arXiv subjects

S. D. Wilson

Publications and source records attributed to S. D. Wilson.

44 records · Page 3Linked to original sources

arXiv2015

Fermi Arcs vs. Fermi Pockets in Electron-doped Perovskite Iridates

We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)3Ir2O7. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected "Fermi arcs", reminiscent of those reported recently in surface electron-doped Sr2IrO4. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

cond-mat.str-el↗

arXiv2013

Lifetimes of antiferromagnetic magnons in two and three dimensions: experiment, theory, and numerics

A high-resolution neutron spectroscopic technique is used to measure momentum-resolved magnon lifetimes in the prototypical two- and three-dimensional antiferromagnets Rb2MnF4 and MnF2, over the full Brillouin zone and a wide range of temperatures. We rederived theories of the lifetime resulting from magnon-magnon scattering, thereby broadening their applicability beyond asymptotically small regions of wavevector and temperature. Corresponding computations, combined with a small contribution reflecting collisions with domain boundaries, yield excellent quantitative agreement with the data.

cond-mat.str-el↗

arXiv2012

Ripple modulated electronic structure of a 3D topological insulator

3D topological insulators, similar to the Dirac material graphene, host linearly dispersing states with unique properties and a strong potential for applications. A key, missing element in realizing some of the more exotic states in topological insulators is the ability to manipulate local electronic properties. Analogy with graphene suggests a possible avenue via a topographic route by the formation of superlattice structures such as a moiré patterns or ripples, which can induce controlled potential variations. However, while the charge and lattice degrees of freedom are intimately coupled in graphene, it is not clear a priori how a physical buckling or ripples might influence the electronic structure of topological insulators. Here we use Fourier transform scanning tunneling spectroscopy to determine the effects of a one-dimensional periodic buckling on the electronic properties of Bi2Te3. By tracking the spatial variations of the scattering vector of the interference patterns as well as features associated with bulk density of states, we show that the buckling creates a periodic potential modulation, which in turn modulates the surface and the bulk states. The strong correlation between the topographic ripples and electronic structure indicates that while doping alone is insufficient to create predetermined potential landscapes, creating ripples provides a path to controlling the potential seen by the Dirac electrons on a local scale. Such rippled features may be engineered by strain in thin films and may find use in future applications of topological insulators.

cond-mat.mes-hall↗

arXiv2010

Heat capacity study of BaFe$_{2}$As$_{2}$: effects of annealing

Heat-capacity, X-ray diffraction, and resistivity measurements on a high-quality BaFe$_{2}$As$_{2}$ sample show an evolution of the magneto-structural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 $μΩ$cm, with a residual resistance ratio $\sim$36; the heat-capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of $\sim$0.15 K, and is unchanged in a magnetic field $μ_{0}$H = 14 T. The X-ray and heat-capacity data combined suggest that there is a first order jump in the structural order parameter. The entropy of the transition is reported.

cond-mat.supr-con↗

arXiv2009

Phase diagram of the PrFeAsO$_{1-x}$F$_{x}$ superconductor

The electronic phase diagram of PrFeAsO$_{1-x}$F$_{x}$ (0$\leq$x$\leq$0.225) has been determined using synchrotron X-ray powder diffraction, magnetization and resistivity measurements. The structural transition temperature is suppressed from 154 K to $\approx$120 K and the magnetic phase transitions of both iron and praseodymium ions are completely suppressed by x$\approx$0.08 fluorine doping, coinciding with the emergence of superconductivity. The optimal doping is x$\approx$0.15 when T$_{C}$=47 K, while the maximum solubility of fluorine in PrFeAsO$_{1-x}$F$_{x}$ is reached around x=0.22. The structural, magnetic and superconducting phase diagram is presented.

cond-mat.supr-con↗

arXiv2009

Core Level and Valence Band Study of LaO$_{0.9}$F$_{0.1}$FeAs

Using angle-integrated photoemission spectroscopy we have probed the novel LaO$_{0.9}$F$_{0.1}$FeAs superconductor over a wide range of photon energies and temperatures. We have provided the first full characterization of the orbital character of the VB DOS and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90K where a pseudogap-like feature appears to close and 120K where a sudden change in the DOS near E$_F$ occurs. We associate these phenomena with the SDW magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics and structural distortion in the physics of Fe-based superconductors.

cond-mat.str-el↗

arXiv2007

Magnetic fluctuations in n-type high-$T_c$ superconductors reveal breakdown of fermiology

By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$ with theoretical calculations we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a step-like feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.

cond-mat.supr-con↗

arXiv2007

Effects of Measurement back-action in the stabilization of a Bose-Einstein condensate through feedback

We apply quantum filtering and control to a particle in a harmonic trap under continuous position measurement, and show that a simple static feedback law can be used to cool the system. The final steady state is Gaussian and dependent on the feedback strength and coupling between the system and probe. In the limit of weak coupling this final state becomes the ground state. An earlier model by Haine et. al. (PRA 69, 2004) without measurement back-action showed dark states: states that did not display error signals, thus remaining unaffected by the control. This paper shows that for a realistic measurement process this is not true, which indicates that a Bose-Einstein condensate may be driven towards the ground state from any arbitrary initial state.

quant-ph↗