Distinguishing bulk and surface electron-phonon coupling in the topological insulator Bi(2)Se(3) using time-resolved photoemission spectroscopy

J A Sobota; S-L Yang; D Leuenberger; A F Kemper; J G Analytis; I R Fisher; P S Kirchmann; T P Devereaux; Z-X Shen

doi:10.1103/PhysRevLett.113.157401

Distinguishing bulk and surface electron-phonon coupling in the topological insulator Bi(2)Se(3) using time-resolved photoemission spectroscopy

Phys Rev Lett. 2014 Oct 10;113(15):157401. doi: 10.1103/PhysRevLett.113.157401. Epub 2014 Oct 10.

Authors

J A Sobota¹, S-L Yang², D Leuenberger³, A F Kemper⁴, J G Analytis⁵, I R Fisher³, P S Kirchmann⁶, T P Devereaux³, Z-X Shen²

Affiliations

¹ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
² Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA and Department of Physics, Stanford University, Stanford, California 94305, USA.
³ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
⁴ Computational Research Division, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, California 94720, USA.
⁵ Department of Physics, University of California, Berkeley, California 94720, USA.
⁶ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.

PMID: 25375740
DOI: 10.1103/PhysRevLett.113.157401

Abstract

We report time- and angle-resolved photoemission spectroscopy measurements on the topological insulator Bi(2)Se(3). We observe oscillatory modulations of the electronic structure of both the bulk and surface states at a frequency of 2.23 THz due to coherent excitation of an A(1g) phonon mode. A distinct, additional frequency of 2.05 THz is observed in the surface state only. The lower phonon frequency at the surface is attributed to the termination of the crystal and thus reduction of interlayer van der Waals forces, which serve as restorative forces for out-of-plane lattice distortions. Density functional theory calculations quantitatively reproduce the magnitude of the surface phonon softening. These results represent the first band-resolved evidence of the A(1g) phonon mode coupling to the surface state in a topological insulator.