Yiping Lin

Effects of impurity scattering on the quantized conductance of a quasi-one-dimensional quantum wire

We report an experimental observation of how the presence of an impurity in a quasi-one-dimensional wire influences the quantized conductance. The impurity is a chemically etched nanohole, relative to which the walls of the wire can be tuned via external gate voltages. Depending on the positions of the sidewalls, resonance features are observed in the quantized conductance due to either the multiple scatterings between the impurity and the wall of wire or the channel interference. Meanwhile, the differential conductance exhibits the well-known half-plateau features in a single channel wire or saturates in a wire with coupled two channels.

Crystallographic and physical properties of new orthorhombic Cu-1212 R(Ba2−xR′x)Cu3O7+y system (R, R′La, Pr, Nd; 0.65<x<1)

Abstract Structural, magnetic, calorimetric and transport results are reported for the new orthorhombic Cu-1212 R(Ba 2−x R′ x )Cu 3 O 7+y cuprates (R, R′La, Pr, Nd; 0.65 1.7 Ba 1.3 Cu 3 O 7+y (RLa, Pr, Nd; y ∼ 0.3) indicates that the new orthorhombic O(II)-phase with space group Cmmm and lattice parameters a 0 o ∼ 0.55 nm, c ∼ 1.16 nm is very similar to the Bi-2212 structure except that (BiO) 2 bi-layer is replaced by a single CuO 1+y plane. For the oxygenated Pr(Ba 2−x R x )Cu 3 O 7+y O(II)-phase cuprates (RLa, Pr; y > 0.2), anomalous Pr ordering temperature T N (Pr) decreases sharply from 18 K for O(I)-phase PrBa 2 Cu 3 O 7 (space group Pmmm, a o o ∼ 0.39 nm and c ∼ 1.17 nm), to 5.5 K for Pr(Ba 1.3 Pr 0.7 )Cu 3 O 7.25 and 6 K for Pr(Ba 1.3 La 0.7 )Cu 3 O 7.29 . The dramatically decreasing T N (Pr) is closely related with longer PrO bond length in the O(II)-phase which effectively decreases Pr 4f-O 2p π orbital hybridization. No superconductivity was observed for these new insulating cuprates.

Mode Dependency of Quantum Decoherence Studied via an Aharonov-Bohm Interferometer.

We investigate the dependence of decoherence on the mode number M in a multiple-mode Aharonov-Bohm (AB) interferometer. The design of the AB interferometer allows us to precisely determine M by the additivity rule of ballistic conductors; meanwhile, the decoherence rate is simultaneously deduced by the variance of the AB oscillation amplitude. The AB amplitude decreases and fluctuates with depopulating M. Moreover, the normalized amplitude exhibits a maximum at a specific M (∼9). Data analysis reveals that the charge-fluctuation-induced dephasing, which depends on the geometry and the charge relaxation resistance of the system, could play an essential role in the decoherence process. Our results suggest that the phase coherence, in principle, can be optimized using a deliberated design and pave one of the ways toward the engineering of quantum coherence.

Magnetic properties of high-oxygen pressure prepared PrBa2Cu3O7-y cuprates

High oxygen pressure annealed PrBa2Cu3O7−y (y∼0) cuprates were prepared in order to study the effect of oxygen stoichiometric parameter y on the unusual Pr/Cu magnetic properties and/or recently reported superconductivity. The oxygen-rich orthorhombic 123-chain phase is highly unstable under high-oxygen pressure synthesis and decomposes completely in 10 bar pressure. For a smaller 2 bar prepared sample a relatively clean phase was preserved with an oxygen parameter y=0.05, as compared with y=0.11 from a conventional 1 bar flowing oxygen method. No superconductivity can be detected for all high-oxygen pressure prepared samples. Instead, Mott-insulator behavior with anomalous high Pr ordering TN(Pr)=19 K was observed for PrBa2Cu3O6.95. Comparison with other Pr/Ba intersubstituted Pr1−xBa2−xCu3O7−y cuprates is discussed.

Variation of crystal symmetry, superconductivity and weak ferromagnetism in (R1−yGdy)1.85Ce0.15CuO4−δ (R=Nd, Eu) cuprates

Abstract Metal–insulator transition in the Gd-doped (R 1− y Gd y ) 1.85 Ce 0.15 CuO 4− δ systems occurred around y ∼0.1 for R=Eu and y ∼0.65 for R= Nd with a simultaneous structural transition from the tetragonal T ′-phase (space group I4/mmm) to an orthorhombic O′-phase (Acam, a o ⩽ b o ∼√2 a t ). The structural distortion is due to the lattice mismatch between smaller (R,Gd,Ce) 2 O 2 layer and CuO 2 plane which results in an oxygen distortion in the otherwise perfect CuO 2 square plane. The phase diagram indicates that the superconductivity can only occur in the metallic T′-phase cuprates where the metallic state is controlled by a delicate balance between oxygen reduction and structural stability. The Cu 2+ weak-ferromagnetic/canted-antiferromagnetic (WF/CAF) order observed in the insulating region is the direct result of non-180° α(Cu–O–Cu) canting angle of the O′-phase.