AIP Advances

This is a new journal that was recently launched in the field of applied physical science. It differs from the prestigious journals such as Physical Reviews, Nature and Science by its editor policy. It is through peer review, but the reviewers are not expected to comment on the significance of a submission, which is supposed to be recognized by post-publication discussions from scientists across the world. It is waiting to see whether it will be successful. But definitely, it gives a channel for those who are working on very cold topics that hardly lead to appearing in a mainstream journals.

As a community-supported journal, AIP Advances welcomes full participation from a wide spectrum of physical scientists. Researchers interested in becoming reviewers are invited to register at http://AIPadvances.peerx-press.org. Direct questions about the review process to aip.advances@aip.org.

The Executive Editors, aided by the Academic Editors, set editorial policy for the journal. Submitted manuscripts are assigned to a particular Academic Editor who provides oversight of the peer-review process, and, based on reviewer feedback, decides to accept the paper, request revisions of the author, or rejects the paper.

Reviewers and editors are not expected to judge the significance of the scientific results. The Academic Editors use the following guidelines in accepting a submission for publication:

• Does the manuscript present results of primary scientific research?
• Does the manuscript present research in an area of applied physical science?
• Have the results been published elsewhere?
• Does the analysis represent rigorous technical standards; is the detail presented sufficient?
• Are conclusions supported by the data presented?
• Is the manuscript understandable; is it written in good scientific English?

Reviewers assigned to a manuscript will use the Journal's online system for all aspects of the process. A checklist is provided within the online system to assist the reviewer. [http://aipadvances.aip.org/reviewers/reviewer_guidelines]

On the properties of wave functions

In standard textbooks on preliminary quantum mechanics, it is usually stated that, any physical wave function must be single-valued, which is surely all the time true, as long as the wave function is interpreted as the probability amplitude. Besides, it is usually also stated that, the wave functions (together with its first derivatives) have to be continuous. Obviously, the single-valued-ness does not warrant any continuity. Here I just want to emphasize that, the former property is a direct sequel-a of the Born interpretation, whereas the latter is never a must. Actually, the latter is model dependent: different Hamiltonian can lead to different matching conditions that may not necessarily demand the wave function itself or its derivative be continuous. Indeed, in the conventional p^2/2m case (free from singular potentials), from the Schrodinger equation, H wavefunction=E wave function, directly follows the continuity of the first derivative of the physical wave functions, from which follows the continuity of wave functions themselves. On the other hand, for Dirac-type Hamiltonian that is linear in p (also free from singular potentials), one can only derive from the corresponding Schrodinger equation the continuity of the wave functions, and none can be imposed upon their derivatives. Even more, in the case of singular potentials, for the Dirac (conventional) case, the wave functions (the first derivative) must be discontinuous to satisfy the Schrodinger equation.

Definitely, the above discussions apply to any kind of wave equations, such as Maxwell equations. In summary: (1) single-valued-ness is a must; (2) continuity is not.

More on This LAO/STO layer

2D electron gas was observed at the interface between LAO and STO. This 2DEG displays properties including superconductivity. Now this report [Science, 332:825(2011)] says electron correlation effects can lead to negative compressibility and thus enhance capacitance.

Increases in the gate capacitance of field-effect transistor structures allow the production of lower-power devices that are compatible with higher clock rates, driving the race for developing high-κ dielectrics. However, many-body effects in an electronic system can also enhance capacitance. Onto the electron system that forms at the LaAlO₃/SrTiO₃ interface, we fabricated top-gate electrodes that can fully deplete the interface of all mobile electrons. Near depletion, we found a greater than 40% enhancement of the gate capacitance. Using an electric-field penetration measurement method, we show that this capacitance originates from a negative compressibility of the interface electron system. Capacitance enhancement exists at room temperature and arises at low electron densities, in which disorder is strong and the in-plane conductance is much smaller than the quantum conductance.

