Harvard University Department of Physics

Structure and Topology of Band Structures in the 1651 Magnetic Space Groups

Breaking down band structures — system could help researchers design new materials with specific properties...

Striking Isotope Effect on the Metallization Phase Lines of Liquid Hydrogen and Deuterium

Metallizaton of hydrogen and its isotopes has been one of the great challenging problems in condensed matter physics. There are two pathways to metallic hydrogen: very high pressure and low temperatures to make solid metallic hydrogen, or intermediate pressures...

Halperin Awarded 2019 APS Medal

Prof. Bertrand Halperin has been awarded the 2019 Medal for Exceptional Achievement in Research by the American Physical Society...

UPCOMING EVENTS

Today

Professor Subir Sachdev, Harvard University
Start: 04:15pm - End: 05:15pm
- Strange metals and black holes
  
  The ‘strange metal’, is a state of matter formed by electrons in many modern materials, including the compounds which exhibit high temperature superconductivity.
  In this state, electrons quantum entangle with each other and conduct electric current collectively (rather than one-by-one, as in an ordinary metal like copper).
  Quantum entanglement also has remarkable effects near the horizon of a black hole, leading to the Bekenstein-Hawking black hole entropy, and the Hawking temperature.
  Surprisingly, there is a deep connection between the nature of quantum entanglement in strange metals and black holes, and this has led to mutually beneficial insights.
  This connection is simply described by the Sachdev-Ye-Kitaev model, which leads to a common set of equations describing the quantum dynamics of certain strange metals and black holes.
- 04:15pm
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Tomorrow

Special ITAMP Lunch Seminar: Adi Pick (Technion)
Start: 12:00pm - End: 01:30pm
- 12:00pm
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CUA Seminar: Kristian Helmerson (Monash University)
Start: 04:00pm - End: 05:30pm
- Evolution of large-scale flow from turbulence in a two-dimensional superfluidIn two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices, in which the persistent large-scale vortices correspond to negative temperature states. I will describe the experimental confirmation of Onsager's model in a superfluid gas of atoms. We drag grid barriers through an oblate atomic gas Bose-Einstein condensate to generate non-equilibrium distributions of vortices. We observe, in the subsequent evolution of the superfluid, signatures of an inverse energy cascade driven by the evaporative heating of vortices, leading to steady-state configurations characterized by negative absolute temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven out of equilibrium.
- 04:00pm
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MATH: Pavel Etingof (MIT), “New symmetric tensor categories in positive characteristic”
Start: 04:00pm - End: 05:00pm
- 04:00pm
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Special CMP Seminar - Mallika Randeria
Start: 04:30pm - End: 05:30pm
- 04:30pm
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Wednesday, September 26th

Joint Quantum Sciences Colloquium - Peter Drummond (Swinburne University of Technology)
Start: 04:00pm - End: 06:00pm
- Simulations of many-body systems: Furry and Coleman revisited Peter D DrummondWendell Furry [1] and Sydney Coleman [5] were two of Harvard's most original quantum theorists. What can modern technology contribute to their work? Experimentally tested simulations of opto-mechanics[4] and atom interferometers [3], with thermal noise and losses, will be used to analyse proposals for testing Furry's nonlocal decoherence, and Coleman's QFT tunnelling to the true vacuum. Both entanglement decoherence and massive Schrodinger cats are testable [4] through an optomechanical memory, simulated using the positive-P representation. Coleman's vacuum tunnelling idea will be applied to construct a proposal for a laboratory model of the quantum fluctuations in the 'Big Bang', using a coupled BEC experiment simulated with a Wigner representation [6]. Who needs a ship in a bottle, when you can have a universe on table-top? [1] W. H. Furry, Phys. Rev. 49, 393 (1936).[2] A. Einstein, B. Podolsky, and N. Rosen, Phys. Rev. 47, 777  (1935).[3] M. Egorov et. al,  Phys. Rev. A 84, 021605 (2011).[4] S. Kiesewetter, R. Y. Teh, P. Drummond and M. Reid, Phys. Rev. Lett. 119, 023601 (2017).[5] S. Coleman, Phys. Rev. D 15, 2929 (1977).[6] O. Fialko et. al., J. Phys. B 50 024003 (2017).
- 04:00pm
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Prof. Hyunsik Yoon - SEOULTECH
Start: 06:00pm - End: 07:30pm
- 06:00pm
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Thursday, September 27th

CMP Seminar: Christos Panagopoulos (NTU Singapore), hosted by Jenny Hoffman
Start: 12:00pm - End: 01:00pm
- Title: Tunable Room Temperature Skyrmions
  
  Abstract: Using particle-like spin structures as a paradigm, I will argue the states induced by engineering spin orbit coupling and inversion symmetry breaking open a broad perspective, with significant impact also in the practical technology of spin topology. In one such example, multilayers of Ir/Fe(x)/Co(y)/Pt enable us tailor the magnetic interactions governing skyrmion (Sk) properties, thereby tuning their thermodynamic stability parameter by an order of magnitude. We have shown that Sk’s exhibit a smooth crossover between isolated (metastable) and disordered lattice configurations across samples, while their size and density can be tuned by factors of 2 and 10, respectively.
  
  To investigate the magnetization dynamics, we also determined the damping parameter characterizing the magnetization response, and identified a gyrotropic Sk excitation that persists over a wide range of temperatures and across varying sample compositions. Furthermore, to tailor the phenomenology of nanoscale Sk’s, including topological stability and malleability we studied their formation and evolution at zero field through confinement effects. The zero field Sk size can be as small as 50 nm, and varies by a factor of 4 with dot size and magnetic parameters.
  
  Time permitting, I will discuss a detailed microscopic investigation which allowed us identify magnetic structures forming via Sk-Sk interaction and their role in interpreting electrical signatures in materials and devices hosting Sk’s. In particular, we establish direct correspondence between Sk’s and their topological Hall signature.
- 12:00pm
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ITAMP Lunch Seminar
Start: 12:00pm - End: 01:00pm
- Speaker: Florentin Reiter
- 12:00pm
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Friday, September 28th

CMP Special Seminar: Andrew Mackenzie, hosted by Ashvin Vishwanath
Start: 11:00am - End: 12:00pm
- Title: Strain tuning of quantum materials
  
  Abstract: In this talk I will discuss the development of novel methods of applying uniaxial pressure to single crystals of quantum materials. Much of our work so far has been on ruthenates, but I will also mention projects on other materials. I will show that it is now possible to strain single crystals, reversibly, to change lattice parameters by at least 1%, and that this provides a ‘tuning energy scale’ equivalent to the Zeeman energy of magnetic fields of well over 1000 T. Uniaxial techniques are particularly suited to controlled tuning through Lifshitz transitions, and are also a useful complement to epitaxial strain in then films, which is usually biaxial.
- 11:00am
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