scholarly journals Interplay of Coulomb interactions and disorder in three-dimensional quadratic band crossings without time-reversal symmetry and with unequal masses for conduction and valence bands

2018 ◽  
Vol 97 (12) ◽  
Author(s):  
Ipsita Mandal ◽  
Rahul M. Nandkishore
Keyword(s):  
Time Reversal ◽  
Three Dimensional ◽  
Time Reversal Symmetry ◽  
Coulomb Interactions ◽  
Valence Bands

scholarly journals The Casimir Effect in Topological Matter

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 237
Author(s):  
Bing-Sui Lu
Keyword(s):  
Time Reversal ◽  
Casimir Effect ◽  
Relativistic Quantum ◽  
Three Dimensional ◽  
Mutual Orientation ◽  
Electromagnetic Properties ◽  
Time Reversal Symmetry ◽  
Electronic Band ◽  
Chern Insulators ◽  
Work Done

We give an overview of the work done during the past ten years on the Casimir interaction in electronic topological materials, our focus being solids, which possess surface or bulk electronic band structures with nontrivial topologies, which can be evinced through optical properties that are characterizable in terms of nonzero topological invariants. The examples we review are three-dimensional magnetic topological insulators, two-dimensional Chern insulators, graphene monolayers exhibiting the relativistic quantum Hall effect, and time reversal symmetry-broken Weyl semimetals, which are fascinating systems in the context of Casimir physics. Firstly, this is for the reason that they possess electromagnetic properties characterizable by axial vectors (because of time reversal symmetry breaking), and, depending on the mutual orientation of a pair of such axial vectors, two systems can experience a repulsive Casimir–Lifshitz force, even though they may be dielectrically identical. Secondly, the repulsion thus generated is potentially robust against weak disorder, as such repulsion is associated with the Hall conductivity that is topologically protected in the zero-frequency limit. Finally, the far-field low-temperature behavior of the Casimir force of such systems can provide signatures of topological quantization.

scholarly journals Topological thermal Hall effect due to Weyl magnons

2018 ◽  
Vol 96 (11) ◽  
pp. 1216-1223 ◽  
Author(s):  
S.A. Owerre
Keyword(s):  
Hall Effect ◽  
Time Reversal ◽  
Low Temperatures ◽  
Three Dimensional ◽  
Zero Magnetic Field ◽  
Time Reversal Symmetry ◽  
Frustrated Magnets ◽  
Berry Curvature ◽  
Theoretical Evidence ◽  
Distribution Distance

We present the first theoretical evidence of zero magnetic field topological (anomalous) thermal Hall effect due to Weyl magnons in stacked noncoplanar frustrated kagomé antiferromagnets. The Weyl magnons in this system result from macroscopically broken time-reversal symmetry by the scalar spin chirality of noncoplanar chiral spin textures. Most importantly, they come from the lowest excitation, therefore they can be easily observed experimentally at low temperatures due to the population effect. Similar to electronic Weyl nodes close to the Fermi energy, Weyl magnon nodes at the lowest excitation are the most important. Indeed, we show that the topological (anomalous) thermal Hall effect in this system arises from nonvanishing Berry curvature due to Weyl magnon nodes at the lowest excitation, and it depends on their distribution (distance) in momentum space. The present result paves the way to directly probe low excitation Weyl magnons and macroscopically broken time-reversal symmetry in three-dimensional frustrated magnets with the anomalous thermal Hall effect.

scholarly journals Electron hydrodynamics in anisotropic materials

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Georgios Varnavides ◽  
Adam S. Jermyn ◽  
Polina Anikeeva ◽  
Claudia Felser ◽  
Prineha Narang
Keyword(s):  
Flow Pattern ◽  
Time Reversal ◽  
Large Scale ◽  
Three Dimensional ◽  
Anisotropic Materials ◽  
Three Dimensions ◽  
Time Reversal Symmetry ◽  
Classical Fluids ◽  
Large Scale Flow ◽  
Breaking Time

Abstract Rotational invariance strongly constrains the viscosity tensor of classical fluids. When this symmetry is broken in anisotropic materials a wide array of novel phenomena become possible. We explore electron fluid behaviors arising from the most general viscosity tensors in two and three dimensions, constrained only thermodynamics and crystal symmetries. We find nontrivial behaviors in both two- and three-dimensional materials, including imprints of the crystal symmetry on the large-scale flow pattern. Breaking time-reversal symmetry introduces a non-dissipative Hall component to the viscosity tensor, and while this vanishes for 3D isotropic systems we show it need not for anisotropic materials. Further, for such systems we find that the electronic fluid stress can couple to the vorticity without breaking time-reversal symmetry. Our work demonstrates the anomalous landscape for electron hydrodynamics in systems beyond graphene, and presents experimental geometries to quantify the effects of electronic viscosity.

Valence electron energy loss spectroscopy in reflection geometry

1989 ◽  
Vol 47 ◽  
pp. 378-379
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Energy Loss ◽  
Valence Electron ◽  
Interband Transition ◽  
Specular Reflection ◽  
Three Dimensional ◽  
Electron Excitation ◽  
Transmission Electron ◽  
Yield Information ◽  
Valence Bands ◽  
Excitation Processes

The low energy loss region of a EELS spectrum carries information about the valence electron excitation processes (e.g., collective excitations for free electron like materials and interband transitions for insulators). The relative intensities and the positions of the interband transition energy loss peaks observed in EELS spectra are determined by the joint density of states (DOS) of the initial and final states of the excitation processes. Thus it is expected that EELS in reflection mode could yield information about the perturbation of the DOS of the conduction and valence bands of the bulk crystals caused by the termination of the three dimensional periodicity at the crystal surfaces. The experiments were performed in a Philipps 400T transmission electron microscope operated at 120 kV. The reflection EELS spectra were obtained by a Gatan 607 EELS spectrometer together with a Tracor data acquisition system and the resolution of the spectrometer was about 0.8 eV. All the reflection spectra are obtained from the specular reflection spots satisfying surface resonance conditions.

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