| Autor: |
Lu YF; Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan., Kono H; Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan., Larkin TI; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany., Rost AW; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany.; Institute for Functional Matter and Quantum Technologies, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany., Takayama T; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany., Boris AV; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany., Keimer B; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany., Takagi H; Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.; Max Planck Institute for Solid State Research, Heisenbergstrsse 1, 70569 Stuttgart, Germany.; Institute for Functional Matter and Quantum Technologies, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany. |
| Abstrakt: |
The excitonic insulator is a long conjectured correlated electron phase of narrow-gap semiconductors and semimetals, driven by weakly screened electron-hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta 2 NiSe 5 is a narrow-gap semiconductor with a small one-electron bandgap E G of <50 meV. Below T C =326 K, a putative excitonic insulator is stabilized. Here we report an optical excitation gap E op ∼0.16 eV below T C comparable to the estimated exciton binding energy E B . Specific heat measurements show the entropy associated with the transition being consistent with a primarily electronic origin. To further explore this physics, we map the T C -E G phase diagram tuning E G via chemical and physical pressure. The dome-like behaviour around E G ∼0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta 2 NiSe 5 . |
