Surprises from Time Crystals

Recent years have witnessed a remarkable confluence of diverse areas of physics coming together to inform fundamental questions about many-body quantum matter. A unifying theme in this enterprise has been the study of many-body quantum dynamics in systems ranging from electrons in solids to cold atomic gases to black holes. One of the foundational pillars in the study of many-body systems is the theory of equilibrium statistical mechanics characterized by two fundamental ideas: thermalization (that interacting systems generically approach thermal equilibrium at late times) and phase structure (that equilibrium states of matter can display various forms of order separated by sharp phase transitions). Recent progress, particularly in the field of many-body localization, has led to generalizations of these fundamental ideas to the out-of-equilibrium setting. I will describe this progress, particularly as applied to periodically driven or Floquet systems. I will show that not only can non-equilibrium systems exhibit a sharp notion of phase structure, but that some of these phases are completely novel and unique to the out-of-equilibrium setting. For example, certain phases of matter that are forbidden in equilibrium, such as quantum time crystals, have found new life in the out-of-equilibrium setting. I will review the state of this rapidly evolving field, focusing in particular on some of the remarkable properties of the time crystal phase, and the surprises coming out of its study. I will provide a detailed overview of existing experiments, with a view towards identifying the ingredients needed for an unambiguous observation of this phase in the future.

Reference: Khemani, Moessner, Sondhi, "A Brief History of Time Crystals", arXiv:1910.10745

Tuning magnetic anisotropy in nanostructures for biomedical and electromagnetic applications

Magnetic nanoparticles have been building blocks in applications ranging from high density recording tospintronics and nanomedicine [1]. Magnetic anisotropies in nanoparticles arising from surfaces, shapes and interfaces in hybrid structures are important in determining the functional response in various applications. In this talk I will first introduce the basic aspects of anisotropy and discuss resonant RF transverse susceptibility, that we have used extensively, as a powerful method to probe the effective anisotropy in magnetic materials. Tuning anisotropy has a direct impact on the performance of functional magnetic nanoparticles in biomedical applications such as contrast enhancement in MRI and magnetic hyperthermia cancer therapy. I will focus on the role of tuning surface and interfacial anisotropy with a goal to enhance specific absorption rate (SAR) or heating efficiency. Strategies going beyond simple spherical structures such as exchange coupled core-shell nanoparticles, nanowire, nanotube geometries can be exploited to increase heating efficiency in magnetic hyperthermia [2,3]. In addition to biomedical applications, composites of anisotropic nanoparticles dispersed in polymers pave the way to a range of electrically and magnetically tunable materials for RF and microwave device applications [4]. This lecture will combine insights into fundamental physics of magnetic nanostructures along with recent research advances in their application in nanomedicine and electromagnetic devices.

References:
[1] E.A. Périgo et al., "Fundamentals and advances in magnetic hyperthermia", Appl. Phys. Rev. vol. 2, 041302 (2015)
[2] Z. Nemati et al., "Core-shell iron/iron oxide nanoparticles: Are they promising for magnetic hyperthermia?",RSC Advances vol. 6, 38697 (2016)
[3] H. Khurshid et al., "Tuning exchange bias in Fe/gamma-Fe2O3 core-shell nanoparticles: Impacts of interface and surface spins", Appl. Phys. Lett. vol. 104, 072407 (2014)
[4] K. Stojak et al., "Polymer nanocomposites exhibiting magnetically tunable microwave properties", Nanotechnology vol. 22, 135602 (2011)

Biography
Hari Srikanth is a Professor of Physics at the University of South Florida in Tampa, FL. He received his Ph.D. in experimental condensed matter physics from the Indian Institute of Science. After postdoctoral research for several years, Hari joined USF in 2000 and established the Functional Materials Laboratory. His research spans a wide range of topics including magnetic nanoparticles, magnetic refrigerant materials, spin calorics andcomplex oxides. He has around 250 journal publications and given numerous invited talks. Hari is a Fellow of the American Physical Societyand a Senior Member of IEEE. He is also an Associate Editor for Journal of Applied Physics. Hari has been closely involved with the MMM and INTERMAG conferences for more than 15 years serving as Publication Editor, Publication Chair and on program committees.

NMR quantum processors: Aspects and Prospects

That an ensemble of nuclear spins in ordinary liquids and solids under ambient conditions allow precise manipulation of their quantum dynamics, retain quantum superpositions for long durations, and allow accurate measurement of the final states is remarkable. Thanks to decades of methodology developments in nuclear magnetic resonance (NMR) spectroscopy, we can conveniently implement various quantum gates, algorithms, and simulations using nuclear-spin quantum processors controlled by amplitude and phase modulated radio frequency pulses. After a brief introduction on NMR, I will explain how one can initialize, control, and measure a set of spin-qubits. Subsequently, I will describe some of the recent developments in our group. Finally, I will point out certain limitations of NMR quantum processors and potential solutions that have been proposed to overcome them.

Tunable symmetries and Berry's phase in few layer graphene

There have been extensive studies on monolayer graphene where unique properties result from the symmetry of the honeycomb lattice. Few layer graphene systems are of interest as they offer interesting opportunities to study effect of electronic interactions [1] due to flatter bands while monolayer graphene was largely understood in terms of independent electron picture. In addition, few layer graphene offer an opportunity to break simple symmetries and study their consequence [2]. Berry’s phase can be probed using magneto-transport measurements. These measurements can throw up interesting questions in multiband system of few layer graphene. I will briefly discuss our efforts to measure and understand Berry’s phase in a complex multiband system.
1. Biswajit Datta, et al. Nature Communications 8, 14518 (2017).
2. Biswajit Datta, et al. Physical Review Letters 121, 056801 (2018).

Quantum Matter Twisted and Torn

I shall present a broad overview of quantum phases of many fermions to bring out two key ideas -- topology and entanglement-- that are essential for their description. Focussing on topology, I will present, in a form accessible to a broad audience, a simple picture of where and how topology ("twist") enters the description of many-fermion phases. This will be followed by a more technical overview of symmetry classification of fermionic systems and how these give rise to symmetry protected topological phases of noninteracting fermions. I shall touch upon how these ideas can revolutionize electronic technology, even resulting in epoch-changing technologies. I will conclude by discussing exciting open problems, particularly in understanding systems with interactions.