Event Time: Thursday, January 17, 2019 | 2:00 pm - 3:00 pm
Event Location:
311 - 2355 East Mall
Add to Calendar 2019-01-17T14:00:00 2019-01-17T15:00:00 CM Seminar: Coherent soft X-ray scattering and imaging of electronic textures in quantum solids Event Information: Strongly-correlated electron systems with competing collective electronic phases are often inherently granular. The spatial organization of the electronic degrees of freedom is essential to understand the phenomenology of these complex systems, yet there are currently no probes of the charge, spin, and orbital degrees of freedom that can simultaneously afford momentum-space sensitivity and nanoscale spatial resolution.   In this talk, I will show recent resonant soft X-ray scattering and imaging studies of the spatial textures of electronic orders (charge/spin-density-waves) in cuprate high-Tcs and rare earth nickelate thin films.  For the cuprates, I will present evidence of a doping-induced transition from a 'Wigner glass' to a 'Wigner crystal' state in electron-doped Nd2CuO4, that occurs around the characteristic doping of the Fermi surface reconstruction (~10%). For thin films of rare earth nickelate NdNiO3, I will discuss scanning resonant magnetic nanodiffraction (<100 nm resolution) experiments to elucidate the spatial organization of spin-density-wave domains as a function of temperature across the Neel transition. Intriguingly, we have observed a return-point-memory effect in the spin degrees of freedom and intrinsic scale-invariant textures with power-law correlations that might be suggestive of a second-order nature of the magnetic transition in this material.   I will conclude with some perspectives and a glimpse to very recent resonant coherent diffractive imaging experiments performed at latest-generation, highly-coherent synchrotron X-ray sources to resolve the complex (amplitude/phase) density-wave order parameter down to an ultimate resolution below 30 nm (and beyond).  Event Location: 311 - 2355 East Mall
Event Time: Thursday, January 24, 2019 | 2:00 pm - 3:00 pm
Event Location:
BRIM 311, Stewart Blusson Quantum Matter Institute, 2355 East Mall
Add to Calendar 2019-01-24T14:00:00 2019-01-24T15:00:00 CM Seminar: CHIRAL ANOMALY AND CLASSICAL NEGATIVE MAGNETORESISTANCE OF WEYL METAL Event Information: We present a theory of magnetotransport phenomena related to the chiral anomaly in Weyl semimetals. We show that conductivity, thermal conductivity, thermoelectric and the sound absorption coefficients exhibit strong and anisotropic magnetic field dependences. In the presence of a magnetic field the Wiedeman-Franz law in these materials can be violated. We also discuss properties of magneto-plasmons and magneto-polaritons, whose existence is entirely determined by the chiral anomaly. Finally, we discuss the conditions of applicability of the quasi-classical description of electron transport phenomena related to the chiral anomaly. Event Location: BRIM 311, Stewart Blusson Quantum Matter Institute, 2355 East Mall
Event Time: Thursday, January 31, 2019 | 2:00 pm - 3:00 pm
Event Location:
HENN 318
Add to Calendar 2019-01-31T14:00:00 2019-01-31T15:00:00 CM Seminar: Measurement and Control of Electron Dynamics Using THz Pulses Event Information: Phase-locked, few-cycle pulses of THz frequency light are powerful tools for both probing and driving ultrafast dynamics of low energy (meV scale) excitations in condensed matter. As an example of using THz pulses as a time-resolved probe, I discuss recent multi-THz spectroscopy experiments on the widely researched hybrid organometallic halide perovskites. These solution processable materials have been successfully applied to a variety of optoelectronic devices, most notably high efficiency photovoltaics achieving up to 22% power conversion efficiency in the lab (comparable to silicon). Their long carrier lifetimes and relative insensitivity of their electronic transport properties to the presence of impurities have been puzzling when considering their similarities to other direct band gap semiconductors like GaAs. This led to a proposal that charge carriers exist as large polarons, protected against scattering by their correlation to polar lattice vibrations. In this talk, I show ultrafast THz measurements provide direct evidence for the existence of polarons in these materials, resolving the quantum dynamics of their formation. In addition, strong field THz pulses can now be used to control the motion of charged particles on sub-cycle time scales. Along these lines, I will discuss our recent work on sub-cycle THz field emission of femtosecond electron wave packets from metal nanotips. We show that through field-assisted tunneling directly from the metal’s Fermi level, impressive electron bunch charges up to 106/shot are emitted on a sub-cycle time scale. These electrons are subsequently accelerated in the local THz field in the vicinity of the nanotip to keV energies over 100 nm length scales. We discuss possible applications as a source for single shot ultrafast electron diffraction and as a test bed for high field physics. Event Location: HENN 318