arXiv subjects

Lei Liao

Publications and source records attributed to Lei Liao.

23 records · Page 2Linked to original sources

arXiv2019

Atomic-scale observations of electrical and mechanical manipulation of topological polar flux-closure

The ability to controllably manipulate the complex topological polar configurations, such as polar flux-closure via external stimuli, enables many applications in electromechanical devices and nanoelectronics including high-density information storage. Here, by using the atomically resolved in situ scanning transmission electron microscopy, we find that a polar flux-closure structure in PbTiO3/SrTiO3 superlattices films can be reversibly switched to ordinary mono ferroelectric c domain or a domain under electric field or stress. Specifically, the electric field initially drives the flux-closure move and breaks them to form intermediate a/c striped domains, while the mechanical stress firstly starts to squeeze the flux-closures to convert into small vortices at the interface and form a continues dipole wave. After the removal of the external stimuli, the flux-closure structure spontaneously returns. Our atomic study provides valuable insights into understanding the lattice-charge interactions and the competing interactions balance in these complex topological structures. Such reversible switching between the flux-closure and ordinary ferroelectric domains also provides the foundation for applications such as memories and sensors.

cond-mat.mtrl-sci↗

arXiv2018

Dynamics of a Space-Time Crystal in an Atomic Bose-Einstein Condensate

A space-time crystal has recently been observed in a superfluid Bose gas. Here we construct a variational model that allows us to describe from first principles the coupling between the radial breathing mode and the higher-order axial modes that underlies the observation of the space-time crystal. By comparing with numerical simulations we verify the validity of our variational Ansatz. From the model we determine the requirements for the observation of the space-time crystal and the Ising-like nature of the symmetry breaking involved. Also, we find the onset and growth rate of the space-time crystal, which can be compared to experiments.

cond-mat.quant-gas↗

arXiv2018

Observation of a space-time crystal in a superfluid quantum gas

Time crystals are a phase of matter, for which the discrete time symmetry of the driving Hamiltonian is spontaneously broken. The breaking of discrete time symmetry has been observed in several experiments in driven spin systems. Here, we show the observation of a space-time crystal using ultra-cold atoms, where the periodic structure in both space and time are directly visible in the experimental images. The underlying physics in our superfluid can be described ab initio and allows for a clear identification of the mechanism that causes the spontaneous symmetry breaking. Our results pave the way for the usage of space-time crystals for the discovery of novel nonequilibrium phases of matter.

cond-mat.quant-gas↗

arXiv2017

Metallic vanadium disulfide nanosheets as a platform material for multifunctional electrode applications

Nano-thick metallic transition metal dichalcogenides such as VS$_{2}$ are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such 2D layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS$_{2}$ nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets feature spontaneous superlattice periodicities and excellent electrical conductivities (~3$\times$10$^{3}$ S cm$^{-1}$), which has enabled a variety of applications such as contact electrodes for monolayer MoS$_{2}$ with contact resistances of ~1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous electrolytes showing specific capacitances as high as 8.6$\times$10$^{2}$ F g$^{-1}$. This work provides fresh insights into the delicate structure-property relationship and the broad application prospects of such metallic 2D materials.

cond-mat.mtrl-sci↗

arXiv2015

Ultrasensitive and broadband MoS2 photodetector driven by ferroelectrics

Photodetectors based on two dimensional materials have attracted growing interest. However, the sensitivity is still unsatisfactory even under high gate voltage. Here we demonstrate a MoS2 photodetector with a poly(vinylidene fluoride-trifluoroethylene) ferroelectric layer in place of the oxide layer in a traditional field effect transistor. The dark current of the photodetector is strongly suppressed by ferroelectric polarization. A high detectivity 2.21012 Jones) and photoresponsitivity (2570 A W) detector has been achieved under ZERO gate bias at a wavelength of 635 nm. Most strikingly, the band gap of few-layer MoS2 can be tuned by the ultra-high electrostatic field from the ferroelectric polarization. With this characteristic, photoresponse wavelengths of the photodetector are extended into the near infrared (0.85-1.55m). A ferroelectrics optoelectronics hybrid structure is an effective way to achieve high performance 2D electronic optoelectronic devices.

cond-mat.mes-hall↗