Lu Cao

Spin-dependent bandgap structure and resonant transmission of electrons in ferromagnetic metal/semiconductor cascade junctions

We investigate spin-dependent transport in ferromagnetic metal (FM)/semiconductor (SC) cascade junctions, which can be denoted as (FM∕SC)n∕FM. Here, n is the repeated number of FM/SC junction. In the Landauer framework of ballistic transport, we have calculated the spin-dependent transmission and the spin polarization in these cascade junctions. It is shown that spin-up and spin-down electrons possess different bandgap structures against the Rashba spin-orbit wave vector. As a result, high spin polarization can be achieved. Besides, resonant transmission for spin-up or spin-down electrons can be observed within the bandgap when we intentionally change the magnetization of FM in the center of the cascade junctions. Around resonant wave vector, spin polarization will be reversed. Our investigations may have potential applications in spin filters and spin switches.

Tunable phonon resonances and thermal conductance in weakly nonlinear disordered systems with short-range correlation

We theoretically investigate the resonant transmission of phonons and step-like thermal conductance in a weakly nonlinear generalized random n-mer (NGRN) system, where the impurity cluster with short-range correlation is randomly distributed in the host monatomic chain, and the atoms are connected by anharmonic potentials. The weakly anharmonic potential can be reduced to the quasi-harmonic form, which is tuned by external stretching. Due to the delocalization of phonons, resonant transmission is observed and thermal conductance presents a quantized feature. By applying external stretching on the NGRN system, the number of resonant modes and their locations are tuned. As a consequence, the quantized thermal conductance becomes tunable in this system. This finding may achieve potential applications in designing novel thermal-conducting materials.

Multimode quantized thermal conductance tuned by external field in a quantum wire

In this work, we propose an approach to realize field-dependent multimode quantized thermal conductance by introducing both harmonic and anharmonic couplings to a quantum wire. It is demonstrated theoretically that by stretching (or compressing) the wire, phononic band structures are tuned and multiple phononic channels are opened one by one. In this way, multiple-step quantized thermal conductance is realized. The research opens a way to manipulate heat transfer in mesoscopic phonon systems.

Electronic delocalization and resonant transmission in symmetric metallic nanowires

We report here the theoretical studies on electronic delocalization and resonant transmission in symmetric metallic nanowires (SMNs). Resonant transmissions, which are characterized by multiple perfect transmission peaks, have been found in the electronic band gap. The resonant energy and the number of modes of resonant transmission therein can be manipulated, and the quality factor of the perfect transmission peak can be exponentially increased. We suggest that the resonant transmission originates from the electronic delocalization in SMNs, which is characterized by the extended wave function of electrons around the resonant energy. These features open a unique way to control quantum transport in nanodevices.

Band Structure Perfection and Superconductivity in Type-II Dirac Semimetal Ir1− x Pt x Te2

Topological semimetal is a topic of general interest in material science. Recently, a new kind of topological semimetal called type-II Dirac semimetal with tilted Dirac cones is discovered in PtSe2 family. However, the further investigation is hindered due to the huge energy difference from Dirac points to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we characterize the optimized type-II Dirac dispersions in a metastable 1T phase of IrTe2. Our strategy of Pt doping protects the metastable 1T phase in low temperature and tunes the Fermi level to the Dirac point. As demonstrated by angle-resolved photoemission spectra and first principle calculations, the Fermi surface of Ir1-xPtxTe2 is formed by only a single band with type-II Dirac cone which is tilted strongly along kz momentum direction. Interesting superconductivity is observed in samples for Dirac point close to Fermi level and even survives when Fermi level aligns with the Dirac point as finite density of states created by the tilted cone dispersion. This advantage offers opportunities for possible topological superconductivity and versatile Majorana devices in type-II Dirac semimetals.The discovery of a new type-II Dirac semimetal in Ir1-x Ptx Te2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level close to the Dirac point. The type-II Dirac dispersion in Ir1-x Ptx Te2 is confirmed by angle-resolved photoemission spectroscopy and first-principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir1-x Ptx Te2 is an ideal platform for further studies on the exotic properties and potential applications of type-II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.

Probing plasmon resonances of individual aluminum nanoparticles

The plasmon resonances of individual aluminum nanoparticles are investigated by electron energy-loss spectroscopy (EELS) in scanning transmission electron microscope (STEM). Surface plasmon mode an...

Oscillating planar Hall response in bulk crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S

We report the low-temperature magneto-transport in the bulk-insulating single crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. Shubnikov-de Haas oscillations appear with their reciprocal frequency proportional to cos θ, demonstrating the dominant transport of topological surface states. While the magnetic field rotates on the sample surface, the planar Hall effect arises with sizeable oscillations following a relation of cos θ sin θ. Its amplitude reaches the maximum at the lowest temperature and drops to nearly zero at temperature higher than 100u2009K. All these evidences consolidate such planar Hall oscillations as another golden criterion on the topological surface transport.We report the low-temperature magneto-transport in the bulk-insulating single crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. Shubnikov-de Haas oscillations appear with their reciprocal frequency proportional to cos θ, demonstrating the dominant transport of topological surface states. While the magnetic field rotates on the sample surface, the planar Hall effect arises with sizeable oscillations following a relation of cos θ sin θ. Its amplitude reaches the maximum at the lowest temperature and drops to nearly zero at temperature higher than 100u2009K. All these evidences consolidate such planar Hall oscillations as another golden criterion on the topological surface transport.

2 step of conductance fluctuations due to the broken time-reversal symmetry in bulk-insulating BiSbTeSe2 devices

We extract the quantum conductance fluctuations and study its magnetic field dependence in the gate-dependent transport of the topological electrons in bulk-insulating BiSbTeSe2 devices. While increasing the magnetic field from 0 to 12 Tesla, the fluctuation magnitudes are found reduced by a ratio of sqrt(2) and form a quantized step. The step is observed both in n-type and p-type transport. It is also confirmed in the nonlocal measurements. This essentially demonstrates the breaking of the time reversal symmetry of the three-dimensional Z2 topological insulators.We extract the conductance fluctuations and study their magnetic field dependence in the gate-dependent transport of topological electrons in bulk-insulating BiSbTeSe2 devices. With the increasing magnetic field, the conductance fluctuation magnitudes are found to reduce by a ratio of 2 and form a quantized step. The step is observed both in n-type and p-type transport. This is related to the breaking of the time reversal symmetry of three-dimensional topological insulators.We extract the conductance fluctuations and study their magnetic field dependence in the gate-dependent transport of topological electrons in bulk-insulating BiSbTeSe2 devices. With the increasing magnetic field, the conductance fluctuation magnitudes are found to reduce by a ratio of 2 and form a quantized step. The step is observed both in n-type and p-type transport. This is related to the breaking of the time reversal symmetry of three-dimensional topological insulators.