Condensed Matter Experiment Seminar: Adrian Swartz
Please join us for a CME Seminar presented by Postdoctoral Researcher Adrian Swartz from Stanford Univeristy as he shares his research on “Tunneling spectroscopy of a dilute oxide superconductor”. Dr. Swartz is part of Professor Harold Hwang’s group in the Stanford Linear Accelerator Center.
The nature of superconductivity in SrTiO3 has remained an open question for more than 50 years. The ongoing debate centers heavily on the role that high energy phonons play in pairing, the relevance of multi-band superconductivity, and the nature of superconductivity in the limit of low carrier density. Tunneling spectroscopy, which probes the electronic density of states, is a powerful tool to investigate the superconducting ground state as well as the electron-phonon (e-ph) coupling strength (λ). Using a newly developed method for engineering band alignments at epitaxial oxide interfaces, we have measured the doping evolution of λ and superconducting gap in Nb-doped SrTiO3 by high resolution tunneling spectroscopy. In the normal state, we observe strong coupling to the high energy longitudinal optical phonon modes indicative of a polaronic regime. Yet when cooled below the superconducting transition temperature Tc, we observe a single superconducting gap corresponding with the weak-coupling limit of BCS theory. I will discuss possible pairing scenarios and the relevance to emerging 2D superconductors such as LaAlO3/SrTiO3 and monolayers of FeSe.
Condensed Matter Experiment Seminar: Sarah Li
Please join us for a CME Seminar presented by Professor Sarah Li from the University of Utah as she shares her research on “Exciton Spin Dynamics in Hybrid Organic-inorganic Perovskites”.
The hybrid organic-inorganic perovskites have emerged as a new class of semiconductors which make excellent solar cells with an efficiency over 20%. They are also highly promising semiconductors for the field of spintronics due to their large and tunable spin-orbit coupling, spin dependent optical selection rules, and predicted electrically tunable Rashba spin splitting. I will present our latest study of exciton spin dynamics on the solution processed polycrystalline methylammonium lead iodide films. With time-resolved Faraday rotation (TRFR) and optical Hanle measurements, we demonstrate the optical orientation and quantum beating of excitons in the perovskites, which confirms the spin-dependent optical transitions. The energy dependence of the Faraday rotation follows the exciton absorption band at low temperatures, confirming its excitonic origin. The TRFR in zero field reveals unexpected long spin lifetimes exceeding 1 ns at 4K, given that Pb and I exhibit large spin-or! bit coupling, and usually lead to fast spin relaxation. Application of a transverse magnetic field causes quantum beating at two distinct frequencies, and the approximate linear relationships give two g-factors, which we assign to electrons and holes as g_e = 2.63, and g_h = -0.33. Temperature dependence and power dependence of the spin lifetimes reveal some clues to the spin relaxation mechanisms.
Physics Education Seminar – Matt Greenwolfe (Cary Academy) The Maiden Voyage of a Kinematic Robot
In this talk, I describe the design of a robotic kinematic apparatus and a curriculum designed to make use of its unique features to shape the inquiry process. Students program a robot by drawing kinematic graphs on a computer, and the robot precisely and reliably produces the motion, providing immediate visual feedback. Preliminary results support the hypothesis that a physics apparatus precise and reliable enough to serve as a control of error minimizes the need for teacher intervention and improves student absorption in inquiry as well as learning outcomes. The importance of optimal feedback inertia emerged from the study. The turn-around time of several minutes to analyze a mistake and test a new idea encourages students to learn from their mistakes and really think things through.
Condensed Matter Experiment Seminar: Chris Leighton
Please join us for a CME Seminar presented by Distinguished Professor Chris Leighton from the University of Minnesota as he shares his research on:
- Electrochemical Materials & Devices
- Electronic, Magnetic & Photonic Materials
- Materials Processing
- Nanomaterials & Nanotechnology
Condensed Matter Seminar: Aviad Frydman
Please join us for a special CM Seminar presented by Professor Aviad Frydman from Bar Ilan University (Israel) as he shares his research on Experimental probing of quantum criticality at the Superconductor-Insulator Quantum Phase Transition:
BioPhysics Seminar – Simon Watkins (University of Pittsburgh) From Little Animals to Moving Molecules
In the last two decades the evolution of the scientific method has moved traditional disciplines forward and has led to the development of multiple completely new fields. In each case the unifying change has been the continued expansive integration of technologies on all fronts, including molecular, biochemical and computer based. Few fields of endeavor have embraced these changes as much as microscopy. At all levels in the last 20 years there has a massive and continuous expansion of the capabilities of the microscope on all fronts. The current research microscope represents the integration of modern optics, robotics, computing, probes and cameras. The impact of modern imaging on our understanding of disease and the potential for therapeutics has been has been extreme, particularly as we continue to expand scientific progress towards discovery rather than reductionist approaches. Equivalently there has been an explosion in the probes suitable for use in the modern microscope such that single molecules can be chased in 3 dimensional space and the local environment assessed in real time. Integrating novel fluorogen based probes into highly sensitive and extremely fast high through put screens to define protein, delivery and function in 3D space at high speed and with absolute certainty of localization has been the focus of our work. This seminar will discuss the extraordinary impact that the integration of modern imaging, robotics and probes has had on biomedical research and presents problems and dilemmas that are becoming increasingly prescient in the future of these approaches.
