Events Archive

When atomically thin two-dimensional (2D) materials are layered, they often form incommensurable noncrystalline structures that exhibit long-period moiré patterns when examined by scanning probes. In this presentation we will use graphene and hexagonal boron nitride as examples of gapless and gapped Dirac materials to illustrate how the moire superlattices due to interlayer coupling can alter the materials' intrinsic electronic properties. The derivation of the effective models for these van der Waals materials heterojunctions for arbitrary twist angles can benefit from input obtained from ab initio calculations carried out for commensurate short period crystalline structures. We will discuss how the moire pattern modified electronic structures give rise to a variety of experimentally measurable features including enhanced density of states through van Hove singularities, and flat bands, or to their suppression due to formation of band gaps.

We investigate the energetic relaxation and spatial localization of photoexcited states in conformationally disordered p-conjugated models, choosing poly(para-phenylene vinylene) as a model system. Assuming vertical excitations, the initial photoexcited eigenstates are obtained via the disordered Frenkel model. The subsequent relaxation and localization of the excited statesis determined via the disordered Frenkel-Holstein model coupled to a dissipative environment. In particular, we solve the Lindblad master equation via the time-evolving block decimation (TEBD) and quantum jump trajectory methods. The values of the model parameters physically relevant to polymer systems naturally lead to a separation of time scales, with the ultra-fast dynamics corresponding to energy transfer from the exciton to the internal phonon modes (i.e., the C-C bond oscillations), while the longer time dynamics correspond to damping of these phonon modes by the external dissipation. Associated with these time scales, we investigate the following processes that are indicative of the system relaxing onto the emissive chromophores of the polymer: 1) Exciton-polaron formation occurs on an ultra-fast time scale, with the associated exciton-phonon correlations present within half a vibrational time period of the C-C bond oscillations. 2) Exciton decoherence is driven by the decay in the vibrational overlaps associated with exciton-polaron formation, occurring on the same time scale. 3) Exciton density localization is driven by the external dissipation, arising from ‘wavefunction collapse’ occurring as a result of the system-environment interactions. Finally, we show how fluorescence anisotropy measurements can be used to investigate the exciton decoherence process during the relaxation dynamics.

Two dimensional (2D) quantum materials provide a versatile experimental platform to probe spin-dependent novel quantum phenomena emerging at the nanoscale. The possibility of on-demand tuning of spin properties of 2D materials by external knobs such as electric field, substrate engineered proximity, etc., can have far-reaching implications for spintronics. I will discuss our experiments demonstrating a strong modulation of spin currents in bilayer graphene using static and fluctuating proximity exchange fields of a ferromagnetic insulator (FMI). We achieve complete spin modulation in graphene layers by controlling the direction of the exchange field of a nearby magnetic material in graphene/FMI heterostructures. A strong magnetic exchange coupling across the interface in graphene/FMI heterostructures leads to the experimental observation of full spin modulation at low externally applied magnetic fields in mesoscopic graphene spin channels. In graphene/FMI heterostructures, we also discover a novel spin dephasing mechanism due to randomly fluctuating magnetic exchange fields. This is manifested as an unusually strong temperature dependence of the non-local spin signals in graphene, which is due to spin relaxation by thermally-induced transverse fluctuations of the FMI magnetization. In the second half of my talk, I will discuss spin-charge interconversion driven by the Rashba effect in van der Waal bonded platinum/graphene (Pt/Gr) heterostructures. The interfacial spin-orbit interaction driven Rashba effect in low-dimensional systems can enable efficient and tunable spin-charge interconversion for spintronics applications. I will show that an applied electric field at the Pt/Gr Rashba interface results in a net spin accumulation in graphene, with spin polarization quantized along a direction transverse to the applied electric field. This current induced non-zero spin accumulation at the Pt/Gr interface is a direct consequence of uncompensated spin-textured Femi surfaces of the graphene Dirac states due to a symmetry-breaking electric field normal to the Pt/Gr heterostructure. Employing the Pt/Gr Rashba interface, we also realize the first experimental demonstration of the Onsager reciprocity between charge and spin via Rashba Edelstein effect (REE) and inverse-REE. This work is a significant advancement in graphene spintronics and provides an alternative experimental approach to generating and detecting spins using extrinsically tunable interfacial spin-orbit phenomena in two-dimensional materials.

