Controlling acoustic phonons, the carriers of sound and heat, has been attracting great attention toward the manipulation of sonic and thermal properties in nanometric devices. In particular, the photo-acoustic effect using ultrafast optical pulses has a promising potential to optically manipulate phonons in picoseconds time regime. However, its mechanism has been so far mostly based on the commonplace thermoelastic expansion in isotropic media, limiting the spectrum of potential applications. We investigate a conceptually new mechanism of photo-acoustic effect involving the structural instability, by utilizing a transition-metal dichalcogenide VTe$_2$ with the ribbon-type charge-density-wave (CDW). Ultrafast electron microscope imaging and diffraction measurements reveal the generation and propagation of unusual acoustic waves in the nanometric thin plate associated with the optically induced instantaneous charge-density-wave dissolution. Our results highlight the capability of photo-induced structural instability as a source of coherent acoustic waves.
Effect of thermal annealing on the heat transfer properties of reduced graphite oxide flakes: a nanoscale characterization via scanning thermal microscopy
Color centers in hexagonal boron nitride (hBN) have emerged as promising candidates for single-photon emitters (SPEs) due to their bright emission characteristics at room temperature. In contrast to mono- and few-layered hBN, color centers in multi-layered flakes show superior emission characteristics such as higher saturation counts and spectral stability. Here, we report a method for determining both the axial position and three-dimensional dipole orientation of SPEs in thick hBN flakes by tuning the photonic local density of states using vanadium dioxide (VO2), a phase change material. Emit…
Modulation of charge density waves in a twisted vortex moire superlattice
Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所，北京凝聚态物理国家研究中心）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Key Laboratory of advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology（北京理工大学物理学院，先进光电子量子架构与测量教育部重点实验室）；International Center for Quantum Materials, Beijing Institute of Technology（北京理工大学量子材料国际中心）
Two-dimensional (2D) transition metal dichalcogenides are potential candidates for ultrathin solid-state lubricants in low-dimensional systems owing to their flatness, high in-plane mechanical strength, and low shear interlayer strength. Yet, the effects of surface topography and surface chemistry on the tribological properties of 2D layers are still unclear. In this work, we performed a comparative investigation of nanoscale tribological properties of ultra-thin highly-ordered PtSe2 layers deposited on the sapphire substrates with the in-plane and out-of-plane crystallographic orientation of …
The research on two-dimensional (2D) van der Waals (vdW) ferromagnets has promoted the development of ultrahigh-density and nanoscale data storage. However, intrinsic ferromagnetism in layered magnets is always subject to many factors, such as stacking orders, interlayer couplings, and the number of layers. Here, we report a magnetic transition from soft to hard ferromagnetic behaviors as the thickness of CrSiTe$_3$ flakes decreases down to several nanometers. Phenomenally, in contrast to the negligible hysteresis loop in the bulk counterparts, atomically thin CrSiTe$_3$ shows a rectangular lo…
Melting point depression of charge density wave in 1T-TiSe$_2$ due to size effects
Cornell University（康奈尔大学）；FAMU-FSU College of Engineering（FAMU-FSU 工程学院）；University of Michigan（密歇根大学）；h-Bar Instruments（h-Bar 仪器公司）；Harvard University（哈佛大学）
Fast Programming of In-Plane Hyperbolic Phonon Polariton Optics Through van der Waals Crystals using the Phase-Change Material In3SbTe2
RWTH Aachen University（亚琛工业大学）；Juelich-Aachen Research Alliance (JARA-FIT)（于利希-亚琛研究联盟）；University of Oviedo（奥维耶多大学）；Center of Research on Nanomaterials and Nanotechnology, CINN (CSIC-Universidad de Oviedo)（纳米材料与纳米技术研究中心，CINN（西班牙国家科研委员会-奥维耶多大学））；Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies（意大利理工学院，生物分子纳米技术中心）
We present a new approach to femtosecond direct laser writing lithography to pattern nanocavities in ferromagnetic thin films. To demonstrate the concept we irradiated 300~nm thin nickel films by single intense femtosecond laser pulses through the glass substrate and created complex surface landscapes at the nickel-air interface. Using a fluence above the ablation threshold the process is destructive and irradiation leads to the formation of 200~nm thin flakes of nickel around the ablation crater as seen by electron microscopy. By progressively lowering the peak laser fluence, slightly below t…
Topological insulators (TIs) represent a novel quantum state of matter, characterized by edge or surface-states, showing up on the topological character of the bulk wave functions. Allowing electrons to move along their surface, but not through their inside, they emerged as an intriguing material platform for the exploration of exotic physical phenomena, somehow resembling the graphene Dirac-cone physics, as well as for exciting applications in optoelectronics, spintronics, nanoscience, low-power electronics, and quantum computing. Investigation of topological surface states (TSS) is conventio…
The synthesis of transition metal dichalcogenides (TMDs) has been a primary focus for 2D nanomaterial research over the last 10 years, however, only a small fraction of this research has been concentrated on transition metal ditellurides. In particular, nanoscale platinum ditelluride (PtTe2) has rarely been investigated, despite its potential applications in catalysis, photonics and spintronics. Of the reports published, the majority examine mechanically-exfoliated flakes from chemical vapor transport (CVT) grown crystals. While this production method is ideal for fundamental studies, it is ve…
