Lin Cao

Composition and temperature-dependent phase transition in miscible Mo 1− x W x Te 2 single crystals

Transition metal dichalcogenides (TMDs) WTe2 and MoTe2 with orthorhombic Td phase, being potential candidates as type-II Weyl semimetals, are attracted much attention recently. Here we synthesized a series of miscible Mo1−xWxTe2 single crystals by bromine vapor transport method. Composition-dependent X-ray diffraction and Raman spectroscopy, as well as composition and temperature-dependent resistivity prove that the tunable crystal structure (from hexagonal (2H), monoclinic (β) to orthorhombic (Td) phase) can be realized by increasing W content in Mo1−xWxTe2. Simultaneously the electrical property gradually evolves from semiconductor to semimetal behavior. Temperature-dependent Raman spectroscopy proves that temperature also can induce the structural phase transition from β to Td phase in Mo1−xWxTe2 crystals. Based on aforementioned characterizations, we map out the temperature and composition dependent phase diagram of Mo1−xWxTe2 system. In addition, a series of electrical parameters, such as carrier type, carrier concentration and mobility, have also been presented. This work offers a scheme to accurately control structural phase in Mo1−xWxTe2 system, which can be used to explore type-II Weyl semimetal, as well as temperature/composition controlled topological phase transition therein.

Polarization state of the transmitted light in the absorptive infrared range through α-quartz

Two peaks of the transmitted waves at 580 and 665 cm � 1 were found to be perpendicularly polarized after propagating through a-quartz, which correspond to the ordinary and extraordinary waves, respectively. This is a new dichroic property of a-quartz in the infrared frequency region, namely the polarization state of the incident light is changed after propagation through a-quartz. # 2003 Elsevier Ltd. All rights reserved.

Magnetic-flux-induced persistent currents in symmetric-polymer mesoscopic rings

We investigate magnetic-flux-induced persistent currents in one-dimensional symmetric-polymer (SP) mesoscopic ring, where a defect cluster is embedded into two periodic clusters and the whole cluster possesses mirror symmetry. Under tight-binding approximation, the flux-dependent energy spectra, electronic wave functions, and persistent currents are obtained. It is shown that the energy spectra form band structure and the defect modes appear in the band gap. The persistent current (PC) depends on the magnetic flux, the site energy, and the Fermi level. Particularly, by changing the Fermi level, the SP ring presents metallic and insulative features alternately. Our investigations provide a possible model to explain the anomalously large PC observed in some experiments and contribute to the potential application in quantum-switch devices.

Magnetic-flux induced persistent currents in quasiperiodic mesoscopic rings

Under the tight-binding approximation, we study the persistent current (PC) in the magnetic-flux-threaded mesoscopic ring which is constructed according to the Fibonacci-class model. It is shown that the energy spectra form band structures and the subbands present a self-similarity. The PC is determined by the magnetic flux, the site energy, and the Fermi level. It is found that the large PC can be observed if the Fermi level reaches a specific value. Our investigation provides detailed information on the structural influence on the PC and contributes a mechanism to understand the large PC observed in the experiments.

Tunable high-frequency magnetostatic waves in Thue-Morse antiferromagnetic multilayers

We theoretically studied the magnetostatic excitation in self-similar antiferromagnetic(AF)/nonmagnetic(NM) multilayers, where the AF and NM layers were arranged in a Thue-Morse sequence. The dispersion relation of magnetostatic spin waves and the precession amplitude of the total magnetization were achieved. It is shown that the distribution of eigenfrequencies possesses two bands of dual structures and each subband presents a hierarchical feature. The states in the finite system can be categorized to three types: critical states in the subband, extended states in the band, and localized surface states in the gaps. The multiformity in frequency spectra leads to the tunable magnetostatic wave, which may have potential applications in designing devices of magnetostatic waves for microwave communications.

The relationship between anisotropic magnetoresistance and topology of Fermi surface in Td-MoTe2 crystal

Layered transition-metal dichalcogenides have been recently attracted a lot of attention because of their unique physical properties, such as extremely large and anisotropic magnetoresistance (MR) in WTe2. In this work, we observed the abnormally anisotropic MR on Td-MoTe2 crystal that is strongly dependent on the temperature, as well as the orientations of both magnetic field B and electric field E with respect to crystallographic axes of Td-MoTe2. When E//a-axis and B//c-axis, MR is parabolically dependent on B and is as high as 520% under 9 T and 2 K conditions; the MR is quasi-linearly dependent on B when E//a-axis and B//b-axis (E//b-axis and B//c-axis), and the corresponding MR is only 130% (220%); MR is initially parabolically dependent on B, then linearly on B, and finally shows a saturate trend under E//B//a-axis (or E//B//b-axis) conditions, and the MR is about 16% (30%). These anisotropic MR behaviors can be qualitatively explained by the features of the Fermi surface of Td-MoTe2. This work may...