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[Fizinfo] Szemináriumok - Seminars: Balla Péter

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  • From: Szeminárium koordinátor <sem-admin AT>
  • To: SZFI Szeminárium <seminar AT>,Fizinfo <fizinfo AT>
  • Cc: Fizinfo <fizinfo AT>
  • Subject: [Fizinfo] Szemináriumok - Seminars: Balla Péter
  • Date: Sat, 11 Jun 2022 06:00:02 +0200 (CEST)
  • Authentication-results: (amavisd-new); dkim=pass (1024-bit key) reason="pass (just generated, assumed good)"

SZFI SzemináriumBalla PéterMTA Wigner FK SZFIGround-state manifolds of
frustrated Heisenberg magnets and magnetooptical selection rules in
multiferroics (PhD házivédés)2022. június 16. csütörtök, 10.00, 1. ép.,
Meeting ID: 828 1434 5310 Passcode: 973614In the first part of the talk, I
consider classical Heisenberg magnets on frustrated lattices, where not all
the bond energies can be simultaneously minimized. This leads to a large
number of energetically equivalent ground states and extended ground-state
manifolds in Fourier space, a pattern markedly different from the usual Bragg
peaks. I analyze the ground-state (zero-temperature) phase diagram of the
Heisenberg model on the face-centered cubic lattice up to third neighbor
interactions. I identify different classes of ground states, with a
particular focus on triple points and phase boundaries, where the extended
ground-state manifolds emerge. I also give a general recipe for constructing
Heisenberg models on any Bravais lattice having extended ground-state
manifolds (curves in 2D and surfaces in 3D). In magnetoelectric
multiferroics, the magnetization and electric polarization are coupled,
meaning that we can manipulate the spins with electric fields or the electric
polarization with magnetic fields. This coupling also manifests itself in the
finite-frequency properties, leading to electromagnons and one-way
transparency. In the second part, I consider the magnetooptical selection
rules in multiferroics and apply them to the absorption measurements of
Sr2CoSi2O7 in its paramagnetic state in high external magnetic fields. I show
that the antiunitary symmetries (time-reversed elements of the magnetic
symmetry group of a crystal) relate the imaginary and real parts of matrix
elements of perturbing operators, leading to a new type of selection
rules.&nbsp;Minden érdeklődőt szívesen látunk! - Everyone is welcome to
attend.Juhász Róbertsem-admin AT

  • [Fizinfo] Szemináriumok - Seminars: Balla Péter, Szeminárium koordinátor, 06/11/2022

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