Seminar

Ordinary classical fluids have a single type of sound waves consisting of longitudinal compressional oscillations of the density. Solids, on the other hand, have also transverse or shear sound waves because of their non-zero restoring force to shear deformations. In this talk, I will illustrate that quantum fermi liquids can radically deviate from this paradigm by developing a sharp collective transverse or shear sound wave when their interactions increase beyond a threshold, even though their ground state remains in a liquid state without any form of proper static crystalline order. I...

Mathias Scheurer is a postdoctoral fellow working on theoretical condensed matter in Prof. Subir Sachdev's group at Harvard University.

Abstract: Two-dimensional (2D) systems have become a very active field of research due to their particularly rich physics. As we know from classical statistical mechanics, 2D systems are special as they are situated right at the lower critical dimension and, as such, just incapable of spontaneously breaking a continuous symmetry at finite temperature. Nonetheless, finite-temperature phase transitions are possible; these are, however, not...

Ashley Cook is a postdoctoral researcher in condensed matter theory in the group of Prof. Joel Moore at UC Berkeley.

Abstract: In our daily lives, we encounter phases of matter distinguished by the symmetries they break, such as steam and ice. Such phases are well-understood with very established theory of Ginzburg and Landau, suggesting the work to characterize and understand phases of matter might be close to completion. In the 1980's, however, physicists were confronted with the integer and fractional quantum Hall effects, phases of matter that cannot be...

2-dimensional (2D) electron gas exposed to an external magnetic field has been a paradigm system to study the effect of electron correlation and resulting emergent quantum ground states. Physical structures available to such a system are constrained by the nature of Coulomb interaction, which is difficult to control in a single 2D confinement. In this talk, I will discuss a variety of highly tunable quantum phenomena emerging from a double-layer structure, which consists of two monolayer graphene separated by a thin insulating barrier. Coulomb interaction in a double layer structure can be...

Cyclotron resonance—the resonant absorption of light by charge carriers in a strong magnetic field—is widely used to measure the effective band mass of (semi-)conducting materials. This works because the CR absorption in systems having a parabolic dispersion—a reasonable description of most materials—is unaffected by inter-particle interactions. An intriguing corollary is that, for instance, in high-mobility GaAs heterostructures when the electronic transport shows remarkably complex behavior in the fractional quantum Hall regime, there is still only a single cyclotron resonance peak that...

In this talk I will illustrate how quantum-mechanical modeling of materials at the atomic scale plays an important role in solar energy research, and how it can be used to design and realize entirely new materials. After an introduction to solar photovoltaics, I will discuss the emergence of perovskite solar cells during the past few years, and explain why this family of materials has attracted so much interest in the scientific community. One of the outstanding challenges in perovskite research is to find new lead-free materials with optoelectronic properties comparable to lead-based...

Machine learning and artificial intelligence applications in science and engineering have received rapidly increasing hype over the last several  years, with Citrine on the front lines of adoption of ML and AI in materials development. In this talk, I will discuss opportunities, open challenges, and recent work in materials informatics drawn from experiences on a wide range of commercial and noncommercial projects, including:

• data    reuse    with    transfer    learning,
• design    of    experiments    with    active    learning,
• domain    knowledge    
...

The ability to efficiently separate, recombine, and direct charge carriers is central to a wide range of applications, including electronics, photovoltaics, displays and solid-state lighting. Engineering band structure and heterointerfaces with atomic precision is an obvious route to achieving such capabilities. To do so through widely-accessible and cost-effective means is not. But such a means would allow rapid advances in these critical application areas. The evolution of colloidal semiconductor nanocrystals from single-composition, “spherical” particles to complex heterostructures of...

Two-mode squeezed light sources exhibiting continuous variable entanglement allow us to reduce the noise floor in optically transduced sensors below the standard quantum limit, enabling greater signal to noise ratios than are possible in the best possible classical sensors.  I will present some of our recent results demonstrating quantum enhanced sensitivity for applications ranging from magnetometry to plasmonic sensing to atomic force microscopy. I will also discuss some of our recent research efforts exploring quantum nanophotonics with plasmonic nanostructures and single photon...

A key feature of quantum physics is the existence of superpositions of single and many-particle quantum states, usually referred to as quantum coherence and entanglement respectively.  Famously, these aspects of quantum theory were also characterized by Einstein as "spooky" and caused him to reject many of its predictions. However, these principles are by now so well established that they have actually become tools in the growing field of quantum information science and technology to realize new paradigms for secure communication, enhanced computation, and precision sensing. 

While...