Seminar

Emergent Phenomena at Oxide Interfaces

Speaker(s): 
Dennis Christensen
Dates: 
Friday, December 8, 2017 - 3:00pm

The plethora of fascinating properties observed in oxide heterostructures has attracted a lot of interest. Most noticeably, the confined electron gas formed at the interface between the two insulators LaAlO3 and SrTiO3 features e.g. gate-tunable superconductivity, ferromagnetism and non-volatile memory effects. Numerous studies have been devoted to understanding the origin of the conductivity along with enhancing its properties. Recently, we found that substituting LaAlO3 with γ-Al2O3 can produce a confined electron gas with an electron mobility exceeding 100,000 cm2/Vs. Here, I show that...

On systems with and without excess energy in environment

Speaker(s): 
Lorenz Cederbaum 
Dates: 
Monday, November 20, 2017 - 11:00am

How does a microscopic system like an atom or a small molecule get rid of the excess electronic energy it has acquired, for instance, by absorbing a photon? If this microscopic system is isolated, the issue has been much investigated and the answer to this question is more or less well known. But what happens if our system has neighbors as is usually the case in nature or in the laboratory? In a human society, if our stress is large, we would like to pass it over to our neighbors. Indeed, this is in brief what happens also to the sufficiently excited microscopic system. A new mechanism of...

Atomic Layer Semiconductor 2D Nanoelectromechanical Systems (NEMS)

Speaker(s): 
Philip Feng
Dates: 
Tuesday, December 12, 2017 - 3:00pm

Atomically thin semiconducting crystals derived from new classes of layered materials have rapidly emerged to enable two-dimensional (2D) nanostructures with unusual electronic, optical, mechanical, and thermal properties.  While graphene has been the forerunner and hallmark of 2D crystals, newly emerged 2D semiconductors offer intriguing, beyond-graphene, attributes.  The sizable and tunable bandgaps of compound and single-element 2D semiconductors offer attractive perspectives for strong multiphysics coupling and efficient transduction across various signal domains.  ...

Fractional Statistics from Topological Magnetism

Speaker(s): 
Kenneth Burch
Dates: 
Wednesday, March 28, 2018 - 4:30pm

There is considerable excitement about in realizing non-Abelian Anyons, particles whose phase upon exchange depends on the path taken. Their observation signals the emergence of new topological phases and offers a route to quantum computation. I will outline the reasons to expect such particles in a particular quantum spin-liquid, where there is long-range entanglement but no magnetic order. I will then describe a particularly promising van-der-Walls material for realizing such particles, RuCl3. Via Raman spectroscopy, we have uncovered the Fermi statistics emerging from the Majorana...

Andreev and Majorana Weyl crossings in multi-terminal Josephson junctions

Speaker(s): 
Manuel Houzet
Dates: 
Thursday, March 29, 2018 - 4:00pm

We analyze the Andreev spectrum in a four-terminal Josephson junction between topological superconductors. We find that a topologically protected crossing in the space of three superconducting phase differences can occur between the two Andreev bound states with lower energy. We discuss the possible detection of this crossing through the transconductance quantization, in units of 2e^2/h, between two voltage-biased terminals. Our prediction provides another example of topology in multi-terminal Josephson junctions.

2D Materials - A New Platform for Strong Light-Matter Interactions

Speaker(s): 
Ajit Srivastava
Dates: 
Thursday, November 16, 2017 - 4:30pm

A recent addition to low-dimensional materials are monolayer transition metal dichalcogenides (TMDs), such as WSe2, with an atomically thin, honeycomb lattice and optical band gaps. In addition to spin, charge carriers in TMDs exhibit a “valley” degree of freedom, which can be optically addressed using circularly polarized light, opening up exciting possibilities for “valleytronics". Another curious aspect of TMDs lies in the non-trivial geometry of their band structure which gives rise to equal but opposite Berry curvature, an effective magnetic field in the momentum...

Strong THz fields and nonlinear THz interactions with charges, dipoles, and spins

Speaker(s): 
Keith Nelson
Dates: 
Monday, November 6, 2017 - 1:00pm

Dramatic advances in tabletop generation of THz pulses with high field levels have enabled nonlinear THz spectroscopy and THz control over molecules and materials. The most widely used approach for generation of strong fields in the 0.2-2 THz range involves excitation of phonon-polaritons in ferroelectric host crystals, and a THz polaritonics platform has been developed that includes capabilities for THz field control and visualization as well as direct and strong coupling to collective spin waves (magnons). Recent developments in THz generation, nonlinear spectroscopy, and control over...

Molecular Phenotypes of Structurally Homologous ETS Transcriptions Factors

Speaker(s): 
Gregory Poon
Dates: 
Thursday, September 28, 2017 - 4:30pm

 ETS transcription factors comprise an evolutionarily related family of genetic regulators that are ubiquitous in animals and control a myriad of physiologically critical processes. ETS proteins are united by a highly conserved DNA-binding domain, with overlapping target DNA preferences on the one hand, but are functionally diverse and non-redundant on the other. This so-called ìspecificity conundrumî besets not only our understanding of ETS homologs but also the structure-activity relationships of eukaryotic transcription factors in general. Translationally, it hampers efforts to develop...

Supercurrent in the quantum Hall regime

Speaker(s): 
Gleb Finkelstein
Dates: 
Thursday, November 9, 2017 - 4:00pm

One of the promising routes towards creating novel topological states and excitations is to combine superconductivity and quantum Hall (QH) effect. However, signatures of superconductivity in the QH regime remain scarce, and a superconducting current through a QH weak link has so far eluded experimental observation. By utilizing high mobility graphene/boron nitride heterostructures we demonstrate the existence of a novel type of supercurrent-carrying states in a QH regime at magnetic fields as high as 2 Tesla. At low magnetic fields, devices demonstrate the Fraunhoffer pattern and Fabri-...

Mesoscopic spin- and quantum phase coherence: geometrical effects and spin-orbit interaction

Speaker(s): 
Jean J. Heremans
Dates: 
Tuesday, October 17, 2017 - 4:00pm

Geometrical effects influencing the measured spin coherence and quantum phase coherence in mesoscopic structures were characterized by low-temperature spin-dependent quantum transport experiments.  The findings are of possible relevance for the design of devices for quantum technologies, and have foundational aspects as well.  The materials studied have strong spin-orbit interaction and are heterostructures of InSb, InAs, or InGaAs, and the semimetal Bi with its surface states. The materials were patterned into mesoscopic stadia, narrow channels or quantum interferometers, of typical size...

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