ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 08 Aug 2022 23:41:22 GMT2022-08-08T23:41:22Z50151- Phonon quarters-wave losshttps://scholarbank.nus.edu.sg/handle/10635/213254Title: Phonon quarters-wave loss
Authors: Xiong, G.; Yu, Z.; Wang, J.-S.; Zhang, L.
Abstract: There has been a growing interest in the phase of phonon, due to the theoretical prediction (Phys. Rev. Lett. 115.11 (2015)) and the experimental observation (Science 359.6379 (2018)) of chiral phonons, which have different phases in different components. While half-wave loss is a well-known concept in optics, in this work, a series of plateaus of quarters-wave loss are first found for the reflected phonon across an interface by using an atomic junction model. These plateaus can be understood by the S-matrix in the system with time-reversal symmetry. If a phonon wave propagates from a low acoustic-impedance material (or a low cutoff frequency material) to a higher one in the long-wave limit (or in the high frequency limit), a half-wave loss takes place for the reflected phonon; however, the plateau of half-wave loss for reflected phonon occurs in the whole frequency domain if phonon transfers to a material with a larger spring constant. Besides the half-wave loss, we also observe plateaus of quarter-wave (three-quarters-wave) loss in long wave limit when the two leads with identical acoustic impedance are coupled by a weak (strong) coupling in comparison with the optimum thermal coupling. The quarters-wave loss for phonons can be applied to chiral phonon manipulation and other phononics devices. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
Tue, 01 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2132542019-01-01T00:00:00Z
- Phonon Hall effect in ionic crystals in the presence of static magnetic fieldhttps://scholarbank.nus.edu.sg/handle/10635/97526Title: Phonon Hall effect in ionic crystals in the presence of static magnetic field
Authors: Agarwalla, B.K.; Zhang, L.; Wang, J.-S.; Li, B.
Abstract: We study phonon Hall effect (PHE) for ionic crystals in the presence of static magnetic field. Using Green-Kubo formula, we present an exact calculation of thermal conductivity tensor by considering both positive and negative frequency phonons. Numerical results are shown for some lattices such as hexagonal lattices, triangular lattices, and square lattices. We find that the PHE occurs on the nonmagnetic ionic crystal NaCl, although the magnitude is very small which is due to the tiny charge-to-mass ratio of the ions. The off-diagonal thermal conductivity is finite for nonzero magnetic field and changes sign for high value of magnetic field at high temperature. We also found that the off-diagonal thermal conductivity diverges as ±1/T at low temperature. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Sun, 01 May 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975262011-05-01T00:00:00Z
- Phonon interference at self-assembled monolayer interfaces: Molecular dynamics simulationshttps://scholarbank.nus.edu.sg/handle/10635/97528Title: Phonon interference at self-assembled monolayer interfaces: Molecular dynamics simulations
Authors: Hu, L.; Zhang, L.; Hu, M.; Wang, J.-S.; Li, B.; Keblinski, P.
Abstract: Using molecular dynamics simulations, we expose phonon interference effects in thermal transports across a self-assembled monolayer (SAM) of alkanethiol molecules covalently bonded to (111) gold substrate and physically bonded to silicon. In particular, we show that the thermal conductance of SAM-Au interface depends on the bonding strength at the SAM-Si interface and that the phonon transmission coefficients show strong and oscillatory dependence on frequency, with oscillatory features diminishing with increasing SAM thickness. To explore the generality of this behavior we analyze a simple model of point junction on a one-dimensional chain using the scattering boundary method. © 2010 The American Physical Society.
Fri, 18 Jun 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975282010-06-18T00:00:00Z
- Thermal transport across metal-insulator interface via electron-phonon interactionhttps://scholarbank.nus.edu.sg/handle/10635/98373Title: Thermal transport across metal-insulator interface via electron-phonon interaction
Authors: Zhang, L.; Lü, J.-T.; Wang, J.-S.; Li, B.