This colloquium aims to explain why classical thermodynamics is insufficient for solids. After a review of classical equilibrium and non-equilibrium thermodynamics, two examples will be considered, grain growth and crystal plasticity, the latter one in more details. The major complication for development of thermodynamic theory for these cases was the lack of understanding of phase flow geometry. Recently, this geometry was described for dynamics of edge dislocations. Based on this finding, thermodynamics of crystal plasticity can be constructed. It includes two new thermodynamic parameters, entropy and temperature of microstructure.They have simple physical meaning: the rate of microstructure entropy coincides with the rate of slip avalanches while microstructure temperature is average energy drop in a slip avalanche. Perhaps, the phase flow geometry and the corresponding thermodynamic are common for many avalanche-type phenomena.

The annual PQI signature event will cover a wide range of topics in quantum science and engineering by featuring prominent invited keynote lecturers and highlighting the current research of PQI members. All talks are colloquium-style and accessible to a broad audience.

Superconducting qubits offer excellent prospects for manipulating quantum information, with good qubit lifetimes, high fidelity single- and two-qubit..

Join Angela Wilson of NSF, Cynthia Burrows of the University of Utah, Theodore Goodson of the University of Michigan, and Glenn Ruskin of ACS for an introduction of two of the most impactful "Big Ideas" as well as an overview of this innovative NSF program that will advance prosperity, security, health, and well-being in the United States. Learn more about : "Why Quantum entangled processes may play a role in our understanding of biological processes?"

The programmed assembly of nanoscale building blocks offers exciting new avenues to creating electronic devices and materials in which structure and functions can be chemically designed and tuned. In this context, the synthesis of inorganic molecular clusters with atomically-defined structures, compositions and surface chemistry provides a rich family of functional building elements. This presentation will describe our efforts to assemble such “designer atoms” into a variety of hierarchical structures and devices, and study the resulting collective properties.

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.

The nature of dark matter is one of the most important open problems in modern physics. Axions, originally introduced to resolve the strong CP..

This workshop is sponsored by PINSE/NFCF, JEOL and Three Rivers Microscopy Society (3RMS). The workshop will provide an introduction to the world of..

Rechargeable lithium ion (Li + ) batteries lose their ability to store charge over time. Whether they power your phone, your laptop, or your automobile, after 500-1000 recharge cycles they lose 20-40% of their capacity and must be replaced. Sony introduced the first commercial Li + battery in 1990, but 27 years later our understanding of WHY they fail is still in its infancy. Li + batteries have four parts: An anode (usually graphite), a cathode (usually a metal oxide), a separator membrane that is located between them, and a salt solution containing Li + . In our research, we have focused attention on one cathode material called ∂-MnO 2 . Our goals have been to increase the amount of energy we can store, to increase the rate at which we can deliver this energy, and to extend the lifetime of the cathode. Now, you might think that the worst way to make a battery cathode last longer would be to make it smaller! But we have discovered a process for preparing ∂-MnO 2 nanowires - just 60 – 600 nm in diameter and up to a centimeter in length – that never fail, and rarely lose any energy storage capacity, across 100,000 charge/recharge cycles. In this talk, I’ll discuss these unusual nanomaterials and what they may mean for the future of electrical energy storage.

In the 1980s, David Mermin derived a simple example of a Bell inequality and showed that it is violated in measurements on entangled quantum systems. In this talk, I reanalyze Mermin’s example, using correlation arrays, the workhorse in Jeffrey Bub’s Bananaworld (2016). For the class of all non-signaling correlations conceivable in the kind of experiment considered by Mermin, I derive both the Bell inequality, a necessary condition for such correlations to be allowed classically, and the Tsirelson bound, a necessary condition for them to be allowed quantum-mechanically. I show that the Tsirelson bound for these experiments follows directly from the geometry going into their quantum-mechanical analysis. I use this example to promote Bubism (not to be confused with QBism though both are information-theoretic approaches to the foundations of quantum mechanics). I do so by comparing the rules for probabilities in quantum mechanics, illustrated by my Bubist reanalysis of Mermin’s example, to the rules for spatio-temporal behavior in special relativity.

