Seminars

A Pitt Physics seminar

Abstract: Magnetic skyrmions and topological spin textures have been investigated as possible information carriers in next generation devices. Among the well-studied B20 materials, MnGe is an interesting outlier that has been shown to host a novel three-dimensional hedgehog/anti-hedgehog lattice (HL) with a very short period (~3 nm). Here, we use spin-polarized scanning tunneling microscopy (SP-STM) at low-temperature (~5 K) to directly observe the spin textures present at the surface of an 80 nm MnGe thin film. We find the HL is not...

Abstract: The advent of quantum computing has created novel opportunities for the direct simulation of quantum systems on quantum hardware. However, in the near term, quantum devices will possess limited scope due to noise and size limitations. Due in part to these constraints, variational algorithms have gained popularity as a powerful yet economical alternative to traditional digital quantum computation. 

In this talk, I will discuss two variational frameworks, parameterized quantum circuits and tensor networks. For each method I will give an overview followed by...

Abstract: Topologists can differentiate between bagels and pretzels by simply counting holes in each bread. The number of holes, formally described by the Euler characteristic, is a topological invariant insensitive to smooth deformation of the shape and size of an object. In condensed matter physics, we study an analogue of pastry, the Fermi sea. Like bread filled with flour, Fermi sea is filled with electrons, and nature provides a variety of exotic topology, e.g. metal copper has a Fermi sea like a pretzel with 4 handles. In this talk, I will introduce physical...

A CMU/Pitt Colloquium

Abstract: The ability to create arbitrary stacking configurations of layered two-dimensional materials has opened the way to the creation of designer band structures.  Twisted bilayer graphene and graphene on hexagonal boron nitride are two of the simplest examples of such a van der Waals heterostructure where the electronic properties of the composite material can be fundamentally different from either individual material.   These van der Waals heterostructures can be formed using a wide variety of layered materials including...

A Pitt/CMU Colloquium

Abstract: The study of quantum materials has emerged as a rapidly developing field of condensed matter and materials physics. Quantum materials are materials that have properties and exhibit phenomena deeply rooted in the laws of quantum physics, which potentially allows us to exploit these laws for future applications in quantum-based energy and computing technology. Furthermore, in addition to providing a desirable resource, quantum materials also offer unique insight into the fundamental and building blocks of matter and the...

A Pitt Chem Seminar

Abstract: Two topics will be covered in the general area of tunneling microscopy: looking at surface dynamics of glasses on a millisecond to hour scale, and excited state dynamics of nanomaterials on the sub-picosecond to nanosecond scale, both with sub-nm resolution. The technique of “SMA-STM” works by shining modulated light on a sample and detecting the resulting change in electron density with an STM tip, which also enhances the evanescent light wave that excites the sample. I’ll show that we can build energy landscapes of glass...

A CMU-PITT Colloquium

Abstract: Electron microscopy is transforming the physical sciences. Aided by a new generation of direct imaging detectors, cryo-electron microscopy won the 2017 Nobel Prize in Chemistry for advancements in visualization of biomolecules.  To go beyond traditional electron microscopy, new detectors must also be developed for the diffraction imaging; here, the scattered electron beam encodes a wealth of information about the structure, chemistry, electrical, optical, and magnetic properties of matter. During my PhD, I co-invented the...

A Pitt/CMU Colloquium

Abstract: The extraordinary advances in quantum control of matter and light have been transformative for atomic and molecular precision measurements enabling probes of the most basic laws of Nature to gain a fundamental understanding of the physical Universe. Exceptional versatility, inventiveness, and rapid development of precision experiments supported by continuous technological advances and improved atomic and molecular theory led to rapid development of many avenues to explore new physics. I will give an overview of atomic and...

A Pitt/CMU Colloquium

Abstract: Superconductivity is a collective state in which many fermions pair up to give rise to a zero-resistance electron transport regime. The majority of superconductors are well described by a Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity in which a weak momentum space attraction between fermions forms bound Cooper pairs separated in real space. When attraction becomes strong the Cooper pair size shrinks until it effectively forms a diatomic Bose molecule that can, in turn, undergo Bose-Einstein condensation (BEC). A solid-...

A Pitt/CMU Colloquium

Abstract: Plasmons, the self-sustained collective density modes in metals, form an integral part of the description of interacting electronic systems. Conventionally, plasmon dynamics are often dominated by the density and effective mass of carriers in its host metal. We will discuss how this description falls short in topological materials where the intricate twisting of wavefunctions (i.e. Bloch band quantum geometry) lead to a new class of plasmonic collective modes. These "topological plasmons" possess a wealth of exotic properties...