Abstract: The thermal transport across a metal-insulator interface can be characterized by electron-phonon interaction through which an electron lead is coupled to a phonon lead if phonon-phonon coupling at the interface is very weak. We investigate the thermal conductance and rectification between the electron part and the phonon part using the nonequilibrium Green's function method. It is found that the thermal conductance has a nonmonotonic behavior as a function of average temperature or the coupling strength between the phonon leads in the metal part and the insulator part. The metal-insulator interface shows a clear thermal rectification effect, which can be reversed by a change in average temperature or the electron-phonon coupling. © 2013 IOP Publishing Ltd.
Wed, 06 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983732013-11-06T00:00:00Z
- Interfacial thermal transport in atomic junctionshttps://scholarbank.nus.edu.sg/handle/10635/96967Title: Interfacial thermal transport in atomic junctions
Authors: Zhang, L.; Keblinski, P.; Wang, J.-S.; Li, B.
Abstract: We study ballistic interfacial thermal transport across atomic junctions. Exact expressions for phonon transmission coefficients are derived for thermal transport in one-junction and two-junction chains, and verified by numerical calculation based on a nonequilibrium Green's function method. For a single-junction case, we find that the phonon transmission coefficient typically decreases monotonically with increasing freqency. However, in the range between the point of equal frequency spectrum and that of equal acoustic impedance, it first increases then decreases, which explains why the Kapitza resistance calculated from the acoustic mismatch model is far larger than the experimental values at low temperatures. The junction thermal conductance reaches a maximum when the interfacial coupling equals the harmonic average of the spring constants of the two semi-infinite chains. For three-dimensional junctions, in the weak coupling limit, we find that the conductance is proportional to the square of the interfacial coupling, while for a intermediate coupling strength the conductance is approximately proportional to the interfacial coupling strength. For two-junction chains, the transmission coefficient oscillates with the frequency due to interference effects. The oscillations between the two envelope lines can be understood analytically, thus providing guidelines for designing phonon frequency filters. © 2011 American Physical Society.
Fri, 11 Feb 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969672011-02-11T00:00:00Z
- Reversal of thermal rectification in quantum systemshttps://scholarbank.nus.edu.sg/handle/10635/97820Title: Reversal of thermal rectification in quantum systems
Authors: Zhang, L.; Yan, Y.; Wu, C.-Q.; Wang, J.-S.; Li, B.
Abstract: We study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy, and size of the spin chains. © 2009 The American Physical Society.
Thu, 12 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978202009-11-12T00:00:00Z
- Nonlinearity enhanced interfacial thermal conductance and rectificationhttps://scholarbank.nus.edu.sg/handle/10635/97352Title: Nonlinearity enhanced interfacial thermal conductance and rectification
Authors: Zhang, L.; Thingna, J.; He, D.; Wang, J.-S.; Li, B.
Abstract: We study the nonlinear interfacial thermal transport across atomic junctions by the quantum self-consistent mean-field (QSCMF) theory based on the nonequilibrium Green's function approach; the QSCMF theory we propose is very precise and matches well with the exact results from quantum master equation. The nonlinearity at the interface is studied by effective temperature-dependent interfacial coupling calculated from the QSCMF theory. We find that nonlinearity can provide an extra channel for phonon transport in addition to the phonon scattering which usually blocks heat transfer. For weak linearly coupled interface, the nonlinearity can enhance the interfacial thermal transport; with increasing nonlinearity or temperature, the thermal conductance shows nonmonotonical behavior. The interfacial nonlinearity also induces thermal rectification, which depends on the mismatch of the two leads and also the interfacial linear coupling. © Copyright EPLA, 2013.