Condensed Matter Experiment Seminar: Nancy Sandler
Please join us for a CME Seminar presented by Professor Nancy Sandler from Ohio University as she shares her research (Title and Abstract TBA). Professor Sandler is a theoretical condensed matter physicist with expertise in electronic and mechanical properties of 2D materials. She has recently been studying strain-induced pseudomagnetic fields and spin orbit coupling in graphene.
Condensed Matter Seminar Series: Wei Han
Please join us for a CME Seminar presented by Professor Wei Han from ICQM, Peking University, China as he shares his research on “Spin and Charge Conversion in 2D Quantum Materials”.
Condensed Matter Seminar Series: Enrique del Barco
Please join us for a CME Seminar presented by Professor Enrique del Barco from the University of Central Florida as he shares his research on “Tunneling In Single-Molecule Junctions: Temperature And Gating Effects.”
Understanding how the mechanism of charge transport through molecular tunnel junctions depends on temperature is crucial to control electronic functionality in molecular electronic devices. So far only a few systems have been investigated as a function of bias and temperature and, consequently, thermal effects in molecular tunnel junctions are still poorly understood. I will present a detailed charge transport study of an individual redox-active molecule (based on ferrocene) over a wide range of temperatures and applied potentials. The results show the temperature dependence of the current to vary strongly as a function of the gate voltage. Specifically, the current across the molecule: i) exponentially increases in the Coulomb blockade regime; ii) decreases at the charge degeneracy points; and, iii) remains constant with temperature at resonance. Our observations can be well accounted for by a formal single-level tunneling model where the temperature dependence relies on the thermal broadening of the Fermi distributions of the electrons in the leads. I will also discuss the temperature behavior of tunneling through a compound molecule which behaves as a double quantum dot. In this case, charging of one dot electrically gates the electrostatic potential of the neighboring dot, making the conduction to transit from the inverted Marcus regime (T-independent) to the thermally activated Marcus regime.
Figure 1: a) 3D plot of the evolution of the tunnel current through a S-(CH2)4-Fc-(CH2)4-S junction vs. gate voltage as the temperature is increased from 80 to 220 K for Vsd = 10 mV. The evolution of the two charge degeneracy points (-0.3 V and 1.7 V), whose magnitude decreases with increasing temperature, can be appreciated following the red arrows in both the 3D data and its 2D horizontal projection in the Vg-T plane. Similarly, the increase with temperature in the Coulomb blockade areas can be seen by following the blue arrows. The black arrow shows the case for which the molecular level matches the electrostatic potential of one of the leads (resonance), a situation leading to almost negligible temperature dependence. b) Corresponding response of the junction as calculated from a coherent single-level tunneling transport model.
Nuclear Physics Seminar – Lijuan Ruan (Brookhaven National Lab) The Electro-Magnetic Probes in A+A and e+A Collisions
The Electro-Magnetic probes have been widely used to study the fundamental properties of hot, dense medium created in heavy ion collisions. Quarkonia through dileptonic decays have been an indicator of the de-confinement while the dileptons radiated from the hot, dense medium have been used to study Chiral Symmetry Restoration, the temperature, and lifetime of the medium.
I will briefly review a few interesting observables in heavy ion collisions and present most-recent STAR results on J/psi and dilepton production in the very low transverse momentum region (pT<0.2 GeV/c) in peripheral and mid-peripheral Au+Au collisions. The results seem to be consistent with the coherent photo-nuclear and two-photon processes, which have been widely studied in ultra-peripheral collisions. Physics implications and possible future measurements will be discussed.
In addition, I will try to make connections to future Electro-Magnetic measurements in e+A collisions.