10,023 research outputs found

    PT\mathcal{PT}-breaking threshold in spatially asymmetric Aubry-Andre Harper models: hidden symmetry and topological states

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    Aubry-Andre Harper (AAH) lattice models, characterized by reflection-asymmetric, sinusoidally varying nearest-neighbor tunneling profile, are well-known for their topological properties. We consider the fate of such models in the presence of balanced gain and loss potentials ±iγ\pm i\gamma located at reflection-symmetric sites. We predict that these models have a finite PT\mathcal{PT} breaking threshold only for {\it specific locations} of the gain-loss potential, and uncover a hidden symmetry that is instrumental to the finite threshold strength. We also show that the topological edge-states remain robust in the PT\mathcal{PT}-symmetry broken phase. Our predictions substantially broaden the possible realizations of a PT\mathcal{PT}-symmetric system.Comment: 8 pages, 5 figure

    Zero-bias peaks in spin-orbit coupled superconducting wires with and without Majorana end-states

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    One of the simplest proposed experimental probes of a Majorana bound-state is a quantized (2e^2/h) value of zero-bias tunneling conductance. When temperature is somewhat larger than the intrinsic width of the Majorana peak, conductance is no longer quantized, but a zero-bias peak can remain. Such a non-quantized zero-bias peak has been recently reported for semiconducting nanowires with proximity induced superconductivity. In this paper we analyze the relation of the zero-bias peak to the presence of Majorana end-states, by simulating the tunneling conductance for multi-band wires with realistic amounts of disorder. We show that this system generically exhibits a (non-quantized) zero-bias peak even when the wire is topologically trivial and does not possess Majorana end-states. We make comparisons to recent experiments, and discuss the necessary requirements for confirming the existence of a Majorana state.Comment: 5 pages, 4 Figure

    Magnetic Field Effects in the Pseudogap Phase: A Precursor Superconductivity Scenario

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    We demonstrate that the observed dependences of TcT_c and TT^* on small magnetic fields can be readily understood in a precursor superconductivity approach to the pseudogap phase. In this approach, the presence of a pseudogap at TcT_c (but not at TT^*) and the associated suppression of the density of states lead to very different sensitivities to pair-breaking perturbations for the two temperatures. Our semi-quantitative results address the puzzling experimental observation that the coherence length ξ\xi is weakly dependent on hole concentration xx throughout most of the phase diagram. We present our results in a form which can be compared with the recent experiments of Shibauchi et al, and argue that orbital effects contribute in an important way to the HH dependence of TT^*.Comment: 6 pages, 1 figure, elsart.cls included. Submitted to the proceeding of SNS 2001, Chicag

    Dynamics of methane ebullition from a peat monolith revealed from a dynamic flux chamber system

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    Methane (CH4) ebullition in northern peatlands is poorly quantified in part due to its high spatiotemporal variability. In this study, a dynamic flux chamber (DFC) system was used to continuously measure CH4 fluxes from a monolith of near‐surface Sphagnum peat at the laboratory scale to understand the complex behavior of CH4 ebullition. Coincident transmission ground penetrating radar measurements of gas content were also acquired at three depths within the monolith. A graphical method was developed to separate diffusion, steady ebullition, and episodic ebullition fluxes from the total CH4 flux recorded and to identify the timing and CH4 content of individual ebullition events. The results show that the application of the DFC had minimal disturbance on air‐peat CH4 exchange and estimated ebullition fluxes were not sensitive to the uncertainties associated with the graphical model. Steady and episodic ebullition fluxes were estimated to be averagely 36 ± 24% and 38 ± 24% of the total fluxes over the study period, respectively. The coupling between episodic CH4 ebullition and gas content within the three layers supports the existence of a threshold gas content regulating CH4 ebullition. However, the threshold at which active ebullition commenced varied between peat layers with a larger threshold (0.14 m3 m−3) observed in the deeper layers, suggesting that the peat physical structure controls gas bubble dynamics in peat. Temperature variation (23°C to 27°C) was likely only responsible for small episodic ebullition events from the upper peat layer, while large ebullition events from the deeper layers were most likely triggered by drops in atmospheric pressure

    Plate boundary trench retreat and dextral shear drive intracontinental fault-slip histories: Neogene dextral faulting across the Gabbs Valley and Gillis Ranges, Central Walker Lane, Nevada

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    The spatial-temporal evolution of intracontinental faults and the forces that drive their style, orientation, and timing are central to understanding tectonic processes. Intracontinental NW-striking dextral faults in the Gabbs Valley–Gillis Ranges (hereafter referred to as the GVGR), Nevada, define a structural domain known as the eastern Central Walker Lane located east of the western margin of the North American plate. To consider how changes in boundary type along the western margin of the North American plate influenced both the initiation and continued dextral fault slip to the present day in the GVGR, we combine our new detailed geologic mapping, structural studies, and 40Ar/39Ar geochronology with published geologic maps to calculate early to middle Miocene dextral fault-slip rates. In the GVGR, Mesozoic basement is nonconformably overlain by a late Oligocene to Miocene sequence dominated by tuffs, lavas, and sedimentary rocks. These rocks are cut and offset by four primary NW-striking dextral faults, from east to west the Petrified Spring, Benton Spring, Gumdrop Hills, and Agai Pah Hills–Indian Head faults. A range of geologic markers, including tuff- and lava-filled paleovalleys, the southern extent of lava flows, and a normal fault, show average dextral offset magnitudes of 9.6 ± 1.1 km, 7.0 ± 1.7 km, 9.7 ± 1.0 km, and 4.9 ± 1.1 km across the four faults, respectively. Cumulative dextral offset across the GVGR is 31.2 ± 2.3 km. Initiation of slip along the Petrified Spring fault is tightly bracketed between 15.99 ± 0.05 Ma and 15.71 ± 0.03 Ma, whereas slip along the other faults initiated after 24.30 ± 0.05 Ma to 20.14 ± 0.26 Ma. Assuming that slip along all four faults initiated at the same time as the Petrified Spring fault yields calculated dextral fault-slip rates of 0.4 ± 0.1–0.6 ± 0.1 mm/yr, 0.4 ± 0.1–0.5 ± 0.1 mm/yr, 0.6 ± 0.1 mm/yr, and 0.3 ± 0.1 mm/yr on the four faults, respectively. Middle Miocene initiation of dextral fault slip across the GVGR overlaps with the onset of normal slip along range-bounding faults in the western Basin and Range to the north and the northern Eastern California shear zone to the south. Based on this spatial-temporal relationship, we propose that dextral fault slip across the GVGR defines a kinematic link or accommodation zone between the two regions of extension. At the time of initiation of dextral slip across the GVGR, the plate-boundary setting to the west was characterized by subduction of the Farallon plate beneath the North American plate. To account for the middle Miocene onset of extension across the Basin and Range and dextral slip in the GVGR, we hypothesize that middle Miocene trench retreat drove westward motion of the Sierra Nevada and behind it, crustal extension across the Basin and Range and NW-dextral shear within the GVGR. During the Pliocene, the plate boundary to the west changed to NW-dextral shear between the Pacific and North American plates, which drove continued dextral slip along the same faults within the GVGR because they were fortuitously aligned subparallel to plate boundary motion
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