Abstract: Electrons confined in a material exhibit rich quantum behavior with no counterpart in free space. In particular, electron-electron interactions give rise to quantized collective particles which we can use to fundamentally understand the properties of materials. For metals, the primary collective mode of electrons is the plasmon - a quantized excitation where all the electrons move together in synchrony. In 1956, David Pines predicted another particle, known as the "demon", inside multiband metals where electrons of different "flavors" move out-of-phase with each other. For over 66 years, the demon remained undetected because demons are both gapless (i.e. massless) and do not couple to light. Nevertheless, demons are predicted to be responsible for diverse phenomena ranging from phase transitions in mixed-valence materials, "soundarons" in Weyl semimetals, and superconductivity in, for example, metal hydrides. In this talk, I will present evidence for the demon in Sr2RuO4 using the newly developed technique of Momentum-resolved Electron Energy-Loss Spectroscopy (M-EELS). Our study confirms the existence of Pines' demon and indicates that demons may be a pervasive feature of multiband metals. Finally, I will discuss emerging experimental efforts for discovering new collective particles in quantum materials that have escaped experimental identification.
Bio: Ali Husain received his B.S. in Physics from the University of California, Berkeley in 2014. In 2020, he completed his Ph.D at the University of Illinois at Urbana-Champaign in condensed matter physics focusing on the problem of charge dynamics in so-called "strange" metals. From 2020-2022, Ali was the SBQMI Postdoctoral Prize Fellow at the University of British Columbia working with George Sawatzky and Steven Dierker to develop new methods for studying quantum materials using electron microscopy and spectroscopy. Since 2022, Ali has been an AMO research scientist at Quantinuum building next-generation trapped-ion quantum computers.
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2024-02-29T11:00:002024-02-29T12:00:00Observation of Pines' Demon in Sr2RuO4Event Information:
Abstract:Electrons confined in a material exhibit rich quantum behavior with no counterpart in free space. In particular, electron-electron interactions give rise to quantized collective particles which we can use to fundamentally understand the properties of materials. For metals, the primary collective mode of electrons is the plasmon - a quantized excitation where all the electrons move together in synchrony. In 1956, David Pines predicted another particle, known as the "demon", inside multiband metals where electrons of different "flavors" move out-of-phase with each other. For over 66 years, the demon remained undetected because demons are both gapless (i.e. massless) and do not couple to light. Nevertheless, demons are predicted to be responsible for diverse phenomena ranging from phase transitions in mixed-valence materials, "soundarons" in Weyl semimetals, and superconductivity in, for example, metal hydrides. In this talk, I will present evidence for the demon in Sr2RuO4 using the newly developed technique of Momentum-resolved Electron Energy-Loss Spectroscopy (M-EELS). Our study confirms the existence of Pines' demon and indicates that demons may be a pervasive feature of multiband metals. Finally, I will discuss emerging experimental efforts for discovering new collective particles in quantum materials that have escaped experimental identification.
Bio:Ali Husain received his B.S. in Physics from the University of California, Berkeley in 2014. In 2020, he completed his Ph.D at the University of Illinois at Urbana-Champaign in condensed matter physics focusing on the problem of charge dynamics in so-called "strange" metals. From 2020-2022, Ali was the SBQMI Postdoctoral Prize Fellow at the University of British Columbia working with George Sawatzky and Steven Dierker to develop new methods for studying quantum materials using electron microscopy and spectroscopy. Since 2022, Ali has been an AMO research scientist at Quantinuum building next-generation trapped-ion quantum computers.Event Location:
HENN 318