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X-WR-CALNAME:Stewart Blusson Quantum Matter Institute
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X-WR-CALDESC:Events for Stewart Blusson Quantum Matter Institute
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SUMMARY:CM Seminar: Topological Landau Theory\, Joseph Maciejko\, University of Alberta
DESCRIPTION:Speaker: Joseph Maciejko\, University of Alberta \nTime: 10:00-11:00am \nLocation: BRIM 311 \nTitle: Topological Landau Theory \nAbstract: I will discuss a notion of topology “hidden” in Landau’s theory of phase transitions. When the order parameter comprises several components in the same irreducible representation of symmetry\, it can possess a nontrivial topology and acquire a Berry phase under the variation of thermodynamic parameters. To illustrate this idea\, I will focus on the superconducting phase transition of an electronic system with tetragonal symmetry and a two-component order parameter. From the time-dependent Ginzburg-Landau equation in the adiabatic limit\, we find that the order parameter acquires a Berry phase after a cyclic evolution of parameters. I will discuss two concrete models — one preserving time-reversal symmetry and one breaking it — and show that the nontrivial topology of the order parameter originates from thermodynamic analogs of gapless Dirac and Weyl points in the phase diagram. Finally\, I will propose an experimental realization of a thermodynamic Dirac point in chiral superconductors under strain\, and its detectable signature in the Josephson effect\, the geometry of vortices\, and the upper critical field.
URL:https://qmi.miffanytark.com/event/cm-seminar-topological-landau-theory-joseph-maciejko-university-of-alberta/
CATEGORIES:CM Seminar
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DTSTART;TZID=America/Vancouver:20260212T100000
DTEND;TZID=America/Vancouver:20260212T110000
DTSTAMP:20260206T191900Z
CREATED:20260206T191900Z
LAST-MODIFIED:20260206T191900Z
UID:9167-1770890400-1770894000@qmi.miffanytark.com
SUMMARY:CM Seminar: Signature of preformed pairs in angle-resolved two-electron coincidence photoemission\, Janez Bonča\, University of Ljubljana.
DESCRIPTION:Speaker: Janez Bonča\, University of Ljubljana \nTime: 10:00-11:00am \nLocation: BRIM 311 \nTitle: Signature of preformed pairs in angle-resolved two-electron coincidence photoemission \nAbstract: We employ density matrix renormalization group (DMRG) and variational exact diagonalization (VED) to compute single- and two-electron removal spectra of the Hubbard–Holstein model at low electron densities. By tuning electron–phonon coupling and Hubbard repulsion\, we distinguish polaron and bipolaron liquids. While both are metallic\, the polaron liquid exhibits spectral weight up to the Fermi energy\, whereas the bipolaron liquid shows a gap set by the bipolaron binding energy\, suggesting that ARPES can identify liquids of preformed pairs. The bipolaron liquid is well approximated by a gas of hard-core bosons in momentum space [1]. \nTwo-electron coincidence spectra reveal distinct energy and momentum signatures for electrons emitted from the same versus different pairs. These generic fingerprints provide a route to detect pairing and distinguish coherent from incoherent pairs [2].  The pair binding energy can be read off directly from the 2eARPES intensity map when defined as a functiopn of the two distinct frequencies of ejected  photoelectrons. [3] \n  \n[1] K. Kovac\, A. Nocera\,  A.  Damascelli\,  J. Bonca\, and M. Berciu\, Phys. Rev. Lett. 134\, 096502 (2025). \n[2] J. Bonca\,  A.  Damascelli\,  M. Berciu\, under review. \n[3] J. Bonca\,  A. Nocera\, A.  Damascelli\,  M. Berciu\, in preparation.
URL:https://qmi.miffanytark.com/event/cm-seminar-signature-of-preformed-pairs-in-angle-resolved-two-electron-coincidence-photoemission-janez-bonca-university-of-ljubljana/
CATEGORIES:CM Seminar
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DTSTART;TZID=America/Vancouver:20260226T100000
DTEND;TZID=America/Vancouver:20260226T110000
DTSTAMP:20260224T000532Z
CREATED:20260224T000532Z
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UID:9183-1772100000-1772103600@qmi.miffanytark.com
SUMMARY:CM Seminar: Cryogenic electron microscopy of polar order in a quantum paraelectric\, Ismail El Baggari\, UBC
DESCRIPTION:Speaker: Ismail El Baggari\, UBC \nTime: 10:00-11:00am \nLocation: BRIM 311 \nTitle: Scanning transmission electron microscopy (STEM) now routinely resolves the atomic structure and chemistry of materials with sub-angstrom resolution. Recent advances in instrumentation further allow spatially resolved mapping of subtle\, picometer-scale atomic shifts that underpin emergent functional properties. In ferroelectrics\, for example\, polarization arises from tiny atomic displacements that break inversion symmetry; STEM can locally visualize these displacements and reveal novel polarization textures.  \nDespite this potential\, STEM applications have traditionally been restricted to room temperature (or higher) because of longstanding challenges in implementing stable liquid-helium cryogenic cooling\, such as vibrations and inadequate temperature control. My group has been addressing these limitations by developing dedicated liquid helium cryogenic STEM instrumentation to probe materials whose emergent properties appear only at low temperatures. We have now overcome key technical hurdles and can cool samples inside the microscope to cryogenic regimes down to ~20 K. I will present recent applications of cryogenic STEM to imaging order and disorder in ferroelectrics. In particular\, I will highlight quantum paraelectric SrTiO₃\, a material that hovers on the verge of ferroelectricity yet remains paraelectric to the lowest temperatures due to quantum fluctuations. Using cryogenic STEM\, we directly visualize emergent nanoscale polar textures and mesoscale correlations in this quantum paraelectric phase. \n  \nZhang et al. “Inverse Melting of Polar Order in Chemically Substituted BaTiO3.” Physical Review Letters 134.25 (2025) \nRennich\, et al. “Ultracold cryogenic TEM with liquid helium and high stability.” Proceedings of the National Academy of Sciences122.36 (2025) \nZhang et al. “Nanoscale Polar Landscapes in Quantum Paraelectric SrTiO3.” arXiv:2509.24969 (2025).
URL:https://qmi.miffanytark.com/event/cm-seminar-cryogenic-electron-microscopy-of-polar-order-in-a-quantum-paraelectric-ismail-el-baggary-ubc/
CATEGORIES:CM Seminar
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