Solid He4

This solid is still very attractive for the likelihood of finding supersolidity in it. Supersolidity encompasses a thermodynamically large number of solid He atoms (or vacancies or dislocations or others) moving coherently. The route seems very ragged. A new report goes like this [Science, 332:821(2011)]:

Using a high-sensitivity torsional oscillator (TO) technique, we mapped the rotational and relaxational dynamics of solid helium-4 (⁴He) throughout the parameter range of the proposed supersolidity. We found evidence that the same microscopic excitations controlling the torsional oscillator motions are generated independently by thermal and mechanical stimulation. Moreover, a measure for the relaxation times of these excitations diverges smoothly without any indication for a critical temperature or critical velocity of a supersolid transition. Finally, we demonstrated that the combined temperature-velocity dependence of the TO response is indistinguishable from the combined temperature-strain dependence of the solid’s shear modulus. This implies that the rotational responses of solid ⁴He attributed to supersolidity are associated with generation of the same microscopic excitations as those produced by direct shear strain.

Ballastic and Diffusive motions

The impacts of heat bath on a small system embedded in it are clear on macroscopic and stationary scale, but they remain a challenging subject from the microscopic and dynamic point of view. A simple example is the Brownian motion of a single particle placed in a air or other medium. The equilibrium statistical theory was forwarded by Einstein a century ago, yet what actually take place over very short periods are still under intensive study (see previous entries). Here comes a new report [Science, 332:802(2011)]:

For many years after Einstein's contributions, it was expected that the transition from ballistic to diffusive motion would be quite sharp, corresponding to an exponential decay of the particle's memory of its earlier velocity. However, about 50 years ago, hints from computer simulations and theory started to suggest a more complex scenario. In particular, hydrodynamic vortices in the liquid created by the particle's motion lead to memory effects, and the particle's velocity decays much more slowly than exponentially, exhibiting a t^−3/2 “long-time-tail” (12). Detailed analysis by Huang et al. of data like that shown in the second figure, panel B, where the ballistic-to-diffusive transition spans more than three decades in time, has now provided a thorough verification of the full, complicated hydrodynamic theory (13, 14). Although several previous experiments had observed the breakdown of the simple diffusion picture [e.g., (15)], the present studies extend into the ballistic regime.

What next? Li et al. mention the fascinating prospect of laser cooling a trapped particle to a temperature at which quantization of the energy of this mesoscopic object could be observed (16). Huang et al. suggest extending their measurements to Brownian motion in confined regions and heterogeneous media. Here, understanding the details of prediffusive motion over subnanometer distances could well be relevant to some biological processes, such as the lock-and-key mechanism of enzyme action.

Cohen in a lecture

He gave a lecture on his recent work, in which he has listed a handful of his work on graphene, on photovoltaics, nano structures and superconductors. It might be worthy to put the link here: http://videochannel.ust.hk/Watch.aspx?Section=Channels&Channel=2&SubType=All&View=Icon&Sort=Date&Page=3&Current=30&Mode=Play

A tutorial on band structure calculation

I have encountered some Phd in physics who even could not calculate band structure ! So, I would like to recommend the following paper (which is brought to my attention thanks to Zapper's blog) to all those avid to know this technique: http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.0220v1.pdf

Delocalization of Cooper pairs by doping ?

This is definitely a very wonderful step forward. Have not read it yet, but eager to tomorrow.
http://www.nature.com/nature/journal/v472/n7344/pdf/nature09998.pdf

What is expected of reviewers

I like his viewpoint:

http://www.nature.com/news/2011/110427/full/472391a.html?WT.ec_id=NATURE-20110428

Electron induced rippling in graphene

Physicists are really blessed by nature in the sense that, they have all the time been offered some new objects that admit very rich phenomena to be explored. Latest examples include Graphene and Topological Insulators. Since its discovery, graphene never stops yielding surprising things for physicists. This time comes something that (again, considering Dirac physics) parallels particle physics: the strain field associated with the flexural phonon condenses in the same way as the Higgs field in the Standard Model [1]. Don't miss reading it !

[1]PRL, 106:045502(2011)

Where enter the doped holes in cuprates？

Years have elapsed without a consensus on the full microscopic understanding of the physics involved in cuprate superconductors. One problem central to experimentalists is the residence of doped holes. Although widely held that at low concentrations of dopants, most holes go to Zhang-Rice orbital, whose character is essentially of planar O p orbital, what happens in the overdoped case is still not clear. In this Science report [1], the workers used high resolution Compton scattering to resolve this issue. They claimed that, doped holes are mostly of Cu d character in the OD case. Their results resonate with a two-orbital model [2] that takes into account both dz^2 and dx^2-y^2 orbital. In ref.[2], the energy difference between these orbital, Delta, is the key parameter in determining Tc. Larger Delta gives larger Tc. What is implied in [1], is perhaps that, such Delta should depend on doping x. As x increases, Delta decreases. This might explain the fact that, the SC dome has a small collapse at its up right corner.

