Ultrafast terahertz spectroscopy study of Kondo insulating thin film SmB${}_6$: evidence for an emergent surface state

Abstract

We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound SmB6, a prototype Kondo insulator. Temperature dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ~T*=20 K, well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20K) indicates the emergence of a surface state with an effective electron mass of 0.1me. Conductivity dynamics following optical excitation are also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20K, indicative of another channel opening up in the low energy electrodynamics. Taken together, these results suggest the onset of a surface state well below the crossover temperature (100K) after long-range coherence of the f-electron Kondo lattice is established.

References in corpus (14)

• Electrodynamics of Correlated Electron Materials
• Correlated Topological Insulators with Mixed Valence
• Unconventional Fermi surface in an insulating state
• Direct observation of the spin texture in strongly correlated SmB6 as evidence of the topological Kondo insulator
• Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6
• Kondo Breakdown in Topological Kondo Insulators
• Kondo Breakdown and Quantum Oscillations in SmB${}_6$
• Additional energy scale in SmB${}_6$ at low temperature
• Anomalous 3D bulk AC conduction within the Kondo gap of SmB${}_6$ single crystals
• Exotic Kondo crossover in a wide temperature region in the topological Kondo insulator SmB6 revealed by high-resolution ARPES
• Topological surface states interacting with bulk excitations in the Kondo insulator SmB${}_6$ revealed via planar tunneling spectroscopy
• Composition-spread Growth and the Robust Topological Surface State of Kondo insulator SmB6 Thin Films
• Robust Surface States indicated by Magnetotransport in SmB6 Thin Films
• Ultrafast observation of electron hybridization and in-gap states formation in Kondo insulator SmB6

Cited by in corpus (4)

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• An STM perspective on hexaborides: Surface states of the Kondo insulator SmB${}_6$
• Microwave Meissner Screening of Proximity coupled Topological Insulator / Superconductor Bilayers
• Robust hybridization gap in a Kondo Insulator YbB${}_{12}$ probed by femtosecond optical spectroscopy