Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Z06: Chiral Phonons in Quantum MaterialsInvited
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Sponsoring Units: DCMP Chair: Gregory Fiete, Northeastern University; Dominik Juraschek, Tel Aviv University Room: L100FG |
Friday, March 8, 2024 11:30AM - 12:06PM |
Z06.00001: Giant effective magnetic moments of chiral phonons Invited Speaker: Swati Chaudhary Circularly polarized lattice vibrations carry angular momentum and lead to magnetic responses in applied magnetic fields or when resonantly driven with ultrashort laser pulses. The phonons associated with such vibrations are known as chiral phonons. On the basis of purely circular ionic motion, these phonons are expected to carry a magnetic moment of the order of a few nuclear magnetons. However, some recent experiments have demonstrated a phonon magnetic moment of the order of a few Bohr magnetons. This kind of giant magnetic response points towards the electronic contribution to the magnetic moment of phonons. Many diverse mechanisms have been discovered for this enhanced magnetic response of chiral phonons. The orbital-lattice coupling is one such mechanism where low-energy electronic excitations on a magnetic ion hybridize with phonons and endow a large magnetic moment to phonons. In this talk, I'll present a microscopic model for the effective magnetic moments of chiral phonons based on this mechanism. We apply our model to two types of materials: rare-earth halide paramagnets and transition-metal oxide magnets. In both cases, we find that chiral phonons can carry giant effective magnetic moments of the order of a Bohr magneton, orders of magnitude larger than previous predictions. |
Friday, March 8, 2024 12:06PM - 12:42PM |
Z06.00002: Connecting Phonon Chirality with Electronic Band Topology Invited Speaker: Felix G Hernandez The symmetries of crystals play an important role in the properties of their phonons. In particular, when the mirror symmetries are broken, the lattice ions can display circular motion with finite angular momentum. These modes, known as chiral phonons, have recently been demonstrated in both rotating and propagating lattice motions. Usually, phonons are insensitive to magnetic fields. On the contrary, chiral phonons carry magnetic moment and directly couple to magnetic fields. Giant magnetic moments are predicted to result from electronic contributions to the magnetism of phonons. While such a mechanism establish the possibility of connecting phonon chirality and electronic topology, no experimental evidence has been reported. In this talk, I will present the magnetic response of transverse optical phonons in a set of Pb1-xSnxTe thin films, which is a topological crystalline insulator for x > 0.32. We studied one sample in the trivial phase (x = 0.24) and two samples in the topological phase (x = 0.42 and 0.56). We observed the occurrence of a ferroelectric phase in all the samples at a composition-dependent critical temperature. Polarization-dependent terahertz magnetospectroscopy measurements revealed Zeeman splittings and diamagnetic shifts, demonstrating a large phonon magnetic moment. Films in the topological phase exhibited phonon magnetic moment values that were larger than those in the topologically trivial samples by two orders of magnitude. Furthermore, the sign of the effective phonon g-factor was opposite in the two phases, a signature of the topological transition according to our model. These results strongly indicate the existence of interplay between the magnetic properties of chiral phonons and the topology of the electronic band structure. Our work opens up new avenues for topology-based devices and applications through magnetic field-based phonon control of electronic states. |
Friday, March 8, 2024 12:42PM - 1:18PM |
Z06.00003: Spin dynamics via chiral phonons Invited Speaker: Hanyu Zhu
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Friday, March 8, 2024 1:18PM - 1:54PM |
Z06.00004: Chiral phono-magnetism and spin-rotation coupling Invited Speaker: R. Matthias Geilhufe High intensity THz lasers allow for the coherent excitation of individual phonon modes. The ultrafast control of emergent magnetism by means of phonons opens up new tuning mechanisms for functional materials. While theoretically predicted phonon magnetic moments are tiny, recent experiments hint towards a significant magnetization in various materials. I will give an introduction into chiral phono-magnetism and outline the current challenges in the field. Furthermore, I introduce a coupling mechanism between rotational degrees of freedom and the electron spin. This coupling introduces the transient level-splitting of spin-up and spin-down channels and a resulting magnetization. |
Friday, March 8, 2024 1:54PM - 2:30PM |
Z06.00005: Chiral-phonon-activated spin Seebeck effect Invited Speaker: Jun Liu Utilization of the interaction between spin and heat currents is the central focus of the field of spin caloritronics. Chiral phonons possessing angular momentum arising from the broken symmetry of a non-magnetic material creates the potential for generating spin currents at room temperature in response to a thermal gradient, precluding the need for a ferromagnetic contact. Here we show the observation of spin currents generated by chiral phonons in a two-dimensional layered hybrid organic-inorganic perovskite implanted with chiral cations when subjected to a thermal gradient. The generated spin current shows a strong dependence on the chirality of the film and external magnetic fields, of which the coefficient is orders of magnitude larger than that produced by the reported spin Seebeck effect. Our findings indicate the potential of chiral phonons for spin caloritronic applications and offer a new route toward spin generation in the absence of magnetic materials. |
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