Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.

Imaging the Fano lattice to ‘hidden order’ transition in URu 2 Si 2

Abstract: Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called ‘heavy fermions’. In URu2Si2 these effects begin at temperatures around 55 K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown. Here we use spectroscopic imaging scanning tunnelling microscopy (SI-STM) to image the evolution of URu2Si2 electronic structure simultaneously in r-space and k-space. Above To, the ‘Fano lattice’ electronic structure predicted for Kondo screening of a magnetic lattice is revealed. Below To, a partial energy gap without any associated density-wave signatures emerges from this Fano lattice. Heavy-quasiparticle interference imaging within this gap reveals its cause as the rapid splitting below To of a light k-space band into two new heavy fermion bands. Thus, the URu2Si2 ‘hidden order’ state emerges directly from the Fano lattice electronic structure and exhibits characteristics, not of a conventional density wave, but of sudden alterations in both the hybridization at each U atom and the associated heavy fermion states. A long-standing mystery in condensed matter physics is that of the appearance of a 'hidden order' state in URu2Si2 at low temperature, an unexpected phase change that is accompanied by a sharp change in bulk properties of the material. The problem is related to the appearance of a 'heavy fermion' state (already at a higher temperature) where electron-like charge carriers propagate through the solid with an effective mass thousands of times larger than that of a free electron. Schmidt et al. have now used scanning tunnelling microscopy and spectroscopy to visualize the electronic structure of URu2Si2 with subatomic resolution. In the process, they observe the electronic structure associated with a magnetic 'Kondo' lattice, which was assumed to cause heavy fermion effects, but never observed directly. Further, the spectroscopic findings show how the hidden order state evolves with decreasing temperature from this lattice. A longstanding mystery in condensed-matter physics involves the appearance of a 'hidden order' state in URu2Si2 at low temperature — an unexpected phase change that is accompanied by a sharp change in the bulk properties of the material. The problem is related to the appearance of a 'heavy fermion' state. Here, scanning tunnelling microscopy and spectroscopy have been used to image the electronic structure of URu2Si2 at sub-atomic resolution, revealing how the hidden order state evolves with decreasing temperature.

Massive Dirac quasiparticles in the optical absorbance of graphene, silicene, germanene, and tinene.

Abstract: We present first-principles studies of the optical absorbance of the group IV honeycomb crystals graphene, silicene, germanene, and tinene. We account for many-body effects on the optical properties by using the non-local hybrid functional HSE06. The optical absorption peaks are blueshifted due to quasiparticle corrections, while the influence on the low-frequency absorbance remains unchanged and reduces to a universal value related to the Sommerfeld fine structure constant. At the Dirac points spin-orbit interaction opens fundamental band gaps; parabolic bands with a very small effective mass emerge. Consequently, the low-frequency absorbance is modified with a spin-orbit-induced transparency region and an increase of the absorbance at the fundamental absorption edge.

Ferromagnetic Spin Fluctuation Induced Superconductivity in Sr 2 RuO 4

Abstract: We propose a quantitative model for triplet superconductivity in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ based on first principles calculations for the electronic structure and magnetic susceptibility. The superconductivity is due to ferromagnetic spin fluctuations that are strong at small wave vectors. The calculated effective mass renormalization, renormalized susceptibility, and superconducting critical temperature are all in good agreement with experiment. The order parameter is of comparable magnitude on all three sheets of the Fermi surface.

Tunable electronic structures of graphene/boron nitride heterobilayers

Abstract: Using first-principles calculations, we show that the band gap and electron effective mass (EEM) of graphene/boron nitride heterobilayers (C/BN HBLs) can be modulated effectively by tuning the interlayer spacing and stacking arrangement. The HBLs have smaller EEM than that of graphene bilayers (GBLs), and thus higher carrier mobility. For specific stacking patterns, the nearly linear band dispersion relation of graphene monolayer can be preserved in the HBLs accompanied by a small band-gap opening. The tunable band gap and high carrier mobility of these C/BN HBLs are promising for building high-performance nanodevices.