Direct observation of highly confined phonon polaritons in suspended monolayer hexagonal boron nitride

Revealing Abnormal Phonon Polaritons Confined at the Edge of Curved Two-Dimensional Boron Nitride

“…Thus, the HPhP signal in folded region can be assigned to the regular HPhP mode of 2L as a result of doubling the thickness of monolayer flakes. In the vacuum region (aloof configuration), a weak signal around 169 meV is observable and is consistent with the occurrence of hyperbolic surface phonon polaritons (HSPhPs) at the boundary of h-BN flakes [4,5]. Strikingly, an energy blue-shifts takes place in HPhPs near the edge with an average increment of 1.4 meV compared to the interior folded region.…”

“…In the interior region away from the folding edge, the peak center is about 170 meV and remains unchanged. Meanwhile, we calculated the energy position of the HPhP in the h-BN slabs with different thickness [3,4]. The calculated peak centers of 1L and 2L are 169.95 meV and 170.04 meV as indicated by two dashed lines in Fig.…”

Spatiotemporal imaging of 2D polariton wave packet dynamics using free electrons

“…EELS enabled the measurement of purely vibrational modes (phonons) in bulk media and on surfaces (60,61) and the extraction of their dispersion relations using electron imaging and diffraction (62,63). In recent years, the improvements in the energy resolution of EELS (59) enabled the imaging of hBN PhP resonances (64) and recently the extraction of the PhP dispersion in extremely thin samples (65). Such experiments translated methodologies in electron microscopy, once applied to plasmons in the visible range (e.g., Refs.…”

Hourglass Weyl and Dirac nodal line phonons, and drumhead-like and torus phonon surface states in orthorhombic-type KCuS

“…It is hoped that these novel phonon surface states can be detected via the following techniques, such as helium scattering, 68 terahertz polarimetry, 69 and highresolution electron energy loss spectroscopy. 70 To support the inspiring findings of the DNL and HWNL phonons, besides KCuS, the DNL and HWL phonons in other material samples, BaSi 2 , ZrSi, and TiB, with space group number 62 are also discussed in this Communication (in the SMs).…”