Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B03: Novel Excitations in Topological SystemsFocus

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Sponsoring Units: DCMP Chair: Herbert Fertig, Indiana University Bloomington Room: BCEC 107B 
Monday, March 4, 2019 11:15AM  11:27AM 
B03.00001: Splitting the hinge mode of higherorder topological insulators Raquel Queiroz We study the effect of the coupling of a helical mode in a twodimensional topological insula 
Monday, March 4, 2019 11:27AM  11:39AM 
B03.00002: Magneto Optic Kerr Effects of an Antiferromagnet  Topological Insulator Heterostructure Tonmoy Bhowmick, Amritanand De, Roger Lake We investigate the magnetooptic memory applications of a topological insulator proximity coupled to an antiferromagnet. We find that this gives rise to a high figure of merit magneto optic Kerr effects. The optical dielectric tensor elements are calculated using the Kubo formula and are based on a tightbinding electronic structure model. We calculate the Fermi level dependence of the MOKE signature and explore the AFMTI optical phase diagram. This system can lead to applications such as a topologically protected high density antiferromagnetic magnetic optic memory device with ultralow error rates. 
Monday, March 4, 2019 11:39AM  11:51AM 
B03.00003: Glideresolved photoemission spectroscopy: measuring topological invariants in nonsymmorphic space groups Aris Alexandradinata, Andrei B Bernevig, Zhijun Wang, Michael Zaletel The two classes of 3D, timereversalinvariant insulators are known to subdivide into four classes in the presence of glide symmetry. Based on abinitio calculations, we predict materials that realize all three, nontrivial insulating phases. We further elucidate the smokinggun experimental signature of each class in the photoemission spectroscopy of surface states. Measuring the Z_4 invariant relies on identifying the glide representation of the initial Bloch state before photoexcitation  this is accomplished with relativistic dipole selection rules, combined with standard spectroscopic techniques to resolve both momentum and spin. As an orthogonal byproduct of our method, we propose how to generate a source of 100% spinpolarized photoelectrons, which have diverse applications in solidstate spectroscopy. 
Monday, March 4, 2019 11:51AM  12:03PM 
B03.00004: Bulkedge correspondence in 1D nonHermitian systems Kazuki Yokomizo, Shuichi Murakami Recently, the role of the topology in nonHermitian systems is attracting much attention. It is known fact is that the conventional bulkedge correspondence breaks down in nonHermitian systems if the Bloch wavevector k is set to be real. Here, to restore the bulkedge correspondence, the nonBloch factor β≡exp(ik), k∈C is introduced in the SSH model with the asymmetric hopping [1]. In this case, one can show the bulkedge correspondence by defining the winding number by using β. However, it is not obvious how to systematically calculate β in general case. In this talk, we show how to calculate β in general 1D models for constructing the continuum bulkbands. It is nontrivial because the states in the continuum bulkbands do not extend over the bulk, unlike those in the Hermitian systems. We also discuss the bulkedge correspondence in general cases by defining the generalized Brillouin zone in terms of β. [1] S.Yao, et al., Phys. Rev. Lett. 121, 086803 (2018) 
Monday, March 4, 2019 12:03PM  12:15PM 
B03.00005: Quantum Control of Current Partition at Trifurcating Topological Channels Tao Hou, Yujie Quan, Yafei Ren, Jeil Jung, Wei Ren, Zhenhua Qiao Topological channels can emerge a network along the domain walls that separate AB and BA stacking regions in minimally twisted bilayer graphene, which have been imaged by using scanning tunneling microscope recently. Here, we design a sixterminal graphene device to study how the incoming valleypolarized current will partition at the topological crossing point. We find that the incoming current not only can be partitioned into the two adjacent topological channels, but also goes straight along the incoming topological channel, which together form a trifurcating beam splitter. We provide a further systematic study on how to externally tune the trifurcating current partition by means of manipulating the system size, Fermienergy, magnetic field, relative masses. 
