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.

Heavy solitons in a fermionic superfluid

Abstract: Solitons—solitary waves that maintain their shape as they propagate—occur as water waves in narrow canals, as light pulses in optical fibres and as quantum mechanical matter waves in superfluids and superconductors. Their highly nonlinear and localized nature makes them very sensitive probes of the medium in which they propagate. Here we create long-lived solitons in a strongly interacting superfluid of fermionic atoms and directly observe their motion. As the interactions are tuned from the regime of Bose–Einstein condensation of tightly bound molecules towards the Bardeen–Cooper–Schrieffer limit of long-range Cooper pairs, the solitons’ effective mass increases markedly, to more than 200 times their bare mass, signalling strong quantum fluctuations. This mass enhancement is more than 50 times larger than the theoretically predicted value. Our work provides a benchmark for theories of non-equilibrium dynamics of strongly interacting fermions. Solitons — solitary waves that maintain their shape as they propagate — in a strongly interacting superfluid of fermionic lithium atoms are found to have an effective mass more than 50 times larger than the theoretically predicted value, a sign of strong quantum fluctuations. Solitons — solitary waves that maintain their shape as they propagate — occur in nonlinear systems ranging from shallow waterways to DNA and act as exquisite probes of the medium in which they propagate. These authors create long-lived solitons in a strongly interacting superfluid of fermionic lithium atoms and directly observe their motion. As the interactions are tuned, the effective mass of the solitons increases by a factor of at least 200, more than fifty times greater than the theoretically predicted value. The observed mass enhancement is a sign of strong quantum fluctuations and provides an important benchmark for theories on non-equilibrium dynamics of strongly interacting fermions.

Electronic structures and unusually robust bandgap in an ultrahigh-mobility layered oxide semiconductor, Bi2O2Se

Abstract: Semiconductors are essential materials that affect our everyday life in the modern world Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi2O2Se, with ultrahigh mobility (~28 × 105 cm2/V⋅s at 20 K) and moderate bandgap (~08 eV) Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi2O2Se with key parameters (for example, effective mass, Fermi velocity, and bandgap) The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi2O2Se an ideal semiconductor for future electronic applications In addition, the structural compatibility between Bi2O2Se and interesting perovskite oxides (for example, cuprate high–transition temperature superconductors and commonly used substrate material SrTiO3) further makes heterostructures between Bi2O2Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers

GeSe monolayer semiconductor with tunable direct band gap and small carrier effective mass

Abstract: Two dimensional materials, befitting nanoscale electronics, can benefit strain-tunable applications due to their ultrathin and flexible nature. Based on the first-principles calculations within the generalized gradient approximation, GeSe monolayer with a distorted NaCl-type structure is predicted. The GeSe monolayer is found to be a direct semiconductor with a band gap of (1.16 ± 0.13) eV against the bulk counterpart. The electronic responses of the GeSe monolayer to strain are found to be sensitive and anisotropic, and the transitions between direct and indirect band gap are repeatedly met in the course of energy engineering by uniaxial and biaxial strains. The direct band gap of the GeSe monolayer is tunable by small strain within a large energy range (0.95–1.48 eV). The carrier effective masses in the GeSe monolayer are also tunable by strain in a low mass range (0.03–0.61 m0). These intriguing properties make GeSe monolayer a promising two-dimensional material for nanomechanics, thermoelectrics, and ...