Is there a sharp transition ?

[1]Science, 332:698(2011)
[2]PRL, 105:057003(2010)

I would like to mention another paper, which measures orbital current in CuO[Science, 332:696(2011)].

Heat Flow In Small Things

Heat flow is definitely a very interesting problem in physics and also other disciplines. Here is a review on the present status of understanding over this subject concerned with small dimensions.

Advances in the fabrication and characterization of nanoscale systems now allow for a better understanding of one of the most basic issues in science and technology: the flow of heat at the microscopic level. In this Colloquium recent advances are surveyed and an understanding of physical mechanisms of energy transport in nanostructures is presented, focusing mainly on molecular junctions and atomic wires. Basic issues are examined such as thermal conductivity, thermoelectricity, local temperature and heating, and the relation between heat current density
and temperature gradient—known as Fourier’s law. Both theoretical and experimental progress are critically reported in each of these issues and future research opportunities in the field are discussed. [REVIEW OF MODERN PHYSICS, VOLUME 83, JANUARY–MARCH 2011]

Cellular networks

Cellular networks are common in nature, such as seen in the cells, bubbles, and polycrystals. In all these problems, a central question is, how do the cell boundaries distribute in time in their geometric structures and textures ? A key phenomena is that, at large times, the evolution of the distribution ubiquitously leads to a steady state that follows Boltzman's law. Here is an attempt to address this problem. The approach is traditional and phenomenological.

Mesoscale experiment and simulation permit harvesting information about both geometric features and texture in polycrystals. The grain boundary character distribution (GBCD) is an empirical distribution of the relative length [in two dimensions (2D)] or area (in 3D) of an interface with a given lattice misorientation and normal. During the growth process, an initially random distribution of boundary types reaches a steady state that is strongly correlated to the interfacial energy density. In simulation, it is found that if the given energy density depends only
on lattice misorientation, then the steady-state GBCD and the energy are related by a Boltzmann distribution. This is among the simplest nonrandom distributions, corresponding to independent trials with respect to the energy. In this paper, we derive an entropy-based theory that suggests that the evolution of the GBCD satisfies a Fokker-Planck equation, an equation whose stationary state is a Boltzmann distribution. Cellular structures coarsen according to a local evolution law, curvature-driven growth, and are limited by space-filling constraints. The interaction between the evolution law and the constraints is governed primarily by the force balance at triple junctions, the natural boundary condition associated with curvature-driven growth, and determines a dissipation relation. A simplified coarsening model is introduced that is driven by the boundary conditions and reflects the network level dissipation relation of the grain growth system. It resembles an ensemble of inertia-free spring-mass dash pots. Application is made of the recent characterization of Fokker-Planck kinetics as a gradient flow for a free energy in deriving the theory. The theory predicts the results of large-scale two-dimensional simulations and
is consistent with experiment. [PHYSICAL REVIEW B 83, 134117 (2011)]

Giant Electroresistance

There are many devices that are of fundamental interest. The most latest and famous may be the one invented by Fert et al., which displays giant magnetoresistance. In the past few years, there have appeared a flurry of work exploiting ferroelectrics as the barrier layer. I have mentioned quite a number of them in this blog. Here comes a new one. It is made up by sandwiching a BTO layer with two LSMO at different dopings. All these efforts are clearly directed to manipulate the interweaving properties of spin, charge and orbital degrees.

A giant tunneling electroresistance effect may be achieved in a ferroelectric tunnel junction by exploiting the magnetoelectric effect at the interface between the ferroelectric barrier and a magnetic La1 xSrxMnO3 electrode. Using first-principles density-functional theory we demonstrate that a few magnetic monolayers of La1 xSrxMnO3 near the interface act, in response to ferroelectric polarization
reversal, as an atomic-scale spin valve by filtering spin-dependent current. This produces more than an order of magnitude change in conductance, and thus constitutes a giant resistive switching effect. [PRL 106, 157203 (2011)]