Monday, March 4, 2019 12:15PM  12:27PM 
B03.00006: Metallicity at the IoffeRegal limit in a topological insulator thin film Ilan Rosen, Indra Yudhistira, Girish Sharma, Maryam Salehi, Jisoo Moon, Deepti Jain, Seongshik Oh, Marc Kastner, Shaffique Adam, David GoldhaberGordon The topological surface states of timereversal invariant 3D topological insulators have applications for spintronics, metrology, and the realization of topological superconductivity. Initial excitement around these surface states, however, focused on the prediction that they should be robust against Anderson localization, even under strong disorder. This prediction has never been directly confirmed by transport measurements. We present lowtemperature transport measurements of a gatetunable Sb_{2}Te_{3} topological insulator thin film that features high mobility and low carrier density. We find that metallicity is preserved at conductivities well below e^{2}/h, where two dimensional electron systems conventionally scale to an insulating state. Near the charge neutrality point, we observe an unusual magnetoconductance response, which we associate with known weak localization/antilocalization behavior, but beyond the IoffeRegal limit k_{F}l ~ 1. 
Monday, March 4, 2019 12:27PM  12:39PM 
B03.00007: High order band topology and fractional charges of vortex bound states Eunwoo Lee, BohmJung Yang In a onedimensional system described by the SSH model, a halfinteger electric charge can be localized at the domain wall between topological and trivial systems. A similar phenomenon can also occur in certain two dimensional systems in which fractional electric charge can be localized at a vortex core. We show that the origin of the zeromode bound to a vortex comes from the higher order topological physics. Considering several concrete examples, we show that vortex bound states can generally be understood as a spatial charge pump between higher order topological phase and trivial phase. In particular, when PT symmetry exists, we show that the pumping of the second StiefelWhitney invariant w_2 corresponds to the number of zero modes localized at the vortex core. 
Monday, March 4, 2019 12:39PM  12:51PM 
B03.00008: Topological phases of nonHermitian systems Flore Kunst, Vatsal Dwivedi NonHermitian fermionic systems are known to exhibit features strikingly different from their Hermitian counterparts, a quintessential example being the lack of a bulkboundary correspondence in the conventional sense. In this talk, I will describe a transfer matrix approach to these systems. The algebraic structure of the transfer matrix and a Riemann surface associated with the complex energies provide a clear and intuitive picture of various topological aspects of these systems. 
Monday, March 4, 2019 12:51PM  1:03PM 
B03.00009: ManyBody Invaraints for Electric Multipoles in Higherorder Topological Insulators Byungmin Kang, HyunWoong Kwon, Kwon Park, Gil Young Cho According to the modern theory of polarization, the electric polarization in solids is defined via Berry phase, which definition is fundamentally different from the classical definition of polarization involving charge distribution. In certain classes of crystalline topological insulators, the electric polarization is known to take quantized value due to underlying crystalline symmetries. Recently, the theory of multipole moments in crystalline insulators was developed where the quadrupole moment and higherorder multipole moments can be defined quantum mechanically. Although crytalline symmetries are useful they are not essential in understanding multiple moments, and so far the theory is only applicable to noninteracting crystalline band insulators. In this talk, I will introduce a manybody order parameter for quadrupole moment which provides a way to extend the quantum theory of multipole moments to the most general setting including interacting case. I will also discuss the bulkboundary correspondence for quadrupole moment, relating seemingly unrelated quantities from the bulk and from the boundary. 
Monday, March 4, 2019 1:03PM  1:15PM 
B03.00010: ABSTRACT WITHDRAWN

Monday, March 4, 2019 1:15PM  1:27PM 
B03.00011: Dynamical Phase Transitions in Topological Insulators Nicholas Sedlmayr, Michael Fleischhauer, Jesko Sirker The traditional concept of phase transitions has, in recent years, been widened in a number of interesting ways. The concept of a topological phase transition separating phases with a different ground state topology, rather than phases of different symmetries, has become a large widely studied field in its own right. Additionally an analogy between phase transitions, described by nonanalyticities in the derivatives of the free energy, and nonanalyticities which occur in dynamically evolving correlation functions has been drawn. Here we focus in particular on the way in which these dynamical phase transitions themselves can be used to shed light on topological phase transitions and topological phases. We consider, firstly, the effect of the topologically protected edge states, which are one of the interesting consequences of topological phases, on dynamical phase transitions. Secondly we consider what happens in the experimentally relevant situations where the system is either in a thermal state rather than the ground state, or connected to an external environment. 
