

Dimensional crossover in alternating spin chains

The effect of antiferromagnetic interchain coupling in alternating spin chains is studied by means of spin wave (SW) theory and density matrix renormalization group (DMRG). Two limiting cases are investigated, the two-leg ladder and its two-dimensional (2D) generalization. For the 2D case, SW approximation predicts a smooth-dimensional crossover keeping the ground state ordered, whereas in the ladder case the DMRG results show a gapped ground state for any J>0. Furthermore, the behavior of the correlation functions closely resemble the uniform spin- ladder. However, for small J, the gap behaves quadratically as Δ0.6J². Similarly to uniform spin chains, it is conjectured an analogous spin gap behavior for an arbitrary number of mixed spin chains.     

Dimensional crossover in two-dimensional Bose-Fermi mixtures

We investigate the equilibrium properties of boson-fermion mixtures consisting of a Bose condensate and spin-polarized Fermi gas confined in a harmonic two-dimensional (2D) trap using mean-field theory. Boson-boson and boson-fermion coupling constants have a logarithmic dependence on the density because of the two-dimensional scattering events when the s-wave scattering lengths are on the order of mixture thickness. We show that this modifies the density profiles significantly. It is also shown that the dimensional crossover stabilizes the mixture against collapse and spatial demixing is observed for the case of a negative boson-fermion scattering length.     

Dimensional crossover of thermal conductance in graphene nanoribbons: a first-principles approach

First-principles density-functional calculations are performed to investigate the thermal transport properties in graphene nanoribbons (GNRs). The dimensional crossover of thermal conductance from one to two dimensions (2D) is clearly demonstrated with increasing ribbon width. The thermal conductance of GNRs of a few nanometers width already exhibits an approximate low-temperature dependence of T(1.5), like that of 2D graphene sheets which is attributed to the quadratic nature of the dispersion relation for the out-of-plane acoustic phonon modes. Using a zone-folding method, we heuristically derive the dimensional crossover of thermal conductance with the increase of ribbon width. Combining our calculations with the experimental phonon mean-free path, some typical values of thermal conductivity at room temperature are estimated for GNRs and for 2D graphene sheet. Our findings clarify the issue of the low-temperature dependence of thermal transport in GNRs and suggest a calibration range of thermal conductivity for experimental measurements in graphene-based materials.     

Momentum transfer in crystal lattices with vibrating atoms

A momentum transfer equation previously used to describe non-elastic deformation in crystalline solids represented by point masses at fixed lattice positions is extended to take into account the existence of intrinsic (e.g. thermal) small amplitude vibrations of the masses about their mean positions in a lattice. Use of the time-dependent Schroedinger equation to describe momentum transfer and deformation is also discussed in terms of this vibrating point-mass lattice model. The result is that a modified and identical differential equation for momentum transfer is obtained from each approach; some solutions to this equation are presented. The previous particle momentum wave frequency dependence on wave vector and resulting applications to non-elastic deformation are unchanged, but these particle momentum waves can now be considered as modulating the usual high-frequency waves associated with the elastic modes of a crystalline solid.     

The dynamic Casimir effect within a vibrating metal photonic crystal

The lattice-vibrating metal photonic crystal is exactly a system of dynamical Casimir effect connected in series, and so we can expect that a dynamical Casimir effect is enhanced by the photonic band effect. In the present study, when an electromagnetic field between metal plates is in the ground state in a one-dimensional metal photonic crystal, the radiation of electromagnetic wave in excited states has been investigated by artificially introducing lattice vibration to the photonic crystal. In this case as well as a dynamical Casimir effect, it has been shown that the harmonics of a ground state are generated just by vibrating a photonic crystal even without an incident wave. The dependencies of the radiating power on the number of layers and on the wavenumber of the lattice vibration are remarkable. It has been found that the radiation amplitude on lower excited states is not necessarily large and radiation on specific excited levels is large.     

Dimensional crossover of quantum critical behavior in CeCoIn5

The nature of quantum criticality in CeCoIn5 is studied by low-temperature thermal expansion alpha(T). At the field-induced quantum critical point at H = 5 T a crossover scale T* approximately 0.3 K is observed, separating alpha(T)/T proportional, variant T(-1) from a weaker T(-1/2) divergence. We ascribe this change to a crossover in the dimensionality of the critical fluctuations which may be coupled to a change from unconventional to conventional quantum criticality. Disorder, whose effect on quantum criticality is studied in CeCoIn(5-x)Sn(x) (0 < or = x < or = 0.18), shifts T* towards higher temperatures.     