Sun, 01 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973522013-09-01T00:00:00Z
- Chiral Phonons and Giant Magneto-Optical Effect in CrBr3 2D Magnethttps://scholarbank.nus.edu.sg/handle/10635/229977Title: Chiral Phonons and Giant Magneto-Optical Effect in CrBr3 2D Magnet
Authors: Yin, Tingting; Ulman, Kanchan Ajit; Liu, Sheng; del Aguila, Andres Granados; Huang, Yuqing; Zhang, Lifa; Serra, Marco; Sedmidubsky, David; Sofer, Zdenek; Quek, Su Ying; Xiong, Qihua
Abstract: Phonons with chirality determine the optical helicity of inelastic light scattering processes due to their nonzero angular momentum. Here it is shown that 2D magnetic CrBr3 hosts chiral phonons at the Brillouin-zone center. These chiral phonons are linear combinations of the doubly-degenerate Eg phonons, and the phonon eigenmodes exhibit clockwise and counterclockwise rotational vibrations corresponding to angular momenta of l = ± 1. Such Eg chiral phonons completely switch the polarization of incident circularly polarized light. On the other hand, the non-degenerate non-chiral Ag phonons display a giant magneto-optical effect under an external out-of-plane magnetic field, rotating the plane of polarization of the scattered linearly polarized light. The corresponding degree of polarization of the scattered light changes from 91% to −68% as the magnetic field strength increases from 0 to 5 T. In contrast, the chiral Eg modes display no field dependence. The results lay a foundation for the study of phonon chirality and magneto-optical phenomena in 2D magnetic materials, as well as their related applications, such as the phonon Hall effect, topological photonics, and Raman lasing.
Sat, 24 Jul 2021 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2299772021-07-24T00:00:00Z
- Topological nature of the phonon Hall effecthttps://scholarbank.nus.edu.sg/handle/10635/98421Title: Topological nature of the phonon Hall effect
Authors: Zhang, L.; Ren, J.; Wang, J.-S.; Li, B.
Abstract: We provide a topological understanding of the phonon Hall effect in dielectrics with Raman spin-phonon coupling. A general expression for phonon Hall conductivity is obtained in terms of the Berry curvature of band structures. We find a nonmonotonic behavior of phonon Hall conductivity as a function of the magnetic field. Moreover, we observe a phase transition in the phonon Hall effect, which corresponds to the sudden change of band topology, characterized by the altering of integer Chern numbers. This can be explained by touching and splitting of phonon bands. © 2010 The American Physical Society.
Wed, 24 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984212010-11-24T00:00:00Z
- Phonon Hall effect in four-terminal nano-junctionshttps://scholarbank.nus.edu.sg/handle/10635/97525Title: Phonon Hall effect in four-terminal nano-junctions
Authors: Zhang, L.; Wang, J.-S.; Li, B.
Abstract: Using an exact nonequilibrium Green's function formulation, the phonon Hall effect (PHE) for paramagnetic dielectrics is studied in a nanoscale four-terminal device setting. The temperature difference in the transverse direction of the heat current is calculated for two-dimensional models with the magnetic field perpendicular to the plane. We find that there is a PHE in nanoscale paramagnetic dielectrics, the magnitude of which is comparable to millimeter scale experiments. If the dynamic matrix of the system satisfies mirror reflection symmetry, the PHE disappears. The Hall temperature difference changes sign if the magnetic field is sufficiently large or if the size increases. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 20 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975252009-11-20T00:00:00Z
- Ballistic thermal rectification in nanoscale three-terminal junctionshttps://scholarbank.nus.edu.sg/handle/10635/95845Title: Ballistic thermal rectification in nanoscale three-terminal junctions
Authors: Zhang, L.; Wang, J.-S.; Li, B.
Abstract: We study ballistic thermal transport in three-terminal atomic nanojunctions by the nonequilibrium Green's function method. We find that there is ballistic thermal rectification in asymmetric three-terminal structures because of the incoherent phonon scattering from the control terminal. With spin-phonon interaction, we also find the ballistic thermal rectification even in symmetric three-terminal paramagnetic structures. © 2010 The American Physical Society.
Mon, 22 Mar 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958452010-03-22T00:00:00Z
- Phonon hall thermal conductivity from the Green-Kubo formulahttps://scholarbank.nus.edu.sg/handle/10635/97527Title: Phonon hall thermal conductivity from the Green-Kubo formula
Authors: Wang, J.-S.; Zhang, L.