Monday, March 4, 2019 1:27PM  1:39PM 
B03.00012: Spin Stiffness and Domain Walls in DiracElectron Mediated Magnets Sahinur Reja, Herbert Fertig, Luis Brey We consider the problem of ordering of classical magnetic impurities which are indirectly coupled by twodimensional Dirac electrons, as might be present in graphene or at the surface of a topological insulator. For chemical potential at a Dirac point, the magnetic order parameter develops an emergent longrange form of the spin stiffness, becoming truly longrange as the magnetization density becomes very small. It is demonstrated that this leads to screened Coulomblike interactions among domain walls. A transfer matrix analysis demonstrates that the interaction takes this form from a subtle cancellation between energy contributions from ingap bound states and phase shifts of scattered electrons. Detailed studies of graphene and a topological crystalline insulator surface are used to illustrate the behavior. The nonanalytic behavior of the stiffness on magnetization density is shown to have interesting consequences for the phase diagram of these systems. 
Monday, March 4, 2019 1:39PM  1:51PM 
B03.00013: Topological tunability from evenodd order parameter mixing of monolayer 1TTiSe_{2} charge density wave MingChien Hsu, ShinMing Huang, Bahadur Singh, ChuangHan Hsu, Suyang Xu, Hsin Lin, Chenliang Su, Arun Bansil Monolayer 1TTiSe_{2} has been found to have charge density wave (CDW) experimentally. The primary CDW order parameter takes the M_{1}^{} symmetry having odd parity and will change parity of electronic states of the system. Due to the coexistence of three q vectors from the primary order parameter, a secondary order parameter of even parity is induced inevitably. The mixture of the two oppositeparity order parameters will break inversion symmetry, which fails connection between symmetry and topology. Here we propose a method to decouple the parityodd and parity even CDW gaps, so that we can perform continuously the inversionasymmetric CDW state into an inversionsymmetric one. In this way it helps to understand topological phase transitions in inversion asymmetric systems from the inversionsymmetry point of view. 
Monday, March 4, 2019 1:51PM  2:03PM 
B03.00014: Spectral weight suppression as a gaplike feature in the nonmagnetic states of topological insulators Turgut Yilmaz, Anna Pertsova, William Hines, Alexander Balatsky, Boris Sinkovic Here, we present an answer to one of the much debated questions in the topological insulator research, i.e., the opening of an energy gaplike feature at the Dirac point without long range ferromagnetic order. This is in sharp contrast to the topological protection of the surface states against nonmagnetic perturbations. We carried out a systematic photoemission study on Crdoped Bi_{2}Se_{3} films grown on pristine Bi_{2}Se_{3} films which allow us to monitor the evolution of the topological electronic structure. Our angleresolved photoemission spectroscopy experiments revealed a gaplike feature appears just below the Dirac point leaving the Dirac point unaffected by the doping. Furthermore, the Dirac point is buried under the bulk conduction band which prevented it from being resolved in previous photoemission experiments. The spectral weight suppression just below the Dirac point leads to the gaplike feature being mistakenly identified as an energy gap at the Dirac point. 
Monday, March 4, 2019 2:03PM  2:15PM 
B03.00015: Anomalous dielectric response in insulators with a topological π Zak phase Shuichi Murakami, Yusuke Aihara, Motoaki Hirayama In the topological phase of the SuSchriefferHeeger model, the Zak phase is equal to π. While it corresponds to the e/2 polarization, there is no electric dipole moment because of inversion symmetry. We find that an external electric field gives rise to an abrupt rise of the dipole moment, close to e/2. This sudden uprise of the dipole moment is attributed to the midgap state at the two ends of the system. We also extend this idea to two and threedimensional insulators with the π Zak phase over the whole Brillouin zone, and show that similar sudden uprise of the polarization by an externa electric field happens also in these cases, if the midgap boundary states due to the π Zak phase has sufficiently flat dispersions. Finally, we discuss possible candidate materials for this behavior, including the (111) surface of Si and the (111) surface of a topological electride Sc_{2}C. 
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