Women in Data Science (WiDS) is an international conference primarily located in Stanford, CA with 80+ satellite conferences across every continent except Antarctica. In 2017, over 75,000 people attended the conference in person and via the livestream and Facebook Live. The purpose of WiDS is to inspire and educate data scientists worldwide, regardless of gender, and support women in the field; the conference features exclusively female speakers from academia and industry. Speakers include Marlene Behrmann, Maria Mori Brooks, Amelia Haviland, Kathryn Roeder, and Manuela Veloso.

The AVS Western Pennsylvania Chapter invites you to attend their meeting that will have a guest speaker and student poster session, as well as a tour..

The extreme surface sensitivity of two-dimensional (2D) materials provides an unprecedented opportunity to engineer the physical properties of these..

A moving fluid can become unstable in the presence of an obstruction, leading to a flow pattern that fluctuates in time due to nonlinear dynamics. It..

Quantum optics has had a profound impact on precision measurements, and recently enabled probing various physical quantities, such as magnetic fields..

The realization of large-scale controlled quantum systems is an exciting frontier in modern physical science. In this talk, I will introduce a new..

Over the last several years, research in the field of cavity optomechanics has developed extraordinarily sensitive and low loss devices as well as..

Quantum materials are fascinating platforms where macroscopic quantum phenomena occur. As a prominent example, superconductors conduct electricity..

Berr y phase played an important role in quantum mechanics and underlying the physics of a wide range of materials from topological phases of matters..

Trapped atomic ions are an ideal system for quantum computation, with optically-accessible qubit states with long coherence times and fidelities..

As a premier multidisciplinary, open, and shared research lab, the Carnegie Mellon Nanofabrication Facility, or Nanofab, is a nanomanufacturing hub that plays a vital role in major research thrusts for the College and the University, namely in Information Technology, Internet of Things, Energy, and Life Sciences. The Nanofab serves a broad community at Carnegie Mellon and beyond, providing equipment, services, and process support for the invention, synthesis, and fabrication of new materials and devices in the areas of magnetics and spintronics, MEMS and NEMS, optics and photonics, functional oxides, 2-dimensional materials, bioelectronics, and much more. This talk will focus on the current state of the Nanofab as it relates to both research, equipment capabilities and user interface. In particular, we will highlight the transformative impact that the new Claire and John Bertucci Nanotechnology Laboratory will have for the CMU community and the region. The new facility will play a critical role in facilitating housing of cutting-edge nanomanufacturing equipment as well as creating new synergies and means for research collaboration across campus. We will discuss these new capabilities and some of the future initiatives we would like to purse to revolutionize nanoscale science and engineering within Carnegie Mellon and the region.

Recent progress in the understanding of non-equilibrium quantum dynamics of many-body systems will be discussed. Applications to electron systems and..

Understanding structure-property relationships in fields as diverse as nanoscale electronic junctions, heterogeneous catalysis, electrochemistry and energy storage often starts by meeting the challenge of identifying key structure motifs. For the theorist this is followed by tackling the problem of calculating the relevant functional characteristics, also challenging, particularly for excited state properties. I will discuss the modern toolbox for these problems, including a brief outline of the basic physical ingredients of modern manybody perturbation theory which enables studies of excited state properties. I will then discuss its application in the context of the search to develop new materials for use in photocatalysis. In particular, I will discuss the search for key structural motifs at semiconductor-water interfaces and the connection to electrochemical energy level alignment.

Quantum theory, formed in the early part of the last century, has revolutionized our view on the nature of physical reality. More than half a century..

Statistical mechanics is founded on the assumption that a system can reach thermal equilibrium, regardless of the starting state. Interactions..

Topological materials and two-dimensional (2D) materials (including graphene) have become among the most actively studied systems in condensed matter..

A recent addition to low-dimensional materials are monolayer transition metal dichalcogenides (TMDs), such as WSe2, with an atomically thin,..

Researchers may gain a competitive edge when applying to prestigious annual programs like the Multidisciplinary University Research Initiative (MURI..

One of the promising routes towards creating novel topological states and excitations is to combine superconductivity and quantum Hall (QH) effect..

Graduate and undergraduate PQI students will present their work and mingle with their peers. The PQI Fall Poster Session is a great opportunity for..