Characteristics of phonon scattering in electron diffraction by a vibrating crystal lattice

In a departure from the generally accepted approach using rigid-body potentials, the diffraction of electrons by a deformation (compliant) potential is investigated, where the charge distribution in the crystal is treated as a continuous medium and its elastic deformability is taken into account. The deformability property in the presence of thermal “broadening” of the lattice planes in a metal leads to discontinuities at the boundaries of the Brillouin zone in the electron-phonon scattering spectrum and to the partial suppression of such scattering in the higher zones (or enhancement in the first Brillouin zone). Fiz. Tverd. Tela (St. Petersburg) 39, 18–22 (January 1997)     

Amplification of light in one-dimensional vibrating metal photonic crystal

Photon–phonon interaction on the analogy of electron–phonon interaction is considered in one-dimensional metal photonic crystal. When lattice vibration is artificially introduced to the photonic crystal, a governing equation of electromagnetic field is derived. A simple model is numerically analyzed, and the following novel phenomena are found out. The lattice vibration generates the light of frequency which added the integral multiple of the vibration frequency to that of the incident wave and also amplifies the incident wave resonantly. On a resonance, the amplification factor increases very rapidly with the number of layers. Resonance frequencies change with the phases of lattice vibration. The amplification phenomenon is analytically discussed for low frequency of the lattice vibration and is confirmed by numerical works.     

Dimensional crossover tuned by pressure in layered magnetic NiPS_3

The physical properties of most 2D materials are highly dependent on the nature of their interlayer interaction. In-depth studies of the interlayer interaction are beneficial to the understanding of the physical properties of 2D materials and permit the development of related devices. Layered magnetic NiPS_3 has unique magnetic and electronic properties. The electronic band structure and corresponding magnetic state of NiPS_3 are expected to be sensitive to the interlayer interaction, which can be tuned by external pressure. Here, we report an insulator-metal transition accompanied by the collapse of magnetic order during the 2D-3D structural crossover induced by hydrostatic pressure. A two-stage phase transition from a monoclinic(C2/m) to a trigonal(P31m)lattice is identified via ab initio simulations and confirmed via high-pressure X-ray diffraction and Raman scattering; this transition corresponds to a layer-by-layer slip mechanism along the a-axis. Temperature-dependent resistance measurements and room temperature infrared spectroscopy under different pressures demonstrate that the insulator-metal transition and the collapse of the magnetic order occur at ~20 GPa, which is confirmed by low-temperature Raman scattering measurements and theoretical calculations. These results establish a strong correlation between the structural change, electric transport, and magnetic phase transition and expand our understanding of layered magnetic materials. Moreover, the structural transition caused by the interlayer displacement has significance for designing similar devices at ambient pressure.     

Dimensional crossover and charge order in half-doped manganites and cobaltites

We propose a generic model for understanding the effect of quenched disorder on charge-ordering in half-doped manganese and cobalt oxides with different crystal structures. Current experimental observations are explained in the light of the global phase diagram of the model.     

Repetitive single vortex-loop creation by a vibrating wire in superfluid 3He-B

Spectacular features are observed on the velocity-force characteristics of a vibrating wire resonator in superfluid 3He-B at ultralow temperatures. Both plateaus and discontinuities are seen in the characteristics. The plateaus seem to have two separate critical velocities where first some "event" occurs, which causes the wire to lose energy and slow down, followed by a second lower critical velocity where the event decouples. It is suggested that these events are due to vortex-loop creation at protuberances on the vibrating wire. This opens up the possibility of controlling the creation of vorticity through specially prepared protuberances.     

Dimensional crossover of a Rabi-coupled two-component Bose–Einstein condensate in an optical lattice

Dimensionality is a central concept in developing the theory of low-dimensional physics.However,previous research on dimensional crossover in the context of a Bose-Einstein condensate(BEC) has focused on the single-component BEC.To our best knowledge,further consideration of the two-component internal degrees of freedom on the effects of dimensional crossover is still lacking.In this work,we are motivated to investigate the dimensional crossover in a three-dimensional(3D) Rabi-coupled two-compon...