title: Scanning Tunneling Microscopy Observation of Phonon Condensate.
abstract: Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of all phonon modes, and indicates the formation of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.
authors.affiliation: Nanoelectronic Materials Branch, Air Force Research Laboratory, Wright Patterson AFB, OH 45433, USA.
authors.forename: Igor
authors.initials: I
authors.lastname: Altfeder
authors.affiliation: Nanoelectronic Materials Branch, Air Force Research Laboratory, Wright Patterson AFB, OH 45433, USA.|Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, USA.
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Voevodin
authors.affiliation: Nanoelectronic Materials Branch, Air Force Research Laboratory, Wright Patterson AFB, OH 45433, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Check
authors.affiliation: Department of Materials Science and Engineering and The Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Eichfeld
authors.affiliation: Department of Materials Science and Engineering and The Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Robinson
authors.affiliation: Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.|Nordita, Center for Quantum Materials, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Balatsky