Abstract: We derive an exact formula for the thermal-conductivity tensor of a ballistic phonon Hall model. It is found that, although the diagonal elements of the conductivity tensor diverge to infinite, the off-diagonal elements are finite, antisymmetric, and odd in magnetic field. The off-diagonal elements are nonzero only if the dynamic matrix of the phonon system breaks mirror-reflection symmetry. The results are obtained without perturbative treatment of the spin-phonon interactions. © 2009 The American Physical Society.
Thu, 06 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975272009-08-06T00:00:00Z
- The phonon Hall effect: Theory and applicationhttps://scholarbank.nus.edu.sg/handle/10635/98309Title: The phonon Hall effect: Theory and application
Authors: Zhang, L.; Ren, J.; Wang, J.-S.; Li, B.
Abstract: We present a systematic theory of the phonon Hall effect in a ballistic crystal lattice system, and apply it on the kagome lattice which is ubiquitous in various real materials. By proposing a proper second quantization for the non-Hermitian in the polarization-vector space, we obtain a new heat current density operator with two separate contributions: the normal velocity responsible for the longitudinal phonon transport, and the anomalous velocity manifesting itself as the Hall effect of transverse phonon transport. As exemplified in kagome lattices, our theory predicts that the direction of Hall conductivity at low magnetic field can be reversed by tuning the temperatures, which we hope can be verified by experiments in the future. Three phonon-Hall-conductivity singularities induced by phonon-band-topology change are discovered as well, which correspond to the degeneracies at three different symmetric center points, Γ, K, X, in the wavevector space of the kagome lattice. © 2011 IOP Publishing Ltd.
Wed, 03 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983092011-08-03T00:00:00Z
- Topological magnon insulator in insulating ferromagnethttps://scholarbank.nus.edu.sg/handle/10635/98420Title: Topological magnon insulator in insulating ferromagnet
Authors: Zhang, L.; Ren, J.; Wang, J.-S.; Li, B.
Abstract: In the ferromagnetic insulator with the Dzyaloshinskii-Moriya interaction, we theoretically predict and numerically verify a topological magnon insulator, where the charge-free magnon is topologically protected for transporting along the edge/surface while it is insulating in the bulk. The chiral edge states form a connected loop as a 4π- or 8π-period Möbius strip in the spin-wave vector space, showing the nontrivial topology of magnonic bands. Using the nonequilibrium Green's function method, we explicitly demonstrate that the one-way chiral edge transport is indeed topologically protected from defects or disorders. Moreover, we show that the topological edge state mainly localizes around edges and leaks into the bulk with oscillatory decay. Although the chiral edge magnons and energy current prefer to travel along one edge from the hot region to the cold one, the anomalous transports are identified in the opposite edge, which reversely flow from the cold region to the hot one. Our findings could be validated within wide energy ranges in various magnonic crystals, such as Lu2V2O7. © 2013 American Physical Society.
Mon, 08 Apr 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984202013-04-08T00:00:00Z
- Ballistic magnetothermal transport in a Heisenberg spin chain at low temperatureshttps://scholarbank.nus.edu.sg/handle/10635/95844Title: Ballistic magnetothermal transport in a Heisenberg spin chain at low temperatures
Authors: Zhang, L.; Wang, J.-S.; Li, B.
Abstract: We study ballistic thermal transport in Heisenberg spin chain with nearest-neighbor ferromagnetic interactions at low temperatures. Explicit expressions for transmission coefficients are derived for thermal transport in a periodic spin chain of arbitrary junction length by a spin-wave model. Our analytical results agree very well with the ones from nonequilibrium Green's function method. Our study shows that the transmission coefficient oscillates with the frequency of thermal wave. Moreover, the thermal transmission shows strong dependence on the intrachain coupling, the length of the spin chain, and the external magnetic field. The results demonstrate the possibility of manipulating spin-wave propagation and magnetothermal conductance in the spin-chain junction by adjusting the intrachain coupling and/or the external magnetic field. © 2008 The American Physical Society.
Wed, 15 Oct 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958442008-10-15T00:00:00Z