| Tuesday, February 19, 2019 |
| Quantum physics and quantum engineering in atomically thin crystals | |
| Qiong Ma, MIT | |
| Event Type: CQP Faculty Search | |
| Time: 9:30 AM - 10:30 AM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Abstract: In quantum materials, the interplay of symmetry, topology, quantum geometry and interactions can produce new phases of matter with fundamentally new electronic and optoelectronic properties. Two dimensional van der Waals materials, with highly tunable symmetry, band structure, carrier density and interactions, allow for reaching previously inaccessible experimental parameter regimes. Such highly tunable material platforms provide exciting possibilities to discover new fundamental quantum physics, which can in turn guide the engineering of new quantum technologies for sensing, communications and computations. In this talk, I will present our recent research along this line. First, I will show that the optoelectronic response of graphene can be controlled among highly distinct regimes by tuning the interaction dynamics of photo-excited carriers. In particular, we observe a new type of photocurrent that appears exclusively in charge neutral graphene with unusual ultra-relativistic electron scattering kinematics. Second, I will show that the interplay between nontrivial topology and novel crystalline symmetries in atomically thin WTe2 gives rise to new Berry curvature physics, which can be detected by nonlinear electrical transport and infrared photocurrent measurements. Remarkably, the nonlinear electrical transport in bilayer WTe2 uncovers a new type of electrical Hall effect under the time-reversal-symmetric condition. Such a nonlinear Hall response directly measures the energy-dependent “dipole moment” of the Berry curvature that arises from layer-polarized Dirac fermions. Our work highlights the potential for using intrinsic quantum and topological properties for nonlinear applications including frequency-doubling and rectification in the GHz and infrared regimes. In the end, I will discuss new opportunities towards fundamental physics and device functionalities with the combination of highly tunable material platform and advanced characterization and manipulation methods. | |
| Modjaz Group Mtg | |
| Event Type: Modjaz Group Mtg | |
| Time: 11:00 AM - 12:30 PM | |
| Location: 726 Broadway, 901, Sm Conf | |
| Finding an Alien Biosphere with Computational Chemistry | |
| Clara Sousa-Silva, MIT | |
| Event Type: Astro Seminar | |
| Time: 2:00 PM - 3:15 PM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Abstract: At the edge of our present scientific frontier lies the question: “Can we identify the signs of life on an exoplanet?”. Establishing whether a planet is habitable, or inhabited, relies both on the observation of an exoplanet atmosphere and, crucially, its subsequent interpretation. This interpretation requires knowledge of the spectral behavior of every significant atmospheric molecule. However, though thousands of molecular candidates can contribute towards the spectrum of an atmosphere, data exist for only a few hundred gases. Among these, only a fraction have complete spectra (e.g. ammonia, water). This deep incompleteness in the knowledge of molecular spectra presents a pressing vulnerability in the atmospheric study of planets; there exists a strong possibility of mis-assignment, false positives, and false negatives in molecular detections. The work presented here combines structural organic chemistry and quantum mechanics to obtain the necessary tools for the interpretation of astrophysical spectra and, ultimately, the detection of life on an exoplanet. Whether alien life will produce familiar gases (e.g. oxygen) or exotic biosignatures, painting a confident picture of a potential biosphere will require a holistic interpretation of an atmosphere and its molecules. In this talk I will describe the ongoing efforts to decipher exoplanet atmospheres through the identification of volatile molecules, in particular those that might be produced by non-Earth-like life on exoplanets. | |
| Event Type: Astroparticle Group Meet | |
| Time: 3:30 PM - 5:30 PM | |
| Location: 726 Broadway, 902, Lg Conf | |