Pines’ demon observed as a 3D acoustic plasmon in Sr2RuO4

Abstract

The characteristic excitation of a metal is its plasmon, which is a quantized collective oscillation of its electron density. In 1956, David Pines predicted that a distinct type of plasmon, dubbed a ‘demon’, could exist in three-dimensional (3D) metals containing more than one species of charge carrier1. Consisting of out-of-phase movement of electrons in different bands, demons are acoustic, electrically neutral and do not couple to light, so have never been detected in an equilibrium, 3D metal. Nevertheless, demons are believed to be critical for diverse phenomena including phase transitions in mixed-valence semimetals2, optical properties of metal nanoparticles3, soundarons in Weyl semimetals4 and high-temperature superconductivity in, for example, metal hydrides3,5–7. Here, we present evidence for a demon in Sr2RuO4 from momentum-resolved electron energy-loss spectroscopy. Formed of electrons in the β and γ bands, the demon is gapless with critical momentum qc = 0.08 reciprocal lattice units and room-temperature velocity v = (1.065 ± 0.12) × 105 m s−1 that undergoes a 31% renormalization upon cooling to 30 K because of coupling to the particle–hole continuum. The momentum dependence of the intensity of the demon confirms its neutral character. Our study confirms a 67-year old prediction and indicates that demons may be a pervasive feature of multiband metals.

Insertion semantics of quantum interactions

“…Таким чином, вивчення квантових взаємодій розглядається як одна із основних можливостей у відкритті нових речовин із корисними властивостями (суперпровідність, суперпластичність, квантові точки, магнітоелектричність тощо), оскільки дозволяє зрозуміти структуру та властивості речовини на мікроскопічному рівні, а також процеси, які відбуваються в атомах, молекулах, кристалах, наночастинках та інших квантових системах. Сьогодні особливу увагу привертають дослідження, спрямовані на виробництво сильних магнітів [1,2], дослідження поведінки електронів та, зокрема, «квантової заплутаності» [3][4][5], відкриття нових форм надпровідності [6], отримання чистої енергії [7] тощо. Важливу роль для здійснення досліджень у даних напрямках відіграють методи та системи молекулярного моделювання, зокрема, системи комп'ютерного молекулярного моделювання.…”

“…Будуючи символьну алгебраїчну модель, ми можемо задавати атрибутам агенту довільні початкові значення, наприклад: atoms (1).name== H && atoms (1).principalQuantumNum == 1 && 1<=atoms (1).massNumber <= 2 && atoms (1).electronegativity == 2.2 && atoms (1).Orbital(1,0,1) == 1 && atoms (1).electronsspinQuantumNum(1,0,1,1) == 0. 5…”

Probing the Polarization of Low-Energy Excitations in 2D Materials from Atomic Crystals to Nanophotonic Arrays Using Momentum-Resolved Electron Energy Loss Spectroscopy

“…Historically, techniques employing low-energy electrons, such as low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), high-resolution electron energy-loss spectroscopy (HREELS), and photoemission spectroscopy (PES), have played a critical role in understanding a range of material properties, from local atomic structure − to dispersion relations of materials hosting collective excitations. − The isolation of graphene and other 2D atomic crystals − has furthered the need for state-of-the-art characterization techniques where the excitonic, − phononic, − and plasmonic − excitations in these materials underlie important applications in optoelectronic devices ,,, and quantum information technologies . Due to its atom scale spatial resolution and ability to measure broadband spectral responses, electron energy-loss spectroscopy (EELS) performed inside a scanning transmission electron microscope (STEM) has played an important role in characterizing such 2D materials at their native response scales. ,− However, the high spatial resolution offered by STEM-EELS relies on momentum space integration, limiting its use as a probe of reciprocal-space excitations.…”

“…Due to its atom scale spatial resolution and ability to measure broadband spectral responses, electron energy-loss spectroscopy (EELS) performed inside a scanning transmission electron microscope (STEM) has played an important role in characterizing such 2D materials at their native response scales. ,− However, the high spatial resolution offered by STEM-EELS relies on momentum space integration, limiting its use as a probe of reciprocal-space excitations. By increasing the incident beam width, parallel beam momentum-resolved EELS ( q -EELS) in a STEM or wide-field q -EELS in a TEM overcomes this challenge, offering sufficient momentum resolution to characterize the dispersive responses of graphene , and other 2D materials. ,, Similarly, HREELS ,− ,− ,, and closely related variants ,, have recently demonstrated the ability to retrieve detailed excitation information on 2D materials.…”

“…These differences, together with a breakdown of the quasi-static approximation, thus require consideration of fully retarded light–matter interactions and expanded selection rules to properly interpret inelastic electron scattering signals from 2D periodic materials. Beyond the examples highlighted, the presented theory might be utilized to investigate other material excitations ,− with symmetry selection based on free electron wavefront shaping. ,, …”