The behavior of matter near zero temperature continuous phase transitions, or "quantum critical points" is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical "soup." Here, we report a study of the specific heat across the phase diagram of the model system Sr 3 Ru 2 O 7 , which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above T c . The associated quantum critical point, which is "concealed" by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces.heavy Fermion behavior | nematic metal O ne of the most striking empirical facts about quantum criticality is that, in systems with low disorder, the approach to quantum critical points (QCPs) is often cut off by the formation of new broken symmetry phases. Although this phase formation is widely discussed (1-4), thermodynamic data probing how it occurs are surprisingly sparse. The properties of a low temperature ordered phase are usually linked to those of the metal from which it condenses. Many states form from the background of well understood Fermi liquids, so investigations of the metal are used to gain insight into the properties of the ordered phase. For example, the existence of sharply defined quasiparticles in a simple (Fermi liquid) metal implies the well known "Cooper instability" that leads to the formation of a low temperature superconducting state, and the spectrum of phonons and/or magnetic excitations determines the structure of the gap function in that state. The case of phase formation from a quantum critical background is more challenging and possibly richer, because the metal itself is so mysterious; understanding the thermodynamics of phase formation might yield insight into the quantum critical metal as well as the ordered phase.In-depth studies of the specific heat are difficult in prototypical quantum critical superconductors such as CeIn 3 and CePd 2 Si 2 because of the need to work in pressure cells. Both constructing measurement apparatus suited to the high pressure environment and subtracting the huge addenda background due to the pressure cell are challenging experimental problems that have not yet fully been solved. In this paper we give a concrete example in which the material can be tuned ...

No abstract

Pull-in instability, as an inherent nonlinear problem, continues to become an increasingly important and interesting topic in the design of electrostatic Nano/Micro-electromechanical systems (N/MEMS) devices. Generally, the pull-in instability was studied in a continuous space, but when the electronic devices work in a porous medium, they need to be analyzed in a fractal partner. In this paper, we establish a fractal model for N/MEMS, and find a pull-in stability plateau, which can be controlled by the porous structure, and the pull-in instability can be finally converted to a stable condition. As a result, the pull-in instability can be completely eliminated, realizing the transformation of pull-in instability into pull-in stability.

This paper highlights Li-He’s approach in which the enhanced perturbation method is linked with the parameter expansion technology in order to obtain frequency amplitude formulation of electrically actuated microbeams-based microelectromechanical system (MEMS). The governing equation is a second-order nonlinear ordinary differential equation. The obtained results are compared with the solution achieved numerically by the Runge-Kutta (RK) method that shows the effectiveness of this variation in the homotopy perturbation method (HPM).