Hybrid-Order Topological Insulators in a Phononic Crystal

Abstract

Topological phases, including the conventional first-order and higher-order topological insulators and semimetals, have emerged as a thriving topic in the fields of condensed-matter physics and material science. Usually, a topological insulator is characterized by a fixed order topological invariant and exhibits associated bulkboundary correspondence. Here, we realize a new type of topological insulator in a bilayer phononic crystal, which hosts simultaneously the first-order and second-order topologies, referred here as the hybrid-order topological insulator. The one-dimensional gapless helical edge states, and zero-dimensional corner states coexist in the same system. The new hybrid-order topological phase may produce novel applications in topological acoustic devices.

Toward ferromagnetic semimetal ground state with multiple Weyl nodes in van der Waals crystal MnSb4Te7

“…As one of the most fantastic area of condensed matter physics, topological materials have roused a great deal of interest in the past two decades due to their unconventional physical properties [1][2][3][4][5][6]. A series of topological phase and topological materials, such as topological insulator, Dirac semimetal, Weyl semimetal, nodal line semimetal, axion insulator, topological Mott insulator, and high order topological insulator, were proposed theoretically and realized experimentally [7][8][9][10][11][12][13][14][15][16]. They exhibit plenty of robust physical phenomenons protected by symmetries, such as integer quantum Hall effect, quantum spin Hall effect and quantum anomalous Hall effect, and therefore become excellent platforms for future spintronics applications [17,18].…”

Nonlinear control of photonic higher-order topological bound states in the continuum

“…This is associated with topologically quantized quadrupole and higher-order electric moments in electronic systems 7 . The discovery of HOTIs broadened the concept of the symmetryprotected topological phase and our common understanding of traditional topological insulators, which has thus launched an avalanche of research ventures on HOTIs in a variety of fields, including condensed matter physics, electric circuits, phononic systems, acoustics, and photonics 7,[10][11][12][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] . In terms of fundamental interest, HOTIs are attractive because they are related to many intriguing phenomena such as higher-order band topology in twisted Moiré superlattices 32 , topological lattice disclinations 33 , Majorana bound states 34 and their nontrivial braiding 35 .…”

Topological Phase Transitions and Evolution of Boundary States Induced by Zeeman Fields in Second-Order Topological Insulators

“…Such tunability may benefit the design of devices based on higher-order topological materials for applications [33][34][35]. On the other hand, bound states with different dimensions can coexist in the same system [36], which may result in novel responses absent in conventional topological phases. The higher-order topology also enriches the possibility of topological phase transitions [37][38][39][40][41][42].…”