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Topological phases of matter have attracted significant attention in recent years, due to the unusual robustness of their response to defects and disorder. Various research efforts have been exploring classical and quantum topological wave phenomena in engineered materials, in which different degrees of freedom (DoFs) – for the most part based on broken crystal symmetries associated with pseudo-spins – induce synthetic gauge fields that support topological phases and unveil distinct forms of wave propagation. However, spin is not the only viable option to induce topological effects. Intrinsic orbital DoFs in spinless systems may offer a powerful alternative platform, mostly unexplored to date. Here we reveal orbital-selective wave-matter interactions in acoustic systems supporting multiple orbital DoFs, and report the experimental demonstration of disorder-immune orbital-induced topological edge states in a zigzag acoustic 1D spinless lattice. This work expands the study of topological phases based on orbitals, paving the way to explore other orbital-dependent phenomena in spinless systems. The researchers demonstrate orbital-dependent sound-matter interactions in acoustic systems. They unveil duality symmetry and topological phase transitions beyond the conventional SSH model expanding the fundamental understanding of sound-matter interaction. [ABSTRACT FROM AUTHOR]

We explore the exceptional point (EP) induced phase transition and amplitude/phase modulation in thermal diffusion systems. We start from the asymmetric coupling double-channel model, where the temperature field is unbalanced in the amplitude and locked in the symmetric phase. By extending into the one-dimensional tight-binding non-Hermitian lattice, we study the convection-driven phase locking and the asymmetric-couplinginduced diffusive skin effect with the high-order EPs in static systems. Combining convection and asymmetric couplings, we further show the phase-locking diffusive skin effect. Our work reveals the mechanism of controlling both the amplitude and phase of temperature fields in thermal coupling systems and has potential applications in non-Hermitian topology in thermal diffusion. [ABSTRACT FROM AUTHOR]

Parity-time (PT) symmetry/anti-parity-time (APT) symmetry in non-Hermitian systems reveal profound physics and spawn intriguing effects. Recently, it has been introduced into diffusive systems together with the concept of exceptional points (EPs) from quantum mechanics and the wave systems. With the aid of convection, we can generate complex thermal conductivity and imitate various wavelike dynamics in heat transfer, where heat flow can be "stopped" or moving against the background motion. Non-Hermitian diffusive systems offer us a new platform to investigate the heat wave manipulation. In this review, we first introduce the construction of APT symmetry in a simple double-channel toy model. Then we show the phase transition around the EP. Finally, we extend the double-channel model to the four-channel one for showing the high-order EP and the associated phase transition. In a general conclusion, the phase difference of adjacent channels is always static in the APT symmetric phase, while it dynamically evolves or oscillates when the APT symmetry is broken. [ABSTRACT FROM AUTHOR]

Topological manipulation of sound has recently been a hot spot in acoustics due to the fascinating property of defect immune transport. To the best of our knowledge, the studies on one-dimensional (1D) topological acoustic systems hitherto mainly focus on the case of the Su-Schrieffer-Heeger model. Here, we show that topologically protected bound states may also exist in 1D periodically modulated acoustic waveguide systems, viz., 1D Floquet topological insulators. The results show that tuning the coupling strength in a waveguide lattice could trigger topological phase transition, which gives rise to topologically protected interface states as we put together two waveguide lattices featured with different topological phases or winding numbers. However, for the combined lattice, input at the waveguides other than the interfacial ones will excite bulk states. We have further verified the robustness of interface bound states against the variation of coupling strengths between the two distinct waveguide lattices. This work extends the scope of topological acoustics and may promote potential applications for acoustic devices with topological functionalities. [ABSTRACT FROM AUTHOR]

Various concepts related to parity-time symmetry, including anti–parity-time symmetry, have found broad applications in wave physics. Wave systems are fundamentally described by Hermitian operators, whereas their unusual properties are introduced by incorporation of gain and loss. We propose that the related physics need not be restricted to wave dynamics, and we consider systems described by diffusive dynamics. We study the heat transfer in two countermoving media and show that this system exhibits anti–parity-time symmetry. The spontaneous symmetry breaking results in a phase transition from motionless temperature profiles, despite the mechanical motion of the background, to moving temperature profiles. Our results extend the concepts of parity-time symmetry beyond wave physics and may offer opportunities to manipulate heat and mass transport. [ABSTRACT FROM AUTHOR]