Condensed Matter

The latest news from 3 He Universe are presented together with the extended map of the Universe.

Three-dimensional anisotropic turbulence in classical fluids tends towards isotropy and homogeneity with decreasing scales, allowing --eventually-- the abstract model of "isotropic homogeneous turbulence" to be relevant. We show here that the opposite is true for superfluid 4 He turbulence in 3-dimensional counterflow channel geometry. This flow becomes less isotropic upon decreasing scales, becoming eventually quasi 2-dimensional. The physical reason for this unusual phenomenon is elucidated and supported by theory and simulations.

According to the famous Nielsen-Ninomiya theorem, one can not put a 1d left moving chiral fermion on a 1d lattice with a local hermitian translation-invariant Hamiltonian. This is closely related to the quantum anomaly of the chiral fermion. In this paper, we propose that the Nielsen-Ninomiya theorem can be circumvented by allowing non-hermiticity. We construct a 1d local non-hermitian model with a complex spectrum, where the imaginary part of the energy corresponds to the inverse lifetime of the fermion. We show that despite our non-hermitian Hamiltonian respects the chiral symmetry, the model actually has correct quantum anomaly, including both chiral and gravitational anomaly. We present several evidences in various approaches.

Differential geometry serves as an important tool in different branches of theoretical physics. Here we present a differential geometric treatment of curvature in the auxiliary space for the non-interacting and interacting systems and also the symmetry aspect of it. We present the necessary and sufficient conditions to characterize the topological nature of curve in the auxiliary space. We present the results both for the repulsive and attractive regimes of the parameter space. We try to picture the entire problem from the geometric means of curvature. We characterize the curvature in the auxiliary space, in terms of elliptical and cycloidal motion for the non-interacting and interacting system respectively. We also try to explain the topological aspects of physics in terms of Berry connection curves. To the best of our knowledge, this is the first application of differential geometry to the topological state of matter. This study gives a new perspective for the understanding topological state of a quantum system.

We present a model to study effects from an external magnetic field, chemical potential, and finite size, on the phase structure of a massive four- and six-fermion interacting system. These effects are introduced by a method of compactification of coordinates, a generalization of the standard Matsubara prescription. Through the compactification of the z coordinate and of imaginary time, we describe a heated system with the shape of a film of thickness L , at temperature β ?? undergoing first- or second-order phase transition. We have found a strong dependence of the temperature transition on the constants couplings λ and η . Besides magnetic catalysis and symmetry breaking for both kinds of transition, we have found an inverse symmetry breaking phenomenon with respect to first-order phase transition.

In this work, chiral anomalies and Drude enhancement in Weyl semimetals are separately discussed from a semi-classical and quantum perspective, clarifying the physics behind Weyl semimetals while avoiding explicit use of topological concepts. The intent is to provide a bridge to these modern ideas for educators, students, and scientists not in the field using the familiar language of traditional solid-state physics at the graduate or advanced undergraduate physics level.

A new model is presented for spin-exchange optical pumping using an open-source code, ElmerFEM-CSC. The model builds on previous models by adding the effects of alkali-vapor heterogeneity in optical pumping cells and by modeling the effects of hyperpolarized-gas wall-relaxation using a diffusion model. The code supports full, three-dimensional solutions to optical-pumping models, and solves for (1) laser absorption, (2) alkali vapor concentration, (3) fluid flow parameters, (4) thermal affects due to the pumping laser, and (5) noble gas polarization. The source code for the model is available for researchers to utilize and modify.

We discuss polariton graphs as a new platform for simulating the classical XY and Kuramoto models. Polariton condensates can be imprinted into any two-dimensional graph by spatial modulation of the pumping laser. Polariton simulators have the potential to reach the global minimum of the XY Hamiltonian in a bottom-up approach by gradually increasing excitation density to the threshold or to study large-scale synchronisation phenomena and dynamical phase transitions when operating above the threshold. We consider the modelling of polariton graphs using the complex Ginzburg-Landau model and derive analytical solutions for a single condensate, the XY model, two-mode model and the Kuramoto model establishing the relationships between them.

In this note a one-dimensional band model is proposed based on a periodic Dirac comb having an identical mass distribution m(x) . in each unit cell. The mass function is represented as a Hermitian, non-local separable operator. Two specific cases--a constant mass model and a sinusoidal mass model--are examined. The lowest electron and positron bands for the constant mass case are similar to those for the standard relativistic Kronig-Penney model, suggesting that non-locality has little influence. The results for the sinusoidal case are consistent with the expectation that at low wavenumber an electron "feels" it has am average constant mass, but at high wave number, the particle "sees" the periodic mass variation and the band is distorted.

We seek a rational route to large-deformation, thermo-mechanical modeling of solids with metrical defects. It assumes the reference and deformed geometries to be of the Weyl type and introduces the Weyl one-form -- an additional set of degrees of freedom that determine ratios of lengths in different tangent spaces. The Weyl one-form prevents the metric from being compatible with the connection and enables exploitation of the incompatibility for characterizing metrical defects in the body. When such a body undergoes temperature changes, additional incompatibilities appear and interact with the defects. This interaction is modeled using the Weyl transform, which keeps the Weyl connection invariant whilst changing the non-metricity of the configuration. An immediate consequence of the Weyl connection is that the critical points of the stored energy are shifted. We exploit this feature to represent the residual stresses. In order to relate stress and strain in our non-Euclidean setting, use is made of the Doyle-Ericksen formula, which is interpreted as a relation between the intrinsic geometry of the body and the stresses developed. Thus the Cauchy stress is conjugate to the Weyl transformed metric tensor of the deformed configuration. The evolution equation for the Weyl one-form is consistent with the two laws of thermodynamics. Our temperature evolution equation, which couples temperature, deformation and Weyl one-form, follows from the first law of thermodynamics. Using the model, the self-stress generated by a point defect is calculated and compared with the linear elastic solutions. We also obtain conditions on the defect distribution (Weyl one-form) that render a thermo-mechanical deformation stress-free. Using this condition, we compute specific stress-free deformation profiles for a class of prescribed temperature changes.