Oscillatory deviations from Matthiessen’s rule due to interacting dislocations
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charge transport↗
Engineering topics
Li, Mingda
Publications and source records attributed to Li, Mingda.
Tailoring Superconductivity with Quantum Dislocations
Despite the established knowledge that crystal dislocations can affect a material’s superconducting properties, the exact mechanism of the electron-dislocation interaction in a dislocated superconductor has long been missing. Being a type of defect, dislocations are expected to decrease a material’s superconducting transition temperature (T c ) by breaking the coherence. Yet experimentally, even in isotropic type I superconductors, dislocations can either decrease, increase, or have little influence on T c . These experimental findings have yet to be understood. Although the anisotropic pairing in dirty superconductors has explained impurity-induced T c reduction, no quantitative agreement has been reached in the case a dislocation given its complexity. By generalizing the one-dimensional quantized dislocation field to three dimensions, we reveal that there are indeed two distinct types of electron-dislocation interactions. Besides the usual electron-dislocation potential scattering, there is another interaction driving an effective attraction between electrons that is caused by dislons, which are quantized modes of a dislocation. The role of dislocations to superconductivity is thus clarified as the competition between the classical and quantum effects, showing excellent agreement with existing experimental data. In particular, the existence of both classical and quantum effects provides a plausible explanation for the illusive origin of dislocation-induced superconductivity in semiconducting PbS/PbTe superlattice nanostructures. A quantitative criterion has been derived, in which a dislocated superconductor with low elastic moduli and small electron effective mass and in a confined environment is inclined to enhance T c . This provides a new pathway for engineering a material’s superconducting properties by using dislocations as an additional degree of freedom.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Nonperturbative Quantum Nature of the Dislocation–Phonon Interaction
Despite the long history of dislocation–phonon interaction studies, there are many problems that have not been fully resolved during this development. These include an incompatibility between a perturbative approach and the long-range nature of a dislocation, the relation between static and dynamic scattering, and their capability of dealing with thermal transport phenomena for bulk material only. Here in this paper, by utilizing a fully quantized dislocation field, which we called a “dislon”, a phonon interacting with a dislocation is renormalized as a quasi-phonon, with shifted quasi-phonon energy, and accompanied by a finite quasi-phonon lifetime, which are reducible to classical results. A series of outstanding legacy issues including those above can be directly explained within this unified phonon renormalization approach. For instance, a renormalized phonon naturally resolves the decade-long debate between dynamic and static dislocation–phonon scattering approaches, as two limiting cases. In particular, at nanoscale, both the dynamic and static approaches break down, while the present renormalization approach remains valid by capturing the size effect, showing good agreement with lattice dynamics simulations.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electron energy can oscillate near a crystal dislocation
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Topological semimetal to insulator quantum phase transition in the Zintl compounds B a 2 X ( X = Si , Ge )
By first-principles calculations, we find that Ba 2 X (X = Si, Ge) hosts a topological semimetal phase with one nodal ring in the k x = 0 plane, which is protected by the glide mirror symmetry when spin-orbit coupling (SOC) is ignored. The corresponding drumheadlike surface flat band appears on the (100) surface in surface Green's function calculation. Furthermore, a topological-semimetal-to-insulator transition is found. The nodal line semimetal would evolve into a topological insulator as SOC is turned on. The topologically protected metallic surface states emerge around the Γ point, which could be tuned into the topologically trivial insulator state by more than 3% hydrostatic strain. These results reveal a category of materials showing quantum phase transition between topological semimetal and insulator, and tunability through elastic strain engineering.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Quantum anomalous Hall effect in time-reversal-symmetry breaking topological insulators
The quantum anomalous Hall effect (QAHE), the last member of Hall family, was predicted to reflect quantized Hall conductivity ${{\sigma}_{yx}}=\frac{{{e}^{2}}}{h}$ without any external magnetic field. The QAHE shares a similar physical phenomenon with the integer quantum Hall effect (QHE), whereas its physical origin relies on the intrinsic topological inverted band structure and ferromagnetism. Since the QAHE does not require external energy input in the form of magnetic field, it is believed that this effect has unique potential for applications in future electronic devices with low-power consumption. More recently, the QAHE has been experimentally observed in thin films of the time-reversal symmetry breaking ferromagnetic (FM) topological insulators (TI), Cr- and V- doped (Bi,Sb)2Te3. Here, we review the history of TI based QAHE, the route to the experimental observation of the QAHE in the above two systems, the current status of the research of the QAHE, and finally the prospects for future studies.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Inelastic x-ray scattering measurements of phonon dispersion and lifetimes in PbTe 1− x Se x alloys
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Tian, Zhiting↗
Proximity-driven enhanced magnetic order at ferromagnetic-insulator-magnetic-topological-insulator interface
Magnetic exchange driven proximity effect at a magnetic-insulator–topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. In this study, we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb 2–x V x Te 3 hybrid heterostructure, where V doping is used to drive the TI (Sb 2 Te 3 ) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Hydration-dependent dynamic crossover phenomenon in protein hydration water
We present the characteristic relaxation time τ of protein hydration water exhibits a strong hydration level h dependence. The dynamic crossover is observed when h is higher than the monolayer hydration level h c = 0.2 –0.25 and becomes more visible as h increases. When h is lower than h c , τ only exhibits Arrhenius behavior in the measured temperature range. The activation energy of the Arrhenius behavior is insensitive to h , indicating a local-like motion. Furthermore, the h dependence of the crossover temperature shows that the protein dynamic transition is not directly or solely induced by the dynamic crossover in the hydration water.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Induced electronic anisotropy in bismuth thin films
We use magneto-resistance measurements to investigate the effect of texturing in polycrystalline bismuth thin films. Electrical current in bismuth films with texturing such that all grains are oriented with the trigonal axis normal to the film plane is found to flow in an isotropic manner. By contrast, bismuth films with no texture such that not all grains have the same crystallographic orientation exhibit anisotropic current flow, giving rise to preferential current flow pathways in each grain depending on its orientation. Extraction of the mobility and the phase coherence length in both types of films indicates that carrier scattering is not responsible for the observed anisotropic conduction. Evidence from control experiments on antimony thin films suggests that the anisotropy is a result of bismuth's large electron effective mass anisotropy.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