Pennsylvania Chapter of American Vacuum Society will be hosting two days-long “Plasma Processing; Reactive Sputter Etching and Deposition" workshop at the University Club of the University of Pittsburgh Pittsburgh, PA on October 19-20, 2017.

The U.S. Army Research Laboratory will hold its fourth Open Campus Open House. This year we ask, "Who is the nation’s premier laboratory for land forces focused on discovery and innovation for the Army of 2035 and beyond?" The U.S. Army Research Laboratory is interested in working with you.

The quantum Hall effect, discovered 35 years ago, is a bizarre phenomenon in which a 2D gapped system can nevertheless carry a current. Moreover, the..

Organic and organic-based materials are broadly attractive as a complement to inorganic materials due to their relative ease of fabrication,..

ETS transcription factors comprise an evolutionarily related family of genetic regulators that are ubiquitous in animals and control a myriad of..

The anomalous Hall Effect (AHE) is one of the oldest and most prominent transport phenomena in magnetic materials. However, the microscopic mechanism..

Recent general results on the statistics of nonequilibrium processes have opened up old debates between the exact dynamical and informational..

DARPA will present its Young Faculty Award webinar tomorrow afternoon (2PM-5PM- Tuesday August 29); the Office of Research will host a viewing of the event. Interested early career faculty may contact Ryan Champagne or register online - there is space available. DARPA’s webinars provide an introduction to the agency, describe program requirements, and provide an opportunity to ask questions to the program manager. For more information check the following websites; DARPA Young Faculty awards webinar Young Faculty Award (YFA) Proposers Day

Two-dimensional (2D) crystals have emerged as a new class of materials with diverse electronic properties. This is best exemplified by graphene, and..

Strontium titanate is a bulk insulator that becomes superconducting at remarkably low carrier densities. Even more enigmatic properties become..

David Snoke will be giving six lectures at 2 PM on Mondays, May 29, June 5, June 19, June 26, July 3, and July 10, in G-10 Allen Hall. The basic..

Generation of high harmonics of light fields had led to numerous scientific and technological advancements since its discovery 30 years ago,..

The annual PQI signature event will cover a wide range of topics in quantum science and engineering by featuring prominent invited keynote lecturers and highlighting the current research of PQI members. All talks are colloquium-style and accessible to a broad audience.

Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial..

As Interim Chair of Temple University’s Physics Department, May 20, 2015 was a normal day for me filled with work on my class, research, promotion of..

Reception Immediately following in Mellon Institute Lobby

2D layered materials are like paper: they can be colored, stitched, stacked, and folded to form integrated devices with atomic thickness. In this..

The PQI Quantum Day will bring Taylor-Allderdice High School students to our campuses to experience a day as a physicist, a chemist, or an engineer!

One of the remarkable features of spins in the solid state is the enormous range of time-scales over which coherent manipulation is possible. If one..

Devices that combined electricity with moving parts were crucial to the very earliest electronic communications. Today, electromechanical structures..

Storing and processing information using quantum two level systems (qubits) promises tremendous speed-up for certain computational tasks like finding..

The PQI Women in Quantum Science and Engineering Lecture Series is held in the framework of the Year of Diversity at Pitt to celebrate women scientists. All talks are colloquium-style and open to the public.

Problem solving is a major emphasis area of physics education that has been studied extensively over the past several decades. Frequently, physics..

The PQI Women in Quantum Science and Engineering Lecture Series is held in the framework of the Year of Diversity at Pitt to celebrate women scientists. All talks are colloquium-style and open to the public. Change in location: the seminar will be held in the O'Hara Student Center Ballroom

The Kagome Lattice Heisenberg Model is one of the simplest realistic spin models with a quantum spin-liquid ground state. We discuss the current..

The 2016 Nobel Prize in Physics to Kosterlitz, Thouless and Haldane honors a new set of ideas and theoretical formalism that has gradually become the..

The magnetization of a magnetic material can be reversed by using electric currents that transport spin angular momentum. This was predicted in..

Fundamental understanding of molecular structure and chemical reactivity at complex interfaces is key to many technological applications ranging from..

This talk will provide an overview of our group’s work using both standard and atypical high-performance computational chemistry modeling to..

