Publications
Preliminary characterization of a laser-generated plasma sheet
We present the results from recent experiments to create a flowing plasma sheet. Two groups of three laser beams with nominally 1.5 kJ of energy per group were focused to separate pointing locations, driving a shock into a wedge target. As the shock breaks out of the wedge, the plasma is focused on center, creating a sheet of plasma. Measurements at 60 ns indicate the plasma sheet has propagated 2825 microns with an average velocity of 49 microns/ns. These experiments follow previous experiments [Krauland et al.
Evidence for superconductivity in Li-decorated monolayer graphene
Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron-phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2): 131-134]. Although experiments have shown an adatom-induced enhancement of the electron-phonon coupling, superconductivity has never been observed.
Supercooled spin liquid state in the frustrated pyrochlore Dy2Ti2O7
A "supercooled" liquid develops when a fluid does not crystallize upon cooling below its ordering temperature. Instead, the microscopic relaxation times diverge so rapidly that, upon further cooling, equilibration eventually becomes impossible and glass formation occurs. Classic supercooled liquids exhibit specific identifiers including microscopic relaxation times diverging on a Vogel-Tammann-Fulcher (VTF) trajectory, a Havriliak-Negami (HN) form for the dielectric function ε(ω, T), and a general Kohlrausch-Williams-Watts (KWW) form for time-domain relaxation.
Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3
To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a "Dirac-mass gap" in their spectrum by breaking timereversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states.
Identifying the 'fingerprint' of antiferromagnetic spin fluctuations in iron pnictide superconductors
Cooper pairing in the iron-based high-T c superconductors is often conjectured to involve bosonic fluctuations. Among the candidates are antiferromagnetic spin fluctuations and d-orbital fluctuations amplified by phonons. Any such electron-boson interaction should alter the electron's 'self-energy', and then become detectable through consequent modifications in the energy dependence of the electron's momentum and lifetime.
Spectroscopic Imaging STM: Atomic-Scale Visualization of Electronic Structure and Symmetry in Underdoped Cuprates
Atomically resolved spectroscopic imaging STM (SI-STM) has played a pivotal role in visualization of the electronic structure of cuprate high temperature superconductors. In both the d-wave superconducting (dSC) and the pseudogap (PG) phases of underdoped cuprates, two distinct types of electronic states are observed when using SI-STM.
Direct evidence for a magnetic f-electron-mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5
To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of hightemperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable.
Direct phase-sensitive identification of a d-form factor density wave in underdoped cuprates
The identity of the fundamental broken symmetry (if any) in the underdoped cuprates is unresolved. However, evidence has been accumulating that this state may be an unconventional density wave. Here we carry out site-specific measurements within each CuO2 unit cell, segregating the results into three separate electronic structure images containing only the Cu sites [Cu(r)] and only the x/y axis O sites [Ox (r) and Oy( r)]. Phase-resolved Fourier analysis reveals directly that the modulations in the Ox(r) and Oy(r) sublattice images consistently exhibit a relative phase of π.
Simultaneous transitions in cuprate momentum-space topology and electronic symmetry breaking
The existence of electronic symmetry breaking in the underdoped cuprates and its disappearance with increased hole density p are now widely reported. However, the relation between this transition and the momentum-space (k →-space) electronic structure underpinning the superconductivity has not yet been established. Here, we visualize the Q→ = 0 (intra-unit-cell) and Q→ ≠0 (density-wave) broken-symmetry states, simultaneously with the coherent k→-space topology, for Bi2Sr2CaCu2O8+δ samples spanning the phase diagram 0.06 ≤ p ≤ 0.23.