Ballistic propagation and the light-like dispersion of graphene charge carriers make graphene an attractive platform for optics-inspired graphene..

Abstract: Since the early days of studying electron dynamics in solid state systems, experimental capabilities have taken great strides – from..

Discussions of the infamous measurement problem of quantum foundations tend to focus on how the output of a measurement, the pointer position, can be..

Gertrude E. and John M. Petersen Institute of NanoScience and Engineering (PINSE) Nano-Fabrication and Characterization Facility Overview and..

The Nobel Prizes in Physiology or Medicine, Chemistry and Physics are considered by many to be the most prestigious award available in science. The..

What is called "orthodox" quantum mechanics, as presented in standard foundational discussions, relies on two substantive assumptions --- the..

The field of spintronics, or magnetic electronics, is maturing and giving rise to new subfields. An important ingredient to the vitality of magnetism..

The size reduction and economics of integrated circuits, captured since the 1960’s in the form of Moore’s Law, is under serious challenge. Current..

Hugh Everett III presented pure wave mechanics, sometimes referred to as the many-worlds interpretation, as a solution to the quantum measurement..

We are at a time where the electronics industry is feeling pressure from two sides on the small scale we are facing the fundamental physical limits..

The term “nanofabrication” encompasses the myriad of techniques that can be used to make nanostructures, but only a small subset can make the..

Carbon materials have extraordinary properties, but utilizing these properties in applications requires a deep understanding of the materials..

Two-dimensional (2D) materials are interesting in part because their electron density can be varied in situ by transferring charge from nearby..

The high energy density and low cost of lithium-ion batteries have created a revolution in personal electronics through laptops, tablets, smart..

Ultrafast time-resolved spectroscopy, and in particular its extension to multidimensional techniques, can tell us a lot about solvation dynamics,..

Quantum transport theory yields the celebrated Landauer formula for the conductance of a two-terminal device at zero bias in terms of T(EF,0), the..

Many of the most relevant chemical properties of matter depend explicitly on atomistic details, rendering a first principles approach mandatory. Alas..

Recent research has shown the Many-Body Localised phase to be a robust state of matter, thus furthering renewed interest in the quantum dynamics of..

While both spin dynamics and electron orbital motion have been separately studied for many decades, we are just beginning to probe and understand the..

The Iterated Stockholder Atom (ISA) algorithm [1] is proving to be one of the most interesting methods for atoms‐in‐a‐molecule (AIM): it leads to a..

When metal nanoparticles are placed on different mezoporous or microporous oxide supports the catalytic turnover rates and selectivities markedly..

A superconductor is a homogeneous quantum condensate of Cooper pairs, each formed by binding two electrons into a zero-spin, zero-momentum eigenstate..

For some reason, the theory of the interaction of light with graphene, nanotubes, graphite, etc. got off on the wrong foot 15 years ago. The..

Branched flow results from a common situation involving wave or ray propagation through weakly deflecting random media for long path lengths. In..

We study energy transport at high temperature in the thermal phase of the disordered Heisenberg chain [1]. Starting from nonequilibrium initial..

Advances in solid-state devices have been enabled by the introduction of new materials platforms and their subsequent improvements in carrier..

I will present the first realizations of double quantum dots in dual-gate nanowire transistors. We have observed the spin-blockade effect (useful for spin readout), electrically-driven hole-spin resonance, and, very recently, we obtained the first proof of concept of a CMOS hole-spin qubit.

Dr. Huang received a B.S. in Chemistry from Nanjing University, China in 2000. After receiving an M.S. in 2002 also from Nanjing University, he..

This colloquium will describe a program developed for a desktop computer which carries out a time-dependent simulation of the core of an exploding..

The quest of new states of matter in the time domain and the need for ultrafast control of material properties have been fueled by the recent advance..

Ballistic propagation and the light-like dispersion of graphene charge carriers make graphene an attractive platform for optics-inspired graphene..

PQI Science2015 Information PQI is partnering with the organizers of Science2015 in two distinct ways: PQI Poster Session Where: Alumni Hall 1st..

PQI2014: Quantum Technologies 9-11 April 2014 Our second annual PQI event will be held from Wednesday April 9th to Friday April 11th, 2014. The first..